ASN.1 Compiler Version 6.7 C/C++ Users Guide Reference Manual

ASN.1 Compiler Version 6.7 C/C++ Users Guide Reference Manual
ASN1C
ASN.1 Compiler
Version 6.7
C/C++ Users Guide
Reference Manual
Objective Systems, Inc. version 6.7 — May 2014
The software described in this document is furnished under a license agreement and may be used only in accordance
with the terms of this agreement.
Copyright Notice
Copyright ©1997–2014 Objective Systems, Inc. All rights reserved.
This document may be distributed in any form, electronic or otherwise, provided that it is distributed in its entirety and
that the copyright and this notice are included.
Author’s Contact Information
Comments, suggestions, and inquiries regarding ASN1C may be submitted via electronic mail to info@obj-sys.com.
Table of Contents
1. Overview of ASN1C ....................................................................................................................... 1
2. Using the Compiler ......................................................................................................................... 2
Running ASN1C from the Command-line ....................................................................................... 2
Using the GUI Wizard to Run ASN1C ......................................................................................... 16
Using Projects .................................................................................................................. 16
Common Code Generation Options ...................................................................................... 21
XSD Options ................................................................................................................... 27
C/C++ Code Generation Options ........................................................................................ 29
Compilation ..................................................................................................................... 33
Using the Visual Studio Wizard to Generate ASN1C Projects ........................................................... 35
Compiling and Linking Generated Code ....................................................................................... 47
Porting Run-time Code to Other Platforms .................................................................................... 48
Compiler Configuration File ....................................................................................................... 49
Compiler Error Reporting ........................................................................................................... 59
3. ASN.1 To C/C++ Mappings ............................................................................................................ 61
Type Mappings ........................................................................................................................ 61
BOOLEAN ...................................................................................................................... 61
INTEGER ....................................................................................................................... 61
BIT STRING ................................................................................................................... 63
OCTET STRING .............................................................................................................. 67
ENUMERATED ............................................................................................................... 68
NULL ............................................................................................................................. 70
OBJECT IDENTIFIER ...................................................................................................... 70
RELATIVE-OID .............................................................................................................. 71
REAL ............................................................................................................................. 71
SEQUENCE .................................................................................................................... 72
SET ................................................................................................................................ 77
SEQUENCE OF ............................................................................................................... 77
SET OF .......................................................................................................................... 82
CHOICE ......................................................................................................................... 82
Open Type ...................................................................................................................... 85
Character String Types ...................................................................................................... 86
Time String Types ............................................................................................................ 87
EXTERNAL .................................................................................................................... 88
EMBEDDED PDV ........................................................................................................... 88
Parameterized Types ......................................................................................................... 89
Value Mappings ....................................................................................................................... 90
BOOLEAN Value ............................................................................................................. 91
INTEGER Value .............................................................................................................. 91
REAL Value .................................................................................................................... 92
Enumerated Value Specification .......................................................................................... 92
Binary and Hexadecimal String Value .................................................................................. 92
Character String Value ...................................................................................................... 93
Object Identifier Value Specification .................................................................................... 93
Constructed Type Values ................................................................................................... 93
Table Constraint Related Structures ............................................................................................. 96
Unions Table Constraint Model ........................................................................................... 96
Legacy Table Constraint Model ......................................................................................... 102
4. XSD TO C/C++ TYPE MAPPINGS ............................................................................................... 111
XSD Simple Types .................................................................................................................. 111
XSD Complex Types ............................................................................................................... 112
iii
ASN1C
xsd:sequence ............................................................................................................... 112
xsd:all ........................................................................................................................ 113
xsd:choice and xsd:union ............................................................................................... 113
Repeating Groups ......................................................................................................... 114
Repeating Elements ....................................................................................................... 115
xsd:list ......................................................................................................................... 116
xsd:any ........................................................................................................................ 116
XML Attribute Declarations .......................................................................................... 117
xsd:anyAttribute ........................................................................................................... 118
xsd:simpleContent ........................................................................................................ 119
xsd:complexContent ...................................................................................................... 120
Substitution Groups ...................................................................................................... 121
5. Generated C/C++ Source Code ...................................................................................................... 123
Header (.h) File ...................................................................................................................... 123
Generated C Source Files ......................................................................................................... 126
Maximum Lines per File ................................................................................................. 126
Use of the -maxcfiles Option ............................................................................................ 126
Generated C++ files ................................................................................................................ 127
Generated C/C++ files and the -compat Option ............................................................................ 129
Generated C++ files and the -symbian Option .............................................................................. 129
Writable Static Data ........................................................................................................ 129
Extern Linkage ............................................................................................................... 129
Considerations When Using C++ Standard Library ....................................................................... 130
Generated Build Files .............................................................................................................. 132
Generated Makefile ......................................................................................................... 132
Generated VC++ Project Files ........................................................................................... 133
6. Generated Encode/Decode Function and Methods .............................................................................. 134
Encode/Decode Function Prototypes ........................................................................................... 134
Generated C++ Control Class Definition ..................................................................................... 135
BER/DER or PER Class Definition .................................................................................... 135
XER Class Definition ...................................................................................................... 136
Generated Methods .......................................................................................................... 137
Generated Information Object Table Structures ............................................................................. 137
Simple Form Code Generation .......................................................................................... 139
Unions Table Form Code Generation .................................................................................. 139
Legacy Table Form Code Generation .................................................................................. 140
Additional Code Generated with the -tables option ................................................................ 141
General Procedure for Table Constraint Encoding ................................................................. 143
General Procedure for Table Constraint Decoding ................................................................. 146
General Procedures for Encoding and Decoding ........................................................................... 149
Dynamic Memory Management ........................................................................................ 149
Populating Generated Structure Variables for Encoding ........................................................ 153
Accessing Encoded Message Components ........................................................................... 154
7. Generated BER Functions ............................................................................................................. 156
Generated BER Encode Functions .............................................................................................. 156
Generated C Function Format and Calling Parameters ................................................... 156
Generated C++ Encode Method Format and Calling Parameters ............................................... 160
Generated BER Streaming Encode Functions ............................................................................... 164
Generated Streaming C Function Format and Calling Parameters .......................................... 164
Generated Streaming C++ Encode Method Format and Calling Parameters ............................. 167
Generated BER Decode Functions ............................................................................................. 170
Generated C Function Format and Calling Parameters ......................................................... 171
Generated C++ Decode Method Format and Calling Parameters ............................................ 175
iv
ASN1C
BER Decode Performance Enhancement Techniques ..................................................................... 179
Dynamic Memory Management ......................................................................................... 179
Compact Code Generation ................................................................................................ 180
Decode Fast Copy ........................................................................................................... 180
Using Initialization Functions ......................................................................................... 181
BER/DER Deferred Decoding .......................................................................................... 181
Generated BER Streaming Decode Functions ............................................................................... 182
Generated Streaming C Function Format and Calling Parameters ............................................ 183
Generated Streaming C++ Decode Method Format and Calling Parameters ............................... 187
8. Generated PER Functions ............................................................................................................. 191
Generated PER Encode Functions .............................................................................................. 191
Generated C Function Format and Calling Parameters .......................................................... 191
Generated C++ Encode Method Format and Calling Parameters ............................................ 191
Populating Generated Structure Variables for Encoding ......................................................... 192
Procedure for Calling C Encode Functions .......................................................................... 192
Procedure for Using the C++ Control Class Encode Method .................................................. 194
Encoding a Series of PER Messages using the C++ Interface ................................................. 197
Generated PER Decode Functions .............................................................................................. 197
Generated C Function Format and Calling Parameters .......................................................... 198
Generated C++ Decode Method Format and Calling Parameters ............................................ 198
Procedure for Calling C Decode Functions ......................................................................... 198
Procedure for Using the C++ Control Class Decode Method .................................................. 200
Decoding a Series of Messages Using the C++ Control Class Interface .................................... 201
Performance Considerations: Dynamic Memory Management ................................................. 203
9. Generated Octet Encoding Rules (OER) Functions ............................................................................ 204
Generated OER Encode Functions ............................................................................................. 204
Generated C Function Format and Calling Parameters ......................................................... 204
Populating Generated Structure Variables for Encoding ........................................................ 204
Procedure for Calling C Encode Functions ......................................................................... 204
Generated OER Decode Functions ............................................................................................. 206
Generated C Function Format and Calling Parameters ......................................................... 206
Procedure for Calling C Decode Functions ........................................................................ 207
10. Generated Medical Device Encoding Rules (MDER) Functions .......................................................... 209
Generated MDER Encode Functions ........................................................................................... 209
Generated C Function Format and Calling Parameters ........................................................... 209
Procedure for Calling C Encode Functions .......................................................................... 209
Encoding a Series of Messages Using the C Encode Functions ................................................ 211
Generated MDER Decode Functions .......................................................................................... 211
Generated C Function Format and Calling Parameters ......................................................... 211
Procedure for Calling C Decode Functions ........................................................................ 212
Decoding a Series of Messages Using the C Decode Functions ............................................... 213
Two-Phase Messaging .............................................................................................................. 213
Two-phase Encoding ....................................................................................................... 214
Two-phase Decoding ....................................................................................................... 216
11. Generated XML Functions .......................................................................................................... 218
Overview ............................................................................................................................... 218
Differences between OSys-XER and XER (BASIC-XER) ....................................................... 219
EXTENDED-XER ........................................................................................................... 219
Generated XER Encode Functions (Old Style - Deprecated) ............................................................ 221
Generated C Function Format and Calling Parameters ......................................................... 221
Generated C++ Encode Method Format and Calling Parameters ........................................... 222
Procedure for Calling C Encode Functions ......................................................................... 222
Procedure for Using the C++ Control Class Encode Method ................................................. 223
Tips for Upgrading to the New Style .................................................................................. 225
v
ASN1C
12.
13.
14.
15.
16.
17.
Generated XER Decode Functions (Old Style - Deprecated) ........................................................... 225
Procedure for Using the C Interface .................................................................................. 227
Generated C Function Format and Calling Parameters ......................................................... 227
Procedure for Calling C Decode Functions ........................................................................ 227
Procedure for Using the C++ Interface ............................................................................. 229
Procedure for Interfacing with Other C and C++ X ML Parser Libraries ................................. 230
Tips for Upgrading to the New Style .................................................................................. 231
Generated XML Encode Functions ............................................................................................. 231
Generated C Function Format and Calling Parameters ......................................................... 231
Procedure for Calling C Encode Functions ......................................................................... 232
Generated C++ Encode Method Format and Calling Parameters ........................................... 233
Procedure for Using the C++ Control Class Encode Method ................................................. 234
Generated XML Decode Functions ............................................................................................. 235
Generated C Function Format and Calling Parameters ......................................................... 236
Procedure for Calling C Decode Functions ........................................................................ 236
Generated C++ Decode Method Format and Calling Parameters ........................................... 238
Procedure for Using the C++ Control Class Decode Method ................................................. 238
Generated JavaScript Object Notation (JSON) Functions ................................................................... 240
Generated JSON Encode Functions ............................................................................................ 240
Generated C Function Format and Calling Parameters ............................................................ 240
Procedure for Calling C Encode Functions .......................................................................... 240
Encoding a Series of Messages .......................................................................................... 241
Generated C++ Encoding Methods ..................................................................................... 241
Encoding a Series of Messages using the C++ Control Class ................................................... 242
Generated JSON Decode Functions ............................................................................................ 242
Generated C Function Format and Calling Parameters ......................................................... 242
Procedure for Calling C Decode Functions ......................................................................... 243
Decoding a Series of Messages Using the C Decode Functions ............................................... 244
Generated C++ Encoding Methods ..................................................................................... 244
Decoding a Series of Messages using the C++ Control Class ................................................... 245
Generated 3GPP Layer 3 (3GL3) Functions .................................................................................... 246
Generated 3GPP Layer 3 Encode Functions ................................................................................. 246
Generated C Function Format and Calling Parameters ......................................................... 246
Populating Generated Structure Variables for Encoding ........................................................ 247
Procedure for Calling C Encode Functions ......................................................................... 247
Generated 3GPP Layer 3 Decode Functions ................................................................................. 248
Generated C Function Format and Calling Parameters ......................................................... 248
Procedure for Calling C Decode Functions ........................................................................ 249
Additional Generated Functions .................................................................................................... 252
Generated Initialization Functions .............................................................................................. 252
Generated Memory Free Functions ............................................................................................. 252
Generated Print Functions ......................................................................................................... 253
Print to Standard Output ................................................................................................. 253
Print to String ............................................................................................................... 254
Print to Stream .............................................................................................................. 254
Print Format ................................................................................................................. 255
Generated Compare Functions ................................................................................................... 256
Generated Copy Functions ........................................................................................................ 257
Generated Test Functions ......................................................................................................... 259
Event Handler Interface .............................................................................................................. 261
How it Works ....................................................................................................................... 261
How to Use It ....................................................................................................................... 262
IMPORT/EXPORT of Types ....................................................................................................... 269
ROSE and SNMP Macro Support ................................................................................................. 270
vi
ASN1C
ROSE OPERATION and ERROR ............................................................................................. 270
SNMP OBJECT-TYPE ........................................................................................................... 273
A. Runtime Status Codes .................................................................................................................. 274
ASN1C Error Messages ........................................................................................................... 274
General Status Messages .......................................................................................................... 276
ASN.1-specific Status Messages ................................................................................................ 281
vii
Chapter 1. Overview of ASN1C
The ASN1C code generation tool translates an Abstract Syntax Notation 1 (ASN.1) or XML Schema Definitions
(XSD) source file into computer language source files that allow ASN.1 data to be encoded/decoded. This release of
the compiler includes options to generate code in four different languages: C, C++, C#, or Java. This manual discusses
the C and C++ code generation capabilities. The ASN1C Java User’s Manual discusses the Java code generation
capability. The ASN1C C# User’s Manual discusses the C# code generation capability.
Each ASN.1 module that is encountered in an ASN.1 source file results in the generation of the following two types
of C/C++ language files:
1. An include (.h) file containing C/C++ typedefs and classes that represent each of the ASN.1 productions listed in
the ASN.1 source file, and
2. A set of C/C++ source (.c or .cpp) files containing C/C++ encode and decode functions. One encode and decode
function is generated for each ASN.1 production. The number of files generated can be controlled through
command-line options.
These files, when compiled and linked with the ASN.1 low-level encode/decode function library, provide a complete
package for working with ASN.1 encoded data.
ASN1C works with the version of ASN.1 specified in ITU-T international standards X.680 through X.683 (ISO/IEC
8824). It generates code for encoding/decoding data in accordance with the following encoding rules:
• Basic Encoding Rules (BER), Distinguished Encoding Rules (DER), or Canonical Encoding Rules (CER) as
published in the ITU-T X.690 and ISO/IEC 8825-1 standards.
• Packed Encoding Rules (PER) as published in the ITU-T X.691 and ISO/IEC 8825-2 standards. Both aligned and
unaligned variants are supported via a switch that is set at run-time.
• XML Encoding Rules (XER) as published in the ITU-T X.693 and ISO/IEC 8825-3 standards.
• Medical Device Encoding Rules (MDER) as published in the ISO/IEEE 11073 standards.
• Octet Encoding Rules (OER) as published in the NTCIP 1102:2004 standard.
Additional support for XML is provided in the form of an option to generate an equivalent XML Schema Definitions
(XSD) file for a given ASN.1 specification. Encoders and decoders can then be generated using the -xml option to
format or parse XML documents that conform to this schema. This level of support is closer to the W3C definition of
XML then is the ITU-T X.693 XER definition. As of release version 6.0, it is possible to compile an XML schema
definitions (XSD) file and generate encoders/decoders that can generate XML in compliance with the schema as well
as binary encoders/encoders that implement the ASN.1 binary encoding rules.
ASN1C is capable of parsing all ASN.1 syntax as defined in the standards. It is capable of parsing advanced syntax
including Information Object Specifications as defined in the ITU-T X.681 standard as well as Parameterized Types as
defined in ITU-T X.683. The compiler is also capable of using table constraints as defined in ITU-T X.682 to generate
single-step encoders and decoders that can encode or decode multi-part messages in a single function call.
ASN1C also contains a special command-line option - -asnstd x208 - that allows compilation of deprecated features
from the older X.208 and X.209 standards. These include the ANY data type and unnamed fields in SEQUENCE,
SET, and CHOICE types. The compiler can also parse type syntax from common macro definitions such as the ROSE
OPERATION and ERROR macros.
1
Chapter 2. Using the Compiler
Running ASN1C from the Command-line
The ASN1C compiler distribution contains command-line compiler executables as well as a graphical user interface
(GUI) wizard that can aid in the specification of compiler options. This section describes how to run the commandline version; the next section describes the GUI.
To test if the compiler was successfully installed, enter asn1c with no parameters as follows (note: if you have not
updated your PATH variable, you will need to enter the full pathname):
asn1c
You should observe the following display (or something similar):
ASN1C Compiler, Version 6.7.x
Copyright (c) 1997-2013 Objective Systems, Inc. All Rights Reserved.
Usage: asn1c <filename> <options>
<filename>
language options:
-c
-c++
-c++11
-c#
-java
-cldc
-xsd [<filename>]
ASN.1 or XSD source filename(s). Multiple filenames
may be specified. * and ? wildcards are allowed.
generate
generate
generate
generate
generate
generate
generate
C code
C++ code
C++ code that uses C++11 features
C# code
Java code
Java ME CLDC compatible code
XML schema definitions
encoding rule options:
-ber
generate BER encode/decode functions
-cer
generate CER encode/decode functions
-der
generate DER encode/decode functions
-oer
generate OER encode/decode functions
-mder
generate MDER encode/decode functions
-per
generate PER encode/decode functions
-uper
generate unaligned PER encode/decode functions
-xer
generate XER encode/decode functions
-xml
generate XML encode/decode functions
-json
generate JSON encode/decode functions
-3gl3
generate 3GPP layer 3 encode/decode functions
basic options:
-asn1 [<file>]
-asnstd <std>
-compact
-compat <version>
generate pretty-printed ASN.1 source code
set standard to be used for parsing ASN.1
source file. Possible values - x208, x680, mixed
(default is x680)
generate compact code
generate code compatible with previous
2
Using the Compiler
compiler version. <version> format is
x.x (for example, 5.3)
-config <file>
specify configuration file
-depends
compile main file and dependent IMPORT items
-events
generate code to invoke SAX-like event handlers
-genTest [<filename>] generate sample test functions
-html
generate HTML marked-up version of ASN.1
-I <directory>
set import file directory
-lax
do not generate constraint checks in code
-laxsyntax
do not do a thorough ASN.1 syntax check
-list
generate listing
-allow-ambig-tags
allow ambiguous tags in input specifications
-noContaining
do not generate inline type for CONTAINING <type>
-nodatestamp
do not put date/time stamp in generated files
-nodecode
do not generate decode functions
-noencode
do not generate encode functions
-noIndefLen
do not generate indefinite length tests
-noObjectTypes
do not gen types for items embedded in info objects
-noOpenExt
do not generate open extension elements
-notypes
do not generate type definitions
-noxmlns
do not generate XML namespaces for ASN.1 modules
-o <directory>
set output file directory (also '-srcdir <dir>')
-libdir <directory> set output libraries directory
-bindir <directory> set output binary directory
-objdir <directory> set output object directory
-param <name>=<value> create types from param types using given value
-pdu <type>
designate <type> to be a Protocol Data Unit (PDU)
(<type> may be "all" to select all type definitions)
-usepdu <type>
specify a Protocol Data Unit (PDU) type for which
sample reader/writer programs and test code has to
be generated
-print [<filename>] generate print functions
-prtfmt details | bracetext format of output generated by print
-shortnames
reduce the length of compiler generated names
-strict
do strict checking of table constraint conformance
-syntaxcheck
do syntax check only (no code generation)
-reader
generate sample reader program
-trace
add trace diag msgs to generated code
-[no]UniqueNames
resolve name clashes by generating unique names
default=on, use -noUniqueNames to disable
-warnings
output compiler warning messages
-writer
generate sample writer program
C/C++ options:
-array
use arrays for SEQUENCE OF/SET OF types
-arraySize <size>
specify the size of the array variable
-compare [<filename>] generate comparison functions
-copy [<filename>] generate copy functions
-cppNs <namespace> add a C++ namespace to generated code (C++ only)
-dynamicArray
use dynamic arrays for SEQUENCE OF/SET OF types
-linkedList
use linked-lists for SEQUENCE OF/SET OF types
-hfile <filename>
C or C++ header (.h) filename
(default is <ASN.1 Module Name>.h)
-cfile <filename>
C or C++ source (.c or .cpp) filename
3
Using the Compiler
(default is <ASN.1 Module Name>.c)
generate named bit set, clear, test macros
generate memory free functions for all types
add prefix to header guard #defines in .h files
generate separate file for each function
set limit of number of lines per source file
(default value is 50000)
-noBitStr32
do not use BitStr32 type for small bit strings
-noEnumConvert
do not generate conversion functions for enumerated
items (BER/CER/DER/PER only)
-noInit
do not generate initialization functions
-oh <directory>
set output directory for header files
-perIndef
add support for PER indefinite (fragmented) lengths
-perPadBitStrings
pad bit strings that contain other types to octet
boundary
-prtToStrm [<filename>] generate print-to-stream functions
-static
generate static elements (not pointers)
-stream
generate stream-based encode/decode functions
-strict-size
strictly interpret size constraints
-table-unions
generate union structures for table constraints
-use-enum-types
use generated enum types in code instead of integers
-genBitMacros
-genFree
-hdrGuardPfx <pfx>
-maxcfiles
-maxlines <num>
C/C++ makefile/project options:
-genMake [<filename>] generate makefile to compile generated code
-genMakeDLL [<filename>] generate makefile to build DLL
-genMakeLib [<filename>] generate makefile to build static library
-make [<filename>] same as -genMake as described above.
-nmake [<filename>] generate Windows nmake file (same as -genMake -w32)
-vcproj [<version>] generate Visual Studio project files.
<version> is 2013, 2012, 2010 (default), 2008, 2005,
2003, vc6 (Windows only).
-builddll
generate makefile/project to build DLL
-dll, -usedll
generate makefile/project to use DLL's
-mt
generate makefile/project to use multithreaded libs
-w32
generate code for Windows 32-bit O/S (default=GNU)
-w64
generate code for Windows 64-bit O/S (default=GNU)
Java options:
-compare
-dirs
-genbuild
-genant
-genjsources
-getset
-noevents
-pkgname <text>
-pkgpfx <text>
-tables
-java4
C# options:
-nspfx <text>
-namespace <text>
generate comparison functions
output Java code to module name dirs
generate build script
generate ant build.xml script
generate <modulename>.mk for list of java files
generate get/set methods and protected member vars
disable generation of event handler code. Also
disables element tracking for error handling.
Java package name
Java package prefix
generate table constraint functions
generate code for Java 1.4
C# namespace prefix
C# namespace name
4
Using the Compiler
-dirs
-csfile <filename>
-gencssources
-genMake
-tables
-vcproj [version]
output C# code to module name dirs
generate one .cs file or one per module (*.cs)
generate <modulename>.mk for list of C# files
generate makefile to build generated code
generate table constraint functions
generate Visual Studio C# project files.
[version] is 2012, 2010 (default), 2008, 2005.
(Windows only)
XSD options:
-appinfo [<items>] generate appInfo for ASN.1 items
<items> can be tags, enum, and/or ext
ex: -appinfo tags,enum,ext
default = all if <items> not given
-attrs [<items>]
generate non-native attributes for <items>
<items> is same as for -appinfo
-targetns [<namespace>] Specify target namespace
<namespace> is namespace URI, if not given
no target namespace declaration is added
-useAsn1Xsd
reference types in asn1.xsd schema
license options:
-lickey <key>
set license key value
Note that this usage summary shows all options for the pro version of ASN1C. Some of these options are not available
in the basic version.
To use the compiler, at a minimum, an ASN.1 or XSD source file must be provided. The source file specification can
be a full pathname or only what is necessary to qualify the file. If directory information is not provided, the user's
current default directory is assumed. If a file extension is not provided, the default extension ".asn" is appended to
the name. Multiple source filenames may be specified on the command line to compile a set of files. The wildcard
characters ‘*’ and ‘%’ are also allowed in source filenames (for example, the command asn1c *.asncode> will
compile all ASN.1 files in the current working directory).
The source file(s) must contain ASN.1 productions that define ASN.1 types and/or value specifications. This file
must strictly adhere to the syntax specified in ASN.1 standard ITU-T X.680. The -asnstd x208 command-line option
should be used to parse files based on the 1990 ASN.1 standard (x.208) or that contain references to ROSE macro
specifications.
The following table lists all of the command line options and what they are used for. The options are shown in
alphabetical order. Note that the Java and C# options are not shown here. They are shown in their respective documents.
Option
Argument
Description
-3gl3
None
This option is used to generate code for encoding and
decoding 3GPP Layer 3 messages. Support is primarily
provided for Non-Access Stratum (NAS) message types
as defined in 3GPP TS 24.007, 24.008 , and 24.301 (LTENAS). As of this release, only the C language is supported.
-allow-ambig-tags
None
This option suppresses the check that is done for
ambiguous tags within a SEQUENCE or SET type within
a specification. Special code is generated for the decoder
that assigns values to ambiguous elements within a SET
5
Using the Compiler
Option
Argument
Description
in much the same way as would be done if the elements
were declared to be in a SEQUENCE. This option used to
be called -noAmbigTag.
-appInfo
<items>
This option only has meaning when generating an XML
schema definitions (XSD) file using the -xsd option.
It instructs the compiler to generate an XSD application
information section (<appinfo>) for certain ASN.1-only
items. The items are specified as a comma-delimited list.
Valid values for items are tags, enum, and ext.
<items> is an optional parameter. If it is not specified,
it is assumed that application information should be
produced for all three item classes: ASN.1 tags, ASN.1
enumerations, and extended elements.
-array
none
This option specifies that an array type will be used for
SEQUENCE OF/SET OF constructs.
-arraySize
<size>
This option specifies the default size of static array
variables. This will be overridden by the value of a SIZE
constraint on the given type, if it exists.
-asn1
<filename>
This option causes pretty-printed ASN.1 to be generated to
the given file name or to stdout if no filename was given.
Besides the obvious use of providing neatly formatted
ASN.1 source code, the option is also useful for producing
ASN.1 source code from XML schema document (XSD)
files as well as producing trimmed specifications when
<include> or <exclude> configuration directives are used.
-asnstd
x208
x680
mixed
This option selects the version of ASN.1 syntax to be
parsed. ‘x680’ (the default) refers to modern ASN.1 as
specified in the ITU-T X.680-X.690 series of standards.
‘x208’ refers to the now deprecated X.208 and X.209
standards. This syntax allowed the ANY construct as well
as unnamed fields in SEQUENCE, SET, and CHOICE
constructs. This option also allows for parsing and
generation of code for ROSE OPERATION and ERROR
macros and SNMP OBJECTTYPE macros. The ‘mixed’
option is used to specify a source file that contains
modules with both X.208 and X.680 based syntax.
-attrs
<items>
This option only has meaning when generating an XML
schema definitions (XSD) file using the -xsd option.
It instructs the compiler to generate non-native attributes
for certain ASN.1-only items that cannot be expressed in
XSD. The items are specified as a comma-delimited list.
Valid values for items are tags, enum, and ext.
<items> is an optional parameter. If it is not specified,
it is assumed that application information should be
produced for all three item classes: ASN.1 tags, ASN.1
enumerations, and extended elements.
6
Using the Compiler
Option
Argument
Description
-ber
None
This option is used to generate encode/decode functions
that implement the Basic Encoding Rules (BER) as
specified in the X.690 ASN.1 standard.
-bindir
<directory>
This option is used in conjunction with the -genMake
option to specify the name of the binary executable
directory to be added to the makefile. Linked executable
programs will be output to this directory.
-bitMacros
None
This option is used to generate additional macros to set,
clear, and test named bits in BIT STRING constructs.
By default, only bit number constants are generated. Bit
macros provide slightly better performance because mask
values required to do the operations are computed at
compile time rather than runtime.
-c
None
Generate C source code.
-c# or -csharp
None
Generate C# source code. See the ASN1C C# User’s Guide
for more information and options for generating C# code.
-c++ or -cpp
None
Generate C++ source code.
-c++11 or -cpp11
None
Generate code that uses C++11 features. This includes the
use of std::string for character strings, std::list for lists, and
std::array for static arrays. For more information, refer to
the sections on type mappings for SEQUENCE OF and for
character strings. See also the section on Considerations
When Using C++ Standard Library features.
-cer
None
This option isued to generate encode/decode functions
that implement the Canonical Encoding Rules (CER) as
specified in the X.690 ASN.1 standard.
-cfile
[<filename>]
This option allows the specification of a C or C++ source
(.c or .cpp) file to which all of the generated encode/
decode functions will be written. If not specified, the
default is to write to a series of .c or .cpp files based on the
ASN.1 module name(s) of the documents being compiled.
-compact
None
This option is used to generate more compact code at
the expense of some constraint and error checking. This
is an optimization option that should be used after an
application is thoroughly tested.
-compat
<versionNumber>
Generate code compatible with an older version of
ASN1C. The compiler will attempt to generate code more
closely aligned with the given previous release of the
compiler.
<versionNumber> is specified as x.x (for example, compat 5.2)
-config
<filename>
This option is used to specify the name of a file containing
configuration information for the source file being parsed.
A full discussion of the contents of a configuration file is
provided in the Compiler Configuration File section.
7
Using the Compiler
Option
Argument
Description
-cppns
<namespace>
This option is used to add a C++ namespace name to
generated C++ files.
-depends
None
This option is used to generate a full set of header and
source files that contain only the productions in the main
file being compiled and items those productions depend
on from IMPORT files.
-der
None
This option is used to generate encode/decode functions
that implement the Distinguished Encoding Rules (DER)
as specified in the X.690 ASN.1 standard.
-dll
None
When used in conjunction with the -genMake commandline option, the generated makefile uses dynamicallylinked libraries (DLLs in Windows, or .so files in UNIX)
instead of statically-linked libraries.
-dynamicArray
none
This option specifies that a dynamic array type is to be
used for SEQUENCE OF/SET OF constructs.
-genbuild
None
This option is used to generate a build script when
producing Java source code. The generated build script is
either a batch file (Windows) or a shell script (UNIX).
-genCompare
-compare
[<filename>]
This option allows the specification of a C or C++ source
(.c or .cpp) file to which generated compare functions will
be written. Compare functions allow two variables of a
given ASN.1 type to be compared for equality.
The <filename> argument to this option is optional.
If not specified, the functions will be written to
<modulename>Compare.c where <modulename> is the
name of the module from the ASN.1 source file.
-genCopy
-copy
[<filename>]
This option allows the specification of a C or C++ source
(.c or .cpp) file to which generated copy functions will
be written. Copy functions allow a copy to be made of
an ASN1C generated variable. For C++, they cause copy
constructors and assignment operators to be added to
generated classes.
The <filename> argument to this option is optional.
If not specified, the functions will be written to
<modulename>Copy.c where <modulename> is the name
of the module from the ASN.1 source file.
-genFree
None
This option instructs the compiler to generate a memory
free function for each ASN.1 production. Normally,
memory is freed within ASN1C by using the rtxMemFree
run-time function to free all memory at once that is held
by a context. Generated free functions allow finer grained
control over memory freeing by just allowing the memory
held for specific objects to be freed.
-genMake
[<filename>]
This option instructs the compiler to generate a portable
makefile for compiling the generated C or C++ code. If
used with the -w32 command-line option, a makefile
that is compatible with the Microsoft Visual Studio
8
Using the Compiler
Option
Argument
Description
nmake utility is generated; otherwise, a GNU-compatible
makefile is generated.
Note that the -nmake option may now be used instead of
the -make -w32 combination to produce a Visual Studio
makefile.
-genMakeDLL
[<filename>]
This option instructs the compiler to generate a portable
makefile for compiling the generated C or C++ code into
a Dynamic Link Library (DLL).
-genMakeLib
[<filename>]
This option instructs the compiler to generate a portable
makefile for compiling the generated C or C++ code into
a static library file.
-genPrint
-print
[<filename>]
This option allows the specification of a C or C++ source
(.c or .cpp) file to which generated print functions will be
written. Print functions are debug functions that allow the
contents of generated type variables to be written to stdout.
The <filename> argument to this option is optional.
If not specified, the print functions will be written to
<modulename>Print.c where <modulename> is the name
of the module from the ASN.1 source file.
-genPrtToStr -prtToStr
[<filename>]
This option allows the specification of a C or C++
source (.c or .cpp) file to which generated "print-to-string"
functions will be written. "Print-to-string" functions are
similar to print functions except that the output is written
to a user-provided text buffer instead of stdout. This makes
it possible for the use to display the results on different
output devices (for example, in a text window).
The <filename> argument to this option is optional.
If not specified, the functions will be written to
<modulename>Print.c where <modulename> is the name
of the module from the ASN.1 source file.
-genPrtToStrm -prtToStrm [<filename>]
This option allows the specification of a C or C++ source
(.c or .cpp) file to which generated "print-to-stream"
functions will be written. "Print-to-stream" functions are
similar to print functions except that the output is written
to a user-provided stream instead of stdout. The stream is
in the form of an output callback function that can be set
within the run-time context making it possible to redirect
output to any type of device.
The <filename> argument to this option is optional.
If not specified, the functions will be written to
<modulename>Print.c where <modulename> is the name
of the module from the ASN.1 source file.
-genTables
-tables
[<filename>]
This option is used to generate additional code for the
handling of table constraints as defined in the X.682
standard. See the Generated Information Object Table
Structures section for additional details on the type
of code generated to support table constraints. Note:
9
Using the Compiler
Option
Argument
Description
An alternaitve option for C/C++ is -table-unions which
generates union structures for table constraints. These are
generally easier to work with then the legacy void pointer
approach used in this option.
-genTest
[<filename>]
This option allows the specification of a C or C++ source
(.c or .cpp) file to which generated "test" functions will be
written. "Test" functions are used to populate an instance
of a generated PDU type variable with random test data.
This instance can then be used in an encode function call
to test the encoder. Another advantage of these functions
is that they can act as templates for writing your own
population functions.
The <filename> argument to this option is optional.
If not specified, the functions will be written to
<modulename>Test.c where <modulename> is the name
of the module from the ASN.1 source file.
-hdrGuardPrefix
[<prefix>]
This option allows the specification of a prefix that will
be used in the generated #defines that are added to header
files to make sure they are only included once.
-hfile
[<filename>]
This option allows the specification of a header (.h)
file to which all of the generated typedefs and function
prototypes will be written. If not specified, the default is
<modulename>.h where <modulename> is the name of
the module from the ASN.1 source file.
-html
None
This option is used to generated HTML markup for every
compiled ASN.1 file. This markup contains hyperlinks to
all referenced items within the specifications. One HTML
file is generated for each corresponding ASN.1 source file.
-I
<directory>
This option is used to specify a directory that the compiler
will search for ASN.1 source files for IMPORT items.
Multiple –I qualifiers can be used to specify multiple
directories to search.
-java
None
Generate Java source code. See the ASN1C Java User’s
Guide for more information on Java code generation.
-json
None
This option is used to generate encode/decode functions
for Javascript Object Notation (JSON). See our
whitepaper Javascript Object Notation (JSON) Encoding
Rules for more information.
-lax
None
This option instructs the compiler to not generate code to
check constraints. When used in conjunction with the compact option, it produces the smallest code base for a
given ASN.1 specification.
-laxsyntax
None
This option instructs the compiler to not do a thorough
syntax check when compiling a specification and to
generate code even if the specification contains non-fatal
syntax errors. Use of the code generated in this case can
have unpredictable results; however, if a user knows that
10
Using the Compiler
Option
Argument
Description
certain parts of a specification are not going to be used,
this option can save time.
-libdir
<directory>
This option is used in conjunction with the -genMake
option to specify the name of the library directory to be
added to the makefile.
-lickey
<key-value>
This option is used to enter a license key value that was
provided to the user to enable the compiler for either
evaluation or permanent use.
-linkedList
none
This option specifies that a linked-list type is to be used
for SEQUENCE OF/SET OF constructs.
-list
None
Generate listing. This will dump the source code to the
standard output device as it is parsed. This can be useful
for finding parse errors.
-maxcfiles
None
Maximize number of generated C files. This option
instructs the compiler to generate a separate .c file for each
generated C function. In the case of C++, a separate .cpp
file is generated for each control class, type, and C
function. This is a space optimization option - it can lead
to smaller executable sizes by allowing the linker to only
link in the required program module object files.
-maxlines
<number>
This option is used to specify the maximum number
of lines per generated .c or .cpp file. If this number is
exceeded, a new file is started with a "_n" suffix where "n"
is a sequential number. The default value if not specified
is 50,000 lines which will prevent the VC++ "Maximum
line numbers exceeded" warning that is common when
compiling large ASN.1 source files.
Note that this number is approximate - the next file
will not be started until this number is exceeded and
the compilation unit that is currently being generated is
complete.
-mder
None
This option is used to generate functions that implement
the Medical Device Encoding Rules (MDER) as specified
in the IEEE/ISO 11073 standard.
-mt
None
When used in conjunction with the -genMake commandline option, the generated makefile uses multi-threaded
libraries.
-nmake
[<filename>]
This option instructs the compiler to generate a Visual
Studio compatible makefile. It is equivalent to using the genMake -w32 combination of command-line options.
-noContaining
None
This option suppresses the generation of inline code to
support the CONTAINING keyword. Instead, a normal
OCTET STRING or BIT STRING type is inserted as was
done in previous ASN1C versions.
-nodecode
None
This option suppresses the generation of decode functions.
-noencode
None
This option suppresses the generation of encode functions.
11
Using the Compiler
Option
Argument
Description
-noIndefLen
None
This option instructs the compiler to omit indefinite length
tests in generated decode functions. These tests result in
the generation of a large amount of code. If it is known
that an application only uses definite length encoding, this
option can result in a much smaller code base size.
-noInit
None
This option is used to suppress the generation of
initialization functions. A variable of a generated structure
can always be initialized by memset’ing the variable to
zero. However, this is not usually the most efficient way to
initialize a variable because if it contains large byte arrays,
a significant amount of processing is required to set all
bytes to zero (and they don’t need to be). Initialization
functions provide a smart alternative to memset’ing in that
only what needs to be set to zero actually is.
Note that previous versions of ASN1C did not generate
initialization functions by default. The -genInit switch has
been deprecated in favor of -noInit.
-noEnumConvert
None
This option suppresses the generation of utility functions
in C and C++ that assist in converting enumerated values
to strings and vice versa. XER and XML encodings are
unaffected by this option, since conversions are necessary
for encoding and decoding.
-noObjectTypes
None
This option suppresses the generation of application
language types corresponding to ASN.1 types embedded
within information object definitions.
-noOpenExt
None
This option suppresses addition of an open extension
element (extElem1) in constructs that contain extensibility
markers. The purpose of the element is to collect any
unknown items in a message. If an application does not
care about these unknown items, it can use this option to
reduce the size of the generated code.
-notypes
None
This options suppresses the generation of type definitions.
It is used in conjunction with the -events options to
generate pure parser functions.
-noxmlns
None
This option suppresses the insertion of XML namespace
entries in generated XML documents. This includes
xmlns attributes and prefixed names.
-nouniquenames
None
This option suppresses the automatic generation of unique
names to resolve name clashes in the generated code.
Name clashes can occur, for example, if two modules are
being compiled that contain a production with the same
name. A unique name is generated by prepending the
module name to one of the productions to form a name of
the form <module>_<name>.
Note that name collisions can also be manually resolved
by using the typePrefix, enumPrefix, and valuePrefix
configuration items (see the Compiler Configuration File
section for more details).
12
Using the Compiler
Option
Argument
Description
Previous versions of ASN1C did not generate unique
names by default. The compiler option -uniquenames has
been deprecated in favor of -nouniquenames.
-o
<directory>
This option is used to specify the name of a directory to
which all of the generated files will be written.
-objdir
<directory>
This option is used in conjunction with the -genMake
option to specify the name of the object file directory to be
added to the makefile. Compiled object files will be output
to this directory.
-oh
<directory>
This option is used to specify the name of a directory to
which only the generated header files (*.h) will be written.
-oer
None
This option is used to generate encode/decode functions
that implement the Octet Encoding Rules (OER) as
specified in the NTCIP 1102:2004 standard. Currently
only the C language is supported.
-param
<name>=<value>
This option is used to instantiate all parameterized types
within the ASN.1 modules that are being compiled with
the given parameter value. In this declaration, <name>
refers to the dummy reference in a parameterized type
definition and <value> refers to an actual value.
-pdu
<typeName>
Designate given type name to be a "Protocol Definition
Unit" (PDU) type. This will cause a C++ control class to
be generated for the given type. By default, PDU types are
determined to be types that are not referenced by any other
types within a module. This option allows that behavior
to be overridden.
The "all" keyword may be specified for <typeName> to
indicate that all productions within an ASN.1 module
should be treated as PDU types.
-per
None
This option is used to generate encode/decode functions
that implement the Packed Encoding Rules (PER) as
specified in the ASN.1 standards.
-perindef
None
This option is used to generate encode/decode functions
that implement the Packed Encoding Rules (PER) as
specified in the ASN.1 standards including support for
indefinite (fragmented) lengths.
-prtfmt
bracetext
details
Sets the print format for generated print functions. The
details option causes a line-by-line display of all generated
fields in a generated structure to be printed. The bracetext
option causes a more concise printout showing only the
relevant fields in a C-like brace format. As of release
version 6.0, bractext is the default (details was the default
or only option in previous versions).
-shortnames
None
Generate a shorter form of an element name for a deeply
nested production. By default, all intermediate names are
used to form names for elements in nested types. This
can lead to very long names for deeply nested types.
13
Using the Compiler
Option
Argument
Description
This option causes only the production name and the last
element name to be used to form a generated type name.
-static
None
This has the same effect as specifying the global
<storage> static </storage> configuration item. The
compiler will insert static elements instead of pointer
variables in some generated structures.
-stream
None
This option is used to generate stream-based encoders/
decoders instead of memory buffer based. This makes it
possible to encode directly to or decode directly from a
source or sink such as a file or socket. In the case of BER,
it will also cause forward encoders to be generated which
will use indefinite lengths for all constructed elements in
a message.
Note that stream and memory-buffer based encode/decode
functions cannot be used/combined in any way. The two
are mutually exclusive. If the -stream option is selected,
then only stream-based run-time functions can be used
with the generated code.
-strict
None
This option is used to generate code for strict validation
of table constraints. By default, generated code will not
check for value field constraints.
-strict-size
None
This option causes strict interpretation of size constraints
to be enabled. This may result in the generation of
more optimized code as unnecessary size variable holders
are eliminated. For example, a declaration of OCTET
STRING (SIZE(10)) will result in the generation of a 10
byte static array rather than a structure with a count field
and array.
-syntaxcheck
None
This option is used to do a syntax check of the ASN.1
source files only. No code is generated.
-table-unions
None
This option is used to generate union structures for table
constraints in C/C++ instead of void pointers as is done
when the -tables option is used. These are generally easier
to use as they present all options in a user-friendly way.
-targetns
<namespace>
This option only has meaning when generating an XML
schema definitions (XSD) file using the -xsd option.
It allows specification of a target namespace.
<namespace> is a namespace URI; if it is not provided,
no target namespace declaration is added to the generated
XSD file.
-trace
None
This option is used to tell the compiler to add trace
diagnostic messages to the generated code. These
messages cause print statements to be added to the
generated code to print entry and exit information into
the generated functions. This is a debugging option
that allows encode/decode problems to be isolated to a
given production processing function. Once the code is
14
Using the Compiler
Option
Argument
Description
debugged, this option should not be used as it adversely
affects performance.
-uper
None
This option is used to specify the generation of code to
support the unaligend variant of the Packed Encoding
Rules (PER). This provides for slightly more compact
code than the -per option because alignment checks are
removed from the generated code.
-use-enum-types
None
This option is used to specify that generated enumerated
types are to be used directly in the code as opposed to
integer types. The advantages of integer types are a) they
are of a known size, and b) they can store unknown
identifiers that may be received for extensible enumerated
types. However, the direct use of enumerated types makes
it easier to inspect variables using the debugger in various
IDE's.
-usepdu
<PDU type name>
This option is used to specify the name of the Protocol
Data Unit (PDU) type to be used in generated reader and
writer programs.
-vcproj
vc6
2003
2005
2008
2010
2012
This option is used to generate Visual C++- or Visual
Studio-compatible project files to compile generated
source code. This is a Windows-only option. By passing
one of the listed years, the compiler will generate a project
that links against libraries provided for those versions of
Visual Studio or Visual C++. For example, specifying
2005 will generate a project that links against libraries in
the *_vs2005 directory. Not specifying a year will cause
the compiler to link against libraries compiled for Visual
Studio 2010.
A custom build rule is generated that deletes the generated
source files and then invokes ASN1C to regenerate them
when a rebuild is done. Doing a clean operation will cause
the generated source files to be deleted; a subsequent build
will regenerate them.
For Visual C++ 6.0 project files you can see this build rule
by locating the first ASN.1 file under the Source Files for
the project, right clicking it, choosing Settings... and then
choosing the Custom Build tab.
For Visual Studio 2005, 2008, 2010, and 2012 project files
the procedure to see the custom rule is very similar to
that for Visual C++ 6.0, except that you choose Properties
when you right click on the first ASN.1 file, and then click
on Custom Build Step or Custom Build Tool on the left.
-w32
None
This option is used with makefile and/or Visual Studio
project generation to indicate the generated file is to be
used on a Windows 32-bit system. In the case of makefile
generation, this will cause a makefile to be generated that
is compatible with the Visual Studio nmake utility.
15
Using the Compiler
Option
Argument
Description
-w64
None
This option is similar to the -w32 option documented
above except that it specifies a Windows 64-bit system.
-warnings
None
Output information on compiler generated warnings.
-xer
None
This option is used to generate encode/decode functions
that implement the XML Encoding Rules (XER) as
specified in the X.693 ASN.1 standard. The -xsd option
can be used in conjunction with this option to generate a
schema describing the XML format.
-xml
None
This option is used to generate encode/decode functions
that encode/ decode data in an XML format that is
more closely aligned with World-Wide Web Consortium
(W3C) XML schema. The -xsd option can be used
in conjunction with this option to generate a schema
describing the XML format.
-xsd
[<filename>]
This option is used to generate an equivalent XML
Schema Definition (XSD) for each of the ASN.1
productions in the ASN.1 source file. The definitions are
written to the given filename or to <modulename>.xsd
if the filename argument is not provided. There are
two supported mappings from ASN.1 to XSD, one
corresponding to the -xml option and one corresponding
to the -xer option. The default is to follow the -xml variant.
If the -xer option is given, then that variant is followed.
Using the GUI Wizard to Run ASN1C
ASN1C includes a graphical user interface (GUI) wizard that can be used as an alternative to the command-line version.
It is a cross-platform GUI and has been ported to Windows and several UNIXes. The GUI makes it possible to specify
ASN.1 files and configuration files via file navigation windows, to set command line options by checking boxes, and
to get online help on specific options.
The Windows installation program should have installed an ‘ASN1C Compiler’ option on your computer desktop and
an ‘ASN1C’ option on the start menu. The wizard can be launched using either of these items. The UNIX version
should be installed in ASN1C_INSTALL_DIR/bin; no desktop shortcuts are created, so it will be necessary to create
one or to run the wizard from the command-line.
Using Projects
The wizard is navigated by means of Next and Back buttons. Following is the initial window:
16
Using the Compiler
17
Using the Compiler
The status window will display the version of the software you have installed as well as report any errors upon startup
that occur, such as a missing license file.
The Project Wizard will allow you to save your compilation options and file settings into a project file and retrieve
them later. If you wish to make a new project, click the icon next to Create a New Project:
Previously saved projects may be recalled by clicking the icon next to Open an Existing Project:
18
Using the Compiler
The project format has changed in ASN1C 6.3 to help accommodate the transition to Qt 4.5. Changes to the interface
necessitated changes to the underlying project file format. Projects made with previous versions may be loaded with
version 6.3, but new projects are incompatible with previous versions. Additional metadata are stored in the project
file to help with version tracking.
Files may be added to a project in the following window:
19
Using the Compiler
20
Using the Compiler
In this window, the ASN.1 file or files to be compiled are selected. This is done by clicking the Add button on the right
hand side of the top windows pane. A file selection box will appear allowing you to select the ASN.1 or XSD files to
be compiled. Files can be removed from the pane by highlighting the entry and clicking the Remove button.
ASN.1 specifications and XML Schema Documents must not be compiled in the same project. Once an ".asn" file has
been added, no ".xsd" files may be added.
Include directories are selected in a similar manner in the middle pane. These are directories the compiler will search for
import files. By default, the compiler looks for files in the current working directory with the name of the module being
imported and extension ".asn" or ".xsd". Additional directories can be searched for these files by adding them here.
User-defined configuration files are specified in the third pane. These allow further control of the compilation process.
They are optional and are only needed if the default compilation process is to be altered (for example, if a type prefix is
to be added to a generated type name). See the Compiler Configuration File section for details on defining these files.
Common Code Generation Options
Code generation options common to all language types are specified in the following tabbed window:
21
Using the Compiler
22
Using the Compiler
Language options, pictured above, encompass not only the output language choice, but also input specification type,
encoding rules, and code compatibility options.
Certain options will be inactive (greyed out) depending on the file type selected. For example, if an XSD file is selected,
the option Generate ASN.1 file based on X.694 will be active and the option Generate equivalent XML schema (XSD)
file will be inactive.
Checking Generate code for all dependent imported type definitions will cause the compiler to search and generate
code for modules specified in the IMPORTS statement of an ASN.1 specification.
Basic encoding rules are selected by default. Only one of BER, DER, and CER can be checked at any time. XML and
XER are also mutually exclusive options.
Generated function options are shown in the following tab:
23
Using the Compiler
24
Using the Compiler
The options in this tab control which functions are generated and what modifications are made to those functions.
By default, encoding and decoding functions are generated by the compiler. If the target application does not require
encoding or decoding capabilities (for example, if it is only intended to read messages and does not need to write
them), unchecking the corresponding checkbox will reduce the amount of code generated.
Check Stream to modify generated encode and decode functions to use streams instead of memory buffers. This allows
encoding and decoding to a source or sink such as a file or socket. Stream-based encoding and decoding cannot be
combined with buffer-based.
As an aid to debugging, Print functions may also be generated. Three different different types exist: print to stdout,
print to string, and print to stream. These allow the contents of generated types to be printed to the standard output,
a string, or a stream (such as a file or socket).
Constraint checking may be relaxed or tightened depending on selected options. Constraints may be ignored completely
by checking Do not generate constraint checks. To tighten constraints, check Enable strict constraint checks. ASN1C
supports decoding and encoding values described by table constraints; checking Generate code to handle table
constraints will enable this behavior. This option is a legacy option for C and C++ code generation: generating table
constraints in unions is the preferred method (see the following section).
To reduce the code footprint, several other options may be selected: Generate compact code, Do not generate indefinite
length processing code, Do not generate code to save/restore unknown extensions, and Do not generate types for items
embedded in information objects may all be used to reduce the amount of generated code. Generate compact code
cannot be used in conjunction with Generate compatible code. If XML validation is not needed, check Do not generate
XML namespaces for ASN.1 modules. This will result in a smaller codebase as well as smaller output XML data. Check
Generate short form of type names if generated type names are too long for the target language.
The following tab provides options for generating utility functions and applications:
25
Using the Compiler
26
Using the Compiler
The Sample Program Generation frame allows you to generate boilerplate reader and writer applications as well as
randomized test data for populating a sample encoded message. The items in the Protocol Data Units frame may be
used in conjunction to select the appropriate PDU data type to be used in the sample programs.
The Debugging and Event Handlers frame contains options that generate code for adding trace diagnostics and event
handling hooks into generated code. It is possible to generate a type parser by generating only an event handler and
no data types for the decoded messages. This grants a great deal of flexibility in handling input data at the expense
of generating pre-defined functions for most common encoding and decoding tasks. Users of embedded systems may
find this useful as it will shrink the output considerably while allowing them fine control over decoding procedures.
The Other Options frame contains miscellaneous modifications to code output, including type name resolution
(avoiding duplicate names), date stamp removal (useful when generated code will be stored in source control), and a
line item for including any new command-line features not yet represented in the GUI.
XSD Options
If the Generate equivalent XML schema (XSD) file option was checked in the Common Code Generation Options
screen, the following window will be presented for modifying the contents of the generated XSD:
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These options are described in Running ASN1C from the command-line.
C/C++ Code Generation Options
The following windows describe the options available for generating C or C++ source code.
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The first tab, Code Modifications, contains options for adding C/C++-specific function types, adding type modifiers,
and changing how files are output.
By default, ASN1C generates initialization functions that are used by generated code to ensure that newly-constructed
types have appropriate default values. Memory free functions are not generated by default, but may be added when
users need to free specific types individually instead of relying on ASN1C's built-in memory management functions.
Bit macro functions may also be generated for setting, clearing, and testing bits in BIT STRING productions.
Table constraints in C/C++ were modified for ASN1C version 6.2 to make their data structures easier to manipulate.
The table unions option causes a CHOICE-like union structure to be generated for information object classes. In
practice, the generated code is more compact, easier to read, and confers several advantages for developers (principally
type safety and readability).
The Generate static elements option is used to add static elements to CHOICE constructs instead of pointer values.
Using fully-qualified enumerated types will cause ASN1C to emit enumerated types prefixed by their parent module
name. Enumerated types are often reused in different modules, and ASN1C's automatic name resolution is usually
insufficient to disambiguate which type is which. This option only needs to be selected in C, since C++ enumerations
are contained in classes.
The other options are described in greater detail in Running ASN1C from the command-line.
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The preceding window contains options for generating makefiles and Visual Studio projects. Makefile and project
targets may be modified by selecting Generate Libraries or Link applications using shared libraries. If the latter option
is checked, applications will be dynamically linked instead of statically linked.
Compilation
When all options have been specified, the final screen may be used to execute the compilation command:
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Included in the window are the compiler command, an option to save the project, and the output from compilation.
Selected options are reflected in the command line.
It is also possible to generate a printed listing of the input specifications. Warnings encountered during compilation
will also be printed if the appropriate check box is marked.
Click Finish to terminate the program. The wizard will ask whether or not to save any changes made, whether a new
project has been created or not.
Using the Visual Studio Wizard to Generate
ASN1C Projects
On Windows systems ASN1C includes a Visual Studio wizard to help you with creating projects that use ASN1C in
Visual Studio 2005 or later. The wizard simply invokes the ASN1C GUI program. You use the GUI to define whatever
options you want to have set for generating your code and your project file. Then when you click on the Compile
button on the last screen of the GUI, the project file will be created for you. The wizard then loads the project file
into your Visual Studio workspace.
To use the wizard, follow these steps:
1. Edit the file ASN1CWizard.vsz in the vswizard folder of your ASN1C distribution with a text editor. Make the
customizations to the file that are noted in the comments at the top. Take special note of the instruction to remove
the comment lines, as the wizard mechanism will not function if those lines remain in the file.
2. Copy the ASN1CWizard.vsz file, the ASN1CWizard.vsdir file, and the ASN1CWizard.ico file to the VC\projects
folder of your Visual Studio installation (e.g., C:\Program Files (x86)\Microsoft Visual Studio 8\VC\vcprojects).
The wizard can then be invoked by clicking Visual C++ from the Visual Studio New Project dialog and then
choosing ASN1C as the project template.
For example, let's assume you want to use the Visual Studio Wizard to work with code generated from the employee.asn
file, which is included in numerous samples provided with ASN1C. The first step is to edit the ASN1CWizard.vsz file.
Below is a typical ASN1CWizard.vsz file as furnished with an ASN1C kit (version 6.5.0 in this example):
# These comment-type lines must be removed in order for this .vsz file to work.
#
# The ABSOLUTE_PATH parameter below must be set to the full path specification
# of the vswizard folder within your ASN1C installation.
#
# The OSROOTDIR parameter below can be set to the root of the ASN1C
# installation. If OSROOTDIR is already defined as a Windows environment
# variable, then as long as that definition is what's desired, the definition
# of OSROOTDIR in this file can be removed. If OSROOTDIR is defined both in
# this file and as a Windows environment variable, then the definition in this
# file will take precedence. Since this file needs to be copied into the
# Visual Studio folder hierarchy (see README.txt), this feature can be
# useful if multiple ASN1C and Visual Studio versions are installed, and a
# different version of ASN1C is to be used depending on what version of Visual
# Studio is being used.
VSWIZARD 7.0
Wizard=VsWizard.VsWizardEngine.8.0
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Param="WIZARD_NAME = ASN1CWizard"
Param="ABSOLUTE_PATH = C:\acv650\vswizard
Param="OSROOTDIR = C:\acv650"
Param="FALLBACK_LCID = 1033"
Param="WIZARD_UI = FALSE"
Param="SOURCE_FILTER = txt
For this example let's assume that ASN1C 6.5.0 was installed into E:\acv650 instead of C:\acv650. Let's also assume
that you want to retain the OSROOTDIR setting in this file. You would need to modify this file so it looks like this:
Param="WIZARD_NAME = ASN1CWizard"
Param="ABSOLUTE_PATH = E:\acv650\vswizard
Param="OSROOTDIR = E:\acv650"
Param="FALLBACK_LCID = 1033"
Param="WIZARD_UI = FALSE"
Param="SOURCE_FILTER = txt
Making a copy of the furnished ASN1CWizard.vsz file and editing the copy is recommended.
You then would copy your modified ASN1CWizard.vsz file into the appropriate Visual Studio folder. You would also
copy the ASN1CWizard.ico file and the ASN1CWizard.vsdir file from the vswizard folder of your ASN1C distribution
into the same location.
Now when you invoke the New Project dialog in Visual Studio and click on Visual C++, you'll see a template named
ASN1C:
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In this example Visual Studio 2008 is used and the dialog is invoked without a solution currently loaded. So Visual
Studio suggests ASN1C1 as both the project name and the solution. If, however, the new project dialog is invoked
from within the context of a currently loaded solution, Visual Studio will default to adding the project to the current
solution. Also note that for this example we assume that you have chosen the folder c:\mydocs\temp as the location.
Next a small window appears that simply tells you that the wizard will now invoke the ASN1C GUI:
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When you click OK in this window, the ASN1C GUI launches:
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When the ASN1C GUI is invoked from the Visual Studio wizard, the available options are more limited because the
wizard instructs the GUI only to enable options that are relevant to the project. In this window, for example, the options
to create a new project or open an existing project are disabled.
When you click Next, you are presented with the window that allows you to select the specification files that will be
part of the code generation:
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Notice here that the option to specify an output directory is disabled; this value is pre-established by the Visual Studio
wizard. For purposes of this example, let's assume that you specify employee.asn as the file from which to generate
code:
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When you click Next, you are presented with the Common Code Generation Options screen:
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Notice that the option to generate Java code is disabled because the ASN1C GUI knows that it's generating a Visual
Studio project. The option to generate C# is enabled because Visual Studio can work with C#. The C# wizard capability
is discussed in the ASN1C C# User's Manual.
For the purposes of this example let's assume you choose to generate C code for BER:
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Let's assume that you make no other selections and click Next until you come to the Compile screen. If you look as
you're clicking, you'll see that the option to generate a Visual Studio project file is checked and can't be unchecked,
and the version of Visual Studio is 2008, which is the version you're using.
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At this point you would click the Compile button to do the code generation. Once the generation is done, you would
click the Finish button.
Visual Studio then resumes control. Since in this case the generated project is not part of a solution, it asks you if
you want to create a new .sln file. The suggested folder for the new .sln file in this case is the same folder where the
new .vcproj file was created.
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For this example we'll assume you choose to save the .sln file in the suggested location. You now have a solution with
one project, and the project contains the source code generated from the employee.asn file:
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Compiling and Linking Generated Code
C/C++ source code generated by the compiler can be compiled using any ANSI standard C or C++ compiler. The only
additional option that must be set is the inclusion of the ASN.1 C/C++ header file include directory with the –I option.
When linking a program with compiler-generated code, it is necessary to include the ASN.1 run-time libraries. It is
necessary to include at least one of the encoding rules libraries (asn1ber, asn1per, or asn1xer) as well as the common
run-time functions library (asn1rt). See the ASN1C C/C++ Run-time Reference Manual for further details on these
libraries.
For static linking on Windows systems, the name of the library files are asn1ber_a.lib, asn1per_a.lib, or asn1xer_a.lib
for BER/DER/CER, PER, XER, or XML respectively, and asn1rt_a.lib for the common run-time components. On
UNIX/Linux, the library names are libasn1ber.a, libasn1per.a, libasn1xer.a, libasn1xml.a and libasn1rt.a. The library
files are located in the lib subdirectory. For UNIX, the –L switch should be used to point to the subdirectory path and lasn1ber, -lasn1per, -lasn1xer, -lasn1xml and/or -lasn1rt used to link with the libraries. For Windows, the -LIBPATH
switch should be used to specify the library path.
There are several other variations of the C/C++ run-time library files for Windows. The following table summarizes
what options were used to build each of these variations:
Library Files
Description
asn1rt_a.lib
asn1ber_a.lib
asn1per_a.lib
asn1xer_a.lib
asn1xml_a.lib
Static single-threaded libraries. These are built without -MT (multithreading)
and -MD (dynamic link libraries) options. These are not thread-safe. However,
they provide the smallest footprint of the different libraries.
asn1rt.lib
asn1ber.lib
asn1per.lib
asn1xer.lib
asn1xml.lib
DLL libraries. These are used to link against the DLL versions of the run-time
libraries (asn1rt.dll, etc.)
asn1rtmt_a.lib
asn1bermt_a.lib
asn1permt_a.lib
asn1xermt_a.lib
asn1xmlmt_a.lib
Static multi-threaded libraries. These libraries were built with the -MT option.
They should be used if your application contains threads and you wish to link
with the static libraries. (The DLLs are also thread-safe.)
asn1rtmd_a.lib
asn1bermd_a.lib
asn1permd_a.lib
asn1xermd_a.lib
asn1xmlmd_a.lib
DLL-ready multi-threaded libraries. These libraries were built with the –MD
option. They allow linking additional object modules in with the ASN1C runtime modules to produce larger DLLs.
In Visual Studio 2005 and greater, all libraries are multi-threaded by default,
so these libraries are not available for those versions.
For dynamic linking on UNIX/Linux, a shared object version of each run-time library is included in the lib subdirectory.
This file typically has the extension .so (for shared object) or .sl (for shared library). See the documentation for your
UNIX compiler to determine how to link using these files.
Compiling and linking code generated to support the XML encoding rules (XER) is more complex then the other
rules because XER requires the use of third-party XML parser software. This requires the use of additional include
directories when compiling and libraries when linking. The C++ sample programs that are provided use the EXPAT
XML parser (http://expat.sourceforge.net/). All of the necessary include files and binary libraries are included with
the distribution for using this parser. If a different parser is to be used, consult the vendor’s documentation for compile
and link procedures.
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See the makefile in any of the sample subdirectories of the distribution for an example of what must be included to
build a program using generated source code.
Porting Run-time Code to Other Platforms
The run-time source version of the compiler includes ANSI-standard source code for the base run-time libraries. This
code can be used to build binary versions of the run-time libraries for other operating environments. Included with the
source code is a portable makefile that can be used to build the libraries on the target platform with minimal changes.
All platform-specific items are isolated in the platform.mk file in the root directory of the installation.
The procedure to port the run-time code to a different platform is as follows (note: this assumes common UNIX or
GNU compilation utilities are in place on the target platform).
1. Create a directory tree containing a root directory (the name does not matter) and lib, src, rt*src, and build_lib
subdirectories (note: in these definitions, * is a wildcard character indicating there are multiple directories matching
this pattern). The tree should be as follows:
2. Copy the files ending in extension ".mk" from the root directory of the installation to the root directory of the target
platform (note: if transferring from DOS to UNIX or vice-versa, FTP the files in ASCII mode to ensure lines are
terminated properly).
3. Copy all files from the src and the different rt*src subdirectories from the installation to the src and rt*src directories
on the target platform (note: if transferring from DOS to UNIX or vice-versa, FTP the files in ASCII mode to ensure
lines are terminated properly).
4. Copy the makefile from the build_lib subdirectory of the installation to the build_lib subdirectory on the target
platform (note: if transferring from DOS to UNIX or vice-versa, FTP the files in ASCII mode to ensure lines are
terminated properly).
5. Edit the platform.mk file in the root subdirectory and modify the compilation parameters to fit those of the compiler
of the target system. In general, the following parameters will need to be adjusted:
a. CC: C compiler executable name
b. CCC: C++ compiler executable name
c. CFLAGS_: Flags that should be specified on the C or C++ command line
The platform.w32 and platform.gnu files in the root directory of the installation are sample files for Windows 32
(Visual C++) and GNU compilers respectively. Either of these can be renamed to platform.mk for building in either
of these environments.
6. Invoke the makefile in the build_lib subdirectory.
If all parameters were set up correctly, the result should be binary library files created in the lib subdirectory.
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Compiler Configuration File
In addition to command line options, configuration commands can be used to apply specific compiler options to specific
items within a schema. These options can be applied to specific modules, productions, and elements as well as globally.
Configuration items may be specified in one or two ways (or a combination of both):
• Using special comments embedded directly in an ASN.1 file, or
• Using an external XML configuration file
A simple form of XML is used as the format for the configuration items. XML was chosen because it is fairly well
known and provides a natural interface for representing hierarchical data such as the structure of ASN.1 modules and
productions.
In the case of embeddeding directives directly in the ASN.1 source file, the directive is included as a comment directly
before the item to which it is to be applied. For example:
BackupBearerCapOctetGroup5 ::= SEQUENCE {
octet5 BearerCapOctet5,
--<end3GExtElem name="octet5.ext"/>
octet5a BearerCapOctet5a
}
In this case, the end3GExtElem configuration item would be applied to the octet5a element.
An external configuration file would target the item to which the directive is to be applied by specifying module,
production, and element in an XML hierarchy. An example of this is as follows:
<asn1config>
<module name=”TS24008IES”>
<production name=”BackupBearerCapOctetGroup5”>
<element name=”octet5a”>
<end3GExtElem name="octet5.ext"/>
</element>
</production>
</module>
</asn1config>
At the outer level of the markup is the <asn1config> </asn1config> tag pair. Within this tag pair, the
specification of global items and modules can be made. Global items are applied to all items in all modules. An example
would be the <storage> qualifier. A storage class such as dynamic can be specified and applied to all productions
in all modules. This will cause dynamic storage (pointers) to be used for any embedded structures within all of the
generated code to reduce memory consumption demands.
The specification of a module is done using the <module></module> tag pair. This tag pair can only be nested
within the top-level <asn1config> section. The module is identified by using the required <name></name> tag
pair or by specifying the name as an attribute (for example, <module name="MyModule">). Other attributes
specified within the <module> section apply only to that module and not to other modules specified within the
specification. A complete list of all module attributes is provided in the table at the end of this section.
The specification of an individual production is done using the <production></production> tag pair. This
tag pair can only be nested within a <module> section. The production is identified by using the required <name></
name> tag pair or by specifying the name as an attribute (for example, <production name="MyProd">). Other
attributes within the production section apply only to the referenced production and nothing else. A complete list of
attributes that can be applied to individual productions is provided in the table at the end of this section.
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When an attribute is specified in more than one section, the most specific application is always used. For example,
assume a <typePrefix> qualifier is used within a module specification to specify a prefix for all generated types
in the module and another one is used to a specify a prefix for a single production. The production with the type prefix
will be generated with the type prefix assigned to it and all other generated types will contain the type prefix assigned
at the module level.
Values in the different sections can be specified in one of the following ways:
1. Using the <name>value</name> form. This assigns the given value to the given name. For example, the
following would be used to specify the name of the "H323-MESSAGES" module in a module section:
<name>H323-MESSAGES</name>
2. Flag variables that turn some attribute on or off would be specified using a single <name/> entry. For example,
to specify a given production is a PDU, the following would be specified in a production section:
<isPDU/>
3. An attribute list can be associated with some items. This is normally used as a shorthand form for specifying lists
of names. For example, to specify a list of type names to be included in the generated code for a particular module,
the following would be used:
<include types="TypeName1,TypeName2,TypeName3"/>
The following are some examples of configuration specifications:
<asn1config><storage>dynamic</storage></asn1config>
This specification indicates dynamic storage should be used in all places where its use would result in significant
memory usage savings within all modules in the specified source file.
<asn1config>
<module>
<name>H323-MESSAGES</name>
<sourceFile>h225.asn</sourceFile>
<typePrefix>H225</typePrefix>
</module>
...
</asn1config>
This specification applies to module ‘H323-MESSAGES’ in the source file being processed. For IMPORT statements
involving this module, it indicates that the source file ‘h225.asn’ should be searched for specifications. It also indicates
that when C or C++ types are generated, they should be prefixed with ‘H225’. This can help prevent name clashes if
one or more modules are involved and they contain productions with common names.
The following tables specify the list of attributes that can be applied at all of the different levels: global, module, and
individual production:
Global Level
These attributes can be applied at the global level by including them within the <asn1config> section:
Name
Values
Description
<events></events>
defaultValue keyword.
This configuration item is for use with Event Handling as
described in a later section in this document. It is used to
include a special event that is fired when a PER message
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Name
Values
Description
is being parsed. This event occurs at the location a value
should be present in the message but is not and a default
value has been specified in the ASN.1 file for the element.
In this case, the normal event sequence (startElement,
contents, endElement) is executed using the default value.
<includedir></includedir>
<Include directory>
This configuration item is used to specify a directory that
will be search for IMPORT files. It is equivalent to the I command-line option.
<protocol></protocol>
<Protocol identifier>
Specifies a protocol identifier to be associated with the
ASN.1 specification set. For C/C++, this specifies a prefix
that will be used with generated encode and decode
functions. Currently, this only applies to 3GPP Layer 3
functions.
<rootdir></rootdir>
<ASN1C root directory>
This configuration item is used to specify the root
directory of the ASN1C installation for makefile or Visual
Studio project generation. It is only needed if generation
of these items is done outside of the ASN1C installation.
<storage></storage>
One of the following
keywords: dynamic, static,
list, array, dynamicArray,
std::list,
std::vector,
std::deque.
If dynamic , it indicates that dynamic storage (i.e.,
pointers) should be used everywhere within the generated
types where use could result in lower memory
consumption. These places include the array element for
sized SEQUENCE OF/SET OF types and all alternative
elements within CHOICE constructs.
If static, it indicates static types should be used in these
places. In general, static types are easier to work with.
If list, a linked-list type will be used for SEQUENCE OF/
SET OF constructs instead of an array type.
If array, an array type will be used for SEQUENCE OF/
SET OF constructs. The maxSize attribute can be used
in this case to specify the size of the array variable (for
example, <storage maxSize="12"> array </storage>).
If dynamicArray, a dynamic array will be used for
SEQUENCE OF/SET OF constructs. A dynamic array is
an array that uses dynamic storage for the array elements.
If std::array the result is the same as for array, except
that std::array will be used instead of a plain C/C++ static
array. You must specify -cpp11 on the command line to
use this option.
If one of std::list, std::vector, std::deque, then the
corresponding C++ Standard Library container class will
be used. You must specify -cpp11 on the command line to
use one of these options.
Module Level
These attributes can be applied at the module level by including them within a <module> section:
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Name
Values
Description
<name> </name>
module name
This attribute identifies the module to which this section
applies. Either this or the <oid> element/attribute is
required.
<oid>
module
OID
identifier)
(object This attribute provides for an alternate form of module
identification for the case when module name is not
unique. For example, a given ASN.1 module may have
multiple versions. A unique version of the module can be
identified using the OID value.
<codename> </codename> C/C++, Java, or C# name
This item specifies an alternate name for the module to be
used in generated code. By default, the module name is
used in the form it appears in the ASN.1 specification with
hyphens converted to underscores.
<include
types="names" ASN.1 type or value names This item allows a list of ASN.1 types and/or values
values="names"/>
are specified as an attribute to be included in the generated code. By default, the
list
compiler generates code for all types and values within a
specification. This allows the user to reduce the size of the
generated code base by selecting only a subset of the types/
values in a specification for compilation. Note that if a
type or value is included that has dependent types or values
(for example, the element types in a SEQUENCE, SET, or
CHOICE), all of the dependent types will be automatically
included as well.
<include
encoders="names"/>
ASN.1 type names specified This item allows a list of ASN.1 types to be included in
as an attribute list.
the generated code for which only encode functions will
be generated.
<include
decoders="names"/>
ASN.1 type names specified This item allows a list of ASN.1 types to be included in
as an attribute list.
the generated code for which only decode functions will
be generated.
<include
memfree="names"/>
ASN.1 type names specified This item allows a list of ASN.1 types to be included in
as an attribute list.
the generated code for which only memory free functions
will be generated.
<include
"name"/>
importsFrom= ASN.1 module name(s) This form of the include directive tells the compiler to only
specified as an attribute list. include types and/or values in the generated code that are
imported by the given module(s).
<exclude
types="names" ASN.1 type or values names This item allows a list of ASN.1 types and/or values
values="names"/>
are specified as an attribute to be excluded in the generated code. By default, the
list
compiler generates code for all types and values within
a specification. This is generally not as useful as in
include directive because most types in a specification are
referenced by other types. If an attempt is made to exclude
a type or value referenced by another item, the directive
will be ignored.
<storage> </storage>
One of the following The definition is the same as for the global case except that
keywords: dynamic, static, the specified storage type will only be applied to generated
list, array, dynamicArray, C and C++ types from the given module.
std::list,
std::vector,
std::deque.
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Name
Values
Description
<sourceFile> </sourceFile> source file name
Indicates the given module is contained within the given
ASN.1 source file. This is used on IMPORTs to instruct
the compiler where to look for imported definitions.
<prefix> </prefix>
prefix text
This is used to specify a general prefix that will be applied
to all generated C and C++ names (note: for C++ types, the
prefix is applied after the standard ‘ASN1T_’ prefix). This
can be used to prevent name clashes if multiple modules
are involved in a compilation and they all contain common
names.
<typePrefix> </typePrefix> prefix text
This is used to specify a prefix that will be applied to all
generated C and C++ typedef names (note: for C++, the
prefix is applied after the standard ‘ASN1T_’ prefix). This
can be used to prevent name clashes if multiple modules
are involved in a compilation and they all contain common
names.
<enumPrefix>
enumPrefix>
</ prefix text
This is used to specify a prefix that will be applied to
all generated enumerated identifiers within a module.
This can be used to prevent name clashes if multiple
modules are involved in a compilation. (note: this attribute
is normally not needed for C++ enumerated identifiers
because they are already wrapped in a structure to allows
the type name to be used as an additional identifier).
<valuePrefix>
valuePrefix>
</ prefix text
This is used to specify a prefix that will be applied to
all generated value constants within a module. This can
be used to prevent name clashes if multiple modules
are involved that use a common name for two or more
different value declarations.
<classPrefix>
classPrefix>
</ prefix text
This is used to specify a prefix that will be applied to
all generated items in a module derived from an ASN.1
CLASS definition.
<objectPrefix>
objectPrefix>
</ prefix text
This is used to specify a prefix that will be applied to
all generated items in a module derived from an ASN.1
Information Object definition.
<objectsetPrefix>
objectsetPrefix>
</ prefix text
This is used to specify a prefix that will be applied to
all generated items in a module derived from an ASN.1
Information Object Set definition.
<noPDU/>
n/a
Indicates that this module contains no PDU definitions.
This is normally true in modules that are imported
to get common type definitions (for example,
InformationFramework). This will prevent the C++
version of the compiler from generating any control class
definitions for the types in the module.
<intCType>
byte, int16, uint16, int32, This is used to specify a specific C integer type be used for
uint32, int64, string
all unconstrained integer types. By default, ASN1C will
use the int32 (32-bit integer) type for all unconstrained
integers.
53
Using the Compiler
Name
Values
Description
<arcCType>
int32, int64
The is used to specify a specific C integer type be used for
the arc types in Object Identifier definitions. By default,
int32 (32-bit integer arc values) are generated.
<namespace>
namespace>
</ namespace URI
This is used to specify the target namespace for the given
module when generating XSD and/or XML code. By
default, the compiler will not include a targetNamespace
directive in the generated XSD code (i.e. all items will
not be assigned to any namespace). This option only has
meaning when used with the - xml / -xsd command line
options.
<hFile> </hFile>
C/C++ header filename
This is used to specify the name of a C/C++ header file to
be used to store generated definitions for the module. By
default, the header file name is set to the ASN.1 name of
the module with '.h' appended to the end.
<alias asn1name="name" ASN.1
to
computer This item allows a name in the ASN.1 specification
codename="name"/>
language name mapping
being compiled to be mapped to an alternate name in
the generated computer language files. The primary use
is to allow shorter names to be used in places where a
combination of names may be very long. In this release,
the only names that can be used in the alias statement are
information object set names.
Production Level
These attributes can be applied at the production level by including them within a <production> section:
Name
Values
Description
<name>
</name>
production name
This attribute identifies the production (type) to which this
section applies. It is required.
<addarg
name="name" Argument name, type, and This item adds an argument to the generated C encode and/
type="type" func="encode| function specified using or decode function. The name and C type of the argument
decode"/>
attributes.
are specified in the name and type attributes respectively.
The func attribute is optional and only required if the
argument should be added to either the encode or decode
function only. By default, the argument is added to
both the encode and decode function. This item is only
supported for C 3GPP layer 3 code generation.
<aligned/>
n/a
This item is used to specify that byte alignment is to be
done after encoding or decoding an instance of the targeted
type. This item is only supported for C 3GPP layer 3 code
generation.
<cDecFuncName>
cDecFuncName>
</ <C source file name
This item is used to substitute the C source code contained
within the given file for what would have been generated
for the C decode function for the given type. The current
include path is searched for the given filename. This item
is only supported for C 3GPP layer 3 code generation.
<cEncFuncName>
cEncFuncName>
</ <C source file name
This item is used to substitute the C source code contained
within the given file for what would have been generated
for the C encode function for the given type. The current
54
Using the Compiler
Name
Values
<ctype>
byte, int16, uint16, int32, This is used to specify a specific C integer or character
uint32,
int64,
string, string type be used in place of the default definition
chararray
generated by ASN1C. In the case of integers, ASN1C will
normally try and use the smallest integer type available
based on the value or value range constraint on the integer
type. If the integer is not constrained, the int32 (32-bit
integer) type will be used. For character string, ASN1C
will use a character string pointer (char*) by default. The
'chararray' item can be used on strings with size constrains
to specify a static character array variable be used.
<enumPrefix>
enumPrefix>
<format> </format>
</ prefix text
base64, hex, xmllist
Description
include path is searched for the given filename. This item
is only supported for C 3GPP layer 3 code generation.
This is used to specify a prefix that will be applied to
all generated enumerated identifiers within a module.
This can be used to prevent name clashes if multiple
modules are involved in a compilation. (note: this attribute
is normally not needed for C++ enumerated identifiers
because they are already wrapped in a structure to allows
the type name to be used as an additional identifier).
This is used to set format options specific to XER
encoding. The base64 or hex alternative is used to set
the output format that binary data in OCTET STRING
variables is displayed in in XML markup. The xmllist
alternative is used with SEQUENCE OF or SET OF types
to denote that items should be displayed in XML spaceseparated list format as opposed to a using a separate
element for each list item.
<is3GExtList pre-eol="0|1" n/a
post-eol="0|1"/>
This item specifies that this production will be modelled
as a 3G extended list. This can only be applied to
SEQUENCE OF productions. It is used in 3G layer
3 messages when the extension of a repeating type is
controlled by an extension bit that occurs either before
or after the record. If the pre-eol attribute (short for
"preceding end-of-list") is specified, it indicate a bit before
the record signals whether another record follows. The
value (0 or 1) indicates which bit value signal end-of-list.
The post-eol attribute is the same except that it indicates
the control bit follows after the record. This item is only
supported for C 3GPP layer 3 code generation.
<is3GMessage/>
n/a
This item specifies that this production represents a
3G layer 3 message type as opposed to a 3G layer 3
information element (IE). This item is only supported for
C 3GPP layer 3 code generation.
<isBigInteger/>
n/a
This item specifies that this production will be used to
store an integer larger than the C or C++ int type on
the given system (normally 32 bits). A C string type
(char*) will be used to hold a textual representation of the
value. This qualifier can be applied to either an integer
or constructed type. If constructed, all integer elements
within the constructed type are flagged as big integers.
55
Using the Compiler
Name
Values
Description
<isOpenType/>
n/a
This item is used to indicate that any element of this type
will be decoded as an open type (i.e. skipped). Refer to
the section on deferred decoding for further information.
Note that this variable can only be used with BER, CER,
or DER encoding rules.
<isPDU/>
n/a
This item is used to indicate that this production
represents a Protocol Data Unit (PDU). This is defined
as a production that will be encoded or decoded from
within the application code. This attribute only makes
a difference in the generation of C++ classes. Control
classes that are only used in the application code are only
generated for types with this attribute set.
<isTBCDString/>
n/a
This item is used to indicate that this production is to be
encoded and decoded as a telephony binary coded string
(TBCD). This is type is not part of the ASN.1 standards
but is a widely used encoding format in telephony
applications.
fixed- n/a
This item is used to configure a length field in an OCTET
STRING type for 3GPP layer 3 messages. By default, a
length field is a single byte, but there are occasions where
the field width may be different. This allows a fixed-size
encoded field width to be specified. The most common
values are 0 (no length field) or 2.
<noDecoder/>
n/a
Indicates that no decode function should be generated for
this production. This item is only supported for C 3GPP
layer 3 code generation.
<noEncoder/>
n/a
Indicates that no encode function should be generated for
this production. This item is only supported for C 3GPP
layer 3 code generation.
<setvar
name="name" n/a
value="value"/>
This item is used within encode and decode functions to
set a given variable within a generated structure to the
given value. Normally it is used in conjunction with the
'addarg' configuration item to set a variable to value of an
additional argument passed into a function. This item is
only supported for C 3GPP layer 3 code generation.
<length
size="number"/>
<storage> </storage>
One of the following The definition is the same as for the global case except
keywords: dynamic, static, that the specified storage type will only be applied to the
list, array, dynamicArray, generated C or C++ type for the given production.
std::list,
std::vector,
std::deque.
<typePrefix> </typePrefix> prefix text
This is used to specify a prefix that will be applied to all
generated C and C++ typedef names (note: for C++, the
prefix is applied after the standard ‘ASN1T_’ prefix). This
can be used to prevent name clashes if multiple modules
are involved in a compilation and they all contain common
names.
Element Level
56
Using the Compiler
These attributes can be applied at the element level by including them within an <element> section:
Name
Values
Description
<name>
</name>
element name
This attribute identifies the element within a SEQUENCE,
SET, or CHOICE construct to which this section applies.
It is required.
<addarg
name="name" Argument name, function This item adds an argument to the generated C encode and/
func="encode|decode"/>
specified using attributes. or decode function that is invoked to encode or decode
the element. The name attribute specified the value to be
passed. The func attribute is optional and only required
if the argument should be added to either the encode or
decode function only. By default, the argument is added
to both the encode and decode function. This item is only
supported for C 3GPP layer 3 code generation.
<aligned/>
n/a
This item is used to specify that byte alignment is to be
done after encoding or decoding this element. This item is
only supported for C 3GPP layer 3 code generation.
<cDecSrcName>
cDecSrcName>
</ <C source file name
This item is used to substitute the C source code contained
within the given file for what would have been generated
for decoding the element. The code in this case is not a
complete function but rather a snippet to be inserted within
a larger function. The current include path is searched
for the given filename. This item is only supported for C
3GPP layer 3 code generation.
<cEncSrcName>
cEncSrcName>
</ <C source file name
This item is used to substitute the C source code contained
within the given file for what would have been generated
for encoding the element. The code in this case is not a
complete function but rather a snippet to be inserted within
a larger function. The current include path is searched
for the given filename. This item is only supported for C
3GPP layer 3 code generation.
<ctype>
chararray
This is used to specify a specific C type be used in
place of the default definition generated by ASN1C. In
the case of elements, the only supported customization
is for character string types which would normally be
represented by a character pointer type (char*) to be
changed to use static character arrays. This can only be
done if the string type contains a size constraint.
<end3GExtElem
name="element name"/>
<Element name> attribute
This item is used to delimit a group of optional elements
that start with an 'ext' boolean element. A common
pattern in the specification of 3GPP IE's is to include an
extension bit to signal the presence or absence of group
of elements (these normally comprise a single octet). This
is essentially an alternative way to specify an optional
element group in ASN.1. This item is only supported for
C 3GPP layer 3 code generation.
<iei
format="t|tv|tlv" IEI hex value
length="length"/>
This item is used to indicate an element is part of the nonimperative part 3GPP layer 3 message. These are optional
elements with single byte tags. The tag is the IEI hex value
specified at the value of the item. The format attribute
specifies if the item is a tag (t), tag/value (tv), or tag/length/
57
Using the Compiler
Name
Values
Description
value (tlv). The length attribute is only required if format
if tv to specify the length of the value. This item is only
supported for C 3GPP layer 3 code generation.
<inline/>
n/a
This item is used to indicate that code generated for a
nested item within a constructed type should be expanded
inline rather than pulled out to create a separate new type.
<is3GExtList pre-eol="0|1" n/a
post-eol="0|1"/>
This item specifies that this element will be modelled as a
3G extended list. This can only be applied to elements of
type SEQUENCE OF. It is used in 3G layer 3 messages
when the extension of a repeating type is controlled by an
extension bit that occurs either before or after the record.
If the pre-eol attribute (short for "preceding end-of-list") is
specified, it indicate a bit before the record signals whether
another record follows. The value (0 or 1) indicates which
bit value signal end-of-list. The post-eol attribute is the
same except that it indicates the control bit follows after
the record. This item is only supported for C 3GPP layer
3 code generation.
<is3GLength
bitFieldSize="nbits"
units="bits|bytes"/>
n/a
This item is used to mark an element as a 3GPP length
field element. Normally this an element with the name
'length' of type INTEGER that is the first element in a
SEQUENCE. This indicates special processing should be
done on the element. On encode, any value populated
in this field will be ignored and the actual length of the
encoded data will be calculated and populated in this
field after encoding is complete. On decode, this element
is used to determine when end of message occurs. The
'bitFieldLength' attribute is used to specify the field size if
it not an even octet (8 bits). The 'units' attribute specifies
the units stored in the length field (bits or bytes). This item
is only supported for C 3GPP layer 3 code generation.
<is3GVarLenList
lengthElem="name"/>
n/a
This item specifies that this element will be modelled
as a 3G variable length list. This can only be applied to
elements of type SEQUENCE OF. It is used in 3G layer
3 messages when a length element is used to determine
the number of items in the list. The 'lengthElem' attribute
specifies the element within the structure that contains this
count. This item is only supported for C 3GPP layer 3 code
generation.
<isBigInteger/>
n/a
This item specifies that this element will be used to
store an integer larger than the C or C++ int type on
the given system (normally 32 bits). A C string type
(char*) will be used to hold a textual representation of the
value. This qualifier can be applied to either an integer
or constructed type. If constructed, all integer elements
within the constructed type are flagged as big integers.
<isOpenType/>
n/a
This flag variable specifies that this element will be
decoded as an open type (i.e. skipped). Refer to the section
on deferred decoding for further information. Note that
58
Using the Compiler
Name
<length
size="number"/>
<notUsed/>
<perEncoding>
perEncoding>
Values
Description
this variable can only be used with BER, CER, or DER
encoding rules.
fixed- n/a
This item is used to configure a length field in an OCTET
STRING type for 3GPP layer 3 messages. By default, a
length field is a single byte, but there are occasions where
the field width may be different. This allows a fixed-size
encoded field width to be specified. The most common
values are 0 (no length field) or 2. This item is only
supported for C 3GPP layer 3 code generation.
n/a
This flag variable specifies that this element will not be
used at all in the generated code. It can only be applied
to optional elements within a SEQUENCE or SET, or to
elements within a CHOICE. Its purpose is for production
of more compact code by allowing users to configure out
items that are of no interest to them.
</ hex data
This variable allows a user to substitute a known binary
PER encoding for the given element. This encoding will
be inserted into the encoded data stream on encoding and
skipped over on decoding. Its purpose is the production
of more compact and faster code for PER by bypassing
run-time calculations needed to encode or decode variable
data.
<selector element="name" n/a
value="value"/>
This item is used to configure an element within a
CHOICE in a 3GPP layer 3 message. It specifies the value
of another element within the container type which selects
this element. The 'element' field specifies the name of
the element within the container type and 'value' specifies
the value. are 0 (no length field) or 2. This item is only
supported for C 3GPP layer 3 code generation.
<setvar
name="name" n/a
value="value"/>
This item is used within encode and decode functions to
set a given variable within a generated structure to the
given value. Normally it is used in conjunction with the
'addarg' configuration item to set a variable to value of an
additional argument passed into a function. This item is
only supported for C 3GPP layer 3 code generation.
<storage> </storage>
One of the following The definition is the same as for the global case except
keywords: dynamic, static, that the specified storage type will only be applied to the
list, array, dynamicArray, generated C or C++ type for this element.
std::list,
std::vector,
std::deque.
Compiler Error Reporting
Errors that can occur when generating source code from an ASN.1 source specification take two forms: syntax errors
and semantics errors.
Syntax errors are errors in the ASN.1 source specification itself. These occur when the rules specified in the ASN.1
grammar are not followed. ASN1C will flag these types of errors with the error message ‘Syntax Error’ and abort
compilation on the source file. The offending line number will be provided. The user can re-run the compilation with
the ‘-l’ flag specified to see the lines listed as they are parsed. This can be quite helpful in tracking down a syntax error.
59
Using the Compiler
The most common types of syntax errors are as follows:
• Invalid case on identifiers: module name must begin with an uppercase letter, productions (types) must begin with an
uppercase letter, and element names within constructors (SEQUENCE, SET, CHOICE) must begin with lowercase
letters.
• Elements within constructors not properly delimited with commas: either a comma is omitted at the end of an
element declaration, or an extra comma is added at the end of an element declaration before the closing brace.
• Invalid special characters: only letters, numbers, and the hyphen (-) character are allowed. The use of the underscore
character (_) in identifiers is not allowed in ASN.1, but is allowed in C. Since C does not allow hyphens in identifiers,
ASN1C converts all hyphens in an ASN.1 specification to underscore characters in the generated code.
Semantics errors occur on the compiler back-end as the code is being generated. In this case, parsing was successful,
but the compiler does not know how to generate the code. These errors are flagged by embedding error messages
directly in the generated code. The error messages always begin with an identifier with the prefix ‘%ASN-’, so a search
can be done for this string in order to find the locations of the errors. A single error message is output to stderr after
compilation on the unit is complete to indicate error conditions exist.
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Chapter 3. ASN.1 To C/C++ Mappings
Type Mappings
BOOLEAN
The ASN.1 BOOLEAN type is converted into a C type named OSBOOL. In the global include file osSysTypes.h,
OSBOOL is defined to be an unsigned char.
ASN.1 production:
<name> ::= BOOLEAN
Generated C code:
typedef OSBOOL <name>;
Generated C++ code:
typedef OSBOOL ASN1T_<name>;
For example, if B ::= [PRIVATE 10] BOOLEAN was defined as an ASN.1 production, the generated C type
definition would be typedef OSBOOL B. Note that the tag information is not represented in the type definition.
It is handled within the generated encode/decode functions.
The only difference between the C and C++ mapping is the addition of the ASN1T_ prefix on the C++ type.
INTEGER
The ASN.1 INTEGER type is converted into one of several different C types depending on constraints specified on
the type. By default, an INTEGER with no constraints results in the generation of an OSINT32 type. In the global
include file osSysTypes.h, OSINT32 is defined to be an int which is normally a signed 32-bit integer value on most
computer systems.
ASN.1 production:
<name> ::= INTEGER
Generated C code:
typedef OSINT32 <name>;
Generated C++ code:
typedef OSINT32 ASN1T_<name>;
Value range constraints can be used to alter the C type used to represent a given integer value. For example, the
following declaration from the SNMP SMI specification would cause an OSUINT32 type (mapped to a C unsigned
int) to be used:
Counter ::= [APPLICATION 1] IMPLICIT INTEGER (0..4294967295)
In this case, an OSINT32 could not be used because all values within the given range could not be represented. Other
value ranges would cause different integer types to be used that provide the most efficient amount of storage. The
following table shows the types that would be used for the different range values:
61
ASN.1 To C/C++ Mappings
Min Lower Bound
Max Upper Bound
ASN1C Type
C Type
-128
127
OSINT8
char (signed 8-bit int)
0
255
OSUINT8
unsigned
char
(unsigned 8-bit number)
-32768
32767
OSINT16
short (signed 16-bit int)
0
65535
OSUINT16
unsigned
short
(unsigned 16-bit int)
-2147483648
2147483647
OSINT32
int (signed 32-bit integer)
0
4294967295
OSUINT32
unsigned int (unsigned
32-bit integer)
The C type that is used to represent a given integer value can also be altered using the "<ctype>" configuration variable
setting. This allows any of the integer types above to be used for a given integer type as well as a 64-bit integer type.
The values that can be used with <ctype> are: byte, int16, uint16, int32, uint32, and int64. An example of using this
setting is as follows:
Suppose you have the following integer declaration in your ASN.1 source file:
MyIntType ::= [APPLICATION 1] INTEGER
You could then have ASN1C use a 64-bit integer type for this integer by adding the following declaration to a
configuration file to be associated with this module:
<production>
<name>MyIntType</name>
<intCType>int64</intCType>
</production>
The <intCType> setting is also available at the module level to specify that the given C integer type be used for
all unconstrained integers within the module.
Large Integer Support
In C and C++, the maximum size for an integer type is normally 64 bits (or 32 bits on some older platforms). ASN.1
has no such limitation on integer sizes and some applications (security key values for example) demand larger sizes.
In order to accommodate these types of applications, the ASN1C compiler allows an integer to be declared a "big
integer" via a configuration file variable (the <isBigInteger/> setting is used to do this - see the section describing the
configuration file for full details). When the compiler detects this setting, it will declare the integer to be a character
string variable instead of a C int or unsigned int type. The character string would then be populated with a character
string representation of the value to be encoded. Supported character string representations are hexadecimal (strings
starting with 0x), octal (strings starting with 0o) and decimal (no prefix).
For example, the following INTEGER type might be declared in the ASN.1 source file:
SecurityKeyType ::= [APPLICATION 2] INTEGER
Then, in a configuration file used with the ASN.1 definition above, the following declaration can be made:
<production>
<name>SecurityKeyType</name>
<isBigInteger/>
</production>
This will cause the compiler to generate the following type declaration:
62
ASN.1 To C/C++ Mappings
typedef const char* SecurityKeyType
The SecurityKeyType variable can now be populated with a hexadecimal string for encoding such as the following:
SecurityKeyType secKey = "0xfd09874da875cc90240087cd12fd";
Note that in this definition the 0x prefix is required to identify the string as containing hexadecimal characters.
On the decode side, the decoder will populate the variable with the same type of character string after decoding.
There are also a number of run-time functions available for big integer support. This set of functions provides an
arbitrary length integer math package that can be used to perform mathematical operations as well as convert values
into various string forms. See the ASN1C C/C++ Common Run-time User's Manual for a description of these functions.
BIT STRING
The ASN.1 BIT STRING type is converted into a C or C++ structured type containing an integer to hold the number
of bits and an array of unsigned characters ("OCTETs") to hold the bit string contents. The number of bits integer
specifies the actual number of bits used in the bit string and takes into account any unused bits in the last byte.
The type definition of the contents field depends on how the bit string is specified in the ASN.1 definition. If a size
constraint is used, a static array is generated; otherwise, a pointer variable is generated to hold a dynamically allocated
string. The decoder will automatically allocate memory to hold a parsed string based on the received length of the string.
In the static case, the length of the character array is determined by adjusting the given size value (which represents
the number of bits) into the number of bytes required to hold the bits.
Dynamic Bit String
ASN.1 production:
<name> ::= BIT STRING
Generated C code:
typedef ASN1DynBitStr <name>;
Generated C++ code:
typedef ASN1TDynBitStr ASN1T_<name>;
In this case, different base types are used for C and C++. The difference between the two is the C++ version includes
constructors that initialize the value and methods for setting the value.
The ASN1DynBitStr type (i.e., the type used in the C mapping) is defined in the asn1type.h header file as follows:
typedef struct ASN1DynBitStr {
OSUINT32 numbits;
const OSOCTET* data;
} ASN1DynBitStr;
The ASN1TDynBitStr type is defined in the asn1CppTypes.h header file as follows:
struct ASN1TDynBitStr : public ASN1DynBitStr {
// ctors
ASN1TDynBitStr () : numbits(0) {}
ASN1TDynBitStr (OSUINT32 _numbits, OSOCTET* _data);
63
ASN.1 To C/C++ Mappings
ASN1TDynBitStr (ASN1DynBitStr& _bs);
} ASN1TDynBitStr;
Note that memory management of the byte array containing the bit string data is the responsibility of the user. The
wrapper class does not free the memory on destruction nor deep-copy the data when a string is copied.
Static (sized) BIT STRING
ASN.1 production:
<name> ::= BIT STRING (SIZE (<len>))
Generated C code:
typedef struct {
OSUINT32 numbits;
OSOCTET data[<adjusted_len>*];
} <name>;
If the -strict-size command-line option is used, the numbits component within this type definition may be of a different
type (OSUINT8 or OSUINT16) or eliminated completely if the type is constrained to be a fixed-size.
Generated C++ code:
typedef struct <name> {
OSUINT32 numbits;
OSOCTET data[<adjusted_len>*];
// ctors
ASN1T_<name> ();
ASN1T_<name> (OSUINT32 _numbits, const OSOCTET* _data);
} ASN1T_<name>;
* <adjusted_len> = ((<len> - 1)/8) + 1;
If the -strict-size command-line option is used, the numbits component within this type definition may be of a different
type (OSUINT8 or OSUINT16) or eliminated completely if the type is constrained to be a fixed-size.
For example, the following ASN.1 production:
BS ::= [PRIVATE 220] BIT STRING (SIZE (42))
Would translate to the following C typedef:
typedef struct BS {
OSUINT32 numbits;
OSOCTET data[6];
} BS;
In this case, six octets would be required to hold the 42 bits: eight in the first five bytes, and two in the last byte.
In the case of small-sized strings (less than or equal to 32 bits), a built-in type is used rather than generating a custom
type. This built-in type is defined as follows:
typedef struct ASN1BitStr32 {
OSUINT32 numbits;
OSOCTET data[4];
64
ASN.1 To C/C++ Mappings
} ASN1BitStr32;
The C++ variant (ASN1TBitStr32) adds constructors for initialization and copying.
Note that for C++, ASN1C generates special constructors and assignment operators to make populating a structure
easier. In this case, two constructors were generated: a default constructor and one that takes numbits and data as
arguments.
If the -strict-size command-line option is used, the numbits component would be eliminated since the type is
constrained to be a fixed-size.
Named Bits
In the ASN.1 standard, it is possible to define an enumerated bit string that specifies named constants for different bit
positions. ASN1C provides support for this type by generating symbolic constants and optional macros that can be
used to set, clear, or test these named bits. These symbolic constants equate the bit name to the bit number defined
in the specification. They can be used with the rtBitSet, rtBitClear, and rtBitTest run-time functions to set, clear, and
test the named bits. In addition, generated C++ code contains an enumerated constant added to the control class with
an entry for each of the bit numbers. These entries can be used in calls to the methods of the ASN1CBitStr class to
set, clear, and test bits.
The -genBitMacros command line option can be used to generate macros to set, clear, or test the named bits in a bit
string structure. These macros offer better performance then using the run-time functions because all calculations of
mask and index values are done at compile time. However, they can result in a large amount of additional generated
code.
For example, the following ASN.1 production:
NamedBS ::= BIT STRING { bitOne(1), bitTen(10) }
Would translate to the following if -genBitMacros was specified:
/* Named bit constants */
#define NamedBS_bitOne
1
#define SET_BS3_bitOne(bs) \
<code to set bit..>
#define CLEAR_BS3_bitOne(bs) \
<code to clear bit..>
#define TEST_BS3_bitOne(bs) \
<code to test bit..>
#define NamedBS_bitTen
10
#define SET_BS3_bitTen(bs) \
<code to set bit..>
#define CLEAR_BS3_bitTen(bs) \
<code to clear bit..>
#define TEST_BS3_bitTen(bs) \
<code to test bit..>
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ASN.1 To C/C++ Mappings
/* Type definitions */
typedef struct ASN1T_NamedBS {
OSUINT32 numbits;
OSOCTET data[2];
} NamedBS;
The named bit constants would be used to access the data array within the ASN1T_NamedBS type. If bit macros were
not generated, the rtxSetBit function could be used to set the named bit bitOne with the following code:
NamedBS bs;
memset (&bs, 0, sizeof(bs));
rtxSetBit (bs.data, 10, NamedBS_bitOne);
The statement to clear the bit using rtxClearBit would be as follows:
rtxClearBit (bs.data, 10, NamedBS_bitOne);
Finally, the bit could be tested using rtxTestBit with the following statement:
if (rtxTestBit (bs.data, 10, NamedBS_bitOne) {
... bit is set
}
Note that the compiler generated a fixed length data array for this specification. It did this because the maximum size of
the string is known due to the named bits - it must only be large enough to hold the maximum valued named bit constant.
Contents Constraint
It is possible to specify a contents constraint on a BIT STRING type using the CONTAINING keyword. This indicates
that the encoded contents of the specified type should be packed within the BIT STRING container. An example of
this type of constraint is as follows:
ContainingBS ::= BIT STRING (CONTAINING INTEGER)
ASN1C will generate a type definition that references the type that is within the containing constraint. In this case,
that would be INTEGER; therefore, the generated type definition would be as follows:
typedef OSINT32 ContainingBS;
The generated encoders and decoders would handle the extra packing and unpacking required to get this to and from a
BIT STRING container. This direct use of the containing type can be suppressed through the use of the -noContaining
command-line argument. In this case, a normal BIT STRING type will be used and it will be the users responsibility
to do the necessary packing and unpacking operations to encode and decode the variable correctly.
ASN1CBitStr Control Class
When C++ code generation is specified, a control class is generated for operating on the target bit string. This class is
derived from the ASN1CBitStr class. This class contains methods for operating on bits within the string.
Objects of this class can also be declared inline to make operating on bits within other ASN.1 constructs easier. For
example, in a SEQUENCE containing a bit string element the generated type will contain a public member variable
containing the ASN1T type that holds the message data. If one wanted to operate on the bit string contained within
that element, they could do so by using the ASN1CBitStr class inline as follows:
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ASN.1 To C/C++ Mappings
ASN1CBitStr bs (<seqVar>.<element>);
bs.set (0);
In this example, <seqVar> would represent a generated SEQUENCE variable type and <element> would represent a
bit string element within this type.
See the section on the ASN1CBitStr class in the ASN1C C/C++ Common Run-time User's Manual for details on all
of the methods available in this class.
OCTET STRING
The ASN.1 OCTET STRING type is converted into a C structured type containing an integer to hold the number of
octets and an array of unsigned characters (OCTETs) to hold the octet string contents. The number of octets integer
specifies the actual number of octets in the contents field.
The allocation for the contents field depends on how the octet string is specified in the ASN.1 definition. If a size
constraint is used, a static array of that size is generated; otherwise, a pointer variable is generated to hold a dynamically
allocated string. The decoder will automatically allocate memory to hold a parsed string based on the received length
of the string.
For C++, constructors and assignment operators are generated to make assigning variables to the structures easier.
In addition to the default constructor, a constructor is provided for string or binary data. An assignment operator is
generated for direct assignment of a null-terminated string to the structure (note: this assignment operator copies the
null terminator at the end of the string to the data).
Dynamic OCTET STRING
ASN.1 production:
<name> ::= OCTET STRING
Generated C code:
typedef ASN1DynOctStr <name>;
Generated C++ code:
typedef ASN1TDynOctStr ASN1T_<name>;
In this case, different base types are used for C and C++. The difference between the two is the C++ version includes
constructors, assignment operators, and other helper methods that make it easier to manipulate binary data.
The ASN1DynOctStr type (i.e., the type used in the C mapping) is defined in the asn1type.h header file as follows:
typedef struct ASN1DynOctStr {
OSUINT32 numocts;
const OSOCTET* data;
} ASN1DynOctStr;
The ASN1TDynOctStr type is defined in the ASN1TOctStr.h header file. This class extends the C ASN1DynOctStr
class and adds many additional constructors and methods. See the C/C++ Common Run-time Reference Manual for
a complete description of this class.
Static (sized) OCTET STRING
ASN.1 production:
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ASN.1 To C/C++ Mappings
<name> ::= OCTET STRING (SIZE (<len>))
Generated C code:
typedef struct {
OSUINT32 numocts;
OSOCTET data[<len>];
} <name>;
If the -strict-size command-line option is used, the numocts component within this type definition may be of a different
type (OSUINT8 or OSUINT16) or eliminated completely if the type is constrained to be a fixed-size.
Generated C++ code:
typedef struct {
OSUINT32 numocts;
OSOCTET data[<len>];
// ctors
ASN1T_<name> ();
ASN1T_<name> (OSUINT32 _numocts,
const OSOCTET* _data);
ASN1T_<name> (const char* cstring);
// assignment operators
ASN1T_<name>& operator= (const char* cstring);
} ASN1T_<name>;
If the -strict-size command-line option is used, the numocts component within this type definition may be of a different
type (OSUINT8 or OSUINT16) or eliminated completely if the type is constrained to be a fixed-size.
Contents Constraint
It is possible to specify a contents constraint on an OCTET STRING type using the CONTAINING keyword. This
indicates that the encoded contents of the specified type should be packed within the OCTET STRING container. An
example of this type of constraint is as follows:
ContainingOS ::= OCTET STRING (CONTAINING INTEGER)
ASN1C will generate a type definition that references the type that is within the containing constraint. In this case,
that would be INTEGER; therefore, the generated type definition would be as follows:
typedef OSINT32 ContainingOS;
The generated encoders and decoders would handle the extra packing and unpacking required to get this to and from
an OCTET STRING container. This direct use of the containing type can be suppressed through the use of the noContaining command-line argument. In this case, a normal OCTET STRING type will be used and it will be the
users responsibility to do the necessary packing and unpacking operations to encode and decode the variable correctly.
ENUMERATED
The ASN.1 ENUMERATED type is converted into different types depending on whether C or C++ code is being
generated. The C mapping is either a C enum or integer type depending on whether or not the ASN.1 type is extensible
or not. The C++ mapping adds a struct wrapper around this type to provide a namespace to aid in making the enumerated
values unique across all modules.
C Mapping
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ASN.1 To C/C++ Mappings
ASN.1 production:
<name> ::= ENUMERATED (<id1>(<val1>), <id2>(<val2>), ...)
Generated code :
typedef enum {
id1 = val1,
id2 = val2,
...
} <name>_Root
typedef OSUINT32 <name>;
The compiler will automatically generate a new identifier value if it detects a duplicate within the source specification.
The format of this generated identifier is 'id_n' where id is the original identifier and n is a sequential number. The
compiler will output an informational message when this is done. This message is only displayed if the -warnings
qualifier is specified on the command line.
A configuration setting is also available to further disambiguate duplicate enumerated item names. This is the "enum
prefix" setting that is available at both the module and production levels. For example, the following would cause the
prefix "h225" to be added to all enumerated identifiers within the H225 module:
<module>
<name>H225</name>
<enumPrefix>h225</enumPrefix>
</module>
The -fqenum (fully-qualified enum) option may also be used to make C names unique. When specified, enumerated
identifiers will be automatically prefixed with the enclosing type name. In the specification above, each of the
identifiers would have the form "<name>_<id>". This can be useful in situations where common identifiers are often
repeated in different types. This is not a problem in C++ because the identifiers are wrapped in a struct declaration
which provides a namespace for the values (see the C++ section below for more details).
The -use-enum-types (use enumerated types) option causes the direct use of the generated enum type as the C type.
The general pattern in this case is:
typedef enum {
id1 = val1,
id2 = val2,
...
<name>_UNKNOWN_
} <name>;
The advantages of the type generated in the former case are a) the integer type is of a known size, and b) it can hold
unknown values or PER index values in the case of an unknown extensible value being received. However, some users
don't care about this and would prefer the second case which provide a more debug friendly format for modern IDE's
which can normally shown the symbolic value rather than the numeric.
In addition to the generated type definition, helper functions are also generated to make it easier to convert to/from
enumerated and string format. The signatures of these functions are as follows:
const OSUTF8CHAR* <name>_ToString (OSINT32 value);
int <name>_ToEnum (OSCTXT* pctxt, const OSUTF8CHAR* value, <name>* pvalue);
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ASN.1 To C/C++ Mappings
The first function would be used to convert an enumerated value into string form. The second would do the opposite
- convert from string to enumerated.
C++ Mapping
ASN.1 production:
<name> ::= ENUMERATED (<id1>(<val1>), <id2>(<val2>), ...)
Generated code :
struct <name> {
enum Root {
id1 = val1,
id2 = val2,
...
}
[ enum Ext {
extid1 = extval1,
...
} ]
} ;
typedef OSUINT32 ASN1T_<name>
The struct type provides a namespace for the enumerated elements. This allows the same enumerated constant names
to be used in different productions within the ASN.1 specification. An enumerated item is specified in the code using
the <name>::<id> form.
Every generated definition contains a Root enumerated specification and, optionally, an Ext specification. The Root
specification contains the root elements of the type (or all of the elements if it is not an extended type), and the Ext
specification contains the extension enumerated items.
The form of the typedef following the struct specification depends on whether or not the enumerated type contains
an extension marker or not. If a marker is present, it means the type can contain values outside the root enumeration.
An OSUINT32 is always used in the final typedef to ensure a consistent size of an enumerated variable and to handle
the case of unknown extension values.
If the -use-enum-types (use enumerated types) command-line option is selected, the type generated for C++ is identical
to what is generated for the C case documented above when this option is selected.
NULL
The ASN.1 NULL type does not generate an associated C or C++ type definition
OBJECT IDENTIFIER
The ASN.1 OBJECT IDENTIFIER type is converted into a C or C++ structured type to hold the subidentifier values
that make up the object identifier.
ASN.1 production:
<name> ::= OBJECT IDENTIFIER
Generated C code:
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ASN.1 To C/C++ Mappings
typedef ASN1OBJID <name>;
Generated C++ code:
typedef ASN1TObjId ASN1T_<name>;
In this case, different base types are used for C and C++. The difference between the two is the C++ version includes
constructors and assignment operators that make setting the value a bit easier.
The ASN1OBJID type (i.e., the type used in the C mapping) is defined in asn1type.h to be the following:
typedef struct {
OSUINT32 numids; /* number of subidentifiers */
OSUINT32 subid[ASN_K_MAXSUBIDS];/* subidentifier values */
} ASN1OBJID;
The constant ASN_K_MAXSUBIDS specifies the maximum number of sub-identifiers that can be assigned to a value
of the type. This constant is set to 128 as per the ASN.1 standard.
The ASN1TObjId type used in the C++ mapping is defined in ASN1TObjId.h. This class extends the C ASN1OBJID
structure and adds many additional constructors and helper methods. See the ASN1C C/C++ Common Run-time
Reference Manual for more details.
RELATIVE-OID
The ASN.1 RELATIVE-OID type is converted into a C or C++ structured type that is identical to that of the OBJECT
IDENTIFIER described above:
ASN.1 production:
<name> ::= RELATIVE-OID
Generated C code:
typedef ASN1OBJID <name>;
Generated C++ code:
typedef ASN1TObjId ASN1T_<name>;
A RELATIVE-OID is identical to an OBJECT IDENTIFIER except that it does not contain the restriction on the initial
two arc values that they fall within a certain range (see the X.680 standard for more details on this).
REAL
The ASN.1 REAL type is mapped to the C type OSREAL. In the global include file osSysTypes.h, OSREAL is defined
to be a double.
ASN.1 production:
ASN.1 production:
Generated C code:
typedef OSREAL <name>;
Generated C++ code:
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ASN.1 To C/C++ Mappings
typedef OSREAL ASN1T_<name>;
SEQUENCE
This section discusses the mapping of an ASN.1 SEQUENCE type to C. The C++ mapping is similar but there are
some differences. These are discussed in the C++ Mapping of SEQUENCE subsection at the end of this section.
An ASN.1 SEQUENCE is a constructed type consisting of a series of element definitions. These elements can be of
any ASN.1 type including other constructed types. For example, it is possible to nest a SEQUENCE definition within
another SEQUENCE definition as follows:
A ::= SEQUENCE {
x SEQUENCE {
a1 INTEGER,
a2 BOOLEAN
},
y OCTET STRING (SIZE (10))
}
In this example, the production has two elements: x and y. The nested SEQUENCE x has two additional elements:
a1 and a2.
The ASN1C compiler first recursively pulls all of the embedded constructed elements out of the
SEQUENCE and forms new internal types. The names of these types are of the form <name>_<elementname1>_<elementname2>_ ... <element-nameN>. For example, in the definition above, two temporary
types would be generated: A_x and A_y (A_yis generated because a static OCTET STRING maps to a C++ struct
type).
The general form is as follows:
ASN.1 production:
<name> ::= SEQUENCE {
<element1-name> <element1-type>,
<element2-name> <element2-type>,
...
}
Generated C code:
typedef struct {
<type1> <element1-name>;
<type2> <element2-name>;
...
} <name>;
- or typedef struct {
...
} <tempName1>
typedef struct {
...
} <tempName2>
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ASN.1 To C/C++ Mappings
typedef struct {
<tempName1> <element1-name>;
<tempName2> <element2-name>;
...
} <name>;
The <type1> and <type2> placeholders represent the equivalent C types for the ASN.1 types <element1type> and <element2-type> respectively. This form of the structure will be generated if the internal types are
primitive. <tempName1> and <tempName2> are formed using the algorithm described above for pulling structured
types out of the definition. This form is used for constructed elements and elements that map to structured C types.
The example above would result in the following generated C typedefs:
typedef struct A_x {
OSINT32 a1;
OSBOOL a2;
} A_x;
typedef struct A_y {
OSUINT32 numocts;
OSOCTET data[10];
} A_y;
typedef struct A {
A_x x;
A_y y;
} A;
In this case, elements x and y map to structured C types, so temporary typedefs are generated.
In the case of nesting levels greater than two, all of the intermediate element names are used to form the final name.
For example, consider the following type definition that contains three nesting levels:
X ::= SEQUENCE {
a SEQUENCE {
aa SEQUENCE { x INTEGER, y BOOLEAN },
bb INTEGER
}
}
In this case, the generation of temporary types results in the following equivalent type definitions:
X-a-aa ::= SEQUENCE { x INTEGER, y BOOLEAN }
X-a ::= SEQUENCE { aa X-a-aa, bb INTEGER }
X ::= SEQUENCE { X-a a }
Note that the name for the aa element type is X-a-aa. It contains both the name for a (at level 1) and aa (at level
2). The concatanation of all of the intermediate element names can lead to very long names in some cases. To get
around the problem, the -shortnames command-line option can be used to form shorter names. In this case, only the
type name and the last element name are used. In the example above, this would lead to an element name of X-aa.
The disadvantage of this is that the names may not always be unique. If using this option results in non-unique names,
an _n suffix is added where n is a sequential number to make the names unique.
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ASN.1 To C/C++ Mappings
It is possible to suppress the pulling out of nested types to form new types through the use of the <inline/>
configuration item. This will not work in all cases, however. It is at times necessary to use the sizeof operator on
an intermediate type to determine the size of a structure for memory allocations. If a temporary type is not created, it
will not be possible to determine this size. An error will be reported in this case.
Note that although the compiler can handle embedded constructed types within productions, it is generally not
considered good style to define productions this way. It is much better to manually define the constructed types for
use in the final production definition. For example, the production defined at the start of this section can be rewritten
as the following set of productions:
X ::= SEQUENCE {
a1 INTEGER,
a2 BOOLEAN
}
Y ::= OCTET STRING
A ::= SEQUENCE {
X x,
Y y
}
This makes the generated code easier to understand for the end user.
Unnamed Elements
Note
As of X.680, unnamed elements are not allowed: elements must be named. ASN1C still provides backward
compatibility support for this syntax however.
In an ASN.1 SEQUENCE definition, the <element-name> tokens at the beginning of element declarations are optional.
It is possible to include only a type name without a field identifier to define an element. This is normally done with
defined type elements, but can be done with built-in types as well. An example of a SEQUENCE with unnamed
elements would be as follows:
AnInt ::= [PRIVATE 1] INTEGER
Aseq ::= [PRIVATE 2] SEQUENCE {
x
INTEGER,
AnInt
}
In this case, the first element (x) is named and the second element is unnamed.
ASN1C handles this by generating an element name using the type name with the first character set to lower case.
For built-in types, a constant element name is used for each type (for example, aInt is used for INTEGER). There is
one caveat, however. ASN1C cannot handle multiple unnamed elements in a SEQUENCE or SET with the same type
names. Element names must be used in this case to distinguish the elements.
So, for the example above, the generated code would be as follows:
typedef OSINT32 AnInt;
typedef struct Aseq {
OSINT32 x;
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ASN.1 To C/C++ Mappings
AnInt anInt;
} Aseq;
OPTIONAL keyword
Elements within a sequence can be declared to be optional using the OPTIONAL keyword. This indicates that the
element is not required in the encoded message. An additional construct is added to the generated code to indicate
whether an optional element is present in the message or not. This construct is a bit structure placed at the beginning
of the generated sequence structure. This structure always has variable name 'm' and contains single-bit elements of
the form '<element-name>Present' as follows:
struct {
unsigned <element-name1>Present : 1,
unsigned <element-name2>Present : 1,
...
} m;
In this case, the elements included in this construct correspond to only those elements marked as OPTIONAL within
the production. If a production contains no optional elements, the entire construct is omitted.
For example, the production in the previous example can be changed to make both elements optional:
Aseq ::= [PRIVATE 2] SEQUENCE {
x
INTEGER OPTIONAL,
AnInt
OPTIONAL
}
In this case, the following C typedef is generated:
typedef struct Aseq {
struct {
unsigned xPresent : 1,
unsigned anIntPresent : 1
} m;
OSINT32
x;
AnInt
anInt;
} Aseq;
When this structure is populated for encoding, the developer must set the xPresent and anIntPresent flags accordingly
to indicate whether the elements are to be included in the encoded message or not. Conversely, when a message is
decoded into this structure, the developer must test the flags to determine if the element was provided in the message
or not.
The generated C++ structure will contain a constructor if OPTIONAL elements are present. This constructor will set all
optional bits to zero when a variable of the structured type is declared. The programmer therefore does not have to be
worried about clearing bits for elements that are not used; only with setting bits for the elements that are to be encoded.
DEFAULT keyword
The DEFAULT keyword allows a default value to be specified for elements within the SEQUENCE. ASN1C will
parse this specification and treat it as it does an optional element. Note that the value specification is only parsed in
simple cases for primitive values. It is up to the programmer to provide the value in complex cases. For BER encoding,
a value must be specified be it the default or other value.
For DER or PER, it is a requirement that no value be present in the encoding for the default value. For integer and
boolean default values, the compiler automatically generates code to handle this requirement based on the value in
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ASN.1 To C/C++ Mappings
the structure. For other values, an optional present flag bit is generated. The programmer must set this bit to false
on the encode side to specify default value selected. If this is done, a value is not encoded into the message. On the
decode side, the developer must test for present bit not set. If this is the case, the default value specified in the ASN.1
specification must be used and the value in the structure ignored.
Extension Elements
If the SEQUENCE type contains an open extension field (i.e., a ... at the end of the specification or a ..., ... in the
middle), a special element will be inserted to capture encoded extension elements for inclusion in the final encoded
message. This element will be of type OSRTDList and have the name extElem1. This is a linked list of open type fields.
Each entry in the list is of type ASN1OpenType. The fields will contain complete encodings of any extension elements
that may have been present in a message when it is decoded. On subsequent encode of the type, the extension fields
will be copied into the new message.
The -noOpenExt command line option can be used to alter this default behavior. If this option is specified, the extElem1
element is not included in the generated code and extension data that may be present in a decoded message is simply
dropped.
If the SEQUENCE type contains an extension marker and extension elements, then the actual extension elements
will be present in addition to the extElem1 element. These elements will be treated as optional elements whether they
were declared that way or not. The reason is because a version 1 message could be received that does not contain
the elements.
Additional bits will be generated in the bit mask if version brackets are present. These are groupings of extended
elements that typically correspond to a particular version of a protocol. An example would be as follows:
TestSequence ::= SEQUENCE {
item-code
INTEGER (0..254),
item-name
IA5String (SIZE (3..10)) OPTIONAL,
... ! 1,
urgency
ENUMERATED { normal, high } DEFAULT normal,
[[ alternate-item-code
INTEGER (0..254),
alternate-item-name
IA5String (SIZE (3..10)) OPTIONAL
]]
}
In this case, a special bit flag will be added to the mask structure to indicate the presence or absence of the entire
element block. This will be of the form "_v#ExtPresent" where # would be replaced by the sequential version number.
In the example above, this number would be three (two would be the version extension number of the urgency field).
Therefore, the generated bit mask would be as follows:
struct {
unsigned
unsigned
unsigned
unsigned
} m;
item_namePresent : 1;
urgencyPresent : 1;
_v3ExtPresent : 1;
alternate_item_namePresent : 1;
In this case, the setting of the _v3ExtPresent flag would indicate the presence or absence of the entire version block.
Note that it is also possible to have optional items within the block (alternate-item-name).
C++ Mapping of SEQUENCE
The C++ mapping of an ASN.1 SEQUENCE type is very similar to the C mapping. However, there are some important
differences:
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ASN.1 To C/C++ Mappings
1. As with all C++ types, the prefix ASN1T_ is added before the typename to distinguish the data class from the
control class (the control class contains an ASN1C_ prefix).
2. A default constructor is generated to initialize the structure elements. This constructor will initialize all elements
and set any simple default values that may have been specified in the ASN.1 definition.
3. If the -genCopy command line switch was specified, a copy constructor will be generated to allow an instance of
the data contained within a PDU control class object to be copied.
4. Also if -genCopy was specified, a destructor is generated if the type contains dynamic fields. This destructor will
free all memory held by the type when the object is deleted or goes out of scope.
SET
The ASN.1 SET type is converted into a C or C++ structured type that is identical to that for SEQUENCE as described
in the previous section. The only difference between SEQUENCE and SET is that elements may be transmitted in any
order in a SET whereas they must be in the defined order in a SEQUENCE. The only impact this has on ASN1C is
in the generated decoder for a SET type.
The decoder must take into account the possibility of out-of-order elements. This is handled by using a loop to parse
each element in the message. Each time an item is parsed, an internal mask bit within the decoder is set to indicate
the element was received. The complete set of received elements is then checked after the loop is completed to verify
all required elements were received.
SEQUENCE OF
The ASN.1 SEQUENCE OF type is converted into one of the following C/C++ types:
• A doubly-linked list structure (OSRTDList for C, or ASN1TSeqOfList, a class derived from OSRTDList, for C++)
• A structure containing an integer count of elements and a pointer to hold an array of the referenced data type (a
dynamic array)
• A structure containing an integer count of elements and a fixed-sized array of the referenced data type (a static array)
• A C++ Standard Library container class, such as std::list (when -cpp11 is specified on the command line)
The linked list option is the default for constructed types. An array is used for a sequence of primitive types. The
allocation for the contents field of the array depends on how the SEQUENCE OF is specified in the ASN.1 definition.
If a size constraint is used, a static array of that size is generated; otherwise, a pointer variable is generated to hold a
dynamically allocated array of values. The decoder will automatically allocate memory to hold parsed SEQUENCE
OF data values.
The default type may be altered through the use of command-line options:
The -array option may be used to indicate an array type should be used as the default instead of a linked list for all
types. If the type does not contain a size constraint, a dynamic array will be used; otherwise a static array of the given
size will be used. The -arraySize option may be used to force use of a static array for all types. SEQUENCE OF types
not having a size constraint will result in a static array being generated of the size specified in the -arraySize option.
The -cpp11 option will alter the code to use std::array instead of plain C++ static arrays.
The -dynamicArray option will result in the use of a dynamic array for all SEQUENCE OF types.
The -linkedList option will result in the use of a linked list for all of these types. The -cpp11 option will result in using
std::list wherever a linked list would have been used othewise.
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ASN.1 To C/C++ Mappings
The type used for a given SEQUENCE OF construct can be modified by the use of a configuration item. The <storage>
qualifier is used for this purpose. The dynamicArray keyword can be used at the global, module, or production level
to specify that dynamic memory (i.e., a pointer) is used for the array. The syntax of this qualifier is as follows:
<storage>dynamicArray</storage>
The array keyword is used to specify that a static array is to be generated to hold the data. In this case, if the
SEQUENCE OF production does not contain a size constraint, the maxSize attribute must be used to specify the
maximum size of the array. For example:
<storage maxSize="100">array</storage>
If maxSize is not specified and the ASN.1 production contains no size constraint, then a dynamic array is used.
The std::array keyword is identical to the array keyword except that it specifies use of std::array instead of a plain C
++ static array. Its use requires the -cpp11 command line option.
The list keyword can also be used in a similar fashion to specify the use of a linked-linked structure to hold the elements:
<storage>list</storage>
When -cpp11 is specified on the command line, you can also use the following storage options to select the use of C
++ Standard Library container classes:
<storage>std::list</storage>
<storage>std::vector</storage>
<storage>std::deque</storage>
See the section entitled Compiler Configuration File for further details on setting up a configuration file.
Dynamic SEQUENCE OF Type
ASN.1 production:
<name> ::= SEQUENCE OF <type>
Generated C code:
typedef struct {
OSUINT32 n;
<type>* elem;
} <name>;
Generated C++ code:
typedef struct [ : public ASN1TPDU ] {
OSUINT32 n;
<type>* elem;
ASN1T_<name>();
[~ASN1T_<name>();]
} ASN1T_<name>;
Note that parsed values can be accessed from the dynamic data variable just as they would be from a static array
variable; i.e., an array subscript can be used (ex: elem[0], elem[1]...).
In the case of C++, a constructor is generated to initialize the element count to zero. If the type represents a PDU type
(either by default by not referencing any other types or explicitly via the -pdu command-line option), the ASN1TPDU
78
ASN.1 To C/C++ Mappings
base class is extended and a destructor is added. This destructor ensures that memory allocated for elements is freed
upon destruction of the object.
Static (sized) SEQUENCE OF Type
ASN.1 production:
<name> ::= SEQUENCE (SIZE (<len>)) OF <type>
Generated C code:
typedef struct {
OSUINT32 n;
<type> elem[<len>];
} <name>;
Generated C++ code:
typedef struct {
OSUINT32 n;
<type> elem[<len>];
} ASN1T_<name>;
Generated C++ code with -cpp11:
typedef struct {
OSUINT32 n;
std::array<<type>, <len>> elem;
} ASN1T_<name>;
If the -strict-size command-line option is used, the n component within this type definition may be of a different type
(OSUINT8 or OSUINT16) or eliminated completely if the type is constrained to be a fixed-size.
List-based SEQUENCE OF Type
A doubly-linked list header type (OSRTDList) is used for the type definition if the list storage configuration setting
is used (see above). This can be used for either a sized or unsized SEQUENCE OF construct. The generated C or C
++ code is as follows:
Generated C code:
typedef OSRTDList <name>;
Generated C++ code:
typedef ASN1TSeqOfList ASN1T_<name>;
The type definition of the OSRTDList structure can be found in the osSysTypes.h header file. The common run-time
utility functions beginning with the prefix rtxDList are available for initializing and adding elements to the list. See
the C/C++ Common Run-time Reference Manual for a full description of these functions.
For C++, the ASN1TSeqOfList class is used, or, in the case of PDU types, the ASN1TPDUSeqOfList class.
The ASN1TSeqOfList extends the C OSRTDList structure and adds constructors and other helper methods.
The ASN1TPDUSeqOfList is similar except that it also extends the ASN1TPDU base class to add additional
memory management capabilities needed by PDU types to automatically release memory on destruction. See the
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ASN.1 To C/C++ Mappings
ASN1CSeqOfList section in the C/C++ Common Run-time Reference Manual for details on all of the methods available
in this class.
Populating Linked-List Structures
Populating generated list-based SEQUENCE OF structures for the most part requires the use of dynamic memory to
allocate elements to be added to the list (note that it is possible to use static elements for this, but this is unusual).
The recommended method is to use the built in run-time memory management facilities available within the ASN1C
runtime library. This allows all list memory to be freed with one call after encoding is complete.
In the case of C, the rtxMemAlloc or rtxMemAllocType function would first be used to allocate a record of the element
type. This element would then be initialized and populated with data. The rtxDListAppend function would then be
called to append it to the given list.
For C++, the compiler generates the helper methods NewElement and Append in the generated control class for a
SEQUENCE OF type. An instance of this class can be created using the list element within a generated structure as
a parameter. The helper methods can then be used to allocate and initialize an element and then append it to the list
after it is populated.
See the cpp/sample_ber/employee/writer.cpp file for an example of how these methods are used. In this
program, the following logic is used to populate one of the elements in the children list for encoding:
ASN1T_ChildInformation* pChildInfo;
ASN1C__SeqOfChildInformation listHelper (encodeBuffer, msgData.children);
...
pChildInfo = listHelper.NewElement();
fill_Name (&pChildInfo->name, "Ralph", "T", "Smith");
pChildInfo->dateOfBirth = "19571111";
listHelper.Append (pChildInfo);
In this example, msgData is an instance of the main PDU class being encoded (PersonnelRecord). This object
contains an element called children which is a linked-list of ChildInformation records. The code snippet
illustrates how to use the generated control class for the list to allocate a record, populate it, and append it to the list.
ASN1C also generates helper methods in SEQUENCE, SET, and CHOICE control classes to assist in allocating
and adding elements to inline SEQUENCE OF lists. These methods are named new_<elem>_element and
append_to_<elem> where <elem> would be replaced with the name of the element they apply to.
C++ Standard Library Containers for SEQUNCE OF Type
As noted above, -cpp11 can be used (among other things) to specify that std::list should be used for SEQUENCE
OF types where a linked list would otherwise be used, while other C++ Standard library containers (e.g. std::vector)
can be specified by using a configuration file. When a C++ STL class is used, the generated C++ code will resemble
the following:
typedef std::list<ASN1T_<ElementTypeName*> ASN1T_<SeqOfTypeName>;
The contained type will always be a pointer type.
Generation of Temporary Types for SEQUENCE OF Elements
As with other constructed types, the <type> variable can reference any ASN.1 type, including other ASN.1
constructed types. Therefore, it is possible to have a SEQUENCE OF SEQUENCE, SEQUENCE OF CHOICE, etc.
When a constructed type or type that maps to a C structured type is referenced, a temporary type is generated for use
in the final production. The format of this temporary type name is as follows:
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ASN.1 To C/C++ Mappings
<prodName>_element
In this definition, <prodName> refers to the name of the production containing the SEQUENCE OF type.
For example, a simple (and very common) single level nested SEQUENCE OF construct might be as follows:
A ::= SEQUENCE OF SEQUENCE { a INTEGER, b BOOLEAN }
In this case, a temporary type is generated for the element of the SEQUENCE OF production. This results in the
following two equivalent ASN.1 types:
A-element ::= SEQUENCE { a INTEGER, b BOOLEAN }
A ::= SEQUENCE OF A-element
These types are then converted into the equivalent C or C++ typedefs using the standard mapping that was previously
described.
SEQUENCE OF Type Elements in Other Constructed Types
Frequently, a SEQUENCE OF construct is used to define an array of some common type in an element in some other
constructed type (for example, a SEQUENCE). An example of this is as follows:
SomePDU ::= SEQUENCE {
addresses SEQUENCE OF AliasAddress,
...
}
Normally, this would result in the addresses element being pulled out and used to create a temporary type with a
name equal to SomePDU-addresses as follows:
SomePDU-addresses ::= SEQUENCE OF AliasAddress
SomePDU ::= SEQUENCE {
addresses SomePDU-addresses,
...
}
However, when the SEQUENCE OF element references a simple defined type as above with no additional tagging
or constraint information, an optimization is done to reduce the size of the generated code. This optimization is to
generate a common name for the new temporary type that can be used for other similar references. The form of this
common name is as follows:
_SeqOf<elementProdName>
So instead of this:
SomePDU-addresses ::= SEQUENCE OF AliasAddress
The following equivalent type would be generated:
_SeqOfAliasAddress ::= SEQUENCE OF AliasAddress
The advantage is that the new type can now be easily reused if SEQUENCE OF AliasAddress is used in any other
element declarations. Note the (illegal) use of an underscore in the first position. This is to ensure that no name
collisions occur with other ASN.1 productions defined within the specification.
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ASN.1 To C/C++ Mappings
Some SEQUENCE OF elements in constructed types are inlined. In other words, no temporary type is created; instead,
either the OSRTDList reference (for linked list) or the array definition is inserted directly into the generated C
structure. This is particularly true when XSD files are being compiled.
SET OF
The ASN.1 SET OF type is converted into a C or C++ structured type that is identical to that for SEQUENCE OF
as described in the previous section.
CHOICE
The ASN.1 CHOICE type is converted into a C or C++ structured type containing an integer for the choice tag value
(t) followed by a union (u) of all of the equivalent types that make up the CHOICE elements.
The tag value is simply a sequential number starting at one for each alternative in the CHOICE. A #define constant
is generated for each of these values. The format of this constant is T_<name>_<element-name> where <name>
is the name of the ASN.1 production and <element-name> is the name of the CHOICE alternative. If a CHOICE
alternative is not given an explicit name, then <element-name> is automatically generated by taking the type name
and making the first letter lowercase (this is the same as was done for the ASN.1 SEQUENCE type with unnamed
elements). If the generated name is not unique, a sequential number is appended to make it unique.
The union of choice alternatives is made of the equivalent C or C++ type definition followed by the element name
for each of the elements. The rules for element generation are essentially the same as was described for SEQUENCE
above. Constructed types or elements that map to C structured types are pulled out and temporary types are created.
Unnamed elements names are automatically generated from the type name by making the first character of the name
lowercase.
One difference between temporary types used in a SEQUENCE and in a CHOICE is that a pointer variable will be
generated for use within the CHOICE union construct.
ASN.1 production:
<name> ::= CHOICE {
<element1-name> <element1-type>,
<element2-name> <element2-type>,
...
}
Generated C code:
#define T_<name>_<element1-name> 1
#define T_<name>_<element2-name> 2
...
typedef struct {
int
t;
union {
<type1> <element1-name>;
<type2> <element2-name>;
...
} u;
} <name>;
- or -
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ASN.1 To C/C++ Mappings
typedef struct {
...
} <tempName1>;
typedef struct {
...
} <tempName2>;
typedef struct {
int t;
union {
<tempName1>* <element1-name>;
<tempName2>* <element2-name>;
...
} u;
} <name>;
If the -use-enum-types command-line option is used, an enumerated type is used instead of the #define statements and
integer t member variable as follows:
typedef struct {
enum T {
T_<name>_<element1-name>,
T_<name>_<element2-name>,
...
} t;
union {
<type1> <element1-name>;
<type2> <element2-name>;
...
} u;
} <name>;
If the -static command line option or <storage> static </storage> configuration variable is set for the
given production, then pointers will not be used for the variable declarations.
Note
This is true for the C case only; for C++, pointers must be used due to the fact that the generated code will
not compile if constructors are used in a non-pointer variable within a union construct.
The C++ mapping is the same with the exception that the ASN1T_ prefix is added to the generated type name.
<type1> and <type2> are the equivalent C types representing the ASN.1 types <element1-type> and
<element2-type> respectively. <tempName1> and <tempName2> represent the names of temporary types that
may have been generated as the result of using nested constructed types within the definition.
Choice alternatives may be unnamed, in which case <element-name> is derived from <element-type> by
making the first letter lowercase. One needs to be careful when nesting CHOICE structures at different levels within
other nested ASN.1 structures (SEQUENCEs, SETs, or other CHOICEs). A problem arises when CHOICE element
names at different levels are not unique (this is likely when elements are unnamed). The problem is that generated tag
constants are not guaranteed to be unique since only the production and end element names are used.
The compiler gets around this problem by checking for duplicates. If the generated name is not unique, a sequential
number is appended to make it unique. The compiler outputs an informational message when it does this.
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ASN.1 To C/C++ Mappings
An example of this can be found in the following production:
C ::= CHOICE {
[0] INTEGER,
[1] CHOICE {
[0] INTEGER,
[1] BOOLEAN
}
}
This will produce the following C code:
#define
#define
#define
#define
T_C_aInt
T_C_aChoice
T_C_aInt_1
T_C_aBool
1
2
1
2
typedef struct {
int t;
union {
OSINT32 aInt;
struct {
int t;
union {
OSINT32 aInt;
OSBOOL aBool;
} u;
} aChoice;
} C;
Note that _1 was appended to the second instance of T_C_aInt. Developers must take care to ensure they are using
the correct tag constant value when this happens.
Populating Generated Choice Structures
Populating generated CHOICE structures is more complex then for other generated types due to the use of pointers
within the union construct. As previously mentioned, the use of pointers with C can be prevented by using the static command line option. If this is done, the elements within the union construct will be standard inline variable
declarations and can be populated directly. Otherwise, the methods listed below can be used to populate the variables.
The recommended way to populate the pointer elements is to declare variables of the embedded type to be used on the
stack prior to populating the CHOICE structure. The embedded variable would then be populated with the data to be
encoded and then the address of this variable would be plugged into the CHOICE union pointer field.
Consider the following definitions:
AsciiString ::= [PRIVATE 28] OCTET STRING
EBCDICString ::= [PRIVATE 29] OCTET STRING
String ::= CHOICE { AsciiString, EBCDICString }
This would result in the following type definitions:
typedef OSDynOctStr AsciiString;
typedef OSDynOctStr EBCDICString;
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ASN.1 To C/C++ Mappings
typedef struct String {
int t;
union {
/* t = 1 */
AsciiString *asciiString;
/* t = 2 */
EBCDICString *eBCDICString;
} u;
} String;
To set the AsciiString choice value, one would first declare an AsciiString variable, populate it, and then plug the
address into a variable of type String structure as follows:
AsciiString asciiString;
String
string;
asciiString = "Hello!";
string.t = T_String_AsciiString;
string.u.asciiString = &asciiString;
It is also possible to allocate dynamic memory for the CHOICE union option variable; but one must be careful to
release this memory when done with the structure. If the built in memory-management functions/macros are used
(rtxMem), all memory used for the variables is automatically released when rtxMemFree is called.
Open Type
Note
The X.680 Open Type replaces the X.208 ANY or ANY DEFINED BY constructs. An ANY or ANY
DEFINED BY encountered within an ASN.1 module will result in the generation of code corresponding to
the Open Type described below.
An Open Type as defined in the X.680 standard is specified as a reference to a Type Field in an Information Object
Class. The most common form of this is when the Type field in the built-in TYPE-IDENTIFIER class is referenced
as follows:
TYPE-IDENTIFIER.&Type
See the section in this document on Information Objects for a more detailed explanation.
The Open Type is converted into a C or C++ structure used to model a dynamic OCTET STRING type. This structure
contains a pointer and length field. The pointer is assumed to point at a string of previously encoded ASN.1 data. When
a message containing an open type is decoded, the address of the open type contents field is stored in the pointer field
and the length of the component is stored in the length field.
The general mapping of an Open Type to C/C++ is as follows:
ASN.1 production:
<name> ::= ANY
Generated C code:
typedef ASN1OpenType <name>;
Generated C++ code:
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ASN.1 To C/C++ Mappings
typedef ASN1TOpenType <name>;
The difference between the two types is the C++ version contains constructors to initialize the value to zero or to a
given open type value.
If the -tables command line option is selected and the ASN.1 type definition references a table constraint, the code
generated is different. In this case, ASN1OpenType above is replaced with ASN1Object (or ASN1TObject for C++).
This is defined in asn1type.h as follows:
typedef struct { /* generic table constraint value holder */
ASN1OpenType encoded;
void*
decoded;
OSINT32
index;
/* table index */
} ASN1Object;
This allows a value of any ASN.1 type to be represented in both encoded and decoded forms. Encoded form is the
open type form shown above. It is simply a pointer to a byte buffer and a count of the number of byes in the encoded
message component. The decoded form is a pointer to a variable of a specific type. The pointer is void because there
could be a potentially large number of different types that can be represented in the table constraint used to constrain
a type field to a given set of values. The index member of the type is for internal use by table constraint processing
functions to keep track of which row in a table is being referenced.
If the -table-unions command line option is used, a more specialized type of structure is generated. In this case, instead
of a void pointer being used to hold an instance of a type containing data to be encoded, all entries from the referenced
Information Object Set are used in a union structure in much the same way as is done in a CHOICE construct.
If code is being generated from an XML schema file and the file contains an <xsd:any> wildcard declaration, a special
type of any structure is inserted into the generated C/C++ code. This is the type OSXSDAny which is defined in the
osSysTypes.h header file. This structure contains a union which contains alternatives for data in either binary or XML
text form. This makes it possible to transfer data in either binary form if working with binary encoding rules or XML
form if working with XML.
Character String Types
8-bit character character-string types are either represented using a character pointer (const char*) or, if -cpp11
is specified on the command line, std::string. In the case of const char*, the pointer is used to hold a nullterminated C string for encoding/decoding. For encoding, the string can either be static (i.e., a string literal or address
of a static buffer) or dynamic. The decoder allocates dynamic memory from within its context to hold the memory for
the string. This memory is released when the rtxMemFree function is called.
The useful character string types in ASN.1 are as follows:
UTF8String
NumericString
PrintableString
T61String
VideotexString
IA5String
UTCTime
GeneralizedTime
GraphicString
VisibleString
GeneralString
UniversalString
BMPString
::=
::=
::=
::=
::=
::=
::=
::=
::=
::=
::=
::=
::=
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
[UNIVERSAL
12]
18]
19]
20]
21]
22]
23]
24]
25]
26]
27]
28]
30]
86
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
IMPLICIT
OCTET STRING
IA5String
IA5String
OCTET STRING
OCTET STRING
OCTET STRING
GeneralizedTime
IA5String
OCTET STRING
OCTET STRING
OCTET STRING
OCTET STRING
OCTET STRING
ASN.1 To C/C++ Mappings
ObjectDescriptor
::=
[UNIVERSAL 7]
Of these, all are represented by const
UniversalString, and UTF8String types.
char
IMPLICIT GraphicString
* pointers (or std::string)except for the BMPString,
The BMPString type is a 16-bit character string for which the following structure is used:
typedef struct {
OSUINT32 nchars;
OSUNICHAR* data;
} Asn116BitCharString;
The OSUNICHAR type used in this definition represents a Unicode character (UTF-16) and is defined to be a C
unsigned short type.
See the rtBMPToCString, rtBMPToNewCString, and the rtCToBMPString run-time function descriptions
for information on utilities that can convert standard C strings to and from BMP string format.
The UniversalString type is a 32-bit character string for which the following structure is used:
typedef struct {
OSUINT32 nchars;
OS32BITCHAR* data;
} Asn132BitCharString;
The OS32BITCHAR type used in this definition is defined to be a C unsigned int type.
See the rtUCSToCString, rtUCSToNewCString, and the rtCToUCSString run-time function descriptions
for information on utilities that can convert standard C strings to and from Universal Character Set (UCS-4) string
format. See also the rtUCSToWCSString and rtWCSToUCSString for information on utilities that can convert
standard wide character string to and from UniversalString type.
The UTF8String type is represented as a string of unsigned characters using the OSUTF8CHAR data type. This type
is defined to be unsigned char. This makes it possible to use the characters in the upper range of the UTF-8
space as positive numbers. The contents of this string type are assumed to contain the UTF-8 encoding of a character
string. For the most part, standard C character string functions such as strcpy, strcat, etc. can be used with these
strings with some type casting.
Utility functions are provided for working with UTF-8 string data. The UTF-8 encoding for a standard ASCII string is
simply the string itself. For Unicode strings represented in C/C++ using the wide character type (wchar_t), the runtime functions rtxUTF8ToWCS and rtxWCSToUTF8 can be used for converting to and from UTF-8 format. The
function rtxValidateUTF8 can be used to ensure that a given UTF-8 encoding is valid. See the C/C++ Run-Time
Library Reference Manual for a complete description of these functions.
Time String Types
The ASN.1 GeneralizedTime and UTCTime types are mapped to standard C/C++ null-terminated character string types.
The C++ version of the product contains additional control classes for parsing and formatting time string values. When
C++ code generation is specified, a control class is generated for operating on the target time string. This class is derived
from the ASN1CGeneralizedTime or ASN1CUTCTime class for GeneralizedTime or UTCTime respectively. These
classes contain methods for formatting or parsing time components such as month, day, year, etc. from the strings.
Objects of these classes can be declared inline to make the task of formatting or parsing time strings easier. For example,
in a SEQUENCE containing a time string element the generated type will contain a public member variable containing
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ASN.1 To C/C++ Mappings
the ASN1T type that holds the message data. If one wanted to operate on the time string contained within that element,
they could do so by using one of the time string classes inline as follows:
ASN1CGeneralizedTime gtime (msgbuf, <seqVar>.<element>);
gtime.setMonth (ASN1CTime::November);
In this example, <seqVar> would represent a generated SEQUENCE variable type and <element> would represent
a time string element within this type.
See the ASN1CTime, ASN1CGeneralizedTime, and ASN1CUTCTime subsections in the C/C++ Run-Time
Library Reference Manual for details on all of the methods available in these classes.
EXTERNAL
The ASN.1 EXTERNAL type is a useful type used to include non-ASN.1 or other data within an ASN.1 encoded
message. This type is described using the following ASN.1 SEQUENCE:
EXTERNAL ::= [UNIVERSAL 8] IMPLICIT SEQUENCE {
direct-reference OBJECT IDENTIFIER OPTIONAL,
indirect-reference INTEGER OPTIONAL,
data-value-descriptor ObjectDescriptor OPTIONAL,
encoding CHOICE {
single-ASN1-type [0] ABSTRACT-SYNTAX.&Type,
octet-aligned [1] IMPLICIT OCTET STRING,
arbitrary [2] IMPLICIT BIT STRING
}
}
The ASN1C compiler is used to create a meta-definition for this structure. This code will always be generated in the
Asn1External.h and Asn1External.c/cpp files. The code will only be generated if the given ASN.1 source
specification requires this definition. The resulting C structure is populated just like any other compiler-generated
structure for working with ASN.1 data.
Note
NOTE: It is recommended that if a specification contains multiple ASN.1 source files that reference
EXTERNAL, all of these source files be compiled with a single ASN1C call in order to ensure that only a
single copy of the Asn1External source files are generated.
EMBEDDED PDV
The ASN.1 EMBEDDED PDV type is a useful type used to include non-ASN.1 or other data within an ASN.1 encoded
message. This type is described using the following ASN.1 SEQUENCE:
EmbeddedPDV ::= [UNIVERSAL 11] IMPLICIT SEQUENCE {
identification CHOICE {
syntaxes SEQUENCE {
abstract OBJECT IDENTIFIER,
transfer OBJECT IDENTIFIER
},
syntax OBJECT IDENTIFIER,
presentation-context-id INTEGER,
context-negotiation SEQUENCE {
presentation-context-id INTEGER,
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ASN.1 To C/C++ Mappings
transfer-syntax OBJECT IDENTIFIER
},
transfer-syntax OBJECT IDENTIFIER,
fixed NULL
},
data-value-descriptor ObjectDescriptor OPTIONAL,
data-value OCTET STRING
}( WITH COMPONENTS { ... , data-value-descriptor ABSENT})
The ASN1C compiler is used to create a meta-definition for this structure. This code will be always generated in
the Asn1EmbeddedPDV.h and Asn1EmbeddedPDV.c/cpp files. The code will only be generated if the given
ASN.1 source specification requires this definition. The resulting C structure is populated just like any other compilergenerated structure for working with ASN.1 data.
Note
NOTE: It is recommended that if a specification contains multiple ASN.1 source files that reference
EMBEDDEDPDV, all of these source files be compiled with a single ASN1C call in order to ensure that only
a singled copy of the Asn1EmbeddedPDV source files are generated.
Parameterized Types
The ASN1C compiler can parse parameterized type definitions and references as specified in the X.683 standard.
These types allow dummy parameters to be declared that will be replaced with actual parameters when the type is
referenced. This is similar to templates in C++.
A simple and common example of the use of parameterized types is for the declaration of an upper bound on a sized
type as follows:
SizedOctetString{INTEGER:ub} ::= OCTET STRING (SIZE (1..ub))
In this definition, ub would be replaced with an actual value when the type is referenced. For example, a sized octet
string with an upper bound of 32 would be declared as follows:
OctetString32 ::= SizedOctetString{32}
The compiler would handle this in the same way as if the original type was declared to be an octet string of size 1 to
32. That is, it will generate a C structure containing a static byte array of size 32 as follows:
typedef struct OctetString32 {
OSUINT32 numocts;
OSOCTET data[32];
} OctetString32;
Another common example of parameterization is the substitution of a given type inside a common container type. For
example, security specifications frequently contain a 'signed' parameterized type that allows a digital signature to be
applied to other types. An example of this is as follows:
SIGNED { ToBeSigned } ::= SEQUENCE {
toBeSigned
ToBeSigned,
algorithmOID OBJECT IDENTIFIER,
paramS
Params,
signature
BIT STRING
}
An example of a reference to this definition would be as follows:
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ASN.1 To C/C++ Mappings
SignedName ::= SIGNED { Name }
where Name would be another type defined elsewhere within the module.
The compiler performs the substitution to create the proper C typedef for SignedName:
typedef struct SignedName {
Name
toBeSigned;
ASN1OBJID
algorithmOID;
Params
paramS;
ASN1DynBitStr signature;
} SignedName;
When processing parameterized type definitions, the compiler will first look to see if the parameters are actually used
in the final generated code. If not, they will simply be discarded and the parameterized type converted to a normal
type reference. For example, when used with information objects, parameterized types are frequently used to pass
information object set definitions to impose table constraints on the final type. Since table constraints do not affect
the code that is generated by the compiler when table constraint code generation is not enabled, the parameterized
type definition is reduced to a normal type definition and references to it are handled in the same way as defined type
references. This can lead to a significant reduction in generated code in cases where a parameterized type is referenced
over and over again.
For example, consider the following often-repeated pattern from the UMTS 3GPP specs:
ProtocolIE-Field {RANAP-PROTOCOL-IES : IEsSetParam} ::= SEQUENCE {
id
RANAP-PROTOCOL-IES.&id
({IEsSetParam}),
criticality
RANAP-PROTOCOL-IES.&criticality ({IEsSetParam}{@id}),
value
RANAP-PROTOCOL-IES.&Value
({IEsSetParam}{@id})
}
In this case, IEsSetParam refers to an information object set specification that constrains the values that are allowed
to be passed for any given instance of a type referencing a ProtocolIE-Field. The compiler does not add any extra
code to check for these values, so the parameter can be discarded (note that this is not true if the -tables compiler option
is specified). After processing the Information Object Class references within the construct (refer to the section on
Information Objects for information on how this is done), the reduced definition for ProtocolIE-Field becomes
the following:
ProtocolIE-Field ::= SEQUENCE {
id ProtocolIE-ID,
criticality Criticality,
value ASN.1 OPEN TYPE
}
References to the field are simply replaced with a reference to the ProtocolID-Field typedef.
If -tables is specified, the parameters are used and a new type instance is created in accordance with the rules above.
Value Mappings
ASN1C can parse any type of ASN.1 value specification, but it will only generate code for following value
specifications:
• BOOLEAN
• INTEGER
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ASN.1 To C/C++ Mappings
• REAL
• ENUMERATED
• Binary String
• Hexadecimal String
• Character String
• OBJECT IDENTIFER
All value types except INTEGER and REAL cause an "extern" statement to be generated in the header file and a global
value assignment to be added to the C or C++ source file. INTEGER and REAL value specifications cause #define
statements to be generated.
BOOLEAN Value
A BOOLEAN value causes an extern statement to be generated in the header file and a global declaration of type
OSBOOL to be generated in the C or C++ source file. The mapping of ASN.1 declaration to global C or C++ value
declaration is as follows:
ASN.1 production:
<name> BOOLEAN ::= <value>
Generated code:
OSBOOL <name> = <value>;
INTEGER Value
The INTEGER type causes a #define statement to be generated in the header file of the form
ASN1V_<valueName> where <valueName> would be replaced with the name in the ASN.1 source file. The
reason for doing this is the common use of INTEGER values for size and value range constraints in the ASN.1
specifications. By generating #define statements, the symbolic names can be included in the source code making
it easier to adjust the boundary values.
This mapping is defined as follows:
ASN.1 production:
<name> INTEGER ::= <value>
Generated code:
#define ASN1V_<name> <value>;
For example, the following declaration:
ivalue INTEGER ::= 5
will cause the following statement to be added to the generated header file:
#define ASN1V_ivalue 5
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ASN.1 To C/C++ Mappings
The reason the ASN1V_ prefix is added is to prevent collisions with INTEGER value declarations and other
declarations such as enumeration items with the same name.
REAL Value
The REAL type causes a #define statement to be generated in the header file of the form ASN1V_<valueName>
where <valueName> would be replaced with the name in the ASN.1 source file. By generating #define statements,
the symbolic names can be included in the source code making it easier to adjust the boundary values.
This mapping is defined as follows:
ASN.1 production:
<name> REAL ::= <value>
Generated code:
#define ASN1V_<name> <value>;
For example, the following declaration:
rvalue REAL ::= 5.5
will cause the following statement to be added to the generated header file:
#define ASN1V_rvalue 5.5
The reason the ASN1V_ prefix is added is to prevent collisions with other declarations such as enumeration items
with the same name.
Enumerated Value Specification
The mapping of an ASN.1 enumerated value declaration to a global C or C++ value declaration is as follows:
ASN.1 production:
<name> <EnumType> ::= <value>
Generated code:
OSUINT32 <name> = <value>;
Binary and Hexadecimal String Value
Binary and hexadecimal string value specifications cause two global C variables to be generated: a numocts variable
describing the length of the string and a data variable describing the string contents. The mapping for a binary string
is as follows (note: BIT STRING can also be used as the type in this type of declaration):
ASN.1 production:
<name> OCTET STRING ::= '<bstring>'B
Generated code :
OSUINT32 <name>_numocts = <length>;
OSOCTET <name>_data[] = <data>;
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ASN.1 To C/C++ Mappings
A hexadecimal string would be the same except the ASN.1 constant would end in a 'H'.
Character String Value
A character string declaration would cause a C or C++ const char * declaration to be generated:
ASN.1 production:
<name> <string-type> ::= <value>
Generated code:
const char* <name> = <value>;
In this definition, <string-type> could be any of the standard 8-bit characters string types such as IA5String,
PrintableString, etc.
Note
Code generation is not currently supported for value declarations of larger character string types such as
BMPString.
Object Identifier Value Specification
Object identifier values result in a structure being populated in the C or C++ source file.
ASN.1 production:
<name> OBJECT IDENTIFIER ::= <value>
Generated code:
ASN1OBJID <name> = <value>;
For example, consider the following declaration:
oid OBJECT IDENTIFIER ::= { ccitt b(5) 10 }
This would result in the following definition in the C or C++ source file:
ASN1OBJID oid = {
3, { 0, 5, 10 }
} ;
To populate a variable in a generated structure with this value, the rtSetOID utility function can be used (see the C/
C++ Run-Time Library Reference Manual for a full description of this function). In addition, the C++ base type for
this construct (ASN1TObjId) contains constructors and assignment operators that allow direct assignment of values
in this form to the target variable.
Constructed Type Values
ASN1C will generate code for following remaining value definitions only when their use is required in legacy table
constraint validation code:
• SEQUENCE
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ASN.1 To C/C++ Mappings
• SET
• SEQUENCE OF
• SET OF
• CHOICE
Note
SEQUENCE, SET , SEQUENCE OF, SET OF and CHOICE values are available only when the -tables option
is selected.
The values are initialized in a module value initialization function. The format of this function name is as
follows:
init_<ModuleName>Value (OSCTXT*
pctxt)
Where <ModuleName> would be replaced with the name of the module containing the value specifications.
The only required argument is an initialized context block structure used to hold dynamic memory allocated
in the creation of the value structures.
If the value definitions are used in table constraint definitions, then the generated table constraint processing
code will handle the initialization of these definitions; otherwise, the initialization function must be called
explicitly.
SEQUENCE or SET Value Specification
The mapping of an ASN.1 SEQUENCE or SET value declaration to a global C or C++ value declaration is as follows:
ASN.1 production:
<name> <SeqType> ::= <value>
Generated code :
<SeqType> <name>;
The sequence value will be initialized in the value initialization function.
For example, consider the following declaration:
SeqType ::= SEQUENCE {
id INTEGER ,
name VisibleString
}
value SeqType ::= { id 12, name "abc" }
This would result in the following definition in the C or C++ source file:
SeqType value;
Code generated in value initialization function would be as follows:
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ASN.1 To C/C++ Mappings
value.id = 12;
value.name = "abc";
SEQUENCE OF/SET OF Value
The mapping of an ASN.1 SEQUENCE OF or SET OF value declaration to a global C or C++ value declaration is
as follows:
ASN.1 production:
<name> <SeqOfType> ::= <value>
Generated code :
<SeqOfType> <name>;
The sequence of value will be initialized in the value initialization function.
For example, consider the following declaration:
SeqOfType ::= SEQUENCE OF (SIZE(2)) INTEGER
value SeqOfType ::= { 1, 2 }
This would result in the following definition in the C or C++ source file:
SeqOfType value;
Code generated in the value initialization function would be as follows:
value.n = 2;
value.element[0] = 1;
value.element[1] = 2;
CHOICE Value
The mapping of an ASN.1 CHOICE value declaration to a global C or C++ value declaration is as follows:
ASN.1 production:
<name> <ChoiceType> ::= <value>
Generated code :
<ChoiceType> <name>;
The choice value will be initialized in the value initialization function.
For example, consider the following declaration:
ChoiceType ::= CHOICE { oid OBJECT IDENTIFIER, id INTEGER }
value ChoiceType ::= id: 1
This would result in the following definition in the C or C++ source file:
ChoiceType value;
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ASN.1 To C/C++ Mappings
Code generated in the value initialization function would be as follows:
value.t = T_ChoiceType_id;
value.u.id = 1;
Table Constraint Related Structures
The following sections describe changes to generated code that occur when the -tables or -table-unions option is
specified on the command-line or when Table Constraint Options are selected from the GUI. This option causes
additional code to be generated for items required to support table constraints as specified in the X.682 standard. This
includes the generation of structures and classes for Information Object Classes, Information Objects, and Information
Object Sets as specified in the X.681 standard.
Most of the additional items that are generated are read-only tables for use by the run-time for data validation
purposes. However, generated structures for types that use table constraints are different than when table constraint
code generation is not enabled. These differences will be pointed out.
There are two models currently supported for table contraint generation: Unions and Legacy. These are documented
in the following sections:
Unions Table Constraint Model
The unions table constraint model originated from common patterns used in a series of ASN.1 specifications in-use
in 3rd Generation Partnership Project (3GPP) standards. These standards include Node Application Part B (NBAP),
Radio Access Network Application Part (RANAP), and Radio Network Subsystem Application Part (RNSAP) in the
current 3G network and in S1AP and X2AP protocols in the newer 4G network (LTE) standards. This model was
later extended to generate these type of structures for other specifications that made use of table constraints including
security and legacy telecom speifications.
Generated C Type Definitions for Message Types
The standard message type used by many specifications that employ table constraints is usually a SEQUENCE type
with elements that use a relational table constraint that uses fixed-type and type fields. The general form is as follows:
<Type> ::= SEQUENCE {
<element1> <Class>.&<fixed-type-field> ({<ObjectSet>}),
<element2> <Class>.&<fixed-type-field> ({<ObjectSet>)){@element1}
<element3> <Class>.&<type-field> ({<ObjectSet>)){@element1}
}
In this definition, <Class> would be replaced with a reference to an Information Object Class, <fixed-typefield> would be a fixed-type field wtihin that class, and <type-field> would be a type field within the class.
<ObjectSet> would be a reference to an Information Object Set which would define all of the possibilities for
content within the message. The first element (<element1>) would be used as the index element in the object set
relation.
An example of this pattern from the S1AP LTE specification is as follows:
InitiatingMessage ::= SEQUENCE {
procedureCode
S1AP-ELEMENTARY-PROCEDURE.&procedureCode
({S1AP-ELEMENTARY-PROCEDURES}),
criticality
S1AP-ELEMENTARY-PROCEDURE.&criticality
({S1AP-ELEMENTARY-PROCEDURES}{@procedureCode}),
value
S1AP-ELEMENTARY-PROCEDURE.&InitiatingMessage
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ASN.1 To C/C++ Mappings
({S1AP-ELEMENTARY-PROCEDURES}{@procedureCode})
}
In this definition, procedureCode and criticality are defined to be a enumerated fixed types, and value is
defined to be an open type field to hold variable content as defined in the object set definition.
In the legacy model defined below, a loose coupling would be defined for the open type field using the built-in
ASN1Object structure. This structure uses a void pointer to hold a link to a variable of the typed data structure.
This is inconvenient for the developer because he would need to consult the object set definition within the ASN.1
specification in order to determine what type of data is to be used with each procedure code. It is also error prone in
that the void pointer provides for no type checking at compile time.
In the new model, the generated structure is designed to be similar as to what is used to represent a CHOICE type.
That is to say, the structure is a union with a choice selector value and all possible types listed out in a union structure.
This is the general form:
typedef struct <Type> {
<Element1Type> <element1>;
<Element2Type> <element2>;
/**
* information object selector
*/
<SelectorEnumType> t;
/**
* <ObjectSet> information objects
*/
union {
/**
* <element1> : <object1-element1-value>
* <element2> : <object1-element2-value>
*/
<object1-element3-type>* <object1-name>;
/**
* <element1> : <object2-element1-value>
* <element2> : <object2-element2-value>
*/
<object2-element3-type>* <object2-name>;
...
} u;
} ;
In this definition, the first two elements of the sequence would use the equivalent C or C++ type as defined in the
fixed-type field in the information object. This is the same as in the legacy model. The open type field (element3)
would be expanded into the union structure as is shown. The <SelectorEnumType> would be an enumerated type that
is generated to represent each of the choices in the referenced information object set. The union then contains an entry
for each of the possible types as defined in the object set that can be used in the open type field. Comments are used
to list the fixed-type fields corresponding to each open type field.
An example of the code that is generated from the S1AP sample ASN.1 snippet above is as follows:
typedef enum {
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ASN.1 To C/C++ Mappings
T_S1AP_PDU_Descriptions_S1AP_ELEMENTARY_PROCEDURES_handoverPreparation,
T_S1AP_PDU_Descriptions_S1AP_ELEMENTARY_PROCEDURES_handoverResourceAllocation,
T_S1AP_PDU_Descriptions_S1AP_ELEMENTARY_PROCEDURES_pathSwitchRequest,
etc..
} S1AP_ELEMENTARY_PROCEDURE_TVALUE;
typedef struct InitiatingMessage {
ProcedureCode procedureCode;
Criticality criticality;
/**
* information object selector
*/
S1AP_ELEMENTARY_PROCEDURE_TVALUE t;
/**
* S1AP-ELEMENTARY-PROCEDURE information objects
*/
union {
/**
* procedureCode: id-HandoverPreparation
* criticality: reject
*/
HandoverRequired* handoverPreparation;
/**
* procedureCode: id-HandoverResourceAllocation
* criticality: reject
*/
HandoverRequest* handoverResourceAllocation;
/**
* procedureCode: id-HandoverNotification
* criticality: ignore
*/
HandoverNotify* handoverNotification;
etc..
} u;
} InitiatingMessage;
Note that the long names generated in the S1AP_ELEMENTARY_PROCEDURE_TVALUE type can be reduced by
using the <alias> configuration element.
Generated C Type Definitions for Information Element (IE) Types
In addition to message types, another common pattern in 3GPP specifications is protocol information element (IE)
types. The general form of these types is a list of information elements as follows:
<ProtocolIEsType> ::= <ProtocolIE-ContainerType> { <ObjectSet> }
<ProtocolIE-ContainerType> { <Class> : <ObjectSetParam> } ::=
SEQUENCE (SIZE (<size>)) OF <ProtocolIE-FieldType> {{ObjectSetParam}}
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ASN.1 To C/C++ Mappings
<ProtocolIE-FieldType> { <Class> : <ObjectSetParam> } ::= SEQUENCE {
<element1> <Class>.&<fixed-type-field> ({ObjectSetParam}),
<element2> <Class>.&<fixed-type-field> ({ObjectSetParam}{@element1}),
<element3> <Class>.&<Type-field> ({ObjectSetParam}{@element1})
}
There are a few different variations of this, but the overall pattern is similar in all cases. A parameterized type is used
as a shorthand notation to pass an information object set into a container type. The container type holds a list of the
IE fields. The structure of an IE field type is similar to a message type: the first element is used as an index element
to the remaining elements. That is followed by one or more fixed type or variable type elements. In the case defined
above, only a single fixed-type and variable type element is shown, but there may be more.
An example of this pattern from the S1AP LTE specification follows:
HandoverRequired ::= SEQUENCE {
protocolIEs
ProtocolIE-Container
...
}
{ { HandoverRequiredIEs} },
ProtocolIE-Container {S1AP-PROTOCOL-IES : IEsSetParam} ::=
SEQUENCE (SIZE (0..maxProtocolIEs)) OF ProtocolIE-Field {{IEsSetParam}}
ProtocolIE-Field {S1AP-PROTOCOL-IES : IEsSetParam} ::= SEQUENCE {
id
S1AP-PROTOCOL-IES.&id
({IEsSetParam}),
criticality
S1AP-PROTOCOL-IES.&criticality
({IEsSetParam}{@id}),
value
S1AP-PROTOCOL-IES.&Value
({IEsSetParam}{@id})
}
In this case, standard parameterized type instantiation is used to create a type definition for the protocolIEs element.
This results in a list type being generated:
/* List of HandoverRequired_protocolIEs_element */
typedef OSRTDList HandoverRequired_protocolIEs;
The type for the protocol IE list element is created in much the same way as the main message type was above:
typedef struct HandoverRequired_protocolIEs_element {
ProtocolIE_ID id;
Criticality criticality;
struct {
/**
* information object selector
*/
HandoverRequiredIEs_TVALUE t;
/**
* HandoverRequiredIEs information objects
*/
union {
/**
* id: id-MME-UE-S1AP-ID
* criticality: reject
* presence: mandatory
*/
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ASN.1 To C/C++ Mappings
MME_UE_S1AP_ID *_HandoverRequiredIEs_id_MME_UE_S1AP_ID;
/**
* id: id-HandoverType
* criticality: reject
* presence: mandatory
*/
HandoverType *_HandoverRequiredIEs_id_HandoverType;
/**
* id: id-Cause
* criticality: ignore
* presence: mandatory
*/
...
} u;
} value;
} HandoverRequired_protocolIEs_element;
In this case, the protocol IE id field and criticality are generated as usual using the fixed-type field type definitions.
The open type field once again results in the generation of a union structure of all possible type fields that can be used.
Note in this case the field names are automatically generated (_HandoverRequiredIEs_id_MME_UE_S1AP_ID, etc.).
The reason for this was the use of inline information object definitions in the information object set as opposed to
defined object definitions. This is a sample from that set:
HandoverRequiredIEs S1AP-PROTOCOL-IES ::= {
{ ID id-MME-UE-S1AP-ID
CRITICALITY reject
{ ID id-HandoverType
CRITICALITY reject
...
TYPE MME-UE-S1AP-ID
TYPE HandoverType
In this case, the name is formed by combining the information object set name with the name of each key field within
the set.
PRESENCE ma
PRESENCE ma
Generated IE Append Function
A user would need to allocate objects of this structure, populate them, and add them to the protocol IE list. In order
to make this easier, helper functions are generated assist in adding information items to the list. The general format
of these append functions is as follows:
int asn1Append_<ProtocolIEsType>_<KeyValueName>
(OSCTXT* pctxt, <ProtocolIEsType>* plist, <ValueType> value);
In this definition, <ProtocolIEsType> refers to the main list type (SEQUENCE OF) defining the information
element list. <KeyValueName> is the name of the primary key field defined in the associated information object
set. <ValueType> is the type of the value for the indexed information object set item.
An example of this type of function from the S1AP definitions is as follows:
/* Append IE with value type MME_UE_S1AP_ID to list */
int asn1Append_HandoverRequired_protocolIEs_id_MME_UE_S1AP_ID (OSCTXT* pctxt,
HandoverRequired_protocolIEs* plist, MME_UE_S1AP_ID value);
Generated IE Get Function
In addition to the list append function, a second type of helper function is generated to make it easier to find an item
in the list based on the key field. The general format for this type of function is as follows:
<ProtocolIE-FieldType>* asn1Get_<ProtocolIEsType>
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ASN.1 To C/C++ Mappings
(<KeyFieldType> <key>, <ProtocolIEsType>* plist);
In this definition, <ProtocolIEsType> refers to the main list type (SEQUENCE OF) defining the information
element list. <ProtocolIE-FieldType> is the type of an element within this list and <KeyFieldType> is the
type of index key field.
An example of this type of function from the S1AP definitions is as follows:
/* Get IE using id key value */
HandoverRequired_protocolIEs_element* asn1Get_HandoverRequired_protocolIEs
(ProtocolIE_ID id, HandoverRequired_protocolIEs* plist);
Generated Set Table Constraint (SetTC) Function
The set table constraint helper function sets the fixed type value fields, the table union tag (t) value, and sets a pointer
to the variable typed value field to be encoded. The general format for this type of function is as follows:
void asn1SetTC_<Type>_<InfoObject>
(OSCTXT* pctxt, <Type>* pElem, <ValueType> value);
In this definition, <Type> refers to the container type in which the table-constrained items are defined and
<ValueType> is the type of the value for the indexed information object set item.
An example of this type of function from the S1AP definitions is as follows:
void asn1SetTC_HandoverRequired_protocolIEs_element_HandoverRequiredIEs_id_MME_UE_S1AP_I
(OSCTXT* pctxt, HandoverRequired_protocolIEs_element* pElem, MME_UE_S1AP_ID value);
Generated C++ Classes and Methods
This section discusses items that are generated idfferently for C++ for union table constraints.
Choice Selector TVALUE Type
For C, an enumerated type is generated for each of the options in a type field union. These correspond to each of
the items in the information object set associated with the union. For example, the TVALUE type generated for
S1AP_ELEMENTARY_PROCEDURES is as follows:
typedef enum {
T_S1AP_PDU_Descriptions_S1AP_ELEMENTARY_PROCEDURES_UNDEF_,
T_S1AP_PDU_Descriptions_S1AP_ELEMENTARY_PROCEDURES_handoverPreparation,
T_S1AP_PDU_Descriptions_S1AP_ELEMENTARY_PROCEDURES_handoverResourceAllocation,
T_S1AP_PDU_Descriptions_S1AP_ELEMENTARY_PROCEDURES_pathSwitchRequest,
...
} S1AP_ELEMENTARY_PROCEDURES_TVALUE;
The generated names include the name of the module, object set, and object in order to ensure that no name clashes
occur between enumerations with common names. For C++, this type is generated as a class with TVALUE as a public
member inside:
class S1AP_ELEMENTARY_PROCEDURES {
public:
enum TVALUE {
T_UNDEF_,
T_handoverPreparation,
T_handoverResourceAllocation,
T_pathSwitchRequest,
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ASN.1 To C/C++ Mappings
...
} ;
} ;
In this case, the type module and object set names are not needed because the class name provides for unambiguous
enumerated item names.
Generated Helper Methods
For C, special asn1Append_<name> and asn1GetIE_<name> functions are generated to help a user append
information elements (IE's) to a list and get an indexed IE respectively. For C++, these are added as methods to the
generated control class for the list type.
For example, for the HandoverRequired_protocolIEs type, the following methods are added to the control
class:
class EXTERN ASN1C_HandoverRequired_protocolIEs : public ASN1CSeqOfList
{
...
/* Append IE with value type ASN1T_MME_UE_S1AP_ID to list */
int Append_id_MME_UE_S1AP_ID (ASN1T_MME_UE_S1AP_ID value);
/* Append IE with value type ASN1T_HandoverType to list */
int Appendid_eNB_UE_S1AP_ID (ASN1T_HandoverType value);
...
/* Get IE using id key value */
ASN1T_HandoverRequired_protocolIEs_element* GetIE (ASN1T_ProtocolIE_ID id);
} ;
Legacy Table Constraint Model
The primary difference as to what a user sees and works with in the legacy model as opposed to the unions model lies
in the representation of open type elements that contain a table constraint. The standard form of an open type element
constrained with a table constraint within a SEQUENCE container is as follows:
<Type> ::= SEQUENCE {
<element> <Class>.&<type-field> ({<ObjectSet>)){@index-element}
}
If -tables is not specified on the command line, a standard open type structure is used to hold the element value:
typedef struct <Type> {
ASN1OpenType <element>;
}
The ASN1OpenType built-in type holds the element data in encoded form. The only validation that is done on the
element is to verify that it is a well-formed tag-length-value (TLV) structure if BER encoding is used or a valid length
prefixed structure for PER.
If the -tables command line option is selected, the code generated is different. In this case, ASN1OpenType above is
replaced with ASN1Object (or ASN1TObject for C++). This is defined in asn1type.h as follows:
typedef struct { /* generic table constraint value holder */
ASN1OpenType encoded;
void*
decoded;
OSINT32
index;
/* table index */
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ASN.1 To C/C++ Mappings
} ASN1Object;
This allows a value of any ASN.1 type to be represented in both encoded and decoded forms. Encoded form is the
open type form shown above. It is simply a pointer to a byte buffer and a count of the number of byes in the encoded
message component. The decoded form is a pointer to a variable of a specific type. The pointer is void because there
could be a potentially large number of different types that can be represented in the table constraint used to constrain
a type field to a given set of values. The index member of the type is for internal use by table constraint processing
functions to keep track of which row in a table is being referenced.
In addition to this change in how open types are represented, a large amount of supporting code is generated to support
the table constraint validation process. This additional code is described below. Note that it is not necessary for the
average user to understand this as it is not for use by users in accomplishing encoding and decoding of messages. It is
only described for completeness in order to know what that additional code is used for.
CLASS specification
All of the Class code will be generated in a module class header file with the following filename format:
<ModuleName>Class.h
In this definition, <ModuleName> would be replaced with the name of the ASN.1 module name for this class
definition.
C Code generation
The C structure definition generated to model an ASN.1 class contains member variables for each of the fields within
the class.
For each of the following class fields, the corresponding member variable is included in the generated C structure
as follows:
For a Value Field:
<TypeName> <FieldName>;
For TypeField definitions, an encode and decode function pointer and type size field is generated to hold the
information of the type for the OpenType. If the -print option is selected, a print function pointer is also added.
int <FieldName>Size;
int (*encode<FieldName>) (... );
int (*decode<FieldName>) (... );
void (*print<FieldName>) (...);
For an Object Field:
<ClassName>* <FieldName>;
For an ObjectSetField definition, an array of class definitions is generated to hold the list of information objects.
<ClassName>* <FieldName>;
In each of these definitions:
<FieldName> would be replaced with the name of the field (without the leading '&').
<TypeName> would be replaced with the C type name for the ASN.1 Type.
<ClassName> would be replaced with the C type name of the class for the Information Object.
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ASN.1 To C/C++ Mappings
As an example, consider the following ASN.1 class definition :
ATTRIBUTE ::= CLASS {
&Type,
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX { &Type ID &id }
This would result in the following definition in the C source file:
typedef struct ATTRIBUTE {
int TypeSize;
int (*encodeType) (OSCTXT* , void *, ASN1TagType );
int (*decodeType) (OSCTXT* , void *, ASN1TagType, int );
ASN1OBJID id;
}
C++ Code generation
The C++ abstract class generated to model an ASN.1 CLASS contains member variables for each of the fields within
the class. Derived information object classes are required to populate these variables with the values defined in the
ASN.1 information object specification. The C++ class also contains virtual methods representing each of the type
fields within the ASN.1 class specification. If the field is not defined to be OPTIONAL in the ASN.1 specification,
then it is declared to be abstract in the generated class definition. A class generated for an ASN.1 information object
that references this base class is required to implement these abstract virtual methods.
For each of the following CLASS fields, a corresponding member variable is generated in the C++ class definition
as follows:
For a Value Field definition, the following member variable will be added. Also, an Equals() method will be added
if required for table constraint processing.
<TypeName> <FieldName>;
inline OSBOOL idEquals (<TypeName>* pvalue)
For a Type Field definition, a virtual method is added for each encoding rules type to call the generated C encode and
decode functions. If -print is specified, a print method is also generated.
virtual int encode<ER><FieldName>
(OSCTXT* pctxt, ASN1TObject& object) { return 0; }
virtual int decode<ER><FieldName>
(OSCTXT* pctxt, ASN1TObject& object) { return 0; }
virtual void print<FieldName>
(ASN1ConstCharPtr name, ASN1TObject& object) {}
For an Object Field:
class <ClassName>* <FieldName>;
In each of these definitions:
<FieldName> would be replaced with the name of the field (without the leading '&').
<TypeName> would be replaced with the C type name for the ASN.1 Type.
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<ClassName> would be replaced with the C type name of the class for the Information Object.
<ER> would be replaced by an encoding rules type (BER, PER, or XER).
As an example, consider the following ASN.1 class definition :
ATTRIBUTE ::= CLASS {
&Type,
&ParameterType OPTIONAL,
&id
OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX { &Type ID &id }
This would result in the following definition in the C++ source file:
class EXTERN ATTRIBUTE {
protected:
ASN1TObjId id;
ATTRIBUTE ();
public:
virtual int encodeBERType
(OSCTXT* pctxt, ASN1TObject& object) = 0;
virtual int decodeBERType
(OSCTXT* pctxt, ASN1TObject& object) = 0;
OSBOOL isParameterTypePresent() {
if(m.ParameterTypePresent) {return TRUE;} else {return FALSE;}
}
virtual int encodeBERParameterType
(OSCTXT* pctxt, ASN1TObject& object) { return 0; }
virtual int decodeBERParameterType
(OSCTXT* pctxt, ASN1TObject& object) { return 0; }
inline OSBOOL idEquals (ASN1TObjId* pvalue)
{
return (0 == rtCmpTCOID (&id, pvalue));
}
} ;
This assumes that only BER or DER was specified as the encoding rules type.
First notice that member variables have been generated for the fixed-type fields in the definition. These include the id
field. Information object classes derived from this definition are expected to populate these fields in their constructors.
Also, virtual methods have been generated for each of the type fields in the class. These include the Type fields. The
method generated for Type is abstract and must be implemented in a derived information object class. The method
generated for the ParameterType field has a default implementations that does nothing. That is because it is a
optional field.
Also generated are Equals methods for the fixed-type fields. These are used by the generated code to verify that data
in a generated structure to be encoded (or data that has just been decoded) matches the table constraint values. This
method will be generated only if it is required to check a table constraint.
OPTIONAL keyword
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Fields within a CLASS can be declared to be optional using the OPTIONAL keyword. This indicates that the field
is not required in the information object. An additional construct is added to the generated code to indicate whether
an optional field is present in the information object or not. This construct is a bit structure placed at the beginning
of the generated structure. This structure always has variable name 'm' and contains single-bit elements of the form
<fieldname>Present as follows:
struct {
unsigned <field-name1>Present : 1,
unsigned <field-name2>Present : 1,
...
} m;
In this case, the fields included in this construct correspond to only those fields marked as OPTIONAL within the
CLASS. If a CLASS contains no optional fields, the entire construct is omitted.
For example, we will change the CLASS in the previous example to make one field optional:
ATTRIBUTE ::= CLASS {
&Type OPTIONAL,
&id OBJECT IDENTIFIER UNIQUE
}
In this case, the following C typedef is generated in C struct or C++ class definition:
struct {
unsigned TypePresent : 1;
} m;
When this structure is populated for encoding, the information object processing code will set TypePresent flag
accordingly to indicate whether the field is present or not.
In C++ code generation, an additional method is generated for an optional field as follows:
OSBOOL is<FieldName>Present() {
if (m.<FieldName>Present) {return TRUE;} else {return FALSE;}
}
This function is used to check if the field value is present in an information object definition.
Generation of New ASN.1 Assignments from CLASS Assignments:
During CLASS definition code generation, the following new assignments are created for C or C++ code generation:
1. A new Type Assignment is created for a TypeField's type definition, as follows:
_<ClassName>_<FieldName> ::= <Type>
Here ClassName is replaced with name of the Class Assignment and FieldName is replaced with name of this
field. Type is the type definition in CLASS's TypeField.
This type is used as a defined type in the information object definition for an absent value of the TypeField. It is
also useful for generation of a value for a related Open Type definition in a table constraint.
2. A new Type Assignment is created for a Value Field or Value Set Field type definition as follows (if the type
definition is one of the following: ConstraintedType / ENUMERATED / NamedList BIT STRING / SEQUENCE /
SET / CHOICE / SEQUENCE OF / SET OF ):
_<ClassName>_<FieldName> ::= <Type>
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ASN.1 To C/C++ Mappings
Here ClassName is replaced with the name of the CLASS assignment and FieldName is replaced with name
of the ValueField or ValueSetField. Type is the type definition in the CLASS's ValueField or ValueSetField. This
type will appear as a defined type in the CLASS's ValueField or ValueSetField.
This new type assignment is used for compiler internal code generation purpose. It is not required for a user to
understand this logic.
3. A new Value Assignment is created for a ValueField's default value definition as follows:
_<ClassName>_<FieldName>_default <Type> ::= <Value>
Here ClassName is replaced with name of the Class Assignment and FieldName is replaced with name of this
ValueField. Value is the default value in the Class's ValueField and Type is the type in Class's ValueField.
This value is used as a defined value in the information object definition for an absent value of the field. This new
value assignment is used for compiler internal code generation purpose. It is not required for user to understand
this logic.
ABSTRACT-SYNTAX and TYPE-IDENTIFIER
The ASN.1 ABTRACT-SYNTAX and TYPE-IDENTIFIER classes are useful ASN.1 definitions. These classes are
described using the following ASN.1 definitions:
TYPE-IDENTIFIER ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Type
}
WITH SYNTAX { &Type IDENTIFIED BY &id }
ABSTRACT-SYNTAX ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Type,
&property BIT STRING { handles-invalid-encoding(0)} DEFAULT {}
}
WITH SYNTAX {
&Type IDENTIFIED BY &id [HAS PROPERTY &property]
}
The ASN1C compiler generates code for these constructs when they are referenced in the ASN.1 source file that is
being compiled. The generated code for these constructs is written to the RtClass.h and .c/.cpp source files.
Information Object
Information Object code will be generated in a header and source file with a C struct / C++ class to hold the values.
The name of the header and source file are of the following format:
<ModuleName>Table.h
<ModuleName>Table.c/cpp
In this definition, <ModuleName> would be replaced with the name of the ASN.1 module in which the information
object is defined.
C Code Generation
For C, a global variable is generated to hold the information object definition. This is very similar to the code generated
for a value definition.
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ASN.1 To C/C++ Mappings
An example of an information object definition that is derived from the ASN.1 ATTRIBUTE class above is as follows:
name ATTRIBUTE ::= {
WITH SYNTAX
VisibleString
ID
{ 0 1 1 } }
This results in the generation of the following C constant:
ATTRIBUTE name;
Code generated in information object initialization function:
name.TypeSize = sizeof(_name_Type);
name.encodeType = &asn1E__name_Type;
name.decodeType = &asn1D__name_Type;
name.id.numids = 3;
name.id.subid[0] = 0;
name.id.subid[1] = 1;
name.id.subid[2] = 1;
C++ Code Generation
The C++ classes generated for ASN.1 information objects are derived from the ASN.1 class objects. The constructors
in these classes populate the fixed-type field member variables with the values specified in the information object. The
classes also implement the virtual methods generated for the information object type fields. All non-optional methods
are required to be implemented. The optional methods are only implemented if they are defined in the information
object definition.
An example of an information object definition that is derived from the ASN.1 class above is as follows:
name ATTRIBUTE ::= {
WITH SYNTAX
VisibleString
ID
{ 0 1 1 } }
This results in the generation of the following C++ class:
class EXTERN name : public ATTRIBUTE {
public:
name();
virtual int encodeBERType
(OSCTXT* pctxt, ASN1TObject& object);
virtual int decodeBERType
(OSCTXT* pctxt, ASN1TObject& object);
} ;
The constructor implementation for this class (not shown) sets the fixed type fields (id) to the assigned values ({0 1
1}). The class also implements the virtual methods for the type field virtual methods defined in the base class. These
methods simply call the BER encode or decode method for the assigned type (this example assumes -ber was specified
for code generation - other encode rules could have been used as well).
Generated Type Assignments
If the information object contains an embedded type definition, it is extracted from the definition to form a new type
to be added to the generated C or C++ code. The format of the new type name is as follows:
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_<ObjectName>_<FieldName>
where <ObjectName> is replaced with the information object name and <FieldName> is replaced with the name
of the field from within the object.
Information Object Set
Table constraint processing code to support Information Object Sets is generated in a header and source file with a C
struct / C++ class to hold the values. The name of the header and source file are of the following format:
<ModuleName >Table.h
<ModuleName >Table.c/cpp
In this definition, <ModuleName> would be replaced with the name of the ASN.1 module in which the information
object is defined.
C Code Generation
A C global variable is generated containing a static array of values for the ASN.1 CLASS definition. Each structure
in the array is the equivalent C structure representing the corresponding ASN.1 information object
An example of an Information Object Set definition that is derived from the ASN.1 ATTRIBUTE class above is as
follows:
SupportedAttributes ATTRIBUTE ::= { name | commonName }
This results in the generation of the following C constant:
ATTRIBUTE SupportedAttributes[2];
int SupportedAttributes_Size = 2;
Code generated in the Information Object Set initialization function:
SupportedAttributes[0].TypeSize = sizeof(_name_Type);
SupportedAttributes[0].encodeType = &asn1E__name_Type;
SupportedAttributes[0].decodeType = &asn1D__name_Type;
SupportedAttributes[0].id.numids = 3;
SupportedAttributes[0].id.subid[0] = 0;
SupportedAttributes[0].id.subid[1] = 1;
SupportedAttributes[0].id.subid[2] = 1;
SupportedAttributes[1].TypeSize = sizeof(_commonName_Type);
SupportedAttributes[1].encodeType = &asn1E__commonName_Type;
SupportedAttributes[1].decodeType = &asn1D__commonName_Type;
SupportedAttributes[1].id.numids = 3;
SupportedAttributes[1].id.subid[0] = 0;
SupportedAttributes[1].id.subid[1] = 1;
SupportedAttributes[1].id.subid[2] = 1;
SupportedAttributes[1].id.subid[3] = 1;
C++ Code Generation
In C++, ASN.1 information object sets are mapped to C++ classes. In this case, a C++ singleton class is generated.
This class contains a container to hold an instance of each of the ASN.1 information object C++ objects in a static
array. The class also contains an object lookup method for each of the key fields. Key fields are identified in the class
as either a) fields that are marked unique, or b) fields that are referenced in table constraints with the '@' notation.
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ASN.1 To C/C++ Mappings
The generated constructor initializes all required values and information objects.
An example of an information object set that uses the information object class defined above is as follows:
SupportedAttributes ATTRIBUTE ::= { name | commonName }
This results in the generation of the following C++ class:
class EXTERN SupportedAttributes {
protected:
ATTRIBUTE* mObjectSet[2];
const size_t mNumObjects;
static SupportedAttributes* mpInstance;
SupportedAttributes (OSCTXT* pctxt);
public:
ATTRIBUTE* lookupObject (ASN1TObjId _id);
static SupportedAttributes* instance(OSCTXT* pctxt);
} ;
The mObjectSet array is the container for the information object classes. These objects are created and this array
populated in the class constructor. Note that this is a singleton class (as evidenced by the protected constructor and
instance methods). Therefore, the object set array is only initialized once the first time the instance method
is invoked.
The other method of interest is the lookupObject method. This was generated for the id field because it was
identified as a key field. This determination was made because id was declared to be UNIQUE in the class definition
above. A field can also be determined to be a key field if it is referenced via the @ notation in a table constraint in a
standard type definition. For example, in the following element assignment:
argument OPERATION.&Type ({SupportedAttributes}{@opcode})
the opcode element's ATTRIBUTE class field is identified as a key field.
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Chapter 4. XSD TO C/C++ TYPE MAPPINGS
ASN1C can accept as input XML schema definition (XSD) specifications in addition to ASN.1 specifications. If an
XSD specification is compiled, the compiler does internal translations of the XSD types into equivalent ASN.1 types
as specified in ITU-T standard X.694. The following sections provide information on the translations and the C/C++
type definitions generated for the different XSD types.
XSD Simple Types
The translation of XSD simple types into ASN.1 types is straightforward; in most cases, a one-to-one mapping from
XSD simple type to ASN.1 primitive type exists. The following table summarizes these mappings:
XSD Simple Type
ASN.1 Type
anyURI
UTF8String
base64Binary
OCTET STRING
boolean
BOOLEAN
byte
INTEGER (-128..127)
date
UTF8String
datetime
UTF8String
decimal
UTF8String
double
REAL
duration
UTF8String
ENTITIES
SEQUENCE OF UTF8String
ENTITY
UTF8String
float
REAL
gDay
UTF8String
gMonth
UTF8String
gMonthDay
UTF8String
gYear
UTF8String
gYearMonth
UTF8String
hexBinary
OCTET STRING
ID
UTF8String
IDREF
UTF8String
IDREFS
SEQUENCE OF UTF8String
integer
INTEGER
int
INTEGER (-2147483648..2147483647)
language
UTF8String
long
INTEGER
(-9223372036854775808..9223372036854775807)
Name
UTF8String
NCName
UTF8String
negativeInteger
INTEGER (MIN..-1)
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XSD Simple Type
ASN.1 Type
NMTOKEN
UTF8String
NMTOKENS
SEQUENCE OF UTF8String
nonNegativeInteger
INTEGER (0..MAX)
nonPositiveInteger
INTEGER (MIN..0)
normalizedString
UTF8String
positiveInteger
INTEGER (1..MAX)
short
INTEGER (-32768..32767)
string
UTF8String
time
UTF8String
token
UTF8String
unsignedByte
INTEGER (0..255)
unsignedShort
INTEGER (0..65535)
unsignedInt
INTEGER (0..4294967295)
unsignedLong
INTEGER (0..18446744073709551615)
The C/C++ mappings for these types can be found in the section above on ASN.1 type mappings.
XSD Complex Types
XSD complex types and selected simple types are mapped to equivalent ASN.1 constructed types. In some cases,
simplifications are done to make the generated code easier to work with. The following are mappings for specific
XSD complex types.
xsd:sequence
The XSD sequence type is normally mapped to an ASN.1 SEQUENCE type. The following items describe special
processing that may occur when processing a sequence definition:
• If the resulting SEQUENCE type contains only a single repeating element, it is converted into a SEQUENCE OF
type. This can occur if either the sequence declaration has a maxOccurs attribute with a value greater than one or
if the single element inside has a similar maxOccurs attribute.
• If the sequence contains an element that has a ‘minOccurs=“0”’ attribute declaration, the element is mapped to be
an OPTIONAL element in the resulting ASN.1 SEQUENCE assignment.
• If the sequence contains a repeating element (denoted by having a ‘maxOccurs’ attribute with a value greater than
one), then a SEQUENCE OF type for this element is used in the ASN.1 SEQUENCE for the element.
• If attributes are defined within the complex type container containing the sequence group, attributes are defined,
these attribute declarations are added to the resulting ASN.1 as element declarations as per the X.694 standard. In
XML encodings, these appear as attributes in the markup; in binary encodings, they are elements.
Example
<xsd:complexType name="Name">
<xsd:sequence>
<xsd:element name="givenName" type="xsd:string "/>
<xsd:element name="initial" type="xsd:string" minOccurs="0"/>
<xsd:element name="familyName" type="xsd:string"/>
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</xsd:sequence>
</xsd:complexType>
would result in the creation of the following C type definition:
typedef struct EXTERN Name {
struct {
unsigned initialPresent : 1;
} m;
const OSUTF8CHAR* givenName;
const OSUTF8CHAR* initial;
const OSUTF8CHAR* familyName;
} Name;
xsd:all
The xsd:all type is similar to an ASN.1 SET in that it allows for a series of elements to be specified that can be
transmitted in any order. However, due to some technicalities with the type, it is modeled in X.694 to be a SEQUENCE
type with a special embedded array called order. This array specifies the order in which XML elements were received
if XML decoding of an XML instance was done. If this information were then retransmitted in binary using BER or
PER, the order information would be encoded and transmitted followed by the SEQUENCE elements in the declared
order. If the data were then serialized back into XML, the order information would be used to put the elements back
in the same order in which they were originally received.
The mapping to C type would be the same as for xsd:sequence above with the addition of the special order array. An
example of this is as follows:
<xsd:complexType name="Name">
<xsd:all>
<xsd:element name="givenName" type="xsd:string "/>
<xsd:element name="initial" type="xsd:string"/>
<xsd:element name="familyName" type="xsd:string"/>
</xsd:all>
</xsd:complexType>
would result in the creation of the following C type definition:
typedef struct EXTERN Name {
struct {
OSUINT32 n;
OSUINT8 elem[3];
} _order;
const OSUTF8CHAR* givenName;
const OSUTF8CHAR* initial;
const OSUTF8CHAR* familyName;
} Name;
In this case, the _order element is for the order element described earlier. Normally, the user does not need to deal
with this item. When the generated initialization is called for the type (or C++ constructor), the array will be set to
indicate elements should be transmitted in the declared order. If XML decoding is done, the contents of the array will
be adjusted to indicate the order the elements were received in.
xsd:choice and xsd:union
The xsd:choice type is converted to an ASN.1 CHOICE type. ASN1C generates exactly the same code. For example:
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XSD TO C/C++ TYPE MAPPINGS
<xsd:complexType name="NamePart">
<xsd:choice>
<xsd:element name="givenName" type="xsd:string "/>
<xsd:element name="initial" type="xsd:string"/>
<xsd:element name="familyName" type="xsd:string"/>
</xsd:choice>
</xsd:complexType>
in this case, the generated code is the same as for ASN.1 CHOICE:
#define T_NamePart_givenName
#define T_NamePart_initial
#define T_NamePart_familyName
1
2
3
typedef struct EXTERN NamePart {
int t;
union {
/* t = 1 */
const OSUTF8CHAR* givenName;
/* t = 2 */
const OSUTF8CHAR* initial;
/* t = 3 */
const OSUTF8CHAR* familyName;
} u;
} NamePart;
Similar to xsd:choice is xsd:union. The main difference is that xsd:union alternatives are unnamed. As specified in
X.694, special names are generated in this case using the base name “alt”. The generated name for the first member
is “alt”; names for successive members are “alt-n” where n is a sequential number starting at 1. An example of this
naming is as follows:
<xsd:simpleType name="MyType">
<xsd:union memberTypes="xsd:int xsd:language"/>
</xsd:simpleType>
This generates the following C type definition:
#define T_MyType_alt
#define T_MyType_alt_1
1
2
typedef struct EXTERN MyType {
int t;
union {
/* t = 1 */
OSINT32 alt;
/* t = 2 */
const OSUTF8CHAR* alt_1;
} u;
} MyType;
Repeating Groups
Repeating groups are specified in XML schema definitions using the minOccurs and maxOccurs facets on sequence
or choice definitions. These items are converted to ASN.1 SEQUENCE OF types.
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XSD TO C/C++ TYPE MAPPINGS
An example of a repeating group is as follows:
<xsd:complexType name="Names">
<xsd:sequence maxOccurs="unbounded">
<xsd:element name="givenName" type="xsd:string "/>
<xsd:element name="initial" type="xsd:string"/>
<xsd:element name="familyName" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
in this case, ASN1C pulls the group out to form a type of form <name>-element where <name> would be replaced
with the complex type name. In this case, the name would be Names-element. A SEQUENCE OF type is then formed
based on this newly formed type (SEQUENCE OF Names-element). The generated C code corresponding to this is
as follows:
typedef struct EXTERN Names_element {
const OSUTF8CHAR* givenName;
const OSUTF8CHAR* initial;
const OSUTF8CHAR* familyName;
} Names_element;
/* List of Names_element */
typedef OSRTDList Names;
This generated code is not identical to the code generated by performing an X.694 translation to ASN.1 and compiling
the resulting specification with ASN1C; it is much simpler. The generated encoder and decoder make the necessary
adjustments to ensure that the encodings are the same regardless of the process used.
Repeating Elements
It is common in XSD to specify that elements within a composite group can occur a multiple number of times. For
example:
<xsd:complexType name="Name">
<xsd:sequence>
<xsd:element name="givenName" type="xsd:string "/>
<xsd:element name="initial" type="xsd:string"/>
<xsd:element name="familyName" type="xsd:string" maxOccurs="2"/>
</xsd:sequence>
</xsd:complexType>
In this case, the familyName element may occur one or two times. (If minOccurs is absent, its default value
is 1.) X.694 specifies that a SEQUENCE OF type be formed for this element and then the element renamed to
familyName-list to reference this element. The C code produced by this transformation is as follows:
typedef struct EXTERN Name {
const OSUTF8CHAR* givenName;
const OSUTF8CHAR* initial;
struct {
OSUINT32 n;
const OSUTF8CHAR* elem[2];
} familyName_list;
} Name;
In this case, an array was used to represent familyName_list. In others, a linked list might be used to represent
the repeating item.
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XSD TO C/C++ TYPE MAPPINGS
xsd:list
Another way to represent repeating items in XSD is by using xsd:list. This is a simple type in XSD that refers to a
space-separated list of repeating items. When the list is converted to ASN.1, it is modeled as a SEQUENCE OF type.
For example:
<xsd:simpleType name="MyType">
<xsd:list itemType="xsd:int"/>
</xsd:simpleType>
results in the generation of the following C type:
typedef struct EXTERN MyType {
OSUINT32 n;
OSINT32 *elem;
} MyType;
Special code is added to the generated XML encode and decode function to ensure the data is encoded in spaceseparated
list form instead of as XML elements.
xsd:any
The xsd:any element is a wildcard placeholder that allows an occurence of any element definition to occur at a given
location. It is similar to the ASN.1 open type and can be modeled as such; however, ASN1C uses a special type for
these items (OSXSDAny) that allows for either binary or xml textual data to be stored. This allows items to be stored
in binary form if binary encoding rules are being used and XML text form if XML text encoding is used.
The definition of the OSXSDAny type is as follows:
typedef enum { OSXSDAny_binary, OSXSDAny_xmlText } OSXSDAnyAlt;
typedef struct OSXSDAny {
OSXSDAnyAlt t;
union {
OSOpenType* binary;
const OSUTF8CHAR* xmlText;
} u;
} OSXSDAny;
The t value is set to either OSXSDAny_binary or OSXSDAny_xmlText to identify the content type. If binary
decoding is being done (BER, DER, CER, or PER), the decoder will populate the binary alternative element; if
XML decoding is being done, the xmlText field is populated. It is possible to perform XML-to-binary transcoding
of a multi-part message (for example, a SOAP message) by decoding each part and then reencoding in binary form
and switching the content type within this structure.
An example of a sequence with a single wildcard element is as follows:
<xsd:complexType name="MyType">
<xsd:sequence>
<xsd:element name="ElementOne" type="xsd:string"/>
<xsd:element name="ElementTwo" type="xsd:int"/>
<xsd:any processContents="lax"/>
</xsd:sequence>
</xsd:complexType>
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XSD TO C/C++ TYPE MAPPINGS
The generated C type definition is as follows:
typedef struct EXTERN MyType {
const OSUTF8CHAR* elementOne;
OSINT32 elementTwo;
OSXSDAny elem;
} MyType;
As per the X.694 standard, the element was given the standard element name elem.
XML Attribute Declarations
XML attribute declarations in XSD are translated into ASN.1 elements that are added to a SEQUENCE type. In binary
encodings, there is no way to tell encoded attributes apart from encoded elements. They just represent data fields in
ASN.1. For XML, special logic is added to the generated XML encoders and decoders to encode and decode the items
as attributes.
An example of an attribute being added to an xsd:sequence declaration is as follows:
<xsd:complexType name="Name">
<xsd:sequence>
<xsd:element name="givenName" type="xsd:string "/>
<xsd:element name="initial" type="xsd:string"/>
<xsd:element name="familyName" type="xsd:string"/>
</xsd:sequence>
<xsd:attribute name ="occupation" type="xsd:string"/>
</xsd:complexType>
This results in the following C type definition being generated:
typedef struct EXTERN Name {
struct {
unsigned occupationPresent : 1;
} m;
const OSUTF8CHAR* occupation;
const OSUTF8CHAR* givenName;
const OSUTF8CHAR* initial;
const OSUTF8CHAR* familyName;
} Name;
The attribute is marked as optional (hence the occupationPresent flag in the bit mask) since XML attributes are
optional by default. The attribute declarations also occur before the element declarations in the generated structure.
Attributes can also be added to a choice group. In this case, an ASN.1 SEQUENCE is formed consisting of the attribute
elements and an embedded element, choice, for the choice group. An example of this is as follows:
<xsd:complexType name="NamePart">
<xsd:choice>
<xsd:element name="givenName" type="xsd:string "/>
<xsd:element name="initial" type="xsd:string"/>
<xsd:element name="familyName" type="xsd:string"/>
</xsd:choice>
<xsd:attribute name ="occupation" type="xsd:string"/>
</xsd:complexType>
This results in the following C type definitions being generated:
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XSD TO C/C++ TYPE MAPPINGS
#define T_NamePart_choice_givenName
#define T_NamePart_choice_initial
#define T_NamePart_choice_familyName
1
2
3
typedef struct EXTERN NamePart_choice {
int t;
union {
/* t = 1 */
const OSUTF8CHAR* givenName;
/* t = 2 */
const OSUTF8CHAR* initial;
/* t = 3 */
const OSUTF8CHAR* familyName;
} u;
} NamePart_choice;
typedef struct EXTERN NamePart {
struct {
unsigned occupationPresent : 1;
} m;
const OSUTF8CHAR* occupation;
NamePart_choice choice;
} NamePart;
In this case, occupation attribute declaration was added as before. But the choice group became a separate
embedded element called choice which the ASN1C compiler pulled out to create the NamePart_choice
temporary type. This type was then referenced by the choice element in the generated type definition for NamePart.
xsd:anyAttribute
An xsd:anyAttribute declaration is the attribute equivalent to the xsd:any wildcard element declaration described
earlier. The main difference is that a single xsd:anyAttribute declaration indicates that any number of undeclared
attributes may occur whereas xsd:any without a maxOccurs facet indicates that only a single wildcard element may
occur at that position.
X.694 models xsd:anyAttribute as a SEQUENCE OF UTF8String in ASN.1. Each string in the sequence is expected to
be in a name=‘value’ format. The generated C type for this is simply a linked list of character strings. For example:
<xsd:complexType name="MyType">
<xsd:anyAttribute processContents="lax"/>
</xsd:complexType>
results in the following C type:
typedef struct EXTERN MyType {
/* List of const OSUTF8CHAR* */
OSRTDList attr;
} MyType;
To populate a variable of this type for encoding, one would add name=‘value’ strings to the list for each attribute.
For example:
MyType myVar;
rtxDListInit (&myVar.attr);
rtxDListAppend (&ctxt, &myVar.attr, OSUTF8(“attr1=‘value1’”));
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XSD TO C/C++ TYPE MAPPINGS
rtxDListAppend (&ctxt, &myVar.attr, OSUTF8(“attr2=‘value2’”));
and so on.
xsd:simpleContent
The xsd:simpleContent type is used to either extend or restrict an existing simple type definition. In the case of
extension, the common use is to add attributes to a simple type. ASN1C will generate a C structure in this case with
an element called base that is of the simple type being extended. An example of this is as follows:
<xsd:complexType name="SizeType">
<xsd:simpleContent>
<xsd:extension base="xsd:integer">
<xsd:attribute name="system" type ="xsd:token"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
this results in the following generated C type definition:
typedef struct EXTERN SizeType {
struct {
unsigned system_Present : 1;
} m;
const OSUTF8CHAR* system_;
OSINT32 base;
} SizeType;
In this case, the attribute system was added first (note the name change to system_ which was the result of system
being determined to be a C reserved word). The base element is then added and is of type OSINT32, the default
type used for xsd:integer.
In the case of a simple content restriction, the processing is similar. A complete new separate type is generated even if
the result of the restriction leaves the original type unaltered (i.e. the restriction is handled by code within the generated
encode and/or decode function). This proves to be a cleaner solution in most cases than trying to reuse the type being
restricted. For example:
<xsd:complexType name="SmallSizeType">
<xsd:simpleContent>
<xsd:restriction base="SizeType">
<xsd:minInclusive value="2"/>
<xsd:maxInclusive value="6"/>
<xsd:attribute name="system" type ="xsd:token" use="required"/>
</xsd:restriction>
</xsd:simpleContent>
</xsd:complexType>
This applies a restriction to the SizeType that was previously derived. In this case, the generated C type is as follows:
typedef struct EXTERN SmallSizeType {
const OSUTF8CHAR* system_;
OSINT32 base;
} SmallSizeType;
In this case, the type definition is almost identical to the original SizeType. The only exception is that the bit mask
field for optional elements is removed—a consequence of the use=“required” attribute that was added to the
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XSD TO C/C++ TYPE MAPPINGS
system attribute declaration. The handling of the minInclusive and maxInclusive attributes is handled inside
the generated encode and decode function in the form of constraint checks.
xsd:complexContent
The xsd:complexContent type is used to extend or restrict complex types in different ways. It is similar to deriving
types from base types in higher level programming languages such as C++ or Java. A common usage pattern in the
case of extension is to add additional elements to an existing sequence or choice group. In this case, a new type is
formed that contains all elements—those declared in the base definition and those in the derived type. Also generated
is a new type with the name <baseType>_derivations which is a choice of all of the different derivations of
the base type. This is used wherever the complex content base type is referenced to allow any derivation of the type
to be used in a message.
An example of this is as follows:
<xsd:complexType name="MyType">
<xsd:sequence>
<xsd:element name="ElementOne" type="xsd:string"/>
<xsd:element name="ElementTwo" type="xsd:int"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="MyExtendedType">
<xsd:complexContent>
<xsd:extension base="MyType">
<xsd:sequence>
<xsd:element name="ElementThree" type="xsd:string"/>
<xsd:element name="ElementFour" type="xsd:int"/>
</xsd:sequence>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
The base type in this case is MyType and it is extended to contain two additional elements in MyExtendedType.
The resulting C type definitions for MyType, MyExtendedType, and the special derivations type are as follows:
typedef struct EXTERN MyType {
const OSUTF8CHAR* elementOne;
OSINT32 elementTwo;
} MyType;
typedef struct EXTERN MyExtendedType {
const OSUTF8CHAR* elementOne;
OSINT32 elementTwo;
const OSUTF8CHAR* elementThree;
OSINT32 elementFour;
} MyExtendedType;
#define T_MyType_derivations_myType 1
#define T_MyType_derivations_myExtendedType 2
typedef struct EXTERN MyType_derivations {
int t;
union {
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XSD TO C/C++ TYPE MAPPINGS
/* t = 1 */
MyType *myType;
/* t = 2 */
MyExtendedType *myExtendedType;
} u;
} MyType_derivations;
The derivations type is a choice between the base type and all derivations of that base type. It will be used wherever
the base type is referenced. This makes it possible to use an instance of the extended type in these places.
The case of restriction is handled in a similar fashion. In this case, instead of creating a new type with additional
elements, a new type is created with all restrictions implemented. This type may be identical to the base type definition.
Substitution Groups
A substitution group is similar to a complex content type in that it allows derivations from a common base. In this
case, however, the base is an XSD element and the substitution group allows any of a set of elements defined to be in
the group to be used in the place of the base element. A simple example of this is as follows:
<xsd:element name="MyElement" type="MyType"/>
<xsd:complexType name="MyType">
<xsd:sequence>
<xsd:element ref="MyBaseElement"/>
</xsd:sequence>
</xsd:complexType>
<xsd:element name="MyBaseElement" type="xsd:string"/>
<xsd:element name="MyExtendedElement" type="xsd:string" substitutionGroup="MyBaseElement
In this case, the global element MyElement references MyType which is defined as a sequence with a single element
reference to MyBaseElement. MyBaseElement is the head element in a substitution group that also includes
MyExtendedElement. This means MyType can either reference MyBaseElement or MyExtendedElement.
As per X.694, ASN1C generates a special type that acts as a container for all the different possible elements in the
substitution group. This is a choice type with the name <BaseElement>_group where <BaseElement> would
be replaced with the name of the subsitution group head element (MyBaseElement in this case).
The generated C type definitions for the above XSD definitions follow:
typedef const OSUTF8CHAR* MyBaseElement;
typedef const OSUTF8CHAR* MyExtendedElement;
#define T_MyBaseElement_group_myBaseElement 1
#define T_MyBaseElement_group_myExtendedElement 2
typedef struct EXTERN MyBaseElement_group {
int t;
union {
/* t = 1 */
MyBaseElement myBaseElement;
/* t = 2 */
MyExtendedElement myExtendedElement;
} u;
} MyBaseElement_group;
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XSD TO C/C++ TYPE MAPPINGS
typedef struct EXTERN MyType {
MyBaseElement_group myBaseElement;
} MyType;
typedef MyType MyElement;
In this case, if MyElement or MyType is used, it can be populated with either base element or extended element data.
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Chapter 5. Generated C/C++ Source Code
Header (.h) File
The generated C or C++ include file contains a section for each ASN.1 production defined in the ASN.1 source file.
Different items will be generated depending on whether the selected output code is C or C++. In general, C++ will
add some additional items (such as a control class definition) onto what is generated for C.
The following items are generated for each ASN.1 production:
• Tag value constant
• Choice tag constants (CHOICE type only)
• Named bit number constants (BIT STRING type only)
• Enumerated type option values (ENUMERATED or INTEGER type only)
• C type definition
• Encode function prototype
• Decode function prototype
• Other function prototypes depending on selected options (for example, print)
• C++ control class definition (C++ only)
A sample section from a C header file is as follows:
/**************************************************************/
/*
*/
/* EmployeeNumber
*/
/*
*/
/**************************************************************/
#define TV_EmployeeNumber(TM_APPL|TM_PRIM|2)
typedef OSINT32 EmployeeNumber;
EXTERN int asn1E_EmployeeNumber (OSCTXT* pctxt,
EmployeeNumber *pvalue, ASN1TagType tagging);
EXTERN int asn1D_EmployeeNumber (OSCTXT* pctxt,
EmployeeNumber *pvalue, ASN1TagType tagging, int length);
This corresponds to the following ASN.1 production specification:
EmployeeNumber ::= [APPLICATION 2] IMPLICIT INTEGER
In this definition, TV_EmployeeNumber is the tag constant. Doing a logical OR on the class, form, and identifier fields
forms this constant. This constant can be used in a comparison operation with a tag parsed from a message.
The following line:
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Generated C/C++ Source Code
typedef OSINT32 EmployeeNumber;
declares EmployeeNumber to be of an integer type (note: OSINT32 and other primitive type definitions can be found
in the osSysTypes.h header file).
asn1E_EmployeeNumber and asn1D_EmployeeNumber are function prototypes for the encode and decode functions
respectively. These are BER function prototypes. If the -per switch is used, PER function prototypes are generated.
The PER prototypes begin with the prefix asn1PE_ and asn1PD_ for encoder and decoder respectively. XER function
prototypes begin with asn1XE_ and asn1XD_.
A sample section from a C++ header file for the same production is as follows:
/**************************************************************/
/*
*/
/* EmployeeNumber
*/
/*
*/
/**************************************************************/
#define TV_EmployeeNumber(TM_APPL|TM_PRIM|2)
typedef OSINT32 ASN1T_EmployeeNumber;
class EXTERN ASN1C_EmployeeNumber :
public ASN1CType
{
protected:
ASN1T_EmployeeNumber& msgData;
public:
ASN1C_EmployeeNumber (ASN1T_EmployeeNumber& data);
ASN1C_EmployeeNumber (
ASN1MessageBufferIF& msgBuf, ASN1T_EmployeeNumber& data);
// standard encode/decode methods (defined in ASN1CType base class):
// int Encode ();
// int Decode ();
// stream encode/decode methods:
int EncodeTo (ASN1MessageBufferIF& msgBuf);
int DecodeFrom (ASN1MessageBufferIF& msgBuf);
} ;
EXTERN int asn1E_EmployeeNumber (OSCTXT* pctxt,
ASN1T_EmployeeNumber *pvalue, ASN1TagType tagging);
EXTERN int asn1D_EmployeeNumber (OSCTXT* pctxt,
ASN1T_EmployeeNumber *pvalue, ASN1TagType tagging, int length);
Note the two main differences between this and the C version:
1. The use of the ASN1T_ prefix on the type definition. The C++ version uses the ASN1T_ prefix for the typedef and
the ASN1C_ prefix for the control class definition.
2. The inclusion of the ASN1C_EmployeeNumber control class.
As of ASN1C version 5.6, control classes are not automatically generated for all ASN.1 types. The only types they
are generated for are those determined to be Protocol Data Units (or PDU’s for short). A PDU is a top-level message
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Generated C/C++ Source Code
type in a specification. These are the only types control classes are required for because the only purpose of a control
class is to provide the user with a simplified calling interface for encoding and decoding a message. They are not used
in any of the ASN1C internally generated logic (the exception to this rule is the XER / XML encoding rules where
they are used internally and still must be generated for all types).
A type is determined to be a PDU in two different ways:
1. If it is explicitly declared to be PDU via the <isPDU/> configuration setting or -pdu command-line option.
2. If no explicit declarations exist, a type is determined to be a PDU if it is not referenced by any other types.
In the employee sample program, EmployeeNumber would not be considered to be a PDU because it is referenced as
an element within the Employee production. For the purpose of this discussion, we will assume EmployeeNumber was
explicitly declared to be a PDU via a configuration setting or command-line specification.
ASN1C_EmployeeNumber is the control class declaration. The purpose of the control class is to provide a linkage
between the message buffer object and the ASN.1 typed object containing the message data. The class provides
methods such as EncodeTo and DecodeFrom for encoding and decoding the contents to the linked objects. It also
provides other utility methods to make populating the typed variable object easier.
ASN1C always adds an ASN1C_prefix to the production name to form the class name. Most generated classes are
derived from the standard ASN1CType base class defined in asn1Message.h. The following ASN.1 types cause code
to be generated from different base classes:
• BIT STRING – The generated control class is derived from the ASN1CBitStr class
• SEQUENCE OF or SET OF with linked list storage – The generated control class is derived from the
ASN1CSeqOfList base class.
• Defined Type – The generated control class for defined types is derived from the generated base class for the
reference type. For example, if we have A ::= INTEGER and B ::= A, then B is a defined type and would inherit
from the base class generated for A (class ASN1C_B : public ASN1C_A { … ).
These intermediate classes are also derived from the ASN1CType base class. Their purpose is the addition of
functionality specific to the given ASN.1 type. For example, the ASN1CBitStr control class provides methods for
setting, clearing and testing bits in the referenced bit string variable.
In the generated control class, the msgData member variable is a reference to a variable of the generated type. The
constructor takes two arguments – an Asn1MessageBufferIF (message buffer interface) object reference and a reference
to a variable of the data type to be encoded or decoded. The message buffer object is a work buffer object for encoding
or decoding. The interface reference can also be used to specify a stream. Stream classes are derived from this same
base class. The data type reference is a reference to the ASN1T_ variable that was generated for the data type.
EncodeFrom and DecodeTo methods are declared that wrap the respective compiler generated C encode and decode
stream functions. Standard Encode and Decode methods exist in the ASN1CType base class for direct encoding and
decoding to a memory buffer. Command-line options may cause additional methods to be generated. For example,
if the –print command line argument was specified; a Print method is generated to wrap the corresponding C print
function.
Specification of the XML encoding rules option (-xer) causes a number of additional methods to be generated
for constructed types. These additional methods are implementations of the standard Simple API for XML (SAX)
content handling interface used to parse content from XML messages. The startElement, characters, and endElement
methods are implemented as well as additional support methods. The control class is also defined to inherit from the
ASN1XERSAXHandler base class as well as ASN1CType (or one of its descendents).
The equivalent C and C++ type definitions for each of the various ASN.1 types follow.
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Generated C/C++ Source Code
Generated C Source Files
By default, the ASN1C compiler generates the following set of .c source files for a given ASN.1 module (note: the
name of the module would be substituted for <moduleName>):
<moduleName>.c
common definitions and functions (for example,
asn1Free_<type>) and/or global value constant
definitions.
<moduleName>Enc.c
encode functions (asn1E_<type>)
<moduleName>Dec.c
decode functions (asn1D_<type>)
If additional options are used (such as –genPrint, -genCopy, etc), additional files will be generated:
<moduleName>Copy.c
copy functions, generated if –genCopy is specified
<moduleName>Print.c
print functions, generated if –genPrint is specified
<moduleName>Compare.c
comparison functions, generated if –genCompare is
specified
<moduleName>PrtToStr.c
print-to-string functions, generated if –genPrtToStr is
specified
<moduleName>PrtToStrm.c
print-to-stream functions, generated if –genPrtToStrm is
specified
<moduleName>Table.c
table constraint functions, generated if –genTable option
is specified
<moduleName>Test.c
test functions, generated if –genTest is specified
If –genCopy, -genPrint, etc have a filename parameter then the code will be written to the given file instead of the
default one. If the –cfile <filename> option is used and –genCopy, -genPrint, etc options do not have parameters then
all code will be placed in one source file with name <filename>.
Maximum Lines per File
In each of the cases above, it is possible to specify an approximate maximum number of lines that each of the
generated .c files may contain. This is done using the -maxlines option. If -maxlines is specified with no parameter, a
default maximum number of lines (50,000) will be set; otherwise, the given value will be used.
If the given maximum lines limit is surpassed in a file, a new file will be started with an “_1” appended, for example
<moduleName>Enc_1.c. Additional files will be numbered sequentially if necessary (_2, _3, etc.). Note that this limit
is a lower threshold and not exact. A complete compilation unit (for example, a function) will not be split because
of this threshold. The way it works is the threshold is checked before the output of a compilation unit. If it is found
to be exceeded, a new file is started at that time. Therefore, a user should plan for a reserve to be in place above the
limit to compensate for this overflow.
The reason for having this limit is because some C/C++ compilers have problems with very large .c files. For example,
one product will not allow the debugger to work on lines in a file over the 64k threshold.
Use of the -maxcfiles Option
The -maxcfiles option allows generation of more compact code by putting each encode, decode, copy, compare, etc
function into a separate file. This allows the linker to link in only the required functions as opposed to all functions
in a compiled object module. This option might be useful for applications that have minimal space requirements (for
example, embedded systems).
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Generated C/C++ Source Code
Note
Some sophisticated linkers have the capability to pull individual functions out of an object module directly
for final inclusion in the target executable or shared object file. In this case, the -maxcfiles option does not
provide any advantage in reducing the size of the application program.
To achieve the best results it is necessary to put all compiled object files into an object library (.a or .lib file) and
include this library in the link command. The –genMake option when used in conjunction with –maxcfiles will generate
a makefile that will compile each of the generated files and add them to a library with a name based on the name of
the ASN.1 module being compiled (<moduleName>.lib for Windows or lib<moduleName>.a for *NIX).
The format of each generated .c file name is as follows:
asn1<suffix>_<prodname>.c
where <suffix> depends on encoding rules and the function type (encode, decode, free, etc.) and <prodname>
is the ASN.1 production name.
For example, consider one type definition within the employee.asn ASN.1 specification:
Employee DEFINITIONS ::= BEGIN
[...]
Name ::= [APPLICATION 1] IMPLICIT SEQUENCE {
givenName IA5String,
initial IA5String,
familyName IA5String
}
[...]
END
By default, the following .c files would be generated (note: this assumes no additional code generation options were
selected):
Employee.c
EmployeeEnc.c
EmployeeDec.c
If -maxcfiles was selected as in the following command line:
asn1c employee.asn -c -ber -trace –maxcfiles
Running ASN1C with the -maxcfiles option, the following .c files for this type would be generated for the Name type:
asn1D_Name.c
asn1E_Name.c
These contain the functions to decode Name and encode Name respectively. Similar files would be generated for the
other productions in the module as well.
Generated C++ files
In general, the generation logic for C++ is similar to the logic for C. Instead of the .c file extension, .cpp is used:
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Generated C/C++ Source Code
<moduleName>.cpp
Common definitions and functions (for example,
asn1Free_<type>) and/or global value constant
definitions. This file also contains constructors,
destructors and all methods for ASN1C_<Type> and
ASN1T_<Type> control classes.
<moduleName>Enc.cpp
C encode functions and C++ encode methods.
<moduleName>Dec.cpp
C decode functions and C++ decode methods.
If additional options are used (such as –genPrint, -genCopy, etc), additional files will be generated:
Filename
Description
<moduleName>Copy.cpp
copy functions, generated if –genCopy is specified
<moduleName>Print.cpp
print functions, generated if –genPrint is specified
<moduleName>Compare.cpp
comparison functions, generated if –genCompare is
specified
<moduleName>PrtToStr.cpp
print-to-string functions, generated if –genPrtToStr is
specified
<moduleName>PrtToStrm.cpp
print-to-stream functions, generated if –genPrtToStrm is
specified
<moduleName>Table.cpp
table constraint functions, generated if –genTable option
is specified
<moduleName>Test.cpp
test functions, generated if –genTest is specified
The -maxcfiles option for C++ works very similar to how it works for C. The only differences are a few additional
files are generated and the .cpp extension is used instead of .c. Additional files are generated to hold ASN1C_<Type>
and ASN1T_<Type> control classes. The format of the filenames of these files is as follows:
asn1<suffix>_<prodname>.cpp
ASN1C_<prodname>.cpp
ASN1T_<prodname>.cpp
where <suffix> depends on the encoding rules and function type selected (encode, decode, free, etc.) and
<prodname> is the ASN.1 production name.
For the example presented previously in the C Files section, the following files would be generated for the Name
production in the employee.asn file:
asn1D_Name.cpp
asn1E_Name.cpp
ASN1T_Name.cpp
ASN1C_Name.cpp
These contain the functions to decode Name and encode Name respectively. The ASN1T_Name.cpp file contains the
type class methods, and the ASN1C_Name.cpp files contains the control class methods. Note that not all productions
have a control class (only PDU types do for BER or PER) therefore the ASN1C_<type>.cpp file may not be generated.
Similar files would be generated for the other productions in the module as well.
Note that for C++, the code reduction effect is less than that for pure C. This is because most of the linkers cannot omit
virtual methods even if they are not being used by the application. These virtual methods refer to separate C functions
and these functions are being linked into the application even if they are not actually used. But, still, the size of the final
application created with –maxcfiles option should be less than the size of the application created without this option.
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Generated C/C++ Source Code
Generated C/C++ files and the -compat Option
ASN1C 5.6 and below did not generate separate files for common definitions, encode and decode functions
(<moduleName>.c/.cpp, <moduleName>Enc.c/.cpp, <moduleName>Dec.c/.cpp). All code was generated in a single
file with the name <moduleName>.c/.cpp. If it is necessary to maintain this behavior then use the –compat 5.6 option.
Also, the behavior of the -cfile option is slightly changed in ASN1C 5.7 and above. In 5.6 and below, the –cfile option
did not have any effect for files containing copy, print, compare, etc functions. For ASN1C 5.7 and above, –cfile causes
everything to be output to one file unless specific filename parameters are specified with –genPrint, -genCopy, etc.
Once again, to maintain the previous behavior the –compat 5.6 option can be used.
Generated C++ files and the -symbian Option
ASN1C version 6.1 introduced the -symbian option to generate code that targets the Symbian platform. While an
exhaustive discussion of the differences between Symbian C++ and standard C++ is impractical for this User's Guide,
the differences in generated code are relatively minimal. Two principle areas of concern are writable static data (WSD)
and extern linkage.
Writable Static Data
Writable static data are per-process data that exist throughout the lifetime of the process. The use of WSD complicates
memory management in many cases, especially in shared libraries. A minimum of four kilobytes is allocated for WSD
every single time a DLL is loaded, even if less space is required. If 50 bytes were needed, for example, 4046 bytes
would be wasted every time the DLL was loaded. For this reason, the use of WSD is highly discouraged.
In practice, WSD are globally scoped: variables declared outside of a function, struct, or class, and static variables
declared in functions. WSD may be eliminated by modifying primitive types with const. Complex types (i.e., classes
or structs) with non-trivial constructors will be marked as WSD whether marked const or not.
It is common in generated code to use lookup tables for some types (e.g., ENUMERATED). These tables are composed
of simple types and marked as const to avoid being marked as WSD by Symbian compilers.
Extern Linkage
Most common compilers support applying external linkage to an entire class, but Symbian’s does not. Symbian also
requires that both prototype and implementation be marked with the appropriate linkage. When the -symbian option
is specified, generated code is modified to accommodate these requirements.
The following specification will demonstrate the differences between code generated with Symbian and without:
Test DEFINITIONS ::= BEGIN
A ::= NULL
END
The usual class definition for this specification looks like this:
class EXTERN ASN1C_A :
public ASN1CType
{
protected:
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Generated C/C++ Source Code
public:
ASN1C_A ();
ASN1C_A (OSRTMessageBufferIF& msgBuf);
ASN1C_A (OSRTContext &context);
// standard encode/decode methods (defined in ASN1CType base class):
// int Encode ();
// int Decode ();
// stream encode/decode methods:
int EncodeTo (OSRTMessageBufferIF& msgBuf);
int DecodeFrom (OSRTMessageBufferIF& msgBuf);
} ;
It is very similar to the Symbian class definition:
class ASN1C_A :
public ASN1CType
{
protected:
public:
EXTERN ASN1C_A ();
EXTERN ASN1C_A (OSRTMessageBufferIF& msgBuf);
EXTERN ASN1C_A (OSRTContext &context);
// standard encode/decode methods (defined in ASN1CType base class):
// int Encode ();
// int Decode ();
// stream encode/decode methods:
EXTERN int EncodeTo (OSRTMessageBufferIF& msgBuf);
EXTERN int DecodeFrom (OSRTMessageBufferIF& msgBuf);
} ;
Note the use of EXTERN in the generated code: it prefixes the constructors and the encoding and decoding functions,
but not the class declaration. These prefixes are repeated in the implementation:
EXTERN ASN1C_A::ASN1C_A () : ASN1CType()
{
}
Users should not have to modify generated code for use on the Symbian platform, but should be aware of these
particular differences when writing Symbian applications.
Considerations When Using C++ Standard
Library
When -cpp11 is specified on the command line, the generated code may use features of the C++ Standard Library such
as std::string for character strings and std::list (or another container class) for SEQUENCE OF types. There are a few
considerations to keep in mind when using this option.
ASN1C generates code that manages memory using OSCTXT and rtxMem* functions. The design of the generated
code and memory management is such that the C++ constructors and destructors generally don't need to be invoked.
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Generated C/C++ Source Code
For example, dynamic memory is allocated using rtxMemAllocType, instead of new, and initialization can be done
by assigning individual fields or else using a generated asn1Init* function, so that the constructor is never invoked.
The C++ Standard Library classes are more typical C++ classes, and failing to invoke their constructor or destructor,
or invoking them more than once, can lead to memory leaks or crashes. This means that when you are using the -cpp11
option, you must take care that the C++ constructors and destructors for the generated classes are invoked exactly
once. Follow these rules to avoid problems:
• When you dynamically allocate an object, use rtxMemAlloc* to allocate the memory, then use a placement new
expression to invoke the constructor.
• C++ destructors don't have access to an OSCTXT for use in freeing memory. Therefore, before an object is destructed,
invoke the generated asn1Free* function for that type to free any dynamically allocated memory that is directly
or indirectly owned by the object. If no asn1Free* function was generated for the type in question, there is no
such memory that needs to be freed and this rule does not apply.
• If you dynamically allocate an object that is not owned by some other object, make sure when you are finished with
the object that you do the following three things, in order:
1. invoke the generated asn1Free* function, if there is one. This will recursively destruct and free memory for
objects directly or indirectly owned by the object.
2. explicitly invoke the destructor for the object. This will recursively destruct objects contained by the object.
3. use rtxMemFreePtr to release the memory
• If you repeatedly use the same object to encode records, use the asn1Init* method with free=TRUE to free previously
allocated data before repopulating the object. If you repeatedly decode into the same object, invoke the Decode
method with free=TRUE.
• Do not use ASN1CType.memReset(). You must use the asn1Free* methods or else memory allocated by the C++
standard library will not be freed. Also, invoking an asn1Free* method after ASN1CType.memReset() is likely to
cause a segmentation fault as dangling pointers are followed.
A few code examples are given below.
EXAMPLE 1, Using a local variable:
//A local variable's constructor & destructor fire automatically. You only need to
//make sure asn1Free* is invoked. Using a control class, as show here, does that for yo
ASN1T_PDU msgData;
ASN1C_PDU controlPDU (encodeBuffer, msgData);
// Populate structure of generated type
...
// Encode
...
// When controlPDU goes out of scope, asn1Free_PDU will be invoked on msgData
// When msgDta goes out of scope, its destructor will fire
EXAMPLE 2, Assigning a dynamically allocated std::string for a choice type:
OSCTXT* pctxt;
...
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Generated C/C++ Source Code
//set the selector indicating which alternative is chosen
pvalue->myChoice.t = 1;
//allocate memory for the chosen alternative
pvalue->myChoice.u.message = rtxMemAllocTypeZ (pctxt, std::string);
//invoke the constructor using placement new expression
new (pvalue->myChoice.u.message) std::string();
//Assign the contents of the string.
*pvalue->myChoice.u.message = "Happy Birthday!";
EXAMPLE 3, Dynamically allocating and freeing an object:
OSCTXT* pctxt;
...
//dynamically allocate and construct the object
ASN1T_StringsInSequence* pvalue = rtxMemAllocType (pctxt, ASN1T_StringsInSequence);
if (pvalue == NULL)
return LOG_RTERR (pctxt, RTERR_NOMEM);
new (pvalue) ASN1T_StringsInSequence();
//do some work, maybe decode into pvalue
...
//invoke asn1Free*, destruct, and free memory
asn1Free_StringsInSequence (pctxt, pvalue);
pvalue->~ASN1T_StringsInSequence();
rtxMemFreePtr (pctxt, (void*)pvalue);
Generated Build Files
Generated Makefile
The -genmake option causes a portable makefile to be generated to assist in the C or C++ compilation of all of the
generated C or C++ source files. This makefile contains a rule to invoke ASN1C to regenerate the .c and .h files if any
of the dependent ASN.1 source files are modified. It also contains rules to compile all of the C or C++ source files.
Header file dependencies are generated for all the C or C++ source files.
Two basic types of makefiles are generated:
1. A GNU compatible makefile. This makefile is compatible with the GNU make utility which is suitable for compiling
code on Linux and many UNIX operating systems, and
2. A Microsoft Visual Studio compatible makefile. This makefile is compatible with the Microsoft Visual Studio
nmake utility.
A GNU compatible makefile is produced by default, the Microsoft compatible file is produced when the –w32
command line option is specified in addition to –genmake.
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Generated C/C++ Source Code
Both of these makefile types rely on definitions in the platform.mk make include file. This file contains parameters
specific to different compiler and linker utilities available on different platforms. Typically, all the needs to be done
to port to a different platform is to adjust the parameters in this file.
When a makefile is generated, it is assumed that the ASN1C project exists within the ASN1C installation directory
tree. The generation logic tries to determine the root directory of the installation by traversing upward from the project
directory in an attempt to locate the rtsrc subdirectory which is assumed to be the installation root directory. The
makefile variable OSROOTDIR is then set to this value. A similar traversal is done to locate the platform.mk and
xmlparser.mk files. These paths are then set in the makefile. If the project directory is located outside of the ASN1C
directory tree, the user must set the OSROOTDIR environment variable to point at the ASN1C root directory in order
for the makefile generation to be successful. If this is done, it is assumed that the platform.mk and xmlparser.mk files
are located in this directory as well. If the compiler is unable to determine the root directory using any of the methods
described above, an error will be generated and the user will need to manually edit the makefile to set the required
root directory parameters and makefile include file paths.
Generated VC++ Project Files
The -vcproj option causes Microsoft Visual Studio project and workspace files to be generated that can be used to build
the generated code. The files are compatible with Visual Studio version 6.0; but higher versions of Visula Studio can
convert these files to the newer formats. This option can be used with the -dll option that will generate project files to
compile all generated code into a DLL and -mt that will add multi-threaded compilation options to generated projects.
Because there are several different versions of Visual Studio, the -vcproj option takes an optional argument: the release
year of the version of Visual Studio used. This modifies the resulting project to link against the appropriate set of
libraries distributed with ASN1C. If no year is specified, the project will link against the usual c and cpp directories. If
2003 is specified, the project will us the c_vs2003 and cpp_vs2003 directories. If 2005 is specified, c_vs2005
and cpp_vs2005 will be used. Likewise, if 2008 is specified, c_vs2008 and cpp_vs2008 will be used.
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Chapter 6. Generated Encode/Decode
Function and Methods
Encode/Decode Function Prototypes
If BER or DER encoding is specified, a BER encode and decode function prototype is generated for each production
(DER uses the same form – there are only minor differences between the two types of generated functions). These
prototypes are of the following general form:
int asn1E_<ProdName> (OSCTXT* pctxt,
<ProdName>* pvalue, ASN1TagType tagging);
int asn1D_<ProdName> (OSCTXT* pctxt,
<ProdName>* pvalue, ASN1TagType tagging, int length);
The prototype with the asn1E_ prefix is for encoding and the one with asn1D_ is for decoding. The first parameter
is a context variable used for reentrancy. This allows the encoder/decoder to keep track of what it is doing between
function invocations.
The second parameter is for passing the actual data variable to be encoded or decoded. This is a pointer to a variable
of the generated type.
The third parameter specifies whether implicit or explicit tagging should be used. In practically all cases, users of the
generated function should set this parameter to ASN1EXPL (explicit). This tells the encoder to include an explicit tag
around the encoded result. The only time this would not be used is when the encoder or decoder is making internal
calls to handle implicit tagging of elements.
The final parameter (decode case only) is length. This is ignored when tagging is set to ASN1EXPL (explicit), so users
can ignore it for the most part and set it to zero. In the implicit case, this specifies the number of octets to be extracted
from the byte stream. This is necessary because implicit indicates no tag/length pair precedes the data; therefore it is
up to the user to indicate how many bytes of data are present.
If PER encoding is specified, the format of the generated prototypes is different. The PER prototypes are of the
following general form:
int asn1PE_<ProdName> (OSCTXT* pctxt, <ProdName>[*] value);
int asn1PD_<ProdName> (OSCTXT* pctxt, <ProdName>* pvalue);
In these prototypes, the prefixes are different (a ‘P’ character is added to indicate they are PER encoders/decoders),
and the tagging argument variables are omitted. In the encode case, the value of the production to be encoded may be
passed by value if it is a simple type (for example, BOOLEAN or INTEGER). Structured values will still be passed
using a pointer argument.
If XER encoding is specified, function prototypes are generated with the following format:
int asn1XE_<ProdName> (OSCTXT* pctxt, <ProdName>[*] value,
const char* elemName,
const char* attributes);
int asn1XD_<ProdName> (OSCTXT* pctxt, <ProdName>* pvalue);
The encode function signature includes arguments for the context and value as in the other cases. It also has an element
name argument (elemName) that contains the name of the element to be encoded and an attributes argument (attributes)
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Generated Encode/Decode Function and Methods
that can be used to encode an attributes string. The decode function is generated for PDU-types only - decoding of
internally referenced types is accomplished through generated SAX handler callback functions which are invoked by
an XML parser.
If XML functions are generated using the -xml switch, the function prototypes are as follows:
int XmlEnc_<ProdName> (OSCTXT* pctxt, <ProdName> value,
const OSUTF8CHAR* elemName, const OSUTF8CHAR* nsPrefix);
int XmlDec_<ProdName> (OSCTXT* pctxt, <ProdName>* pvalue);
In this case, the encode function contains an argument for XML element name (elemName) and also namespace prefix
(nsPrefix).
Generated C++ Control Class Definition
A control class definition is generated for each defined production in the ASN.1 source file that is determined to be a
Protocol Data Unit (PDU). By default, any type defined in an ASN.1 source file that is not referenced by any other type
is a PDU. This default behavior can be overridden by using a configuration file setting (<isPDU/>) or a commandline option (-pdu) to explicitly declare that certain types are PDU’s.
The generated control class is derived from the ASN1CType base class. This class provides a set of common attributes
and methods for encoding/decoding ASN.1 messages. It hides most of the complexity of calling the encode/decode
functions directly.
BER/DER or PER Class Definition
The general form of the class definition for BER, DER, or PER encoding rules is as follows:
class ASN1C_<name> : public ASN1CType {
protected:
ASN1T_<name>& msgData;
public:
ASN1C_<name> (ASN1T_<name>& data);
ASN1C_<name> (
ASN1MessageBufferIF& msgBuf, ASN1T_<name>& data);
// standard encode/decode methods (defined in ASN1CType base class):
// int Encode ();
// int Decode ();
// stream encode/decode methods:
int EncodeTo (ASN1MessageBufferIF& msgBuf);
int DecodeFrom (ASN1MessageBufferIF& msgBuf);
} ;
The name of the generated class is ASN1C_<name> where <name> is the name of the production. The only defined
attribute is a protected variable reference named msgData of the generated type.
Two constructors are generated. The first is for stream operations and allows the control class to be created using only
a reference to a variable of the generated type.
The EncodeTo and DecodeFrom methods can then be used to encode or decode directly to and from a stream. The
<< and >> stream operators can be used as well.
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Generated Encode/Decode Function and Methods
The second constructor is the legacy form that allows a message buffer to be associated with a data variable at the time
of creation. The Encode and Decode methods defined in the ASN1CType base class can be used with this construction
form to encode and decode to the associated buffer.
The constructor arguments are a reference to an ASN1MessageBufferIF (message buffer interface) type and a reference
to an ASN1T_<name> type. The message buffer interface argument is a reference to an abstract message buffer or
stream class. Implementations of the interface class are available for BER/DER, PER, or XER encode or decode
message buffers or for a BER or XER encode or decode stream.
The ASN1T_<name> argument is used to specify the data variable containing data to be encoded or to receive data on
a decode call. The procedure for encoding is to declare a variable of this type, populate it with data, and then instantiate
the ASN1C_<name> object to associate a message buffer object with the data to be encoded. The Encode or Encode
To method can then be called to encode the data. On the decode side, a variable must be declared and passed to the
constructor to receive the decoded data.
Note that the ASN1C_ class declarations are only required in the application code as an entry point for encoding or
decoding a top-level message (or Protocol Data Unit – PDU). As of ASN1C version 5.6, control classes are only
generated for ASN.1 types that are determined to be PDU’s. A type is determined to be a PDU if it is referenced by
no other types. This differs from previous versions of ASN1C where control classes were generated for all types. This
default behavior can be overridden by using a configuration file entry or the -pdu command-line switch to explicitly
declare the PDU types. The <isPDU/> flag is used to declare a type to be a PDU in a configuration file. An example
of this is as follows:
<asn1config>
<module>
<name>H323-MESSAGES</name>
<production>
<name>H323-UserInformation</name>
<isPDU/>
</production>
</module>
</asn1config>
This will cause only a single ASN1C_ control class definition to be added to the generated code for the H323UserInformation production.
If the module contains no PDUs (i.e,. contains support types only), the <noPDU/> empty element can be specified at
the module level to indicate that no control classes should be generated for the module.
XER Class Definition
For the XML encoding rules (XER), the generated class definition is as follows:
class ASN1C_<name> :
public ASN1CType, ASN1XERSAXHandler
{
protected:
ASN1T_<name>& msgData;
... additional control variables
public:
ASN1C_<name> (ASN1T_<name>& data);
ASN1C_<name> (
ASN1MessageBufferIF& msgBuf, ASN1T_<name>& data);
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Generated Encode/Decode Function and Methods
// standard encode/decode methods (defined in ASN1CType base class):
// int Encode ();
// int Decode ();
// stream encode/decode methods:
int EncodeTo (ASN1MessageBufferIF& msgBuf);
int DecodeFrom (ASN1MessageBufferIF& msgBuf);
// SAX Content Handler Interface
virtual void startElement
(const XMLCh* const uri,
const XMLCh* const localname,
const XMLCh* const qname,
const Attributes& attrs);
virtual void characters
(const XMLCh* const chars, const unsigned int length);
virtual void endElement
(const XMLCh* const uri,
const XMLCh* const localname,
const XMLCh* const qname);
} ;
The main differences between the BER/DER/PER control class definition and this are:
1. The class generated for XER inherits from the ASN1XERSAXHandler base class, and
2. The class implements the standard SAX content handler methods.
This allows an object of this class to be registered as a SAX content handler with any SAX-compliant XML parser.
The parser would be used to read and parse XML documents. The methods generated by ASN1C would then receive
the parsed data via the SAX interface and use the results to populate the data variables with the decoded data.
Note that for XML code generation (-xml command-line option), the SAX handler interface is not generated. That is
because XML decoders use a pull-parser instead of SAX code to parse the XML input stream.
Generated Methods
For each production, an EncodeFrom and DecodeTo method is generated within the generated class structure. These
are standard methods that initialize context information and then call the generated C-like encode or decode function.
If the generation of print functions was specified (by including –print on the compiler command line), a Print method
is also generated that calls the C print function.
For XER, additional methods are generated to implement a SAX content handler interface to an XML parser. This
includes a startElement, characters, and endElement method. An init and finalize method may also be generated to
initialize a variable prior to parsing and to complete population of a variable with decoded data.
Generated Information Object Table Structures
Information Objects and Classes are used to define multi-layer protocols in which “holes” are defined within ASN.1
types for passing message components to different layers for processing. These items are also used to define the
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Generated Encode/Decode Function and Methods
contents of various messages that are allowed in a particular exchange of messages. The ASN1C compiler extracts the
types involved in these message exchanges and generates encoders/decoders for them. The “holes” in the types are
accounted for by adding open type holders to the generated structures. These open type holders consist of a byte count
and pointer for storing information on an encoded message fragment for processing at the next level.
The ASN1C compiler is capable of generating code in one of two forms for information in an object specification:
1. Simple form: in this form, references to variable type fields within standard types are simply treated as open types
and an open type placeholder is inserted.
2. Table unions form: in this form, all of the classes, objects, and object sets within a specification result in the
generation of code for parsing and formatting the information field references within standard type structures. Open
types with relational constraints result in the generation of C union structures that enumerate all of allowed fields
as defined by the constraint. This form is selected by using the -table-unions command-line option.
3. Legacy table form: this is similar to 2 in that all information object related items result in the generation of additional
code. In this case, however, instead of a union structure being generated for open types with relational constraints, a
void pointer is used to hold an object in decoded form. This form is selected using the -tables command-line option.
To better understand the support in this area, the individual components of Information Object specifications are
examined. We begin with the “CLASS” specification that provides a schema for Information Object definitions. A
sample class specification is as follows:
OPERATION ::= CLASS {
&operationCode
&ArgumentType,
&ResultType,
&Errors
CHOICE { local INTEGER,
global OBJECT IDENTIFIER },
ERROR
OPTIONAL
}
Users familiar with ASN.1 will recognize this as a simplified definition of the ROSE OPERATION MACRO using
the Information Object format. When a class specification such as this is parsed, information on its fields is maintained
in memory for later reference. In the simple form of code generation, the class definition itself does not result in the
generation of any corresponding C or C++ code. It is only an abstract template that will be used to define new items
later on in the specification. In the table form, if C++ is specified, an abstract base class is generated off of which other
classes are derived for information object specifications.
Fields from within the class can be referenced in standard ASN.1 types. It is these types of references that the compiler
is mainly concerned with. These are typically “header” types that are used to add a common header to a variety of other
message body types. An example would be the following ASN.1 type definition for a ROSE invoke message header:
Invoke ::= SEQUENCE {
invokeID INTEGER,
opcode OPERATION.&operationCode,
argument OPERATION.&ArgumentType
}
This is a very simple case that purposely omits a lot of additional information such as Information Object Set constraints
that are typically a part of definitions such as this. The reason this information is not present is because we are just
interested in showing the items that the compiler is concerned with. We will use this type to demonstrate the simple
form of code generation. We will then add table constraints and discuss what changes when the –tables command
line options is used.
The opcode field within this definition is an example of a fixed type field reference. It is known as this because if you
go back to the original class specification, you will see that operationCode is defined to be of a specific type (namely
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Generated Encode/Decode Function and Methods
a choice between a local and global value). The generated typedef for this field will contain a reference to the type
from the class definition.
The argument field is an example of a variable type field.. In this case, if you refer back to the class definition, you will
see that no type is provided. This means that this field can contain an instance of any encoded type (note: in practice,
table constraints can be used with Information Object Sets to limit the message types that can be placed in this field).
The generated typedef for this field contains an “open type” (ASN1OpenType) reference to hold a previously encoded
component to be specified in the final message.
Simple Form Code Generation
In the simple form of information object code generation, the Invoke type above would result in the following C or
C++ typedefs being generated:
typedef struct Invoke ::= SEQUENCE {
OSINT32 invokeID;
OPERATION_operationCode opcode;
ASN1OpenType argument;
}
The following would be the procedure to add the Invoke header type to an ASN.1 message body:
1. Encode the body type
2. Get the message pointer and length of the encoded body
3. Plug the pointer and length into the numocts and data items of the argument open type field in the Invoke type
variable.
4. Populate the remaining Invoke type fields.
5. Encode the Invoke type to produce the final message.
In this case, the amount of code generated to support the information object references is minimal. The amount of
coding required by a user to encode or decode the variable type field elements, however, can be rather large. This
is a tradeoff that exists between using the compiler generated table constraints solution (as we will see below) and
using the simple form.
Unions Table Form Code Generation
If we now add table constraints to our original type definition, it might look as follows:
Invoke ::= SEQUENCE {
invokeID INTEGER,
opcode OPERATION.&operationCode ({My-ops}),
argument OPERATION.&ArgumentType ({My-ops}{@opcode})
}
The “{My-ops}” constraint on the opcode element specifies an information object set that constrains the element value
to one of the values in the object set. The {My-ops}{@opcode} constraint on the argument element goes a step further
– it ties the type of the field to the type specified in the row that matches the given opcode value.
An example of the information object set and corresponding information objects would be as follows:
My-ops OPERATION ::= { makeCall | fwdCall, ... }
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Generated Encode/Decode Function and Methods
makeCall OPERATION ::= {
&ArgumentType MakeCallArgument,
&operationCode local : 10
}
fwdCall OPERATION ::= {
&ArgumentType FwdCallArgument,
&operationCode local : 11
}
The C or C++ type generated for the SEQUENCE above when –table-unions is specified would be as follows:
typedef struct EXTERN Invoke {
OSINT32 invokeID;
_OPERATION_operationCode opcode;
struct {
/**
* information object selector
*/
My_ops_TVALUE t;
/**
* My_ops information objects
*/
union {
/**
* operationCode: local : 10
*/
MakeCallArgument *makeCall;
/**
* operationCode: local : 11
*/
FwdCallArgument *fwdCall;
ASN1OpenType* extElem1;
} u;
} argument;
} Invoke;
Each of the options from the information object set are enumerated in the union structure. All a user needs to do to
encode a variable of this type is to set the "t" value in the structure to the selected information object field and then
populate the type field. This is very similar to populating a CHOICE construct. The comments in the elements show
what the value of the key element(s) must be if that alternative is selected. The open type field at the end (extElem1) is
added because the object set is extensible and it therefore may contain a value that is currently not included in the set.
Legacy Table Form Code Generation
In the legacy form of table constraint code generation, the following structure would be generated for the Invoke type
above:
typedef struct EXTERN Invoke {
OSINT32 invokeID;
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Generated Encode/Decode Function and Methods
_OPERATION_operationCode opcode;
ASN1Object argument;
}
This is almost identical to the type generated in the simple case. The difference is the ASN1Object type (or ASN1TObject
for C++) that is used instead of ASN1OpenType. This type is defined in the asn1type.h run-time header file as follows:
typedef struct ASN1Object {
ASN1OpenType encoded;
void* decoded;
OSINT32 index;
}
This holds the value to be encoded or decoded in both encoded or decoded form. The way a user uses this to encode
a value of this type is as follows:
1. Populate a variable of the type to be used as the argument to the invoke type.
2. Plug the address of this variable into the decoded void pointer in the structure above.
3. Populate the remaining Invoke type fields.
4. Encode the Invoke type to produce the final message.
Note that in this case, the intermediate type does not need to be manually encoded by the user. The generated encoder
has logic built-in to encode the complete message using the information in the generated tables.
Additional Code Generated with the -tables option
When the –tables command line option is used, additional code is generated to support the additional processing
required to verify table constraints. This code varies depending on whether C or C++ code generation is selected. The
C++ code is designed to take advantage of the object-oriented capabilities of C++. These capabilities are well suited
for modeling the behavior of information objects in practice. The following subsections describe the code generated
for each of these languages.
The code generated to support these constraints is intended for use only in compiler-generated code. Therefore, it is
not necessary for the average user to understand the mappings in order to use the product. The information presented
here is informative only to provide a better understanding of how the compiler handles table constraints.
C Code Generation
For C, code is generated for the Information Object Sets defined within a specification in the form of a global array of
structures. Each structure in the array is an equivalent C structure representing the corresponding ASN.1 information
object.
Additional encode and decode functions are also generated for each type that contains table constraints. These functions
have the following prototypes :
BER/DER
int asn1ETC_<ProdName> (OSCTXT* pctxt, <ProdName>* pvalue);
int asn1DTC_<ProdName> (OSCTXT* pctxt, <ProdName>* pvalue);
PER
int asn1PETC_<ProdName> (OSCTXT* pctxt, <ProdName>* pvalue);
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Generated Encode/Decode Function and Methods
int asn1PDTC_<ProdName> (OSCTXT* pctxt, <ProdName>* pvalue);
The purpose of these functions is to verify the fixed values within the table constraints are what they should be and
to encode or decode the open type fields using the encoder or decoder assigned to the given table row. Calls to these
functions are automatically built into the standard encode or decode functions for the given type. They should be
considered hidden functions not for use within an application that uses the API.
C++ Code Generation
For C++, code is generated for ASN.1 classes, information objects, and information object sets. This code is then
referenced when table constraint processing must be performed.
Each of the generated C++ classes builds on each other. First, the classes generated that correspond to ASN.1 CLASS
definitions form the base class foundation. Then C++ classes derived from these base classes corresponding to the
information objects are generated. Finally, C++ singleton classes corresponding to the information object sets are
generated. Each of these classes provides a container for a collection of C++ objects that make up the object set.
Additional encode and decode functions are also generated as they were in the C code generation case for interfacing
with the object definitions above. These functions have the following prototypes:
BER/DER
int asn1ETC_<ProdName> (OSCTXT* pctxt,
<ProdName>* pvalue,
<ClassName>* pobject);
int asn1DTC_<ProdName> (OSCTXT* pctxt,
<ProdName>* pvalue,
<ClassName>* pobject);
PER
int asn1PETC_<ProdName> (OSCTXT* pctxt,
<ProdName>* pvalue,
<ClassName>* pobject);
int asn1PDTC_<ProdName> (OSCTXT* pctxt,
<ProdName>* pvalue,
<ClassName>* pobject);
These prototypes are identical to the prototypes generated in C code generation case except for the addition of the
pobject argument. This argument is for a pointer to the information object that matches the key field value for a
given encoding. These functions have different logic for processing Relative and Simple table constraints. The logic
associated with each case is as follows:
On the encode side:
Relative Table Constraint:
1. The lookupObject method is invoked on the object set instance to find the class object for the data in the populated
type variable to be encoded.
2. If a match is found, the table constraint encode function as defined above is invoked. This function will verify all
fixed type values match what is defined in the information object definition and will encode all type fields and store
the resulting encoded data in the ASN1TObject.encoded fields.
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Generated Encode/Decode Function and Methods
3. If a match is not found and the information object set is not extensible, then a table constraint error status will be
returned. If the information object set is extensible, a normal status is returned.
Simple Table Constraint:
1. This function will verify all the fixed type values match what is defined in the table constraint information object
set. If an element value does not exist in the table (i.e. the information object set) and the object set is not extensible,
then a table constraint violation exception will be thrown.
The normal encode logic is then performed to encode all of the standard and open type fields in the message.
On the decode side, the logic is reversed:
The normal decode logic is performed to populate the standard and open type fields in the generated structure.
Relative Table Constraint:
1. The lookupObject method is invoked on the decoded key field value to find an object match.
2. If a match is found, the table constraint decode function as defined above is invoked. This function will verify all
fixed type values match what is defined in the information object definition and will fully decode all type fields
and store pointers to the decoded type variables in the ASN1TObject.decoded fields.
3. If a match is not found and the information object set is not extensible, then a table constraint error status will be
returned. If the information object set is extensible, a normal status is returned.
Simple Table Constraint:
1. This function will verify all the fixed type values match what is defined in the table constraint object set. If an
element value does not exist in the table (i.e. the information object set) and the object set is not extensible, then
a table constraint violation exception will be thrown.
General Procedure for Table Constraint Encoding
The general procedure to encode an ASN.1 message with table constraints is the same as without table constraints.
The only difference is in the open type data population procedure.
The -table-unions option will cause union structure to be generated for open type field containing relationsal table
constraints. These are populated for encoding in much the same way CHOICE onstructs are handled.
The -tables option will cause ASN1TObject fields to be inserted in the generated code instead of Asn1OpenType
declarations.
The procedure to populate the value for an ASN1TObject item is as follows:
1. Check the ASN.1 specification or generated C code for the type of the type field value in the information object
set that corresponds to the selected key field value.
2. Create a variable of that type and assign a pointer to it to the Asn1Object.decoded member variable as void*.
3. Follow the common BER/PER/DER encode procedure.
A complete example showing how to assign an open type value in the legacy tables case is as follows:
Test DEFINITIONS ::= BEGIN
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Generated Encode/Decode Function and Methods
ATTRIBUTE ::= CLASS {
&Type,
&id
OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
WITH SYNTAX &Type ID &id }
name ATTRIBUTE ::= {
WITH SYNTAX
VisibleString
ID
{ 0 1 1 } }
name ATTRIBUTE ::= {
WITH SYNTAX
INTEGER
ID
{ 0 1 2 } }
SupportedAttributes ATTRIBUTE ::= { name | commonName }
Invoke ::= SEQUENCE {
opcode ATTRIBUTE.&id
({SupportedAttributes}),
argument ATTRIBUTE.&Type ({SupportedAttributes}{@opcode})
}
END
In the above example, the Invoke type contains a table constraint. Its element opcode refers to the ATTRIBUTE id
field and argument element refers to the ATTRIBUTE Type field. The opcode element is an index element for the
Invoke type’s table constraint. The argument element is an open type whose type is determined by the opcode value.
In this example, opcode is the key field.
The opcode element can have only two possible values: { 0 1 1 } or { 0 1 2 }. If the opcode value is { 0 1 1} then
argument will have a VisibleString value and if the opcode value is { 0 1 2 } then argument will have an INTEGER
value. Any other value of the opcode element will be violation of the Table Constraint.
If the SupportedAttributes information object set was extensible (indicated by a “,...” at the end of the definition), then
the argument element may have a value of a type that is not in the defined set. In this case, if the index element value
is outside the information object set, then the argument element will be assumed to be an Asn1OpenType. The Invoke
type encode function call will use the value from argument.encoded.data field (i.e. it will have to be pre-encoded
because the encode function will not be able to determine from the table constraint how to encode it).
A C++ program fragment that could be used to encode an instance of the Invoke type is as follows:
#include TestTable.h // include file generated by ASN1C
main ()
{
const OSOCTET* msgptr;
OSOCTET msgbuf[1024];
int msglen;
// step 1: construct ASN1C C++ generated class.
// this specifies a static encode message buffer
ASN1BEREncodeBuffer encodeBuffer (msgbuf, sizeof(msgbuf));
// step 2: populate msgData structure with data to be encoded
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Generated Encode/Decode Function and Methods
ASN1T_Invoke msgData;
ASN1C_Invoke invoke (encodeBuffer, msgData);
msgData.opcode.numids = 3;
msgData.opcode.subid[0] = 0;
msgData.opcode.subid[1] = 1;
msgData.opcode.subid[2] = 1;
ASN1VisibleString argument = “objsys”;
msgData.argument.decoded = (void*) &argument;
// note: opcode value is {0 1 1 }, so argument must be
// ASN1VisibleString type
// step 3: invoke Encode method
if ((msglen = invoke.Encode ()) > 0) {
// encoding successful, get pointer to start of message
msgptr = encodeBuffer.getMsgPtr();
}
else
error processing...
}
The encoding procedure for C requires one extra step. This is a call to the module initialization functions after context
initialization is complete. All module initialization functions for all modules in the project must be invoked. The
module initialization function definitions can be found in the <ModuleName>Table.h file.
The format of each module initialization function name is as follows:
void <ModuleName>_init (OSCTXT* pctxt)
Here ModuleName would be replaced with name of the module.
A C program fragment that could be used to encode the Invoke record defined above is as follows:
#include TestTable.h
/* include file generated by ASN1C */
int main ()
{
OSOCTET msgbuf[1024], *msgptr;
int
msglen;
OSCTXT ctxt;
Invoke invoke; /* typedef generated by ASN1C */
/* Step 1: Initialize the context and set the buffer pointer */
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
xe_setp (&ctxt, msgbuf, sizeof(msgbuf));
/* step 2: call module initialization functions */
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Generated Encode/Decode Function and Methods
Test_init (&ctxt);
/* Step 3: Populate the structure to be encoded */
msgData.opcode.numids = 3;
msgData.opcode.subid[0] = 0;
msgData.opcode.subid[1] = 1;
msgData.opcode.subid[2] = 1;
//note: opcode value is {0 1 1 }, so argument must be
//ASN1VisibleString type
ASN1VisibleString argument = “objsys”;
msgData.argument.decoded = (void*) &argument;
...
/* Step 4: Call the generated encode function */
msglen = asn1E_Invoke (&ctxt, &invoke, ASN1EXPL);
/* Step 5: Check the return status (note: the test is */
/* > 0 because the returned value is the length of the */
/* encoded message component)..*/
if (msglen > 0) {
/* Step 6: If encoding is successful, call xe_getp to */
/* fetch a pointer to the start of the encoded message.*/
msgptr = xe_getp (&ctxt);
...
}
else
error processing...
}
General Procedure for Table Constraint Decoding
The general procedure to decode an ASN.1 message with table constraints is the same as without table constraints. The
only difference will exist in the decoded data for open type fields within the message. In this case, the Asn1Object /
Asn1TObject’s decoded member variable will contain the original decoded type and the encoded member variable will
contain the original data in encoded form.
Refer to the BER/DER/PER decoding procedure for further information.
The procedure to retrieve the value for open type fields is as follow:
1. Check the possible Type in the Information Object Set from index element value.
2. Assign or cast the Asn1Object.decoded member variable ( void* ) to the result type.
3. The Asn1Object.encoded field will hold the data in encoded form.
For the above complete example, the Invoke type’s argument element will be decoded as one of the types in the
SupportedAttributes information object set (i.e. either as a VisibleString or INTEGER type). If the SupportedAttributes
information object set is extensible, then the argument element may be of a type not defined in the set. In this case, the
decoder will set the Asn1Object.encoded field as before but the Asn1Object.decoded field will be NULL indicating
the value is of an unknown type.
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Generated Encode/Decode Function and Methods
A C++ program fragment that could be used to decode the Invoke example is as follows:
#include Test.h //
include file generated by ASN1C
main ()
{
OSOCTET msgbuf[1024];
ASN1TAG msgtag;
int msglen, status;
/* step 1: logic to read message into msgbuf */
...
/* step 2: create decode buffer and msg data type */
ASN1BERDecodeBuffer decodeBuffer (msgbuf, len);
ASN1T_Invoke msgData;
ASN1C_Invoke invoke (decodeBuffer, msgData);
/* step 3: call decode function */
if ((status = invoke.Decode ()) == 0)
{
// decoding successful, data in msgData
// use key field value to set type of message data
ASN1OBJID oid1[] = { 3, { 0, 1, 1 }};
ASN1OBJID oid2[] = { 3, { 0, 1, 2 }};
if (msgData.opcode == oid1) {
// argument is a VisibleString
ASN1VisibleString* pArg =
(ASN1VisibleString*) msgData.argument.decoded;
...
}
else if (msgData.opcode == oid2) {
// argument is an INTEGER
OSINT32 arg = (OSINT32) *msgData.argument.decoded;
...
}
}
else {
// error processing
}
In this case, the type of the decoded argument can be determined by testing the key field value. In the example as shown,
the SupportedAttributes information object set is not extensible, therefore, the type of the argument must be one of the
two shown. If the set were extensible (indicated by a “,...” in the definition), then it is possible that an unknown opcode
could be received which would mean the type can not be determined. In this case, the original encoded message data
would be present in msgData.argument.encoded field and it would be up to the user to determine how to process it.
The decoding procedure for C requires one additional step. This is a call to the module initialization functions after
context initialization is complete. All module initialization functions for all modules in the project must be invoked.
The module initialization function definitions can be found in the <ModuleName>Table.h file.
A C program fragment that could be used to decode the Invoke example is as follows:
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Generated Encode/Decode Function and Methods
#include TestTable.h
// include file generated by ASN1C
main ()
{
OSOCTET msgbuf[1024];
ASN1TAG
msgtag;
int
msglen;
OSCTXT
ctxt;
Invoke
invoke;
ASN1OBJID oid1[] = { 3, { 0, 1, 1 }};
ASN1OBJID oid2[] = { 3, { 0, 1, 2 }};
.. logic to read message into msgbuf ..
/* Step 1: Initialize a context variable for decoding */
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
xd_setp (&ctxt, msgbuf, 0, &msgtag, &msglen);
/* step 2: call module initialization functions */
Test_init (&ctxt);
/* Step 3: Call decode function */
status = asn1D_Invoke (&ctxt, &invoke, ASN1EXPL, 0);
/* Step 4: Check return status */
if (status == 0)
{
/* process received data in ‘invoke’ variable */
if (rtCmpTCOID (&invoke.opcode, &oid1) == 0) {
/* argument is a VisibleString */
ASN1VisibleString* pArg =
(ASN1VisibleString*) msgData.argument.decoded;
...
}
else if (rtCmpTCOID (&invoke.opcode, &oid2) == 0) {
/* argument is an INTEGER */
OSINT32 arg = (OSINT32) *msgData.argument.decoded;
...
}
/* Remember to release dynamic memory when done! */
ASN1MEMFREE (&ctxt);
}
else
error processing...
148
Generated Encode/Decode Function and Methods
}
}
General Procedures for Encoding and
Decoding
Encoding functions and methods generated by the ASN1C compiler are designed to be similar in use across the different
encoding rule types. In other words, if you have written an application to use the Basic Encoding Rules (BER) and
then later decide to use the Packed Encoding Rules (PER), it should only be a simple matter of changing a few function
calls to accomplish the change. Procedures for such things as populating data for encoding, accessing decoded data,
and dynamic memory management are the same for all of the different encoding rules.
This section describes common procedures for encoding or decoding data that are applicable to any of the different
encoding rules. Subsequent sections will then describe what will change for the different rules.
Dynamic Memory Management
The ASN1C run-time uses specialized dynamic memory functions to improve the performance of the encoder/decoder.
It is imperative to understand how these functions work in order to avoid memory problems in compiled applications.
ASN1C also provides the capability to plug-in a different memory management scheme at two different levels: the high
level API called by the generated code and the low level API that provides the core memory managment functionality.
The ASN1C Default Memory Manager
The default ASN1C run-time memory manager uses an algorithm called the nibble-allocation algorithm. Large blocks
of memory are allocated up front and then split up to provide memory for smaller allocation requests. This reduces
the number of calls required to the C malloc and free functions. These functions are very expensive in terms of
performance.
The large blocks of memory are tracked through the ASN.1 context block (OSCTXT) structure. For C, this means that
an initialized context block is required for all memory allocations and deallocations. All allocations are done using this
block as an argument to routines such as rtxMemAlloc. All memory can be released at once when a user is done with
a structure containing dynamic memory items by calling rtxMemFree. Other functions are available for doing other
dynamic memory operations as well. See the C/C++ Run-time Reference Manual for details on these.
High Level Memory Management API
The high-level memory management API consists of C macros and functions called in gemerated code and/or in
application programs to allocate and free memory within the ASN1C run-time.
At the top level are a set of macro definitions that begin with the prefix rtxMem. These are mapped to a set of similar
functions that begin with the prefix rtxMemHeap. A table showing this basic mapping is as follows:
Macro
Function
Description
rtxMemAlloc
rtxMemHeapAlloc
Allocate memory
rtxMemAllocZ
rtxMemHeapAllocZ
Allocate and zero memory
rtxMemRealloc
rtxMemHeapRealloc
Reallocate memory
rtxMemFree
rtxMemHeapFreeAll
Free all memory in context
rtxMemFreePtr
rtxMemHeapFreePtr
Free a specific memory block
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Generated Encode/Decode Function and Methods
See the ASN1C C/C++ Common Runtime Reference Manual for further details on these functions and macros.
It is possible to replace the high-level memory allocation functions with functions that implement a custom memory
management scheme. This is done by implementing some (or all) of the C rtxMemHeap functions defined in the
following interface (note: a default implementation is shown that replaces the ASN1C memory manager with direct
calls to the standard C run-time memory management functions):
#include <stdlib.h>
#include "rtxMemory.h"
/* Create a memory heap */
int rtxMemHeapCreate (void** ppvMemHeap) {
return 0;
}
/* Allocate memory */
void* rtxMemHeapAlloc (void** ppvMemHeap, int nbytes) {
return malloc (nbytes);
}
/* Allocate and zero memory */
void* rtxMemHeapAllocZ (void** ppvMemHeap, int nbytes) {
void* ptr = malloc (nbytes);
if (0 != ptr) memset (ptr, 0, nbytes);
return ptr;
}
/* Free memory pointer */
void rtxMemHeapFreePtr (void** ppvMemHeap, void* mem_p) {
free (mem_p);
}
/* Reallocate memory */
void* rtxMemHeapRealloc (void** ppvMemHeap, void* mem_p, int nbytes_) {
return realloc (mem_p, nbytes_);
}
/* Clears heap memory (frees all memory, reset all heap's variables) */
void rtxMemHeapFreeAll (void** ppvMemHeap) {
/* should remove all allocated memory. there is no analog in standard memory
management. */
}
/* Frees all memory and heap structure as well (if was allocated) */
void rtxMemHeapRelease (void** ppvMemHeap) {
/* should free all memory allocated + free memory heap object if exists */
}
In most cases it is only necessary to implement the following functions: rtxMemHeapAlloc, rtxMemHeapAllocZ,
rtxMemHeapFreePtr and rtxMemHeapRealloc. Note that there is no analog in standard memory management for
ASN1C’s rtxMemFree macro (i.e. the rtxMemHeapFreeAll function). A user would be responsible for freeing all items
in a generated ASN1C structure individually if standard memory management is used.
The rtxMemHeapCreate and rtxMemHeapRelease functions are specialized functions used when a special heap is to
be used for allocation (for example, a static block within an embedded system). In this case, rtxMemHeapCreate must
150
Generated Encode/Decode Function and Methods
set the ppvMemHeap argument to point at the block of memory to be used. This will then be passed in to all of the
other memory management functions for their use through the OSCTXT structure. The rtxMemHeapRelease function
can then be used to dispose of this memory when it is no longer needed.
To add these definitions to an application program, compile the C source file (it can have any name) and link the
resulting object file (.OBJ or .O) in with the application.
Built-in Compact Memory Management
A built-in version of the simple memory management API described above (i.e with direct calls to malloc, free, etc.)
is available for users who have the source code version of the run-time. The only difference in this API with what is
described above is that tracking of allocated memory is done through the context. This makes it possible to provide an
implementation of the rtxMemHeapFreeAll function as described above. This memory management scheme is slower
than the default manager (i.e. nibble-based), but has a smaller code footprint.
This form of memory management is enabled by defining the _MEMCOMPACT C compile time setting. This can
be done by either adding -D_MEMCOMPACT to the C compiler command-line arguments, or by uncommenting this
item at the beginning of the rtxMemory.h header file:
/*
* Uncomment this definition before building the C or C++ run-time
* libraries to enable compact memory management. This will have a
* smaller code footprint than the standard memory management; however,
* the performance may not be as good.
*/
/*#define _MEMCOMPACT*/
Low Level Memory Management API
It is possible to replace the core memory management functions used by the ASN1C run-time memory manager. This
has the advantage of preserving the existing management scheme but with the use of different core functions. Using
different core functions may be necessary on some systems that do not have the standard C run-time functions malloc,
free, and realloc, or when extra functionality is desired.
To replace the core functions, the following run-time library function would be used:
void rtxMemSetAllocFuncs (OSMallocFunc malloc_func,
OSReallocFunc realloc_func, OSFreeFunc free_func);
The malloc, realloc, and free functions must have the same prototype as the standard C functions. Some systems do not
have a realloc-like function. In this case, realloc_func may be set to NULL. This will cause the malloc_func/free_func
pair to be used to do reallocations.
This function must be called before the context initialization function (rtInitContext) because context initialization
requires low level memory management facilities be in place in order to do its work.
Note that this function makes use of static global memory to hold the function definitions. This type of memory is not
available in all run-time environments (most notably Symbian). In this case, an alternative function is provided for
setting the memory functions. This function is rtxInitContextExt which must be called in place of the standard context
initialization function (rtInitContext). In this case, there is a bit more work required to initialize a context because the
ASN.1 subcontext must be manually initialized. This is an example of the code required to do this:
int stat = rtxInitContextExt (pctxt, malloc_func, realloc_func, free_func);
if (0 == stat) {
/* Add ASN.1 error codes to global table */
rtErrASN1Init ();
151
Generated Encode/Decode Function and Methods
/* Init ASN.1 info block */
stat = rtCtxtInitASN1Info (pctxt);
}
Memory management can also be tuned by setting the default memory heap block size. The way memory management
works is that a large block of memory is allocated up front on the first memory management call. This block is then
subdivided on subsequent calls until the memory is used up. A new block is then started. The default value is 4K
(4096) bytes. The value can be set lower for space constrained systems and higher to improve performance in systems
that have sufficient memory resources. To set the block size, the following run-time function should be used:
void rtxMemSetDefBlkSize (OSUINT32 blkSize);
This function must be called prior to context initialization.
C++ Memory Management
In the case of C++, the ownership of memory is handled by the control class and message buffer objects. These classes
share a context structure and use reference counting to manage the allocation and release of the context block. When
a message buffer object is created, a context block structure is created as well. When this object is then passed into
a control class constructor, its reference count is incremented. Then when either the control class object or message
buffer object are deleted or go out of scope, the count is decremented. When the count goes to zero (i.e. when both the
message buffer object and control class object go away) the context structure is released.
What this means to the user is that a control class or message buffer object must be kept in scope when using a data
structure associated with that class. A common mistake is to try and pass a data variable out of a method and use it
after the control and message buffer objects go out of scope. For example, consider the following code fragment:
ASN1T_<type>* func2 () {
ASN1T_<type>* p = new ASN1T_<type> ();
ASN1BERDecodeBuffer decbuf;
ASN1C_<type> cc (decbuf, *p);
cc.Decode();
// After return, cc and decbuf go out of scope; therefore
// all memory allocated within struct p is released..
return p;
}
void func1 () {
ASN1T_<type>* pType = func2 ();
// pType is not usable at this point because dynamic memory
// has been released..
}
As can be seen from this example, once func2 exits, all memory that was allocated by the decode function will be
released. Therefore, any items that require dynamic memory within the data variable will be in an undefined state.
An exception to this rule occurs when the type of the message being decoded is a Protocol Data Unit (PDU). These
are the main message types in a specification. The ASN1C compiler designates types that are not referenced by any
other types as PDU types. This behavior can be overridden by using the -pdu command line argument or <isPDU>
configuration file element.
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Generated Encode/Decode Function and Methods
The significance of PDU types is that generated classes for these types are derived from the ASN1TPDU base class.
This class holds a reference to a context object. The context object is set by Decode and copy methods. Thus, even
if control class and message buffer objects go out of scope, the memory will not be freed until the destructor of an
ASN1TPDU inherited class is called. The example above will work correctly without any modifications in this case.
Another way to keep data is to make a copy of the decoded object before it goes out of scope. A method called newCopy
is also generated in the control class for these types which can be used to create a copy of the decoded object. This
copy of the object will persist after the control class and message buffer objects are deleted. The returned object can
be deleted using the standard C++ delete operator when it is no longer needed.
Returning to the example above, it can be made to work if the type being decoded is a PDU type by doing the following:
ASN1T_<type>* func2 () {
ASN1T_<type> msgdata;
ASN1BERDecodeBuffer decbuf;
ASN1C_<type> cc (decbuf, msgdata);
cc.Decode();
// Use newCopy to return a copy of the decoded item..
return cc.newCopy();
}
Populating Generated Structure Variables for Encoding
Prior to calling a compiler generated encode function, a variable of the type generated by the compiler must be
populated. This is normally a straightforward procedure – just plug in the values to be encoded into the defined fields.
However, things get more complicated when more complex, constructed structures are involved. These structures
frequently contain pointer types which means memory management issues must be dealt with.
There are three alternatives for managing memory for these types:
1. Allocate the variables on the stack and plug the address of the variables into the pointer fields,
2. Use the standard malloc and free C functions or new and delete C++ operators to allocate memory to hold the
data, and
3. Use the rxtMemAlloc and rtxMemFree run-time library functions or their associated macros.
Allocating the variables on the stack is an easy way to get temporary memory and have it released when it is no longer
being used. But one has to be careful when using additional functions to populate these types of variables. A common
mistake is the storage of the addresses of automatic variables in the pointer fields of a passed-in structure. An example
of this error is as follows (assume A, B, and C are other structured types):
typedef struct {
A* a;
B* b;
C* c;
} Parent;
void fillParent (Parent* parent)
{
A aa;
B bb;
153
Generated Encode/Decode Function and Methods
C cc;
/* logic to populate aa, bb, and cc */
...
parent->a = &aa;
parent->b = &bb;
parent->c = &cc;
}
main ()
{
Parent parent;
fillParent (&parent);
encodeParent (&parent); /* error! pointers in parent
reference memory that is
out of scope */
...
}
In this example, the automatic variables aa, bb, and cc go out of scope when the fillParent function exits. Yet the
parent structure is still holding pointers to the now out of scope variables (this type of error is commonly known as
“dangling pointers”).
Using the second technique (i.e., using C malloc and free) can solve this problem. In this case, the memory for each
of the elements can be safely freed after the encode function is called. But the downside is that a free call must be
made for each corresponding malloc call. For complex structures, remembering to do this can be difficult thus leading
to problems with memory leaks.
The third technique uses the compiler run-time library memory management functions to allocate and free the memory.
The main advantage of this technique as opposed to using C malloc and free is that all allocated memory can be freed
with a single rtxMemFree call. The rtxMemAlloc macro can be used to allocate memory in much the same way as
the C malloc function with the only difference being that a pointer to an initialized OSCTXT structure is passed in
addition to the number of bytes to allocate. All allocated memory is tracked within the context structure so that when
the rtxMemFree function is called, all memory is released at once.
Accessing Encoded Message Components
After a message has been encoded, the user must obtain the start address and length of the message in order to do
further operations with it. Before a message can be encoded, the user must describe the buffer the message is to be
encoded into by specifying a message buffer start address and size. There are three different types of message buffers
that can be described:
1. static: this is a fixed-size byte array into which the message is encoded
2. dynamic: in this case, the encoder manages the allocation of memory to hold the encoded message
3. stream: in this case, the encoder writes the encoded data directly to an output stream
The static buffer case is generally the better performing case because no dynamic memory allocations are required.
However, the user must know in advance the amount of memory that will be required to hold an encoded message.
There is no fixed formula to determine this number. ASN.1 encoding involves the possible additions of tags and lengths
and other decorations to the provided data that will increase the size beyond the initial size of the populated data
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Generated Encode/Decode Function and Methods
structures. The way to find out is either by trial-and-error (an error will be signaled if the provided buffer is not large
enough) or by using a very large buffer in comparison to the size of the data.
In the dynamic case, the buffer description passed into the encoder is a null buffer pointer and zero size. This tells
the encoder that it is to allocate memory for the message. It does this by allocating an initial amount of memory and
when this is used up, it expands the buffer by reallocating. This can be an expensive operation in terms of performance
– especially if a large number of reallocations are required. For this reason, run-time helper functions are provided
that allow the user to control the size increment of buffer expansions. See the C/C++ Run-Time Library Reference
Manual for a description of these functions.
In either case, after a message is encoded, it is necessary to get the start address and length of the message. Even in the
static buffer case, the message start address may be different then the buffer start address (see the section on encoding
BER messages). For this reason, each set of encoding rules has a run-time C function for getting the message start
address and length. See the C/C++ Run-Time Library Reference Manual for a description of these functions. The C+
+ message buffer classes contain the getMsgPtr, getMsgCopy , and getMsgLength methods for this purpose.
A stream message buffer can be used for BER encoding. This type of buffer is used when the -stream option was used
to generate the encode functions. See the section on BER stream encoding for a complete description on how to set
up an output stream to receive encoded data.
155
Chapter 7. Generated BER Functions
Generated BER Encode Functions
Note
This section assumes standard memory-buffer based encoding is to be done. If stream-based encoding is to be
done (specified by adding -stream to the ASN1C command-line), see the Generated BER Streaming Encode
Functions section for correct procedures on using the stream-based encode functions.
For each ASN.1 production defined in the ASN.1 source file, a C encode function is generated. This function will
convert a populated C variable of the given type into an encoded ASN.1 message.
If C++ code generation is specified, a control class is generated that contains an Encode method that wraps this function.
This function is invoked through the class interface to convert a populated msgData attribute variable into an encoded
ASN.1 message.
Generated C Function Format and Calling Parameters
The format of the name of each generated encode function is as follows:
asn1E_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each encode function is as follows:
len = asn1E_<name> (OSCTXT* pctxt,
<name>* pvalue,
ASN1TagType tagging);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program. The variable
should be initialized using the rtInitContext run-time library function (see the C/C++ Common Run-Time Library
Reference Manual for a complete description of this function).
The pvalue argument holds a pointer to the data to be encoded and is of the type generated from the ASN.1
production.
The tagging argument is for internal use when calls to encode functions are nested to accomplish encoding of
complex variables. It indicates whether the tag associated with the production should be applied or not (implicit versus
explicit tagging). At the top level, the tag should always be applied so this parameter should always be set to the
constant ASN1EXPL (for EXPLICIT).
The function result variable len returns the length of the data actually encoded or an error status code if encoding
fails. Error status codes are negative to tell them apart from length values. Return status values are defined in the
asn1type.h include file.
156
Generated BER Functions
Procedure for Calling C Encode Functions
This section describes the step-by-step procedure for calling a C BER or DER encode function. This method must be
used if C code generation was done. This method can also be used as an alternative to using the control class interface
if C++ code generation was done. Note that the procedures described here cannot be used if stream-based encoding is
to be done (specified by the use of the -stream ASN1C command-line option). In this case, the procedures described
in the Generated BER Streaming Encode Functions section.
Before any encode function can be called; the user must first initialize an encoding context. This is a variable of type
OSCTXT. This variable holds all of the working data used during the encoding of a message. The context variable is
declared as a normal automatic variable within the top-level calling function. It must be initialized before use. This
can be accomplished by using the rtInitContext function as follows:
OSCTXT ctxt;
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
The next step is to specify an encode buffer into which the message will be encoded. This is accomplished by calling
the xe_setp run-time function. The user can either pass the address of a buffer and size allocated in his or her program
(referred to as a static buffer), or set these parameters to zero and let the encode function manage the buffer memory
allocation (referred to as a dynamic buffer). Better performance can normally be attained by using a static buffer
because this eliminates the high-overhead operation of allocating and reallocating memory.
After initializing the context and populating a variable of the structure to be encoded, an encode function can be
called to encode the message. If the return status indicates success (positive length value), the run-time library function
xe_getp can be called to obtain the start address of the encoded message. Note that the returned address is not the
start address of the target buffer. BER encoded messages are constructed from back to front (i.e., starting at the end
of the buffer and working backwards) so the start point will fall somewhere in the middle of the buffer after encoding
is complete. This is illustrated in the following diagram:
In this example, a 1K encode buffer is declared which happens to start at address 0x100. When the context is initialized
with a pointer to this buffer and size equal to 1K, it positions the internal encode pointer to the end of the buffer
(address 0x500). Encoding then proceeds from back-to-front until encoding of the message is complete. In this case,
the encoded message turned out to be 0x300 (768) bytes in length and the start address fell at 0x200. This is the value
that would be returned by the xe_getp function.
A program fragment that could be used to encode an employee record is as follows:
#include employee.h
int main ()
{
OSOCTET
/* include file generated by ASN1C */
msgbuf[1024], *msgptr;
157
Generated BER Functions
int
OSCTXT
Employee
msglen;
ctxt;
employee; /* typedef generated by ASN1C */
/* Step 1: Initialize the context and set the buffer pointer */
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
xe_setp (&ctxt, msgbuf, sizeof(msgbuf));
/* Step 2: Populate the structure to be encoded */
employee.name.givenName = "SMITH";
...
/* Step 3: Call the generated encode function */
msglen = asn1E_Employee (&ctxt, &employee, ASN1EXPL);
/* Step 4: Check the return status (note: the test is
* > 0 because the returned value is the length of the
* encoded message component).. */
if (msglen > 0) {
/* Step 5: If encoding is successful, call xe_getp to
* fetch a pointer to the start of the encoded message. */
msgptr = xe_getp (&ctxt);
...
}
else {
rtxErrPrint (&ctxt);
return msglen;
}
}
In general, static buffers should be used for encoding messages where possible as they offer a substantial performance
benefit over dynamic buffer allocation. The problem with static buffers, however, is that you are required to estimate
in advance the approximate size of the messages you will be encoding. There is no built-in formula to do this; the size
of an ASN.1 message can vary widely based on data types and the number of tags required.
If performance is not a significant issue, then dynamic buffer allocation is a good alternative. Setting the buffer pointer
argument to NULL in the call to xe_setp specifies dynamic allocation. This tells the encoding functions to allocate
a buffer dynamically. The address of the start of the message is obtained as before by calling xe_getp. Note that this
is not the start of the allocated memory; that is maintained within the context structure. To free the memory, either
the rtxMemFree function may be used to free all memory held by the context or the xe_free function used to free the
encode buffer only.
The following code fragment illustrates encoding using a dynamic buffer:
#include employee.h
/* include file generated by ASN1C */
158
Generated BER Functions
main ()
{
OSOCTET*
int
OSCTXT
Employee
msgptr;
msglen;
ctxt;
employee;
/* typedef generated by ASN1C */
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
xe_setp (&ctxt, NULL, 0);
employee.name.givenName = "SMITH";
...
msglen = asn1E_Employee (&ctxt, &employee, ASN1EXPL);
if (msglen > 0) {
msgptr = xe_getp (&ctxt);
...
rtxMemFree (&ctxt); /* don’t call free (msgptr); !!! */
}
else
error processing...
}
Encoding a Series of Messages Using the C Encode Functions
A common application of BER encoding is the repetitive encoding of a series of the same type of message over and
over again. For example, a TAP3 batch application might read billing data out of a database table and encode each
of the records for a batch transmission.
If a user was to repeatedly allocate/free memory and reinitialize the C objects involved in the encoding of a message,
performance would suffer. This is not necessary however, because the C objects and memory heap can be reused to
allow multiple messages to be encoded. As example showing how to do this is as follows:
#include employee.h
/* include file generated by ASN1C */
main ()
{
const OSOCTET* msgptr;
OSOCTET
msgbuf[1024];
int
msglen;
OSCTXT
ctxt;
PersonnelRecord data;
/* Init context structure */
if ((stat = rtInitContext (&ctxt)) != 0) {
159
Generated BER Functions
printf ("rtInitContext failed; stat = %d\n", stat);
return -1;
}
/* Encode loop starts here, this will repeatedly use the
* objects declared above to encode the messages */
for (;;) {
xe_setp (&ctxt, msgbuf, sizeof(msgbuf));
/* logic here to read record from some source (database,
* flat file, socket, etc.).. */
/* populate structure with data to be encoded */
data.name = “SMITH”;
...
/* call encode function */
if ((msglen = asn1E_PersonnelRecord (&ctxt, &data, ASN1EXPL)) > 0) {
/* encoding successful, get pointer to start of message */
msgptr = xe_getp (&ctxt);
/* do something with the encoded message */
...
}
else
error processing...
/* Call rtxMemReset to reset the memory heap for the next
* iteration. Note, all data allocated by rtxMemAlloc will
* become invalid after this call. */
rtxMemReset (&ctxt);
}
rtFreeContext (&ctxt);
}
The rtxMemReset call does not free memory; instead, it marks it as empty so that it may be reused in the next iteration.
Thus, all memory allocated by rtxMemAlloc will be overwritten and data will be lost.
Generated C++ Encode Method Format and Calling
Parameters
When C++ code generation is specified, the ASN1C compiler generates an Encode method in the generated control
class that wraps the C function call. This method provides a more simplified calling interface because it hides things
such as the context structure and the tag type parameters.
160
Generated BER Functions
The calling sequence for the generated C++ class method is as follows:
len = <object>.Encode ();
In this definition, <object> is an instance of the control class (i.e., ASN1C_<prodName>) generated for the given
production. The function result variable len returns the length of the data actually encoded or an error status code if
encoding fails. Error status codes are negative to tell them apart from length values. Return status values are defined
in the asn1type.h include file.
Procedure for Using the C++ Control Class Encode Method
The procedure to encode a message using the C++ class interface is as follows:
1. Create a variable of the ASN1T_<name> type and populate it with the data to be encoded.
2. Create an ASN1BEREncodeBuffer object.
3. Create a variable of the generated ASN1C_<name> class specifying the items created in 1 and 2 as arguments to
the constructor.
4. Invoke the Encode method.
The constructor of the ASN1C_<type> class takes a message buffer object argument. This makes it possible to specify
a static encode message buffer when the class variable is declared. A static buffer can improve encoding performance
greatly as it relieves the internal software from having to repeatedly resize the buffer to hold the encoded message. If
you know the general size of the messages you will be sending, or have a fixed size maximum message length, then
a static buffer should be used. The message buffer argument can also be used to specify the start address and length
of a received message to be decoded.
After the data to be encoded is set, the Encode method is called. This method returns the length of the encoded message
or a negative value indicating that an error occurred. The error codes can be found in the asn1type.h run-time header
file or in Appendix A of the C/C++ Common Functions Reference Manual.
If encoding is successful, a pointer to the encoded message can be obtained by using the getMsgPtr or getMsgCopy
methods available in the ASN1BEREncodeBuffer class. The getMsgPtr method is faster as it simply returns a pointer
to the actual start-of-message that is maintained within the message buffer object. The getMsgCopy method will return
a copy of the message. Memory for this copy will be allocated using the standard new operator, so it is up to the user
to free this memory using delete when finished with the copy.
A program fragment that could be used to encode an employee record is as follows. This example uses a static encode
buffer:
#include employee.h
// include file generated by ASN1C
main ()
{
const OSOCTET* msgptr;
OSOCTET msgbuf[1024];
int msglen;
// step 1: construct ASN1C C++ generated class.
// this specifies a static encode message buffer
ASN1BEREncodeBuffer encodeBuffer (msgbuf, sizeof(msgbuf));
161
Generated BER Functions
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (encodeBuffer, msgData);
// step 2: populate msgData structure with data to be encoded
msgData.name = “SMITH”;
...
// step 3: invoke Encode method
if ((msglen = employee.Encode ()) > 0) {
// encoding successful, get pointer to start of message
msgptr = encodeBuffer.getMsgPtr();
}
else
error processing...
}
The following code fragment illustrates encoding using a dynamic buffer. This also illustrates using the getMsgCopy
method to fetch a copy of the encoded message:
#include employee.h
main ()
{
OSOCTET*
int
// include file generated by ASN1C
msgptr;
msglen;
// construct encodeBuffer class with no arguments
ASN1BEREncodeBuffer encodeBuffer;
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (encodeBuffer, msgData);
// populate msgData structure
msgData.name = "SMITH";
...
// call Encode method
if ((msglen = employee.Encode ()) > 0) {
// encoding successful, get copy of message
msgptr = encodeBuffer.getMsgCopy();
...
delete [] msgptr; // free the dynamic memory!
}
else
error processing...
}
162
Generated BER Functions
Encoding a Series of Messages Using the C++ Control Class
Interface
A common application of BER encoding is the repetitive encoding of a series of the same type of message over and
over again. For example, a TAP3 batch application might read billing data out of a database table and encode each
of the records for a batch transmission.
If a user was to repeatedly instantiate and destroy the C++ objects involved in the encoding of a message, performance
would suffer. This is not necessary however, because the C++ objects can be reused to allow multiple messages to be
encoded. As example showing how to do this is as follows:
#include employee.h
// include file generated by ASN1C
main ()
{
const OSOCTET* msgptr;
OSOCTET msgbuf[1024];
int
msglen;
ASN1BEREncodeBuffer encodeBuffer (msgbuf, sizeof(msgbuf));
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (encodeBuffer, msgData);
// Encode loop starts here, this will repeatedly use the
// objects declared above to encode the messages
for (;;) {
// logic here to read record from some source (database,
// flat file, socket, etc.)..
// populate structure with data to sbe encoded
msgData.name = “SMITH”;
...
// invoke Encode method
if ((msglen = employee.Encode ()) > 0) {
// encoding successful, get pointer to start of message
smsgptr = encodeBuffer.getMsgPtr();
// do something with the encoded message
...
}
else
error processing...
// Call the init method on the encodeBuffer object to
// prepare the buffer for encoding another message..
163
Generated BER Functions
encodeBuffer.init();
}
}
Generated BER Streaming Encode Functions
BER messages can be encoded directly to an output stream such as a file, network or memory stream. The ASN1C
compiler has the -stream option to generate encode functions of this type. For each ASN.1 production defined in the
ASN.1 source file, a C stream encode function is generated. This function will encode a populated C variable of the
given type into an encoded ASN.1 message and write it to a stream.
If the return status indicates success (0), the message will have been encoded to the given stream. Streaming BER
encoding starts from the beginning of the message until the message is complete. This is sometimes referred to as
“forward encoding”. This differs from regular BER where encoding is done from back-to-front. Indefinite lengths are
used for all constructed elements in the message. Also, there is no permanent buffer for streaming encoding, all octets
are written to the stream. The buffer in the context structure is used only as a cache.
If C++ code generation is specified, a control class is generated that contains an EncodeTo method that wraps the
stream encode C function. This function is invoked through the class interface to convert a populated msgData attribute
variable into an encoded ASN.1 message.
Generated Streaming C Function Format and Calling
Parameters
The format of the name of each generated streaming encode function is as follows:
asn1BSE_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each encode function is as follows:
stat = asn1BSE_<name> (OSCTXT* pctxt,
<name>* pvalue,
ASN1TagType tagging);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application.
The user is required to supply a pointer to a variable of this type declared somewhere in his or her program. This
variable must be initialized using both the rtInitContext and rtStreamBufInit run-time library functions (see the C/C+
+ Common Run-Time Library Reference Manual for a description of these functions).
The pvalue argument holds a pointer to the data to be encoded and is of the type generated from the ASN.1
production.
The tagging argument is for internal use when calls to encode functions are nested to accomplish encoding of
complex variables. It indicates whether the tag associated with the production should be applied or not (implicit versus
explicit tagging). At the top level, the tag should always be applied so this parameter should always be set to the
constant ASN1EXPL (for EXPLICIT).
The function result variable stat returns the completion status of the operation. 0 (0) means the success.
164
Generated BER Functions
Procedure for Calling Streaming C Encode Functions
This section describes the step-by-step procedure for calling a streaming C BER encode function. This method must be
used if C code generation was done. This method can also be used as an alternative to using the control class interface
if C++ code generation was done.
Before any encode function can be called; the user must first initialize an encoding context. This is a variable of type
OSCTXT. This variable holds all of the working data used during the encoding of a message. The context variable
is within the top-level calling function. It must be initialized before use. This can be accomplished by using the
berStrmInitContext function:
OSCTXT ctxt;
if (berStrmInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
The next step is to create a stream object within the context. This object is an abstraction of the output device to which
the data is to be encoded and is initialized by calling one of the following functions:
• rtxStreamFileOpen
• rtxStreamFileAttach
• rtxStreamSocketAttach
• rtxStreamMemoryCreate
• rtxStreamMemoryAttach
The flags parameter of these functions should be set to the OSRTSTRMF_OUTPUT constant value to indicate an
output stream is being created (see the C/C++ Common Run-Time Library Reference Manual for a full description
of these functions).
It is also possible to use a simplified form of these function calls to create a writer interface to a file, memory, or
socket stream:
• rtxStreamFileCreateWriter
• rtxStreamMemoryCreateWriter
• rtxStreamSocketCreateWriter
After initializing the context and populating a variable of the structure to be encoded, an encode function can be called
to encode the message to the stream. The stream must then be closed by calling the rtxStreamClose function.
A program fragment that could be used to encode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
int main ()
{
int
stat;
OSCTXT
ctxt;
Employee employee;/* typedef generated by ASN1C */
const char* filename = “message.dat”;
165
Generated BER Functions
/* Step 1: Initialize the context and stream */
if (berStrmInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
/* Step 2: create a file stream object within the context */
stat = rtxStreamFileCreateWriter (&ctxt, filename);
if (stat != 0) {
rtxErrPrint (&ctxt);
return stat;
}
/* Step 3: Populate the structure to be encoded */
employee.name = "SMITH";
...
/* Step 4: Call the generated encode function */
stat = asn1BSE_Employee (&ctxt, &employee, ASN1EXPL);
/* Step 5: Check the return status and close the stream */
if (stat != 0) {
...error processing...
}
rtxStreamClose (&ctxt);
}
In general, streaming encoding is slower than memory buffer based encoding. However, in the case of streaming
encoding, it is not necessary to implement code to write or send the encoded data to an output device. The streaming
functions also use less memory because there is no need for a large destination memory buffer. For this reason, the
final performance of the streaming functions may be the same or better than buffer-oriented functions.
Encoding a Series of Messages Using the Streaming C Encode
Functions
A common application of BER encoding is the repetitive encoding of a series of the same type of message over and
over again. For example, a TAP3 batch application might read billing data out of a database table and encode each
of the records for a batch transmission.
Encoding a series of messages using the streaming C encode functions is very similar to encoding of one message. All
that is necessary is to set up a loop in which the asn1BSE_<name> functions will be called. It is also possible to call
different asn1BSE_<name> functions one after another. An example showing how to do this is as follows:
#include employee.h
// include file generated by ASN1C
166
Generated BER Functions
int main ()
{
int
stat;
OSCTXT
ctxt;
Employee employee;/* typedef generated by ASN1C */
const char* filename = “message.dat”;
/* Step 1: Initialize the context and stream */
if (berStrmInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
stat = rtxStreamFileCreateWriter (&ctxt, filename);
if (stat != 0) {
rtxErrPrint (&ctxt);
return stat;
}
for (;;) {
/* Step 2: Populate the structure to be encoded */
employee.name = "SMITH";
...
/* Step 3: Call the generated encode function */
stat = asn1BSE_Employee (&ctxt, &employee, ASN1EXPL);
/* Step 4: Check the return status and break the loop
if error occurs */
if (stat != 0) {
...error processing...
break;
}
}
/* Step 5: Close the stream */
rtxStreamClose (&ctxt);
}
Generated Streaming C++ Encode Method Format and
Calling Parameters
C++ code generation of stream-based encoders is selected by using the –c++ and –stream compiler command line
options. In this case, ASN1C generates an EncodeTo method that wraps the C function call. This method provides a
more simplified calling interface because it hides things such as the context structure and tag type parameters.
167
Generated BER Functions
The calling sequence for the generated C++ class method is as follows:
stat = <object>.EncodeTo (<outputStream>);
In this definition, <object> is an instance of the control class (i.e., ASN1C_<prodName>) generated for the given
production.
The <outputStream> placeholder represents an output stream object type. This is an object derived from an
ASN1EncodeStream class.
The function result variable stat returns the completion status. Error status codes are negative. Return status values
are defined in the rtxErrCodes.h include file.
Another way to encode a message using the C++ classes is to use the << streaming operator:
<outputStream> << <object>;
Exceptions are not used in ASN1C C++, therefore, the user must fetch the status value following a call such as this in
order to determine if it was successful. The getStatus method in the ASN1EncodeStream class is used for this purpose.
Also, the method Encode without parameters is supported for backward compatibility. In this case it is necessary to
create control class (i.e., ASN1C_<prodName>) using an output stream reference as the first parameter and msgdata
reference as the second parameter of the constructor.
Procedure for Using the Streaming C++ Control Class Encode
Method
The procedure to encode a message directly to an output stream using the C++ class interface is as follows:
1. Create an OSRTOutputStream object for the type of output stream. Choices are OSRTFileOutputStream for a file,
OSRTMemoryOutputStream for a memory buffer, or OSRTSocketOutputStream for an IP socket connection.
2. Create an ASN1BEREncodeStream object using the stream object created in 1) as an argument.
3. Create a variable of the ASN1T_<name> type and populate it with the data to be encoded.
4. Create a variable of the generated ASN1C_<name> class specifying the item created in 2 as an argument to the
constructor.
5. Invoke the EncodeTo method or << operator.
A program fragment that could be used to encode an employee record is as follows. This example uses a file output
stream:
#include employee.h
// include file generated by ASN1C
#include "rtbersrc/ASN1BEREncodeStream.h"
#include "rtxsrc/OSRTFileOutputStream.h"
main ()
{
int msglen;
const char* filename = “message.dat”
// step 1: construct output stream object.
168
Generated BER Functions
ASN1BEREncodeStream out (new OSRTFileOutputStream (filename));
if (out.getStatus () != 0) {
out.printErrorInfo ();
return -1;
}
// step 2: construct ASN1C C++ generated class.
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (msgData);
// step 3: populate msgData structure with data to be
// encoded. (note: this uses the generated assignment
// operator to assign a string).
msgData.name = “SMITH”;
...
// step 4: invoke << operator or EncodeTo method
out << employee;
// or employee.EncodeTo (out); can be used here.
// step 5: check status of the operation
if (out.getStatus () != 0) {
printf ("Encoding failed. Status = %i\n", out.getStatus());
out.printErrorInfo ();
return -1;
}
if (trace) {
printf ("Encoding was successful\n");
}
}
Encoding a Series of Messages Using the Streaming C++ Control
Class Interface
Encoding a series of messages using the streaming C++ control class is similar to the C method of encoding. All that
is necessary is to create a loop in which EncodeTo or Encode methods will be called (or the overloaded << streaming
operator). It is also possible to call different EncodeTo methods (or Encode or operator <<) one after another. An
example showing how to do this is as follows:
#include employee.h
// include file generated by ASN1C
#include "rtbersrc/ASN1BEREncodeStream.h"
#include "rtxsrc/OSRTFileOutputStream.h"
int main ()
{
const
OSOCTET* msgptr;
OSOCTET msgbuf[1024];
int
msglen;
const
char* filename = “message.dat”
169
Generated BER Functions
// step 1: construct stream object.
ASN1BEREncodeStream out (new OSRTFileOutputStream (filename));
if (out.getStatus () != 0) {
out.printErrorInfo ();
return -1;
}
// step 2: construct ASN1C C++ generated class.
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (msgData);
for (;;) {
// step 3: populate msgData structure with data to be
// encoded. (note: this uses the generated assignment
// operator to assign a string).
msgData.name = “SMITH”;
...
// step 4: invoke << operator or EncodeTo method
out << employee;
// or employee.EncodeTo (out); can be used here.
// step 5: fetch and check status
if (out.getStatus () != 0) {
printf ("Encoding failed. Status = %i\n", out.getStatus());
out.printErrorInfo ();
return -1;
}
if (trace) {
printf ("Encoding was successful\n");
}
}
}
Generated BER Decode Functions
NOTE: This section assumes standard memory-buffer based decoding is to be done. If stream-based decoding is to
be done (specified by adding -stream to the ASN1C command-line), see the Generated BER Streaming Decode
Functions section for correct procedures on using the stream-based functions.
For each ASN.1 production defined in an ASN.1 source file, a C decode function is generated. This function will
decode an ASN.1 message into a C variable of the given type.
If C++ code generation is specified, a control class is generated that contains a Decode method that wraps this function.
This function is invoked through the class interface to decode an ASN.1 message into the variable referenced in the
msgData component of the class.
170
Generated BER Functions
Generated C Function Format and Calling Parameters
The format of the name of each decode function generated is as follows:
asn1D_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each decode function is as follows:
status = asn1D_<name> (OSCTXT* pctxt,
<name> *pvalue,
ASN1TagType tagging,
int length);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of decode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program. The variable
must be initialized using the rtInitContext run-time function before use.
The pvalue argument is a pointer to a variable of the generated type that will receive the decoded data.
The tagging and length arguments are for internal use when calls to decode functions are nested to accomplish
decoding of complex variables. At the top level, these parameters should always be set to the constants ASN1EXPL
and zero respectively.
The function result variable status returns the status of the decode operation. The return status will be zero if
decoding is successful or negative if an error occurs. Return status values are defined in the "asn1type.h" include file.
Procedure for Calling C Decode Functions
This section describes the step-by-step procedure for calling a C BER or DER decode function. This method must be
used if C code generation was done. This method can also be used as an alternative to using the control class interface
if C++ code generation was done.
Before any decode function can be called; the user must first initialize a context variable. This is a variable of type
OSCTXT. This variable holds all of the working data used during the decoding of a message. The context variable
is declared as a normal automatic variable within the top-level calling function. It must be initialized before use.
This can be accomplished as follows:
OSCTXT ctxt;
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
The next step is the specification of a buffer containing a message to be decoded. This is accomplished by calling the
xd_setp run-time library function. This function takes as an argument the start address of the message to be decoded.
171
Generated BER Functions
The function returns the starting tag value and overall length of the message. This makes it possible to identify the
type of message received and apply the appropriate decode function to decode it.
A decode function can then be called to decode the message. If the return status indicates success, the C variable
that was passed as an argument will contain the decoded message contents. Note that the decoder may have allocated
dynamic memory and stored pointers to objects in the C structure. After processing on the C structure is complete, the
run-time library function rtxMemFree should be called to free the allocated memory.
A program fragment that could be used to decode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
main ()
{
OSOCTET
msgbuf[1024];
ASN1TAG
msgtag;
int
msglen;
OSCTXT
ctxt;
PersonnelRecord employee;
.. logic to read message into msgbuf ..
/* Step 1: Initialize a context variable for decoding */
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
xd_setp (&ctxt, msgbuf, 0, &msgtag, &msglen);
/* Step 2: Test message tag for type of message received */
/* (note: this is optional, the decode function can be */
/* called directly if the type of message is known).. */
if (msgtag == TV_PersonnelRecord)
{
/* Step 3: Call decode function (note: last two args */
/* should always be ASN1EXPL and 0).. */
status = asn1D_PersonnelRecord (&ctxt,
&employee,
ASN1EXPL, 0);
/* Step 4: Check return status */
if (status == 0)
{
process received data in ‘employee’ variable..
/* Remember to release dynamic memory when done! */
rtxMemFree (&ctxt);
172
Generated BER Functions
}
else
error processing...
}
else
check for other known message types..
}
Decoding a Series of Messages Using the C Decode Functions
The above example is fine as a sample for decoding a single message, but what happens in the more typical scenario
of having a long-running loop that continuously decodes messages? It will be necessary to put the decoding logic
into a loop:
main ()
{
OSOCTET
msgbuf[1024];
ASN1TAG
msgtag;
int
msglen;
OSCTXT
ctxt;
PersonnelRecord employee;
/* Step 1: Initialize a context variable for decoding */
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
for (;;) {
.. logic to read message into msgbuf ..
xd_setp (&ctxt, msgbuf, 0, &msgtag, &msglen);
/* Step 2: Test message tag for type of message received */
/* (note: this is optional, the decode function can be */
/* called directly if the type of message is known).. */
/* Now switch on initial tag value to determine what type of
message was received.. */
switch (msgtag)
{
case TV_PersonnelRecord: /* compiler generated constant */
{
status = asn1D_PersonnelRecord (&ctxt,
&employee,
ASN1EXPL, 0);
if (status == 0)
{
/* decoding successful, data in employee */
173
Generated BER Functions
process received data..
}
else
error processing...
}
break;
default:
/* handle unknown message type here */
} /* switch */
/* Need to reinitialize objects for next iteration */
rtxMemReset (&ctxt);
}
}
The only changes were the addition of the for (;;) loop and the call to rtxMemReset that was added at the bottom of the
loop. This function resets the memory tracking parameters within the context to allow previously allocated memory to
be reused for the next decode operation. Optionally, rtxMemFree can be called to release all memory. This will allow
the loop to start again with no outstanding memory allocations for the next pass.
The example above assumes that logic existed that would read each message to be processed into the same buffer for
every message processed inside the loop (i.e the buffer is reused each time). In the case in which the buffer already
contains multiple messages, encoded back-to-back, it is necessary to advance the buffer pointer in each iteration:
main ()
{
OSOCTET
msgbuf[1024];
ASN1TAG
msgtag;
int
offset = 0, msglen, len;
OSCTXT
ctxt;
PersonnelRecord employee;
FILE*
fp;
/* Step 1: Initialize a context variable for decoding */
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
if (fp = fopen (filename, "rb")) {
msglen = fread (msgbuf, 1, sizeof(msgbuf), fp);
}
else {
... handle error ...
}
for (; offset < msglen; ) {
xd_setp (&ctxt, msgbuf + offset, msglen - offset, &msgtag, &len);
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Generated BER Functions
/* Decode */
if (tag == TV_PersonnelRecord) {
/* Call compiler generated decode function */
stat = asn1D_PersonnelRecord (&ctxt, &employee, ASN1EXPL, 0);
if (stat == 0) {
/* decoding successful, data in employee */
}
else {
/* error handling */
return -1;
}
}
else {
printf ("unexpected tag %hx received\n", tag);
}
offset += ctxt.buffer.byteIndex;
rtxMemReset (&ctxt);
}
}
Generated C++ Decode Method Format and Calling
Parameters
Generated decode functions are invoked through the class interface by calling the base class Decode method. The
calling sequence for this method is as follows:
status = <object>.Decode ();
In this definition, <object> is an instance of the control class (i.e., ASN1C_<prodName>) generated for the given
production
An ASN1BERDecodeBuffer object reference is a required argument to the <object> constructor. This is where the
message start address and length are specified
The message length argument is used to specify the size of the message, if it is known. In ASN.1 BER or DER encoded
messages, the overall length of the message is embedded in the first few bytes of the message, so this variable is
not required. It is used as a test mechanism to determine if a corrupt or partial message was received. If the parsed
message length is greater than this value, an error is returned. If the value is specified to be zero (the default), then
this test is bypassed.
The function result variable status returns the status of the decode operation. The return status will be zero if
decoding is successful or a negative value if an error occurs. Return status values are defined in Appendix A of the C/
C++ Common Functions Reference Manual and online in the asn1type.h include file.
Procedure for Using the C++ Control Class Decode Method
Normally when a message is received and read into a buffer, it can be one of several different message types.
So the first job a programmer has before calling a decode function is determining which function to call. The
ASN1BERDecodeBuffer class has a standard method for parsing the initial tag/length from a message to determine the
175
Generated BER Functions
type of message received. This call is used in conjunction with a switch statement on generated tag constants for the
known message set in order to pick a decoder to call.
Once it is known which type of message has been received, an instance of a generated message class can be instantiated
and the decode function called. The start of message pointer and message length (if known) must be specified either
in the constructor call or in the call to the decode function itself.
A program fragment that could be used to decode an employee record is as follows:
#include employee.h
main ()
{
OSOCTET
ASN1TAG
int
// include file generated by ASN1C
msgbuf[1024];
msgtag;
msglen, status;
.. logic to read message into msgbuf ..
// Use the ASN1BERDecodeBuffer class to parse the initial
// tag/length from the message..
ASN1BERDecodeBuffer decodeBuffer (msgbuf, len);
status = decodeBuffer.ParseTagLen (msgtag, msglen);
if (status != 0) {
// handle error
...
}
// Now switch on initial tag value to determine what type of
// message was received..
switch (msgtag)
{
case TV_PersonnelRecord: // compiler generated constant
{
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (decodeBuffer, msgData);
if ((status = employee.Decode ()) == 0)
{
// decoding successful, data in msgData
process received data..
}
else
error processing...
}
case TV_ ...// handle other known messages
Note that the call to free memory is not required to release dynamic memory when using the C++ interface. This
is because the control class hides all of the details of managing the context and releasing dynamic memory. The
176
Generated BER Functions
memory is automatically released when both the message buffer object (ASN1BERMessageBuffer) and the control
class object (ASN1C_<ProdName>) are deleted or go out of scope. Reference counting of a context variable shared
by both interfaces is used to accomplish this.
Decoding a Series of Messages Using the C++ Control Class
Interface
The above example is fine as a sample for decoding a single message, but what happens in the more typical scenario
of having a long-running loop that continuously decodes messages? The logic shown above would not be optimal
from a performance standpoint because of the constant creation and destruction of the message processing objects.
It would be much better to create all of the required objects outside of the loop and then reuse them to decode and
process each message.
A code fragment showing a way to do this is as follows:
#include employee.h
main ()
{
OSOCTET
ASN1TAG
int
// include file generated by ASN1C
msgbuf[1024];
msgtag;
msglen, status;
// Create message buffer, ASN1T, and ASN1C objects
ASN1BERDecodeBuffer decodeBuffer (msgbuf, len);
ASN1T_PersonnelRecord employeeData;
ASN1C_PersonnelRecord employee (decodeBuffer, employeeData);
for (;;) {
.. logic to read message into msgbuf ..
status = decodeBuffer.ParseTagLen (msgtag, msglen);
if (status != 0) {
// handle error
...
}
// Now switch on initial tag value to determine what type of
// message was received..
switch (msgtag)
{
case TV_PersonnelRecord: // compiler generated constant
{
if ((status = employee.Decode ()) == 0)
{
// decoding successful, data in employeeData
process received data..
}
else
177
Generated BER Functions
error processing...
}
break;
default:
// handle unknown message type here
} // switch
// Need to reinitialize objects for next iteration
if (!isLastIteration) employee.memFreeAll ();
} // end of loop
This is quite similar to the first example. Note that we have pulled the ASN1T_Employee and ASN1C_Employee object
creation logic out of the switch statement and moved it above the loop. These objects can now be reused to process
each received message.
The only other change was the call to employee.memFreeAll that was added at the bottom of the loop. Since we can’t
count on the objects being deleted to automatically release allocated memory, we need to do it manually. This call will
free all memory held within the decoding context. This will allow the loop to start again with no outstanding memory
allocations for the next pass.
If the buffer already contains multiple BER messages encoded back-to-back then it is necessary to modify the buffer
pointer in each iteration. The getByteIndex method should be used at the end of loop to get the current offset in the
buffer. This offset should be used with the decode buffer object’s setBuffer method call at the beginning of the loop
to determine the correct buffer pointer and length:
OSUINT32 offset = 0;
for ( ; offset < msglen;) {
// set buffer pointer and its length to decode
decodeBuffer.setBuffer (&msgbuf[offset], msglen - offset);
int curlen = (int)(msglen - offset);
status = decodeBuffer.ParseTagLen (msgtag, curlen);
if (status != 0) {
// handle error
...
}
// Now switch on initial tag value to determine what type of
// message was received..
switch (msgtag)
{
case TV_PersonnelRecord: // compiler generated constant
{
if ((status = employee.Decode ()) == 0)
{
// decoding successful, data in employeeData
178
Generated BER Functions
process received data..
}
else
error processing...
}
break;
default:
// handle unknown message type here
} // switch
// get new offset
offset += decodeBuffer.getByteIndex ();
// Need to reinitialize objects for next iteration (if it is not
// last iteration)
if (offset < msglen) employee.memFreeAll ();
} // end of loop
BER Decode Performance Enhancement
Techniques
There are a number of different things that can be done in application code to improve BER decode performance.
These include adjusting memory allocation parameters, using compact code generation, using decode fast copy, and
using initialization functions.
Dynamic Memory Management
By far, the biggest performance bottleneck when decoding ASN.1 messages is the allocation of memory from the heap.
Each call to new or malloc is very expensive.
The decoding functions must allocate memory because the sizes of many of the variables that make up a message
are not known at compile time. For example, an OCTET STRING that does not contain a size constraint can be an
indeterminate number of bytes in length.
ASN1C does two things by default to reduce dynamic memory allocations and improve decoding performance:
1. Uses static variables wherever it can. Any BIT STRING, OCTET STRING, character string, or SEQUENCE OF
or SET OF construct that contains a size constraint will result in the generation of a static array of elements sized
to the max constraint bound.
2. Uses a special nibble-allocation algorithm for allocating dynamic memory. This algorithm allocates memory in
large blocks and then splits up these blocks on subsequent memory allocation requests. This results in fewer calls
to the kernel to get memory. The downside is that one request for a few bytes of memory can result in a large
block being allocated.
Common run-time functions are available for controlling the memory allocation process. First, the default size of a
memory block as allocated by the nibble-allocation algorithm can be changed. By default, this value is set to 4K bytes.
The run-time function rtMemSetDefBlkSize can be called to change this size. This takes a single argument - the value
to which the size should be changed.
179
Generated BER Functions
It is also possible to change the underlying functions called from within the memory management abstraction layer
to obtain or free heap memory. By default, the standard C malloc, realloc, and free functions are used. These can
be changed by calling the rtMemSetAllocFuncs function. This function takes as arguments function pointers to the
allocate, reallocate, and free functions to be used in place of the standard C functions.
Another run-time memory management function that can improve performance is rtMemReset. This function is useful
when decoding messages in a loop. It is used instead of rtMemFree at the bottom of the loop to make dynamic memory
available for decoding the next message. The difference is that rtMemReset does not actually free the dynamic memory.
It instead just resets the internal memory management parameters so that memory already allocated can be reused.
Therefore, all the memory required to handle message decoding is normally allocated within the first few passes of
the loop. From that point on, that memory is reused thereby making dynamic memory allocation a negligent issue in
the overall performance of the decoder.
A more detailed explanation of these functions and other memory management functions can be found in the C/ C+
+Common Run-Time Library Reference Manual.
Compact Code Generation
Using the compact code generation option (-compact) and lax validation option (-lax) can also improve decoding
performance.
The -compact option causes code to be generated that contains no diagnostic or error trace messages. In addition, some
status checks and other non-critical code are removed providing a slightly less robust but faster code base.
The –lax option causes all constraint checks to be removed from the generated code.
Performance intensive applications should also be sure to link with the compact version of the base run-time libraries.
These libraries can be found in the lib_opt (for optimized) subdirectory. These run-time libraries also have all
diagnostics and error trace messages removed as well as some non-critical status checks.
Decode Fast Copy
“Fast Copy” is a special run-time flag that can be set for the decoder that can substantially reduce the number of copy
operations that need to be done to decode a message. The copy operations are reduced by taking advantage of the fact
that the data contents of some ASN.1 types already exist in decoded form in the message buffer. Therefore, there is
no need to allocate memory for the data and then copy the data from the buffer into the allocated memory structure.
As an example of what fast copy does, consider a simple ASN.1 SEQUENCE consisting of an element a, an INTEGER
and b, an OCTET STRING:
Simple ::= SEQUENCE {
a INTEGER,
b OCTET STRING
}
Assume an encoded value of this type contains a value of a = 123 (hex 7B) and b contains the hex octets 0x01 0x02
0x03. The generated variable for the OCTET STRING will contain a data pointer. So rather than allocate memory for
this string and copy the data to it, fast copy will simply store a pointer directly to the data in the buffer:
180
Generated BER Functions
The pointer stored in the data structure points directly at data in the message buffer. No memory allocation or copy
is done.
The user must keep in mind that if this technique is used, the message buffer containing the decoded message must be
available as long as the type variable containing the decoded data is in use. This will not work in a producer-consumer
threading model where one thread is decoding messages and the next thread is processing the contents. The producer
thread will overwrite the buffer contents and therefore data referenced in the decoded message type variable that the
consumer is processing.
This will also not work if the message buffer is an automatic variable in a function and the decoded result type is being
passed out. The result type variable will point at data in the buffer variable that has gone out of scope.
To set fast copy, the rtSetFastCopy function must be invoked with the initialized context variable that will be used to
decode a message. This should be done once prior to entering the loop that will be used to decode a stream of messages.
Using Initialization Functions
Initialization functions are generated by the ASN1C compiler when the -genInit option is added to the ASN1C
command-line. These functions can be used as an alternative to memset’ing a variable to zero to prepare it to receive
decoded data. The advantage is that the initialization functions are smarter and know exactly what within the structures
needs to be zeroed as opposed to blindly clearing everything. So, for example, large byte arrays used to hold OCTET
STRING data will not be zeroed. This can add up to significant performance improvements in the long run, particular
in complex, deeply-nested ASN.1 types.
If initialization functions are generated, the generated decode logic will use them wherever it can in place of calls to
zero memory.
BER/DER Deferred Decoding
Another way to improve decoding performance of large messages is through the use of deferred decoding. This allows
for the selective decoding of only parts of a message in a single decode function call. When combined with the fast copy
procedure defined above, this can significantly reduce decoding time because large parts of messages can be skipped.
Deferred decoding can be done on elements defined within a SEQUENCE, SET or CHOICE construct. It is done by
designating an element to be an open type by using the <isOpenType/> configuration setting. This setting causes the
181
Generated BER Functions
ASN1C compiler to insert an Asn1OpenType placeholder in place of the type that would have normally been used
for the element. The data in its original encoded form will be stored in the open type container when the message is
decoded. If fast copy is used, only a pointer to the data in the message buffer is stored so large copies of data are avoided.
The data within the deferred decoding open type container can be fully decoded later by using a special decode function
generated by the ASN1C compiler for this purpose. The format of this function is as follows:
asn1D_<ProdName>_<ElementName>_OpenType (OSCTXT* pctxt, <ElementType>* pvalue)
Here <ProdName> is replaced with name of the type assignment and <ElementName > is replaced with name of the
element. In this function, the argument pctxt is used to pass the a pointer to a context variable initialized with the open
type data and the pvalue argument will hold the final decoded data value.
In following example, decoding of the element id is deferred:
Identifier ::= SEQUENCE {
id INTEGER,
oid OBJECT IDENTIFIER
}
The following configuration file is required to indicate the element id is to be processed as an open type (i.e. that it
will be decoded later):
<asn1config>
<module>
<name>modulename</name>
<production>
<name>Identifier</name>
<element>
<name>id</name>
<isOpenType/>
<element/>
<production/>
<module/>
<asn1config/>
In the generated code, the element id type will be replaced with an open type (Asn1OpenType for C or Asn1TOpenType
for C++) and the following additional function is generated:
EXTERN int asn1D_Identifier_id_OpenType (OSCTXT* pctxt, OSINT32* pvalue);
In the Identifier decode function, element id is decoded as an open type.
Generated BER Streaming Decode Functions
BER messages can be directly read and decoded from an input stream such as a file, network or memory stream using
BER streaming decode functions. The ASN1C compiler -stream option is used to generate decoders of this type. For
each ASN.1 production defined in an ASN.1 source file, a C streaming decode function is generated. This function
will decode an ASN.1 message into a C variable of the given type.
If C++ code generation is specified, a control class is generated that contains a DecodeFrom method that wraps this
function. This function is invoked through the class interface to decode an ASN.1 message into the variable referenced
in the msgData component of the class.
182
Generated BER Functions
In this version, there are three types of streams: file, socket and memory. The most useful are file and socket streams. It
is possible to decode data directly from a file or socket without intermediate copying into memory. If the full amount of
data is not available for reading then the behavior of these streams will be different: the file and memory input streams
will report an error, the socket input stream will block until data is available or an I/O error occurs (for example, the
remote side closes the connection).
Generated Streaming C Function Format and Calling
Parameters
The format of the name of each streaming decode function generated is as follows:
asn1BSD_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each decode function is as follows:
status = asn1BSD_<name> (OSCTXT* pctxt,
<name> *pvalue,
ASN1TagType tagging,
int length);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of decode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program. The variable
must be initialized using the berStrmInitContext run-time function before use.
The pvalue argument is a pointer to a variable of the generated type that will receive the decoded data.
The tagging and length arguments are for internal use when calls to decode functions are nested to accomplish
decoding of complex variables. At the top level, these parameters should always be set to the constants ASN1EXPL
and zero respectively.
The function result variable status returns the status of the decode operation. The return status will be zero if decoding
is successful or negative if an error occurs. Return status values are defined in the rtxErrCodes.h include file.
Procedure for Calling Streaming C Decode Functions
This section describes the step-by-step procedure for calling a streaming C BER decode function. This procedure must
be followed if C code generation was done. This procedure can also be used as an alternative to using the control class
interface if C++ code generation was done.
Before any decode function can be called; the user must first initialize a context variable. This is a variable of type
OSCTXT. This variable holds all of the working data used during the decoding of a message. The context variable is
declared as a normal automatic variable within the top-level calling function. It must be initialized before use. This
can be accomplished by using the berStrmInitContext function.
OSCTXT ctxt; // context variable
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Generated BER Functions
if (berStrmInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
The next step is to create a stream object within the context. This object is an abstraction of the output device to which
the data is to be encoded and is initialized by calling one of the following functions:
• rtxStreamFileOpen
• rtxStreamFileAttach
• rtxStreamSocketAttach
• rtxStreamMemoryCreate
• rtxStreamMemoryAttach
The flags parameter of these functions should be set to the OSRTSTRMF_INPUT constant value to indicate an input
stream is being created (see the C/C++ Common Run-Time Library Reference Manual for a full description of these
functions).
A simplified version of the Open functions are the CreateReader functions:
• rtxStreamFileCreateReader
• rtxStreamMemoryCreateReader
• rtxStreamSocketCreateReader
After initializing the context and populating a variable of the structure to be encoded, a decode function can be called to
decode a message from the stream. If the return status indicates success, the C variable that was passed as an argument
will contain the decoded message contents. Note that the decoder may have allocated dynamic memory and stored
pointers to objects in the C structure. After processing on the C structure is complete, the run-time library function
rtxMemFree should be called to free the allocated memory.
After stream processing is complete, the stream is closed by invoking the rtxStreamClose function.
A program fragment that could be used to decode an employee record is as follows:
#include “employee.h”
/* include file generated by ASN1C */
#include "rtxsrc/rtxStreamFile.h"
main ()
{
ASN1TAG msgtag;
int
msglen;
OSCTXT ctxt;
PersonnelRecord employee;
const char* filename = “message.dat”
/* Step 1: Initialize a context variable for decoding */
184
Generated BER Functions
if (berStrmInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
/* Step 2: Open the input stream to read data */
stat = rtxStreamFileCreateReader (&ctxt, filename);
if (stat != 0) {
rtxErrPrint (&ctxt);
return stat;
}
/* Step 3: Test message tag for type of message received */
/* (note: this is optional, the decode function can be */
/* called directly if the type of message is known).. */
if ((stat = berDecStrmPeekTagAndLen (&ctxt, &tag, &len)) != 0) {
rtxErrPrint (&ctxt);
return stat;
}
if (msgtag == TV_PersonnelRecord)
{
/* Step 4: Call decode function (note: last two args */
/* should always be ASN1EXPL and 0).. */
status = asn1BSD_PersonnelRecord (&ctxt,
&employee,
ASN1EXPL, 0);
/* Step 5: Check return status */
if (status == 0)
{
process received data in ‘employee’ variable..
}
else
error processing...
}
else
check for other known message types..
/* Step 6: Close the stream */
rtxStreamClose (&ctxt);
/* Remember to release dynamic memory when done! */
rtFreeContext (&ctxt);
}
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Generated BER Functions
Decoding a Series of Messages Using the Streaming C Decode
Functions
The above example is fine as a sample for decoding a single message, but what happens in the more typical scenario
of having a long-running loop that continuously decodes messages? It will be necessary to put the decoding logic
into a loop.
A code fragment showing a way to do this is as follows:
#include “employee.h”
/* include file generated by ASN1C */
#include "rtxsrc/rtxStreamFile.h"
main ()
{
ASN1TAG msgtag;
int msglen, stat;
OSCTXT ctxt;
PersonnelRecord employee;
const char* filename = “message.dat”
/* Step 1: Initialize a context variable for decoding */
if (berStrmInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
/* Step 2: Open the input stream to read data */
stat = rtxStreamFileCreateReader (&ctxt, filename);
if (stat != 0) {
rtxErrPrint (&ctxt);
return stat;
}
for (;;) {
/* Step 3: Test message tag for type of message received */
/* (note: this is optional, the decode function can be */
/* called directly if the type of message is known).. */
if ((stat = berDecStrmPeekTagAndLen (&ctxt, &tag, &len)) != 0) {
rtxErrPrint (&ctxt);
return stat;
}
if (msgtag == TV_PersonnelRecord)
{
/* Step 4: Call decode function (note: last two args */
/* should always be ASN1EXPL and 0).. */
stat = asn1BSD_PersonnelRecord (&ctxt,
&employee,
ASN1EXPL, 0);
186
Generated BER Functions
/* Step 5: Check return status */
if (stat == 0)
{
process received data in ‘employee’ variable..
}
else
error processing...
}
else
check for other known message types..
/* Need to reset all memory for next iteration */
rtxMemReset (&ctxt);
} /* end of loop */
/* Step 6: Close the stream */
rtxStreamClose (&ctxt);
/* Remember to release dynamic memory when done! */
rtFreeContext (&ctxt);
}
The only changes were the addition of the for (;;) loop and the call to rtxMemReset that was added at the bottom of the
loop. This function resets the memory tracking parameters within the context to allow previously allocated memory to
be reused for the next decode operation. Optionally, rtxMemFree can be called to release all memory. This will allow
the loop to start again with no outstanding memory allocations for the next pass.
Generated Streaming C++ Decode Method Format and
Calling Parameters
Generated C streaming decode functions are invoked through the C++ class interface by calling the generated
DecodeFrom method. The calling sequence for this method is as follows:
status = <object>.DecodeFrom (<inputStream>);
In this definition, <object> is an instance of the control class (i.e., ASN1C_<prodName>) generated for the given
production.
The <inputStream> placeholder represents an input stream object type. This is an object derived from an
ASN1DecodeStream class.
The function result variable stat returns the completion status. Error status codes are negative. Return status values
are defined in the rtxErrCodes.h include file.
Another way to decode message using the C++ class interface is to use the >> stream operator:
<inputStream> >> <object>;
187
Generated BER Functions
Exceptions are not used in ASN1C C++, therefore, the user must fetch the status value following a call such as this in
order to determine if it was successful. The getStatus method in the ASN1DecodeStream class is used for this purpose.
Also, the method Decode without parameters is supported for backward compatibility. In this case it is necessary to
create a control class object (i.e., ASN1C_<prodName>) using an input stream reference as the first parameter and a
reference to a variable of the generated type as the second parameter of the constructor.
Procedure for Using the Streaming C++ Control Class Decode
Method
Normally the receiving message can be one of several different message types. It is therefore necessary to determine
the type of message that was received so that the appropriate decode function can be called to decode it. The
ASN1BERDecodeStream class has standard methods for parsing the initial tag/length from a message to determine the
type of message received. These calls are used in conjunction with a switch statement on generated tag constants for
the known message set. Each switch case statement contains logic to create an object instance of a specific ASN1C
generated control class and to invoke and then to invoke that object’s decode method.
A program fragment that could be used to decode an employee record is as follows:
#include "Employee.h"
// include file generated by ASN1C
#include "rtbersrc/ASN1BERDecodeStream.h"
#include "rtxsrc/OSRTFileInputStream.h"
main ()
{
ASN1TAG tag;
int i, len;
const char* filename = "message.dat";
OSBOOL trace = TRUE;
// Decode
ASN1BERDecodeStream in (new OSRTFileInputStream (filename));
if (in.getStatus () != 0) {
in.printErrorInfo ();
return -1;
}
if (in.peekTagAndLen (tag, len) != 0) {
printf ("peekTagAndLen failed\n");
in.printErrorInfo ();
return -1;
}
// Now switch on initial tag value to determine what
// type of message was received..
switch (msgtag)
{
case TV_PersonnelRecord: // compiler generated
// constant
{
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (msgData);
188
Generated BER Functions
in >> employee;
if (in.getStatus () != 0) {
printf ("decode of PersonnelRecord failed\n");
in.printErrorInfo ();
return -1;
}
// or employee.DecodeFrom (in);
break;
}
case TV_ ...// handle other known messages
...
}
}
return 0;
}
Note that the call to free memory and the stream close method are not required to release dynamic memory when
using the C++ interface. This is because the control class hides all of the details of managing the context and releasing
dynamic memory. The memory is automatically released when both the input stream object (ASN1BERDecodeStream
and derived classes) and the control class object (ASN1C_<ProdName>) are deleted or go out of scope. Reference
counting of a context variable shared by both interfaces is used to accomplish this.
Decoding a Series of Messages Using the C++ Control Class
Interface
The above example is fine as a sample for decoding a single message, but what happens in the more typical scenario
of having a long-running loop that continuously decodes messages? The logic shown above would not be optimal
from a performance standpoint because of the constant creation and destruction of the message processing objects.
It would be much better to create all of the required objects outside of the loop and then reuse them to decode and
process each message.
A code fragment showing a way to do this is as follows:
#include "Employee.h"
// include file generated by ASN1C
#include "rtbersrc/ASN1BERDecodeStream.h"
#include "rtxsrc/OSRTFileInputStream.h"
int main ()
{
ASN1TAG tag;
int i, len;
const char* filename = "message.dat";
OSBOOL trace = TRUE;
// Decode
ASN1BERDecodeStream in (new OSRTFileInputStream (filename));
if (in.getStatus () != 0) {
in.printErrorInfo ();
return -1;
189
Generated BER Functions
}
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (msgData);
for (;;) {
if (in.peekTagAndLen (tag, len) != 0) {
printf ("peekTagAndLen failed\n");
in.printErrorInfo ();
return -1;
}
// Now switch on initial tag value to determine what
// type of message was received..
switch (msgtag)
{
case TV_PersonnelRecord: // compiler generated
// constant
{
in >> employee;
if (in.getStatus () != 0) {
printf ("decode of PersonnelRecord failed\n");
in.printErrorInfo ();
return -1;
}
// or employee.DecodeFrom (in);
}
case TV_ ...// handle other known messages
...
}
// Need to reinitialize objects for next iteration
employee.memFreeAll ();
} // end of loop
return 0;
}
This is quite similar to the first example. Note that we have pulled the ASN1T_Employee and ASN1C_Employee object
creation logic out of the switch statement and moved it above the loop. These objects can now be reused to process
each received message.
The only other change was the call to employee.memFreeAll that was added at the bottom of the loop. Since the objects
are not deleted to automatically release allocated memory, we need to do it manually. This call will free all memory
held within the decoding context. This will allow the loop to start again with no outstanding memory allocations for
the next pass.
190
Chapter 8. Generated PER Functions
Generated PER Encode Functions
PER encode/decode functions are generated when the -per, -perindef or -uperswitch is specified on the command line.
For each ASN.1 production defined in the ASN.1 source file, a C PER encode function is generated. This function
will convert a populated C variable of the given type into a PER encoded ASN.1 message.
If C++ code generation is specified, a control class is generated that contains an Encode method that wraps this function.
This function is invoked through the class interface to encode an ASN.1 message into the variable referenced in the
msgData component of the class.
Generated C Function Format and Calling Parameters
The format of the name of each generated PER encode function is as follows:
asn1PE_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each encode function is as follows:
status = asn1PE_<name> (OSCTXT* pctxt, <name>[*] value);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program.
The value argument contains the value to be encoded or holds a pointer to the value to be encoded. This variable is
of the type generated from the ASN.1 production. The object is passed by value if it is a primitive ASN.1 data type
such as BOOLEAN, INTEGER, ENUMERATED, etc.. It is passed using a pointer reference if it is a structured ASN.1
type value. Check the generated function prototype in the header file to determine how the value argument is to be
passed for a given function.
The function result variable stat returns the status of the encode operation. Status code 0 (0) indicates the function
was successful. Note that this return value differs from that of BER encode functions in that the encoded length of
the message component is not returned – only an OK status indicating encoding was successful. A negative value
indicates encoding failed. Return status values are defined in the "asn1type.h" include file. The error text and a stack
trace can be displayed using the rtErrPrint function.
Generated C++ Encode Method Format and Calling
Parameters
Generated encode functions are invoked through the class interface by calling the base class Encode method. The
calling sequence for this method is as follows:
stat = <object>.Encode ();
191
Generated PER Functions
In this definition, <object> is an object of the class generated for the given production. The function result variable
stat returns the status value from the PER encode function. This status value will be 0 (0) if encoding was successful
or a negative error status value if encoding fails. Return status values are defined in the "asn1type.h" include file.
The user must call the encode buffer class methods getMsgPtr and getMsgLen to obtain the starting address and length
of the encoded message component.
Populating Generated Structure Variables for Encoding
See the section Populating Generated Structure Variables for Encoding for a discussion on how to populate variables
for encoding. There is no difference in how it is done for BER versus how it is done for PER.
Procedure for Calling C Encode Functions
This section describes the step-by-step procedure for calling a C PER encode function. This method must be used if
C code generation was done. This method can also be used as an alternative to using the control class interface if C
++ code generation was done.
Before a PER encode function can be called, the user must first initialize an encoding context block structure. The
context block is initialized by calling the rtInitContext to initialize the block. The user then must call pu_setBuffer to
specify a message buffer to receive the encoded message. Specification of a dynamic message buffer is possible by
setting the buffer address argument to null and the buffer size argument to zero. The pu_setBuffer function also allows
for the specification of aligned or unaligned encoding.
An encode function can then be called to encode the message. If the return status indicates success (0), then the message
will have been encoded in the given buffer. PER encoding starts from the beginning of the buffer and proceeds from
low memory to high memory until the message is complete. This differs from BER where encoding was done from
back-to-front. Therefore, the buffer start address is where the encoded PER message begins. The length of the encoded
message can be obtained by calling the pe_GetMsgLen run-time function. If dynamic encoding was specified (i.e.,
a buffer start address and length were not given), the run-time routine pe_GetMsgPtr can be used to obtain the start
address of the message. This routine will also return the length of the encoded message.
A program fragment that could be used to encode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
main ()
{
OSOCTET msgbuf[1024];
int msglen, stat;
OSCTXT ctxt;
OSBOOL aligned = TRUE;
Employee employee; /* typedef generated by ASN1C */
/* Populate employee C structure */
employee.name.givenName = "SMITH";
...
/* Allocate and initialize a new context pointer */
stat = rtInitContext (&ctxt);
if (stat != 0) {
printf (“rtInitContext failed (check license)\n“);
192
Generated PER Functions
rtxErrPrint (&ctxt);
return stat;
}
pu_setBuffer (&ctxt, msgbuf, msglen, aligned);
if ((stat = asn1PE_Employee (&ctxt, &employee)) == 0) {
msglen = pe_GetMsgLen (&ctxt);
...
}
else
error processing...
}
In general, static buffers should be used for encoding messages where possible as they offer a substantial performance
benefit over dynamic buffer allocation. The problem with static buffers, however, is that you are required to estimate
in advance the approximate size of the messages you will be encoding. There is no built-in formula to do this, the size
of an ASN.1 message can vary widely based on data types and other factors.
If performance is not a significant issue, then dynamic buffer allocation is a good alternative. Setting the buffer pointer
argument to NULL in the call to pu_setBuffer specifies dynamic allocation. This tells the encoding functions to allocate
a buffer dynamically. The address of the start of the message is obtained after encoding by calling the run-time function
pe_GetMsgPtr .
The following code fragment illustrates PER encoding using a dynamic buffer:
#include employee.h
/* include file generated by ASN1C */
main ()
{
OSOCTET *msgptr;
int msglen, stat;
OSCTXT ctxt;
OSBOOL aligned = TRUE;
Employee employee;/* typedef generated by ASN1C */
employee.name.givenName = "SMITH";
...
stat = rtInitContext (&ctxt);
if (stat != 0) {
printf (“rtInitContext failed (check license)\n“);
rtxErrPrint (&ctxt);
return stat;
}
pu_setBuffer (&ctxt, 0, 0, aligned);
if ((stat = asn1PE_Employee (&ctxt, &employee)) == 0) {
msgptr = pe_GetMsgPtr (&ctxt, &msglen);
...
}
else
193
Generated PER Functions
error processing...
}
It is also possible to encode directly to a stream interface. To do this, the call to pu_setBuffer above would be replaced
with a call to create a stream writer within the context such as rtxStreamFileCreateWriter. The call to the generated
PER encode function would not change - it will automatically know to use the stream interface instead of a memory
buffer.
Procedure for Using the C++ Control Class Encode
Method
The procedure to encode a message using the C++ class interface is as follows:
1. Instantiate an ASN.1 PER encode buffer object (ASN1PEREncodeBuffer) to describe the buffer into which the
message will be encoded. Two overloaded constructors are available. The first form takes as arguments a static
encode buffer and size and a Boolean value indicating whether aligned encoding is to be done. The second form
only takes the Boolean aligned argument. This form is used to specify dynamic encoding.
2. Instantiate an ASN1T_<ProdName> object and populate it with data to be encoded.
3. Instantiate an ASN1C_<ProdName> object to associate the message buffer with the data to be encoded.
4. Invoke the ASN1C_<ProdName> object Encode method.
5. Check the return status. The return value is a status value indicating whether encoding was successful or not.
Zero indicates success. If encoding failed, the status value will be a negative number. The encode buffer method
printErrorInfo can be invoked to get a textual explanation and stack trace of where the error occurred.
6. If encoding was successful, get the start-of-message pointer and message length. The start-of-message pointer is
obtained by calling the getMsgPtr method of the encode buffer object. If static encoding was specified (i.e., a
message buffer address and size were specified to the PER Encode Buffer class constructor), the start-of-message
pointer is the buffer start address. The message length is obtained by calling the getMsgLen method of the encode
buffer object.
A program fragment that could be used to encode an employee record is as follows:
#include employee.h
// include file generated by ASN1C
main ()
{
const OSOCTET* msgptr;
OSOCTET msgbuf[1024];
int msglen, stat;
OSBOOL aligned = TRUE;
// step 1: instantiate an instance of the PER encode
// buffer class. This example specifies a static
// message buffer..
ASN1PEREncodeBuffer encodeBuffer (msgbuf,
sizeof(msgbuf),
aligned);
// step 2: populate msgData with data to be encoded
ASN1T_PersonnelRecord msgData;
194
Generated PER Functions
msgData.name.givenName = "SMITH";
...
// step 3: instantiate an instance of the ASN1C_<ProdName>
// class to associate the encode buffer and message data..
ASN1C_PersonnelRecord employee (encodeBuffer, msgData);
// steps 4 and 5: encode and check return status
if ((stat = employee.Encode ()) == 0)
{
printf ("Encoding was successful\n");
printf ("Hex dump of encoded record:\n");
encodeBuffer.hexDump ();
printf ("Binary dump:\n");
encodeBuffer.binDump ("employee");
// step 6: get start-of-message pointer and message length.
// start-of-message pointer is start of msgbuf
// call getMsgLen to get message length..
msgptr = encodeBuffer.getMsgPtr (); // will return &msgbuf
len = encodeBuffer.getMsgLen ();
}
else
{
printf ("Encoding failed\n");
encodeBuffer.printErrorInfo ();
exit (0);
}
// msgptr and len now describe fully encoded message
...
In general, static buffers should be used for encoding messages where possible as they offer a substantial performance
benefit over dynamic buffer allocation. The problem with static buffers, however, is that you are required to estimate
in advance the approximate size of the messages you will be encoding. There is no built-in formula to do this, the size
of an ASN.1 message can vary widely based on data types and other factors.
If performance is not a significant issue, then dynamic buffer allocation is a good alternative. Using the form of the
ASN1PEREncodeBuffer constructor that does not include buffer address and size arguments specifies dynamic buffer
allocation. This constructor only requires a Boolean value to specify whether aligned or unaligned encoding should
be performed (aligned is true).
The following code fragment illustrates PER encoding using a dynamic buffer:
#include employee.h
// include file generated by ASN1C
main ()
{
OSOCTET* msgptr;
int msglen, stat;
OSBOOL aligned = TRUE;
195
Generated PER Functions
// Create an instance of the compiler generated class.
// This example does dynamic encoding (no message buffer
// is specified)..
ASN1PEREncodeBuffer encodeBuffer (aligned);
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (encodeBuffer, msgData);
// Populate msgData within the class variable
msgData.name.givenName = "SMITH";
...
// Encode
if ((stat = employee.Encode ()) == 0)
{
printf ("Encoding was successful\n");
printf ("Hex dump of encoded record:\n");
encodeBuffer.hexDump ();
printf ("Binary dump:\n");
encodeBuffer.binDump ("employee");
// Get start-of-message pointer and length
msgptr = encodeBuffer.getMsgPtr ();
len = encodeBuffer.getMsgLen ();
}
else
{
printf ("Encoding failed\n");
encodeBuffer.printErrorInfo ();
exit (0);
}
return 0;
}
It is also possible to encode a PER message to a stream rather than a memory buffer. To do this, you would first declare
a variable of one of the OSRT output stream classes. This would then be associated with the encode buffer through
the ASN1PERencode buffer declaration. Everything after that would be similar to the memory buffer based program.
The preceding program fragment rewritten to do streaming output to a file would look like this:
#include employee.h
// include file generated by ASN1C
main ()
{
int stat;
OSBOOL aligned = TRUE;
const char* filename = "message_out.per";
// Create an instance of the compiler generated class.
// This example write output to a file stream..
196
Generated PER Functions
OSRTFileOutputStream fostrm (filename);
ASN1PEREncodeBuffer encodeBuffer (fostrm, aligned);
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (encodeBuffer, msgData);
// Populate msgData within the class variable
msgData.name.givenName = "SMITH";
...
// Encode
if ((stat = employee.Encode ()) == 0)
{
printf ("Encoding was successful\n");
printf ("Hex dump of encoded record:\n");
encodeBuffer.hexDump ();
printf ("Binary dump:\n");
encodeBuffer.binDump ("employee");
}
else
{
printf ("Encoding failed\n");
encodeBuffer.printErrorInfo ();
exit (0);
}
return 0;
}
Note that the encodeBuffer.hexDump and encodeBuffer.binDump commands work despite the fact that the output has
been written to a stream. This is because a capture buffer is used when tracing is enabled to record all of the encoded
information. If memory is tight, a user should ensure that trace output is turned off when using the stream.
Encoding a Series of PER Messages using the C++
Interface
When encoding a series of PER messages using the C++ interface, performance can be improved by reusing the
message processing objects to encode each message rather than creating and destroying the objects each time. A
detailed example of how to do this was given in the section on BER message encoding. The PER case would be similar
with the PER function calls substituted for the BER calls. As was the case for BER, the encode message buffer object
init method can be used to reinitialize the encode buffer between invocations of the encode functions.
Generated PER Decode Functions
PER encode/decode functions are generated when the -per switch is specified on the command line. For each ASN.1
production defined in the ASN.1 source file, a C PER decode function is generated. This function will parse the data
contents from a PER-encoded ASN.1 message and populate a variable of the corresponding type with the data.
If C++ code generation is specified, a control class is generated that contains a Decode method that wraps this function.
This function is invoked through the class interface to encode an ASN.1 message into the variable referenced in the
msgData component of the class.
197
Generated PER Functions
Generated C Function Format and Calling Parameters
The format of the name of each generated PER decode function is as follows:
asn1PD_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each decode function is as follows:
status = asn1PD_<name> (OSCTXT* pctxt, <name>* pvalue);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of decode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program.
The pvalue argument is a pointer to a variable to hold the decoded result. This variable is of the type generated from
the ASN.1 production. The decode function will automatically allocate dynamic memory for variable length fields
within the structure. This memory is tracked within the context structure and is released when the context structure
is freed.
The function result variable stat returns the status of the decode operation. Status code 0 (0) indicates the function
was successful. A negative value indicates decoding failed. Return status values are defined in the "asn1type.h" include
file. The reason text and a stack trace can be displayed using the rtErrPrint function described later in this document.
Generated C++ Decode Method Format and Calling
Parameters
Generated decode functions are invoked through the class interface by calling the base class Decode method. The
calling sequence for this method is as follows:
status = <object>.Decode ();
In this definition, <object> is an object of the class generated for the given production.
An ASN1PERDecodeBuffer object must be passed to the <object> constructor prior to decoding. This is where the
message start address and length are specified. A Boolean argument is also passed indicating whether the message to
be decoded was encoded using aligned or unaligned PER
The function result variable status returns the status of the decode operation. The return status will be zero (0)
if decoding is successful or a negative value if an error occurs. Return status values are documented in the C/C++
Common Functions Reference Manual and in the rtxErrCodes.h include file.
Procedure for Calling C Decode Functions
This section describes the step-by-step procedure for calling a C PER decode function. This method must be used if
C code generation was done. This method can also be used as an alternative to using the control class interface if C
++ code generation was done.
198
Generated PER Functions
Unlike BER, the user must know the ASN.1 type of a PER message before it can be decoded. This is because the type
cannot be determined at run-time. There are no embedded tag values to reference to determine the type of message
received.
The following are the basic steps in calling a compiler-generated decode function:
1. Prepare a context variable for decoding
2. Initialize the data structure to receive the decoded data
3. Call the appropriate compiler-generated decode function to decode the message
4. Free the context after use of the decoded data is complete to free allocated memory structures
Before a PER decode function can be called, the user must first initialize a context block structure. The context block is
initialized by either calling the rtNewContext function (to allocate a dynamic context block), or by calling rtInitContext
to initialize a static block. The pu_setBuffer function must then be called to specify a message buffer that contains the
PER-encoded message to be decoded. This function also allows for the specification of aligned or unaligned decoding.
The variable that is to receive the decoded data must then be initialized. This can be done by either initializing the
variable to zero using memset, or by calling the ASN1C generated initialization function.
A decode function can then be called to decode the message. If the return status indicates success (0), then the message
will have been decoded into the given ASN.1 type variable. The decode function may automatically allocate dynamic
memory to hold variable length variables during the course of decoding. This memory will be tracked in the context
structure, so the programmer does not need to worry about freeing it. It will be released when the context is freed.
The final step of the procedure is to free the context block. This must be done regardless of whether the block is static
(declared on the stack and initialized using rtInitContext), or dynamic (created using rtNewContext). The function to
free the context is rtFreeContext.
A program fragment that could be used to decode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
main ()
{
OSOCTET msgbuf[1024];
ASN1TAG msgtag;
int msglen, stat;
OSCTXT ctxt;
OSBOOL aligned = TRUE;
PersonnelRecord employee;
.. logic to read message into msgbuf ..
/* This example uses a static context block */
/* step 1: prepare the context block */
stat = rtInitContext (&ctxt);
if (stat != 0) {
printf (“rtInitContext failed (check license)\n“);
rtErrPrint (&ctxt);
return stat;
}
199
Generated PER Functions
pu_setBuffer (&ctxt, msgbuf, msglen, aligned);
/* step 2: initialize the data variable */
asn1Init_PersonnelRecord (&employee);
/* step 3: call the decode function */
stat = asn1PD_PersonnelRecord (&ctxt, &employee);
if (stat == 0)
{
process received data..
}
else {
/* error processing... */
rtxErrPrint (&ctxt);
}
/* step 4: free the context */
rtFreeContext (&ctxt);
}
An input stream can be used instead of a memory buffer as the data source by replacing the pu_setBuffer call above
with one of the rtxStream*CreateReader functions to set up a file, memory, or socket stream as input.
Procedure for Using the C++ Control Class Decode
Method
The following are the steps are involved in decoding a PER message using the generated C++ class:
1. Instantiate an ASN.1 PER decode buffer object (ASN1PERDecodeBuffer ) to describe the message to be decoded.
The constructor takes as arguments a pointer to the message to be decoded, the length of the message, and a flag
indicating whether aligned encoding was used or not.
2. Instantiate an ASN1T_<ProdName> object to hold the decoded message data.
3. Instantiate an ASN1C_<ProdName> object to decode the message. This class associates the message buffer object
with the object that is to receive the decoded data. The results of the decode operation will be placed in the variable
declared in step 2.
4. Invoke the ASN1C_<ProdName> object Decode method.
5. Check the return status. The return value is a status value indicating whether decoding was successful or not. Zero
(0) indicates success. If decoding failed, the status value will be a negative number. The decode buffer method
PrintErrorInfo can be invoked to get a textual explanation and stack trace of where the error occurred.
6. Release dynamic memory that was allocated by the decoder. All memory associated with the decode context is
released when both the ASN1PERDecodeBuffer and ASN1C_<ProdName> objects go out of scope.
A program fragment that could be used to decode an employee record is as follows:
#include employee.h
// include file generated by ASN1C
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Generated PER Functions
main ()
{
OSOCTET msgbuf[1024];
int
msglen, stat;
OSBOOL aligned = TRUE;
.. logic to read message into msgbuf ..
// step 1: instantiate a PER decode buffer object
ASN1PERDecodeBuffer decodeBuffer (msgbuf, msglen, aligned);
// step 2: instantiate an ASN1T_<ProdName> object
ASN1T_PersonnelRecord msgData;
// step 3: instantiate an ASN1C_<ProdName> object
ASN1C_PersonnelRecord employee (decodeBuffer, msgData);
// step 4: decode the record
stat = employee.Decode ();
// step 5: check the return status
if (stat == 0)
{
process received data..
}
else {
// error processing..
decodeBuffer.PrintErrorInfo ();
}
// step 6: free dynamic memory (will be done automatically
// when both the decodeBuffer and employee objects go out
// of scope)..
}
A stream can be used as the data input source instead of a memory buffer by creating an OSRT input stream object in
step1 and associating it with the decodeBuffer object. For example, to read from a file input stream, the decodeBuffer
declaration in step 1 would be replaced with the following two statements:
OSRTFileInputStream istrm (filename);
ASN1PERDecodeBuffer decodeBuffer (istrm, aligned);
Decoding a Series of Messages Using the C++ Control
Class Interface
The above example is fine as a sample for decoding a single message, but what happens in the more typical scenario
of having a long-running loop that continuously decodes messages? The logic shown above would not be optimal
from a performance standpoint because of the constant creation and destruction of the message processing objects.
201
Generated PER Functions
It would be much better to create all of the required objects outside of the loop and then reuse them to decode and
process each message.
A code fragment showing a way to do this is as follows:
#include employee.h
// include file generated by ASN1C
main ()
{
OSOCTET msgbuf[1024];
int
msglen, stat;
OSBOOL aligned = TRUE;
// step 1: instantiate a PER decode buffer object
ASN1PERDecodeBuffer decodeBuffer (msgbuf, msglen, aligned);
// step 2: instantiate an ASN1T_<ProdName> object
ASN1T_PersonnelRecord msgData;
// step 3: instantiate an ASN1C_<ProdName> object
ASN1C_PersonnelRecord employee (decodeBuffer, msgData);
// loop to continuously decode records
for (;;) {
.. logic to read message into msgbuf ..
stat = employee.Decode ();
// step 5: check the return status
if (stat == 0)
{
process received data..
}
else {
// error processing..
decodeBuffer.PrintErrorInfo ();
}
// step 6: free dynamic memory
employee.memFreeAll ();
// If reading unaligned data, it is necessary to do a byte align operation to move
// to the next octet boundary before decoding the next message..
decodeBuffer.byteAlign();
}
}
The only difference between this and the previous example is the addition of the decoding loop and the modification
of step 6 in the procedure. The decoding loop is an infinite loop to continuously read and decode messages from some
202
Generated PER Functions
interface such as a network socket. The decode calls are the same, but before in step 6, we were counting on the
message buffer and control objects to go out of scope to cause the memory to be released. Since the objects are now
being reused, this will not happen. So the call to the memFreeAll method that is defined in the ASN1C_Type base class
will force all memory held at that point to be released.
Performance Considerations: Dynamic Memory
Management
Please refer to Performance Considerations: Dynamic Memory Management in the BER Decode Functions section
for a discussion of memory management performance issues. All of the issues that apply to BER and DER also apply
to PER as well.
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Chapter 9. Generated Octet Encoding Rules
(OER) Functions
Generated OER Encode Functions
OER encode/decode functions are generated when the -oer switch is specified on the command line. For each ASN.1
production defined in the ASN.1 source file, a C OER encode function is generated. This function will convert a
populated C variable of the given type into an OER-encoded ASN.1 message.
C++ is not directly supported for OER; however, it is possible to call the generated C functions from a C++ program.
Generated C Function Format and Calling Parameters
The format of the name of each generated PER encode function is as follows:
OEREnc_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each encode function is as follows:
status = OEREnc_<name> (OSCTXT* pctxt, <name>[*] value);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program.
The value argument contains the value to be encoded or holds a pointer to the value to be encoded. This variable is
of the type generated from the ASN.1 production. The object is passed by value if it is a primitive ASN.1 data type
such as BOOLEAN, INTEGER, ENUMERATED, etc.. It is passed using a pointer reference if it is a structured ASN.1
type value. Check the generated function prototype in the header file to determine how the value argument is to be
passed for a given function.
The function result variable stat returns the status of the encode operation. Status code 0 (0) indicates the function
was successful. Note that this return value differs from that of BER encode functions in that the encoded length of
the message component is not returned – only an OK status indicating encoding was successful. A negative value
indicates encoding failed. Return status values are defined in the "asn1type.h" include file. The error text and a stack
trace can be displayed using the rtxErrPrint function.
Populating Generated Structure Variables for Encoding
See the section Populating Generated Structure Variables for Encoding for a discussion on how to populate variables
for encoding. There is no difference in how it is done for BER versus how it is done for OER.
Procedure for Calling C Encode Functions
This section describes the step-by-step procedure for calling a C OER encode function. This method must be used if
C code generation was done.
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Generated Octet Encoding Rules (OER) Functions
Before an OER encode function can be called, the user must first initialize an encoding context block structure. The
context block is initialized by calling the rtInitContext function.
The user then has the option to do stream-based or memory-based encoding. If stream-based is to be done, the user
must call a rtxStreamCreateWriter function for the type of stream to which data will be written. For example, if the
user wishes to write data to a file, the rtxStreamFileCreateWriter function would be called.
To do memory-based encoding, the rtxInitContextBuffer function would be called. This can be used to specify use of a
static or dynamic memory buffer. Specification of a dynamic buffer is possible by setting the buffer address argument
to null and the buffer size argument to zero.
An encode function can then be called to encode the message. If the return status indicates success (0), then the
message will have been encoded in the given buffer or written to the given stream. OER encoding starts from the
beginning of the buffer and proceeds from low memory to high memory until the message is complete. This differs
from definite-length BER where encoding was done from back-to-front. Therefore, the buffer start address is where the
encoded OER message begins. The length of the encoded message can be obtained by calling the rtxCtxtGetMsgLen
run-time function. If dynamic encoding was specified (i.e., a buffer start address and length were not given), the
rtxCtxtGetMsgPtr run-time function can be used to obtain the start address of the message. This routine will also return
the length of the encoded message. If a memory stream was used, the message start address and length can be obtained
by calling the rtxStreamMemoryGetBuffer function.
A program fragment that could be used to encode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
main ()
{
PersonnelRecord employee;
OSCTXT
ctxt;
OSOCTET*
msgptr;
int
i, len, stat;
const char* filename = "message.dat";
/* Populate employee C structure */
asn1Init_PersonnelRecord (&employee);
employee.name.givenName = "SMITH";
...
/* Initialize context */
stat = rtInitContext (&ctxt);
if (stat != 0) {
printf (“rtInitContext failed (check license)\n“);
rtxErrPrint (&ctxt);
return stat;
}
/* Create memory output stream */
stat = rtxStreamMemoryCreateWriter (&ctxt, 0, 0);
if (stat < 0) {
printf ("Create memory output stream failed\n");
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Generated Octet Encoding Rules (OER) Functions
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return stat;
}
/* Encode */
stat = OEREnc_PersonnelRecord (&ctxt, &employee);
msgptr = rtxStreamMemoryGetBuffer (&ctxt, &len);
if (trace) {
printf ("Hex dump of encoded record:\n");
rtxHexDump (msgptr, len);
}
...
}
In general, static buffers should be used for encoding messages where possible as they offer a substantial performance
benefit over dynamic buffer allocation. The problem with static buffers, however, is that you are required to estimate
in advance the approximate size of the messages you will be encoding. There is no built-in formula to do this, the size
of an ASN.1 message can vary widely based on data types and other factors.
The use of streams is a good alternative for large messages as the entire encoded message does not need to fit into
memory.
Generated OER Decode Functions
OER encode/decode functions are generated when the -oer switch is specified on the command line. For each ASN.1
production defined in the ASN.1 source file, a C OER decode function is generated. This function will parse the data
contents from an OER-encoded ASN.1 message and populate a variable of the corresponding type with the data.
Generated C Function Format and Calling Parameters
The format of the name of each generated OER decode function is as follows:
OERDec_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each decode function is as follows:
status = OERDec_<name> (OSCTXT* pctxt, <name>* pvalue);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of decode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program.
The pvalue argument is a pointer to a variable to hold the decoded result. This variable is of the type generated from
the ASN.1 production. The decode function will automatically allocate dynamic memory for variable length fields
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Generated Octet Encoding Rules (OER) Functions
within the structure. This memory is tracked within the context structure and is released when the context structure
is freed.
The function result variable stat returns the status of the decode operation. Status code 0 (0) indicates the function
was successful. A negative value indicates decoding failed. Return status values are defined in the "asn1ErrCodes.h"
and "rtxErrCodes.h" header files. The reason text and a stack trace can be displayed using the rtxErrPrint function
described later in this document.
Procedure for Calling C Decode Functions
This section describes the step-by-step procedure for calling a C OER decode function.
Unlike BER, the user must know the ASN.1 type of an OER message before it can be decoded. This is because the type
cannot be determined at run-time. There are no embedded tag values to reference to determine the type of message
received.
The following are the basic steps in calling a compiler-generated decode function:
1. Prepare a context variable for decoding
2. Initialize the data structure to receive the decoded data
3. Call the appropriate compiler-generated decode function to decode the message
4. Free the context after use of the decoded data is complete to free allocated memory structures
Before an OER decode function can be called, the user must first initialize a context block structure. The context block
is initialized by calling the rtInitContext function.
The user then has the option to do stream-based or memory-based decoding. If stream-based is to be done, the user
must call a rtxStreamCreateReader function for the type of stream from which data will be read. For example, if the
user wishes to read data from a file, the rtxStreamFileCreateReader function would be called.
To do memory-based decoding, the rtxInitContextBuffer function would be called. The message to be decoded must
reside in memory. The arguments to this function would then specify the message buffer in which the data to be
decoded exists.
The variable that is to receive the decoded data must then be initialized. This can be done by either initializing the
variable to zero using memset, or by calling the ASN1C generated initialization function.
A decode function can then be called to decode the message. If the return status indicates success (0), then the message
will have been decoded into the given ASN.1 type variable. The decode function may automatically allocate dynamic
memory to hold variable length variables during the course of decoding. This memory will be tracked in the context
structure, so the programmer does not need to worry about freeing it. It will be released when the either the context is
freed or explicitly when the rtxMemFree or rtxMemReset function is called.
The final step of the procedure is to free the context block. This must be done regardless of whether the block is static
(declared on the stack and initialized using rtInitContext), or dynamic (created using rtNewContext). The function to
free the context is rtFreeContext.
A program fragment that could be used to decode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
main ()
{
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Generated Octet Encoding Rules (OER) Functions
OSOCTET* pMsgBuf;
int len, stat;
OSCTXT ctxt;
PersonnelRecord employee;
const char* filename = "message.dat";
/* step 1: initialize context */
stat = rtInitContext (&ctxt);
if (stat != 0) {
printf (“rtInitContext failed (check license)\n“);
rtErrPrint (&ctxt);
return stat;
}
/* step 2: read input file into a memory buffer */
stat = rtxFileReadBinary (&ctxt, filename, &pMsgBuf, &len);
if (0 == stat) {
stat = rtxInitContextBuffer (&ctxt, pMsgBuf, len);
}
if (0 != stat) {
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return stat;
}
/* step 3: initialize the data variable */
asn1Init_PersonnelRecord (&employee);
/* step 4: call the decode function */
stat = OERDec_PersonnelRecord (&ctxt, &employee);
if (stat == 0)
{
process received data..
}
else {
/* error processing... */
rtxErrPrint (&ctxt);
}
/* step 4: free the context */
rtFreeContext (&ctxt);
}
An input stream can be used instead of a memory buffer as the data source by replacing the rtxFileReadBinary code
block above with one of the rtxStreamCreateReader functions to set up a file, memory, or socket stream as input.
208
Chapter 10. Generated Medical Device
Encoding Rules (MDER) Functions
Note
MDER is available only as a professional compiler option. The encoding and decoding functions are built on
top of ASN1C's streaming functions and will not work with the typical buffer-based implementations seen in
BER or PER. When introduced in version 6.4, no C++ implementation for MDER was available.
The Medical Device Encoding Rules (MDER) are described in IEEE standard 11073-20601-2008, Annex F. This
standard describes a simplified encoding to be used across medical devices. ASN1C can generate encoders and
decoders for specifications based on the IEEE standard, which uses a strict subset of ASN.1.
To generate encoding and decoding functions, use the -mder switch on the command-line or select the appropriate
option in the GUI. The following sections describe the generated encoding and decoding functions. Descriptions of
the MDER run time functions may be found in our C MDER Runtime Library Reference Manual.
Generated MDER Encode Functions
Generated C Function Format and Calling Parameters
The format of the name of each generated encode function is as follows:
MDEREnc_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each encode function follows:
stat = MDEREnc_<name> (OSCTXT* pctxt,
<name>* pvalue);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application.
The user is required to supply a pointer to a variable of this type declared somewhere in his or her program. The
variable should be initialized using the rtInitContext run-time library function (see the C MDER Runtime Library
Reference Manual for a complete description of this function).
The pvalue argument holds a pointer to the data to be encoded and is of the type generated from the ASN.1
production.
The function result variable stat returns an error status code if encoding fails. Return status values are defined in
the asn1type.h include file.
Procedure for Calling C Encode Functions
This section describes the step-by-step procedure for calling a C MDER encode function.
209
Generated Medical Device
Encoding Rules (MDER) Functions
Before any encode function can be called; the user must first initialize an encoding context. This is a variable of type
OSCTXT. This variable holds all of the working data used during the encoding of a message. The context variable is
declared as a normal automatic variable within the top-level calling function. It must be initialized before use. This
can be accomplished by using the rtInitContext function as follows:
OSCTXT ctxt;
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return -1;
}
After initializing the context and populating a variable of the structure to be encoded, an encode function can be called
to encode the message.
A program fragment that could be used to encode a simple release request PDU is as follows:
#include "IEEE-11073-20601-ASN1.h"
int main (void) {
ApduType *pdata;
OSCTXT
ctxt;
OSOCTET* msgptr;
int
stat;
/* include file generated by ASN1C */
/* typedef generated by ASN1C */
/* Step 1: Initialize the context and set the buffer pointer */
stat = rtInitContext (&ctxt);
if (stat != 0) {
/* initialization failed, could be a license problem */
rtxErrPrint (&ctxt);
return stat;
}
/* Step 2: Populate the structure to be encoded */
pdata = rtxMemAllocType (&ctxt, ApduType);
asn1Init_ApduType (pdata);
pdata->t = T_ApduType_rlrq;
pdata->u.rlrq = rtxMemAllocTypeZ (&ctxt, RlrqApdu);
pdata->u.rlrq->reason = normal;
/* Step 3: Call the generated encode function */
stat = MDEREnc_ApduType (&ctxt, pdata);
/* Step 4: Check the return status. */
if (stat < 0) {
rtxErrPrint (&ctxt);
return stat;
}
210
Generated Medical Device
Encoding Rules (MDER) Functions
stat = rtFreeContext (&ctxt);
if (stat != 0) {
printf ("Error freeing context!\n");
return stat;
}
return 0;
}
Encoding a Series of Messages Using the C Encode
Functions
Encoding a series of messages in MDER is very similar to encoding a series of messages in any other set of encoding
rules. Performance can be improved by calling rtxMemReset to avoid allocating new memory for dynamic message
structures, as in the code below:
/* initialize context, et c. */
for ( ; ; ) {
/* initialize / populate message structure to be encoded */
/* call MDEREnc_<messageType> (...); */
/* call rtxMemReset when finished encoding: */
rtxMemReset (pctxt);
}
More details may be found in the sample programs included in the ASN1C software development kit.
Generated MDER Decode Functions
Generated C Function Format and Calling Parameters
The format of the name of each decode function generated is as follows:
MDERDec_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each decode function is as follows:
status = MDERDec_<name> (OSCTXT* pctxt, <name> *pvalue);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of decode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program. The variable
must be initialized using the rtInitContext run-time function before use.
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Generated Medical Device
Encoding Rules (MDER) Functions
The pvalue argument is a pointer to a variable of the generated type that will receive the decoded data.
The function result variable status returns the status of the decode operation. The return status will be greater
than or equal to zero if decoding is successful or negative if an error occurs. Return status values are defined in the
"asn1type.h" include file.
Procedure for Calling C Decode Functions
This section describes the step-by-step procedure for calling a C MDER decode function. This method must be used
if C code generation was done. This method can also be used as an alternative to using the control class interface if
C++ code generation was done.
Before any decode function can be called; the user must first initialize a context variable. This is a variable of type
OSCTXT. This variable holds all of the working data used during the decoding of a message. The context variable
is declared as a normal automatic variable within the top-level calling function. It must be initialized before use.
This can be accomplished as follows:
OSCTXT ctxt;
int stat;
stat = rtInitContext (&ctxt);
if (stat != 0) {
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return stat;
}
The next step is to create a stream reader that will read from the given source. In our example, we read from a file, but
it is also possible to read data from a socket or other source as well.
A decode function can then be called to decode the message. If the return status indicates success, the C variable
that was passed as an argument will contain the decoded message contents. Note that the decoder may have allocated
dynamic memory and stored pointers to objects in the C structure. After processing on the C structure is complete, the
run-time library function rtxMemFree should be called to free the allocated memory.
A program fragment that could be used to decode a simple PDU type follows:
#include IEEE-11073-20601-ASN1.h
#include "rtxsrc/rtxStreamFile.h"
/* include file generated by ASN1C */
int main (void)
{
ApduType data;
OSCTXT
ctxt;
const char* filename = "message.dat";
int
stat;
/* Step 1: Initialize a context variable for decoding */
stat = rtInitContext (&ctxt);
if (stat != 0) {
/* initialization failed, could be a license problem */
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
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Generated Medical Device
Encoding Rules (MDER) Functions
return stat;
}
/* Step 2: Initialize a stream reader */
stat = rtxStreamFileCreateReader (&ctxt, filename);
if (0 != stat) {
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return stat;
}
/* Step 3: decode */
asn1Init_ApduType (&data);
stat = MDERDec_ApduType (&ctxt, &data);
if (stat != 0) {
printf ("decode of data failed\n");
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return -1;
}
}
Decoding a Series of Messages Using the C Decode
Functions
Decoding a series of messages is very similar to the method used for other encoding rules. MDER, however, is simpler.
Users need not concern themselves with idiosyncrasies like byte alignment or length markers.
Short pseudo-code is shown below. As in the encoding example, rtxMemReset is used at the end of the loop to
avoid allocating new memory for dynamic data structures. This helps to improve performance.
/* initialize context, et c. */
for ( ; ; ) {
/* initialize data structure */
/* call MDERDec_<name> function */
/* perform operations on decoded structure */
/* reset memory: */
stat = rtxMemReset (&ctxt);
}
More details may be found in the sample programs included in the ASN1C software development kit.
Two-Phase Messaging
MDER is specified using ITU-T X.208, which uses a two-phase method for encoding and decoding ANY DEFINED
BY types. These types are used to allow flexibility in message transmission by specifying a "hole" in a message to be
filled in by a type specified by an object identifier.
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Generated Medical Device
Encoding Rules (MDER) Functions
Let us assume for sake of example that we wish to transmit a message that has a generic header and a payload defined
by some object identifier. We must first encode the payload and attach it to the message. Then we can encode the
whole message and transmit it. Because this takes two steps, we call this two-phase encoding.
The inverse holds for decoding. The whole message is first decoded. The payload may then be identified and decoded
according to its specific type.
This section describes how to perform two-phase encoding and decoding using the MDER Run Time Library.
Examples are also provided in the distribution.
Two-phase Encoding
We demonstrate an example of two-phase encoding using communication with an electrocardiogram. This code is
based on the ASN.1 specification provided in IEEE 11073-20601-2008 and submitted drafts for an application of this
type.
Two-phase encoding requires the use of multiple encoding contexts to encode both the header and payload. They must
therefore be declared with the rest of the pertinent variables:
ApduType
apdu;
AarqApdu
aarq;
DataProto* pDataProto;
PhdAssociationInformation phdAssocInfo;
OSCTXT
ctxt, ctxt2;
OSOCTET*
msgptr;
int
len;
const char* filename = "message.dat";
We first populate and encode the payload; specific details will vary depending on the application:
/* Populate and encode PhdAssociationInformation */
OSCRTLMEMSET (&phdAssocInfo, 0, sizeof(phdAssocInfo));
phdAssocInfo.protocol_version.numbits = 32;
phdAssocInfo.protocol_version.data[0] = 0x40;
phdAssocInfo.encoding_rules.numbits = 16;
rtxSetBit (phdAssocInfo.encoding_rules.data, 16, EncodingRules_mder);
phdAssocInfo.nomenclature_version.numbits = 32;
rtxSetBit (phdAssocInfo.nomenclature_version.data, 32,
NomenclatureVersion_nom_version1);
phdAssocInfo.functional_units.numbits = 32;
phdAssocInfo.system_type.numbits = 32;
rtxSetBit (phdAssocInfo.system_type.data, 32, SystemType_sys_type_agent);
{
static const OSOCTET sysId[] = {
0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38
} ;
phdAssocInfo.system_id.numocts = (OSUINT32) 8;
phdAssocInfo.system_id.data = (OSOCTET*) sysId;
}
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Generated Medical Device
Encoding Rules (MDER) Functions
phdAssocInfo.dev_config_id = extended_config_start;
phdAssocInfo.data_req_mode_capab.data_req_mode_flags.numbits = 16;
phdAssocInfo.data_req_mode_capab.data_req_init_agent_count = 1;
phdAssocInfo.data_req_mode_capab.data_req_init_manager_count = 0;
/* Create memory output stream */
stat = rtxStreamMemoryCreateWriter (&ctxt, 0, 0);
if (stat < 0) {
printf ("Create memory output stream failed\n");
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return stat;
}
/* Encode */
stat = MDEREnc_PhdAssociationInformation (&ctxt, &phdAssocInfo);
msgptr = rtxStreamMemoryGetBuffer (&ctxt, &len);
In brief, the data structures used for the payload are initialized to zero using the OSCRTLMEMSET macro, which here
acts just like the C runtime library memset function. The data used for populating this example are taken from a
draft specification.
After filling in the necessary fields, the rtxStreamMemoryCreateWriter function is used to create a memory
stream for encoding the payload. More information on this function can be found in the C/C++ Common Run Time
Library manual. In case of failure, errors are trapped and reported.
Finally, the proper MDEREnc function is called to encode the data. A pointer to the message content is retrieved using
the rtxStreamMemoryGetBuffer function. This pointer is used later to fill in the contents of the payload.
After encoding the payload, the rest of the message content must be populated and encoded:
/* Initialize 2nd context structure */
stat = rtInitContext (&ctxt2);
/* Populate apdu with test data */
OSCRTLMEMSET (&aarq, 0, sizeof(AarqApdu));
aarq.assoc_version.numbits = 32;
rtxSetBit (aarq.assoc_version.data, 32, AssociationVersion_assoc_version1);
pDataProto = rtxMemAllocType (&ctxt2, DataProto);
pDataProto->data_proto_id = data_proto_id_20601;
pDataProto->data_proto_info.numocts = len;
pDataProto->data_proto_info.data = msgptr;
rtxDListAppend (&ctxt2, &aarq.data_proto_list, pDataProto);
The msgptr variable is used here to fill in the contents of the data_proto_info structure. The rest of the contents
are initialized and then encoded:
apdu.t = T_ApduType_aarq;
apdu.u.aarq = &aarq;
/* Create memory output stream */
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Generated Medical Device
Encoding Rules (MDER) Functions
stat = rtxStreamMemoryCreateWriter (&ctxt2, 0, 0);
if (stat < 0) {
printf ("Create memory output stream failed\n");
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
}
/* Encode */
stat = MDEREnc_ApduType (&ctxt2, &apdu);
Again, a memory stream writer is used here for encoding, but other options exist to write to a file or a socket.
Two-phase Decoding
Two-phase decoding is the reverse operation of two-phase encoding. In this scenario, a message is received and
decoded. The header and payload are contained in the message, and the payload type and content must be decoded
after the message is received.
This example shows how to decode the message encoded in the previous section. As before, some setup is required
to perform the decode:
ApduType data;
OSCTXT
ctxt;
OSBOOL
trace = TRUE, verbose = FALSE;
const char* filename = "message.dat";
int
i, stat;
/* Initialize context structure */
stat = rtInitContext (&ctxt);
if (stat != 0) {
rtxErrPrint (&ctxt);
return stat;
}
rtxSetDiag (&ctxt, verbose);
In this case, the content is read from an input file, so a file stream is created using rtxStreamFileCreateReader.
Thereafter, the PDU data type is initialized using its initialization function and the message is decoded with the
generated MDERDec function:
/* Create file input stream */
stat = rtxStreamFileCreateReader (&ctxt, filename);
if (0 != stat) {
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return stat;
}
asn1Init_ApduType (&data);
/* Call compiler generated decode function */
stat = MDERDec_ApduType (&ctxt, &data);
if (stat != 0) {
printf ("decode of ApduType failed\n");
rtxErrPrint (&ctxt);
216
Generated Medical Device
Encoding Rules (MDER) Functions
rtFreeContext (&ctxt);
return -1;
}
rtxStreamClose (&ctxt);
The second phase of the decode can now proceed. Because the open type data can appear in a list, a while loop is
used to cycle through the data:
/* Decode APDU open type data */
if (data.t == T_ApduType_aarq) {
OSRTDListNode* pnode = data.u.aarq->data_proto_list.head;
while (0 != pnode) {
PhdAssociationInformation phdAssocInfo;
DataProto* pDataProto = (DataProto*) pnode->data;
/* Create memory input stream */
stat = rtxStreamMemoryCreateReader
(&ctxt, (OSOCTET*)pDataProto->data_proto_info.data,
pDataProto->data_proto_info.numocts);
Note here that the rtxStreamMemoryCreateReader function is used to stream data from the previously decoded
message. It points to the octets held inside of the open type. After initializing the stream reader, the data can be decoded
into the appropriate structure using the corresponding MDERDec function:
/* Decode PhdAssociationInformation */
asn1Init_PhdAssociationInformation (&phdAssocInfo);
stat = MDERDec_PhdAssociationInformation (&ctxt, &phdAssocInfo);
if (stat != 0) {
printf ("decode of ApduType failed\n");
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return -1;
}
rtxStreamClose (&ctxt);
pnode = pnode->next;
}
}
217
Chapter 11. Generated XML Functions
Overview
X.693 specifies XER ("XML Encoding Rules"). There are three variants of XER given: BASIC-XER (often just XER
for short), canonical XER, and EXTENDED-XER. Into this mix, Objective Systems has added its own encoding rules
which we'll call OSys-XER. OSys-XER is very similar to XER, but has a few variations that are meant to produce
XML documents more closely aligned with what you might get if you were using XML Schema to specify your
abstract syntax. Generally, OSys-XER produces fewer tags. The differences between these two sets of encoding rules
are discussed in more detail below.
ASN1C supports BASIC-XER, canonical XER, and OSys-XER. It has for some time supported EXTENDED-XER
via direct compilation of XSD. In version 6.5.0, we have begun to add direct support for EXTENDED-XER by adding
support for some of the XER encoding instructions. Nonetheless, EXTENDED-XER is most fully support today via
direct compilation of XSD. By compiling XSD, you can obtain behavior much the same as with OSys-XER, and more.
Prior to version 6.5.1, ASN1C generated two different styles of code and had two different runtime layers for the
various XML encoding rules. In support of XER (basic and canonical), there was the XER style of generated code
and the XER runtime. In support of OSys-XER and extended-XER (via direct compilation of XSD), there was what
we called simply the XML style of generated code and the XML runtime. These two styles of code generation had
different encode and decode method signatures, and used different XML parsing techniques (SAX vs. pull-parser). As
of version 6.5.1, these have been merged together. The old style of XER code generation has now been deprecated.
XER is now supported using the same style of code and the same runtime that was previously used for OSysXER and extended-XER (via direct XSD compilation).
Depending on the circumstances, the generated code may support more than one set of encoding rules. In these
cases, the OSASN1XER and OSXMLC14N flags (set using rtxCtxtSetFlag) are used to choose, at runtime, which
encoding rules to follow. OSASN1XER should be set when using BASIC-XER, canonical XER, or EXTENDED-XER.
For canonical XER, OSXMLC14N must also be set.. The table below describes the possibilities.
Note that you may use the -xsd switch when generating XML encoders and decoders. The XML schema produced from
the ASN.1 specification using the -xsd switch can be used to validate the XML messages generated using the XML
encode functions. Similarly, an XML instance can be validated using the generated XML schema prior to decoding.
Compiler Invocation
What is Generated
-xer flag is used to compile ASN.1 without XER encoding Generated code supports BASIC-XER, canonical XER,
instructions
and OSys-XER. Set the flags described above to choose
the desired encoding at runtime. Generated PDU methods
will automatically set OSASN1XER for you.
-xsd produces schema that validates BASIC-XER
encodings.
-xer or -xml flag is used to comple ASN.1 with supported Generated code supports EXTENDED-XER only. You
XER encoding instructions (if any instructions are not should set the OSASN1XER flag. If you are using the PDU
supported, all instructions are ignored, and the above entry methods, it will be automatically set for you.
in this table applies)
-xsd produces schema that validates EXTENDED-XER
encodings. As of this writing, this is not fully supported.
-xml used to compile ASN.1
This is the same as the first entry (using -xer) except that
the generated PDU methods will NOT automatically set
OSASN1XER for you. This means you will get OSys-XER
encodings unless you set the flag yourself.
218
Generated XML Functions
Compiler Invocation
-xml used to compile XSD
What is Generated
-xsd produces schema
encodings.
that
validates
OSys-XER
Generated code supports EXTENDED-XER only. You
should set the OSASN1XER flag. If you are using the PDU
methods, it will be automatically set for you.
Differences between OSys-XER and XER (BASIC-XER)
OSys-XER differs from (BASIC-)XER in the following ways:
• Lists of numbers, enumerated tokens, and named bits are expressed in space-separated list form instead of as
individually wrapped elements or value lists.
For example, the ASN.1 specification “A ::= SEQUENCE OF INTEGER” with value “{ 1 2 3 }” would produce
the following encoding in XER:
<A><INTEGER>1</INTEGER><INTEGER>2</INTEGER><INTEGER>3</INTEGER></A>
in XML, it would be the following:
<A>1 2 3</A>
• The values of the BOOLEAN data type are expressed as the lower case words “true” or “false” with no delimiters.
In XER, the values are <true/> and <false/>.
• Enumerated token values are expressed as the identifiers themselves instead of as empty XML elements (i.e.
elements wrapped in ‘< />’). For example, a value of the ASN.1 type “Colors ::= ENUMERATED { red, blue,
green }” equal to “red” would simply be “<color>red</color>” instead of “<color><red/></color>”.
• The special REAL values <NOT-A-NUMBER/>, <PLUS-INFINITY/> and <MINUS-INFINITY/> are represented
as NaN, INF and -INF, respectively.
• GeneralizedTime and UTCTime values are transformed into the XSD representation for dateTime (YYYYMMDDTHH: MM:SS[.SSSS][(Z|(+|-)HH:MM)]) when encoded to XML. When an XML document is decoded, the
time format is transformed into the ASN.1 format.
EXTENDED-XER
EXTENDED-XER (specified in X.693) allows you to vary the XML encoding of ASN.1 by using XER encoding
instructions. ASN1C supports EXTENDED-XER in two different ways: by compiling XSD and by compiling ASN.1
with XER encoding instructions. Support for XER encoding instructions in ASN.1 is limited.
This section relates to our support for XER encoding instructions. If some features you need are not supported, you
might consider using direct compilation of XSD.
How to Generate Code for EXTENDED-XER
If your ASN.1 contains XER encoding instructions, ASN1C will automatically generate code for EXTENDEDXER instead of BASIC-XER. This is true whether you use -xer or -xml on the command line. If, however, any
unsupported encoding instructions are found, ASN1C will ignore all XER encoding instructions, since it would not
be capable of supporting EXTENDED-XER for that specification.
219
Generated XML Functions
Supported Instructions and Brief Summary
ASN1C supports these instructions: ATTRIBUTE and BASE64. Very brief summaries of the effects of these
instructions follow.
• ATTRIBUTE: This instruction causes a component of a sequence to be encoded as an XML attribute.
• BASE64: This instruction causes octet strings to be encoded in a base64 representation, rather than a hexadecimal
one.
Limitations
The following are limitations related to EXTENDED-XER:
• For BASE64: ASN1C only supports BASE64 on octet strings. Using BASE64 with octet stings having contents
constraints, open types, or restricted character strings is not supported.
• For encoder's options: ASN1C decoders do not support the following encoder's options allowed by EXTENDEDXER:
• encoding named bits as empty elements
• encoding named numbers as empty elements
• Enforcement of Encoding Instruction Restrictions: ASN1C does not check that you are using encoding instructions
properly. Misapplication of encoding instructions has undefined results. For example, X.693 does not generally
allow ATTRIBUTE to be applied to a sequence type (there are a few cases where it can be); such an application
produces malformed XML.
In particular, when applying ATTRIBUTE to a restricted character string type, the type should be restricted to
exclude the control characters listed in X.680 15.15.5, since these control characters are encoded as empty elements.
(Another solution would be to use ATTRIBUTE and BASE64 together, except that ASN1C does not currently
support BASE64 for restricted character strings.) ASN1C will not enforce this rule, but you will get malformed
XML if you try to encode a string having control characters as an attribute.
• XSD Generation: The -xsd switch does not currently generate XSD that can be used to validate EXTENDEDXER encodings. (Actually, in the worst cases, it is not possible to produce XSD that validates precisely the set of
valid EXTENDED-XER encodings; the closest approximations would either fail to reject some invalid encodings
or fail to accept some valid encodings. This is a result of the encoder's options, which can produce mixed content
models and XML Schema's limited abilities to constrain mixed content models.)
Working with generated EXTENDED-XER code
Working with the code generated for EXTENDED-XER is the same as for XER, except that you must be sure to have
set the OSASN1XER context flag. The generated PDU encoders and decoders should automatically set OSASN1XER
for you, but if you are not using these methods, you should be sure to set the OSASN1XER flag yourself, using
rtxCtxtSetFlag.
For encoding and decoding, you will work with the "XML" (as opposed to the "XER") runtime. This is actually true
for BASIC-XER also, unless you are using the deprecated, old style XER.
Finally, there is a sample reader and writer program in c/sample_xer/employee-exer and cpp/
sample_xer/employee-exer, should you need to see an example.
220
Generated XML Functions
Generated XER Encode Functions (Old Style Deprecated)
XER stands for “XML Encoding Rules”, a form of XML specified in the X.693 standard for use with ASN.1.
Note
As noted in the Overiew, the style of generated code that is discussed here is now deprecated. To upgrade
to the new style, see the section below for some upgrade tips. The old-style XER encode functions can still
be generated by specifying the -xer -compat 649 (or lower) switches on the command line. This
ability may be removed in some future version of ASN1C, so you are encouraged to upgrade to the new style.
For each ASN.1 prouction defined in the ASN.1 source file, a C XER encode function is generated. This function will
convert a populated C variable of the given type into an XER encoded ASN.1 message (i.e. an XML document).
If C++ code generation is specified, a control class is generated that contains an Encode method that wraps this function.
This function is invoked through the class interface to encode an ASN.1 message into the variable referenced in the
msgData component of the class.
Note that you may use the -xsd switch when generating XER encoders and decoders with -xer. The XML schema
produced from the ASN.1 specification using the -xsd switch can be used to validate the XML messages generated
using the XER encode functions. Similarly, an XML instance can be validated using the generated XML schema prior
to decoding.
Generated C Function Format and Calling Parameters
The format of the name of each generated XER encode function is as follows:
asn1XE_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each encode function is as follows:
status = asn1XE_<name> (OSCTXT* pctxt, <name>[*] value,
const char* elemName,
const char* attributes);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her or her program.
The value argument contains the value to be encoded or holds a pointer to the value to be encoded. This variable is of
the type generated from the ASN.1 production. The object is passed by value if it is a primitive ASN.1 data type such
as BOOLEAN, INTEGER, ENUMERATED, etc.. It is passed using a pointer reference if it is a structured ASN.1 type
value (in this case, the name will be pvalue instead of value). Check the generated function prototype in the header
file to determine how this argument is to be passed for a given function.
221
Generated XML Functions
The elemName and attributes arguments are used to pass the XML element name and attributes respectively. The
elemName argument is the name that will be included in the <name> </name> brackets used to delimit an XML item.
There are three distinct ways this argument can be specified:
1. If it contains standard text, this text will be used as the element name.
2. If it is null, a default element name will be applied. Default names for all of the built-in ASN.1 types are defined in
the 2002 X.680 standard. For example, <BOOLEAN> is the default element name for the BOOLEAN built-in type.
3. If the name is empty (i.e. equal to “”, a zero-length string – not to be confused with null), then no element name
is applied to the encoded data.
The function result variable stat returns the status of the encode operation. Status code zero indicates the function
was successful. A negative value indicates encoding failed. Return status values are defined in the rtxErrCodes.h
include file. The error text and a stack trace can be displayed using the rtxErrPrint function.
Generated C++ Encode Method Format and Calling
Parameters
Generated encode functions are invoked through the class interface by calling the base class Encode method. The
calling sequence for this method is as follows:
stat = <object>.Encode ();
In this definition, <object> is an object of the class generated for the given production. The function result variable
stat returns the status value from the XER encode function. This status value will be zero if encoding was successful
or a negative error status value if encoding fails. Return status values are defined in the rtxErrCodes.h include file.
The user must call the encode buffer class methods getMsgPtr and getMsgLen to obtain the starting address and length
of the encoded message component.
Procedure for Calling C Encode Functions
This section describes the step-by-step procedure for calling C XER encode functions. This procedure is similar to
that for the other encoding methods except that some of the functions used are specific to XER.
Before an XER encode function can be called, the user must first initialize an encoding context block structure. The
context block is initialized by calling rtInitContext to initialize a context block structure. The user then must call the
xerSetEncBufPtr function to specify a message buffer to receive the encoded message. Specification of a dynamic
message buffer is possible by setting the buffer address argument to null and the buffer size argument to zero. This
function also also allows specification of whether standard XER or canonical XER encoding should be done.
An encode function can then be called to encode the message. If the return status indicates success (0), then the message
will have been encoded in the given buffer. XER encoding starts from the beginning of the buffer and proceeds from
low memory to high memory until the message is complete. This differs from BER where encoding was done from
back-to-front. Therefore, the buffer start address is where the encoded XER message begins. The length of the encoded
message can be obtained by calling the xerGetMsgLen run-time function. If dynamic encoding was specified (i.e.,
a buffer start address and length were not given), the run-time routine xerGetMsgPtr can be used to obtain the start
address of the message. This routine will also return the length of the encoded message.
A program fragment that could be used to encode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
main ()
222
Generated XML Functions
{
OSOCTET msgbuf[4096];
int
msglen, stat;
OSCTXT ctxt;
OSBOOL cxer = FALSE; /* canonical XER flag */
OSBOOL aligned = TRUE;
Employee employee; /* typedef generated by ASN1C */
/* Initialize context and set encode buffer pointer */
if (rtInitContext (&ctxt) != 0) {
rtxErrPrint (&ctxt);
return -1;
}
xerSetEncBufPtr (&ctxt, msgbuf, sizeof(msgbuf), cxer);
/* Populate variable with data to be encoded */
employee.name.givenName = “John”;
...
/* Encode data */
stat = asn1XE_Employee (&ctxt, &employee, 0, 0);
if (stat) == 0) {
msglen = xerGetMsgLen (&ctxt);
...
}
else
error processing...
}
rtFreeContext (&ctxt); /* release the context pointer */
After encoding is complete, msgbuf contains the XML textual representation of the data. By default, a UTF-8 encoding
is used. For the ASCII character set, this results in a buffer containing normal textual data. Therefore, the contents
of the buffer are represented as a normal text string and can be displayed using the C printf run-time function or any
other function capable of displaying text.
Procedure for Using the C++ Control Class Encode
Method
The procedure to encode a message using the C++ class interface is as follows:
1. Instantiate an ASN.1 XER encode buffer object (ASN1XEREncodeBuffer) to describe the buffer into which the
message will be encoded. Constructors are available that allow a static message buffer to be specified and/or
canonical encoding to be turned on (canonical encoding removes all encoding options from the final message to
produce a single encoded representation of the data). The default constructor specifies use of a dynamic encode
buffer and canonical encoding set to off.
2. Instantiate an ASN1T_<type> object and populate it with data to be encoded.
3. Instantiate an ASN1C_<type> object to associate the message buffer with the data to be encoded.
4. Invoke the ASN1C_<type> object Encode method.
223
Generated XML Functions
5. Check the return status. The return value is a status value indicating whether encoding was successful or not.
Zero indicates success. If encoding failed, the status value will be a negative number. The encode buffer method
printErrorInfo can be invoked to get a textual explanation and stack trace of where the error occurred.
6. If encoding was successful, get the start-of-message pointer and message length. The start-of-message pointer is
obtained by calling the getMsgPtr method of the encode buffer object. If static encoding was specified (i.e., a
message buffer address and size were specified to the XER Encode Buffer class constructor), the start-of-message
pointer is the buffer start address. The message length is obtained by calling the getMsgLen method of the encode
buffer object.
A program fragment that could be used to encode an employee record is as follows:
#include employee.h
// include file generated by ASN1C
main ()
{
const OSOCTET* msgptr;
OSOCTET msgbuf[1024];
int
msglen, stat;
OSBOOL canonical = FALSE;
// step 1: instantiate an instance of the XER encode
// buffer class. This example specifies a static
// message buffer..
ASN1XEREncodeBuffer encodeBuffer (msgbuf,
sizeof(msgbuf),
canonical);
// step 2: populate msgData with data to be encoded
ASN1T_PersonnelRecord msgData;
msgData.name.givenName = "SMITH";
...
// step 3: instantiate an instance of the ASN1C_<ProdName>
// class to associate the encode buffer and message data..
ASN1C_PersonnelRecord employee (encodeBuffer, msgData);
// steps 4 and 5: encode and check return status
if ((stat
{
printf
printf
printf
= employee.Encode ()) == 0)
("encoded XML message:\n");
((const char*)msgbuf);
(“\n”);
// step 6: get start-of-message pointer and message length.
// start-of-message pointer is start of msgbuf
// call getMsgLen to get message length..
msgptr = encodeBuffer.getMsgPtr (); // will return &msgbuf
len = encodeBuffer.getMsgLen ();
}
224
Generated XML Functions
else
{
printf ("Encoding failed\n");
encodeBuffer.printErrorInfo ();
exit (0);
}
// msgptr and len now describe fully encoded message
...
Tips for Upgrading to the New Style
• The old XER runtime generally has corresponding methods in the XML runtime that you can use. For example,
xerEncStartDocument can be replaced by rtXmlEncStartDocument.
• XmlEnc_<Type>_PDU methods will encode a type along with the start and end of the XML document.
These methods can be used to replace a sequence of calls to xerEncStartDocument, asn1XE_<Type> and
xerEncEndDocument.
• When invoking an XmlEnc_<Type> method, you must pass the correct element name to encode the value within;
unlike asn1XER_<Type>, the xmlasn1typename is not automatically supplied for you. You will want to pass null
for the namespace argument, since XER does not use XML namespaces.
• Calls to rtInitContext should be replaced by calls to rtXmlInitContext
• If you are not using one of the XmlEnc_<Type> methods, you must use rtxCtxtSetFlag to set the OSASN1XER
flag. This signals the generated and runtime code that XER, and not OSys-XER, rules apply.
• xerSetEncBufPtr is replaced by rtXmlSetEncBufPtr. The latter does not accept a "canonical" flag. Use
rtxCtxtSetFlag to set the OSXMLC14N flag if you want to encode using canonical-XER (the OSASN1XER flag
must still also be set).
• xerGetMsgPtr is replaced by rtXmlGetEncBufPtr
• XERBYTECNT can be replaced by rtxCtxtGetMsgLen
• ASN1XEREncodeBuffer is replaced by OSXMLEncodeBuffer. If you used the three or four argument constructor
for ASN1XEREncodeBuffer to specify canonical-XER or open type encoding, then you will now need to set a flag
on the context, using rtxCtxtSetFlag. For canonical-XER set OSXMLC14N (and also OSASN1XER!). For open
type encoding, set OSXMLFRAG to prevent encoding an XML prolog.
• OSXMLEncodeBuffer does not have a << operator. Replace buffer
myObject.EncodeTo(buffer)
<<
myObject with
Generated XER Decode Functions (Old Style Deprecated)
Note
As noted in the Overiew, the style of generated code that is discussed here is now deprecated. To upgrade
to the new style, see the section below for some upgrade tips. The old-style XER decode functions can still
be generated by specifying the -xer -compat 649 (or lower) switches on the command line. This
ability may be removed in some future version of ASN1C, so you are encouraged to upgrade to the new style.
225
Generated XML Functions
The code generated to decode XML messages is different than that of the other encoding rules. This is because offtheshelf XML parser software is used to parse the XML documents to be decoded. This software contains a common
interface known as the Simple API for XML (or SAX) that is a de-facto standard that is supported by most parsers.
ASN1C generates an implementation of the content handler interface defined by this standard. This implementation
receives the parsed XML data and uses it to populate the structures generated by the compiler.
The default XML parser used is the EXPAT parser (http://expat.sourceforge.net). This is a lightweight, open-source
parser that was implemented in C. The C++ SAX interface was added by adapting the headers of the Apache XERCES
C++ XML Parser (http://xml.apache.org) to work with the underlying C code. These headers were used to build a
common C++ SAX interface across different vendor’s SAX interfaces (unlike Java, these interfaces are not all the
same). The ASN1C XER SAX C and C++ libraries come with the EXPAT parser as the default parser and also include
plug-in interfaces that allow the code to work with the Microsoft XML parser (MSXML), The GNOME libxml2 parser,
and the XERCES XML parser. Interfacing to other parsers only requires building an abstraction layer to map the
common interface to the vendor’s interface.
A diagram showing the components used in the XML decode process is as follows:
Step 1: Generate code
Step 2: Build Application
ASN1C generates code to implement the following methods defined in the SAX content handler interface:
startElement
226
Generated XML Functions
characters
endElement
The interface defines other methods that can be implemented as well, but these are sufficient to decode XER encoded
data.
Procedure for Using the C Interface
The ASN1C compiler generates XER decode functions for C for constructed types in a specification. These can be
invoked in the same manner as other decode functions. In this case, they install the generated SAX content handler
functions and invoke the XML parser’s parse function to parse a document. The procedure to call these generated
functions is described below.
Generated C Function Format and Calling Parameters
The format of the name of each generated C XER decode function is as follows:
asn1XD_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each decode function is as follows:
status = asn1XD_<name> (OSCTXT* pctxt, <name>* pvalue);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of decode parameters. This is a basic "handle"
variable that is used to make the function reentrant so that it can be used in an asynchronous or threaded application.
The user is required to supply a pointer to a variable of this type declared somewhere in his or her program. The
variable must be initialized using the rtInitContext run-time function before use.
C XER decoding is stream-oriented. To perform streaming operations, the context pointer pctxt must also be initialized
as a stream by using the rtxStreamInit run-time library function (see the C/C++ Common Run-Time Library Reference
Manual for a description of the run-time stream C functions).
The pvalue argument is a pointer to a variable to hold the decoded result. This variable is of the type generated from
the ASN.1 production. The decode function will automatically allocate dynamic memory for variable length fields
within the structure. This memory is tracked within the context structure and is released when the context structure
is freed.
The function result variable stat returns the status of the decode operation. Status code zero indicates the function
was successful. A negative value indicates decoding failed. Return status values are defined in the rtxErrCodes.h
include file. The reason text and a stack trace can be displayed using the rtxErrPrint function.
Procedure for Calling C Decode Functions
This section describes the step-by-step procedure for calling a C XER decode function. This method must be used if
C code generation was done. This method cannot be used as an alternative to using the control class interface if C+
+ code generation was done. Use the C++ procedure instead.
There are four steps to calling a compiler-generated decode function:
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Generated XML Functions
1. Prepare a context variable for decoding;
2. Open a stream;
3. Call the appropriate compiler-generated decode function to decode the message;
4. Free the context after use of the decoded data is complete to free allocated memory structures
Before a C XER decode function can be called; the user must initialize a context variable. This is a variable of type
OSCTXT. This variable holds all of the working data used during the decoding of a message. The context variable is
declared as a normal automatic variable within the top-level calling function. It must be initialized before use. This
can be accomplished by using the rtInitContext function. Also, the context must be initialized for streaming operations
by calling the rtxStreamInit function:
OSCTXT ctxt; // context variable
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf (“context initialization failed (check license)\n”);
return –1;
}
rtxStreamInit (&ctxt)); // Initialize stream
The next step is to create a stream object within the context. This object is an abstraction of the output device to which
the data is to be encoded and is initialized by calling one of the following functions:
• rtxStreamFileOpen
• rtxStreamFileAttach
• rtxStreamSocketAttach
• rtxStreamMemoryCreate
• rtxStreamMemoryAttach
The flags parameter of these functions should be set to the OSRTSTRMF_INPUT constant value to indicate an input
stream is being created (see the C/C++ Common Run-Time Library Reference Manual for a full description of these
functions).
A decode function can then be called to decode the message. If the return status indicates success (0), then the message
will have been decoded into the given ASN.1 type variable. The decode function may automatically allocate dynamic
memory to hold variable length items during the course of decoding. This memory will be tracked in the context
structure, so the programmer does not need to worry about freeing it. It will be released when the context is freed.
The final step of the procedure is to close the stream and free the context block. The function to free the context is
rtFreeContext.
A program fragment that could be used to decode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
main ()
{
int
stat;
OSCTXT ctxt;
PersonnelRecord employee;
228
Generated XML Functions
ASN1ConstCharPtr filename = "message.xml";
/* Step 1: Init context structure */
if (rtInitContext (&ctxt) != 0) return -1;
rtxStreamInit (&ctxt);
/* Step 2: Open a stream */
stat = rtxStreamFileOpen (&ctxt, filename, OSRTSTRMF_INPUT);
if (stat != 0) {
rtErrPrint (&ctxt.errInfo);
return -1;
}
/* Step 3: decode the record */
stat = asn1XD_PersonnelRecord (&ctxt, &employee);
if (stat == 0) {
if (trace) {
printf ("Decode of PersonnelRecord was successful\n");
printf ("Decoded record:\n");
asn1Print_PersonnelRecord ("Employee", &employee);
}
}
else {
printf ("decode of PersonnelRecord failed\n");
rtxErrPrint (&ctxt);
rtxStreamClose (&ctxt);
return -1;
}
/* Step 4: Close the stream and free the context. */
rtxStreamClose (&ctxt);
rtFreeContext (&ctxt);
return 0;
}
Procedure for Using the C++ Interface
SAX handler methods are added to the C++ control class generated for each ASN.1 production.
The procedure to invoke the generated decode method is similar to that for the other encoding rules. It is as follows:
1. Instantiate an ASN.1 XER decode buffer object (ASN1XERDecodeBuffer) to describe the message to be decoded.
Constructors exist that allow an XML file or memory buffer to be specified as an input source.
2. Instantiate an ASN1T_TypeName object to hold the decoded message data.
3. Instantiate an ASN1C_TypeName object to decode the message. This class associates the message buffer object
with the object that is to receive the decoded data. The results of the decode operation will be placed in the variable
declared in step 2.
229
Generated XML Functions
4. Invoke the ASN1C_TypeName object Decode method. This method initiates and invokes the XML parser’s parse
method to parse the document. This, in turn, invokes the generated SAX handler methods.
5. Release dynamic memory that was allocated by the decoder. All memory associated with the decode context is
released when both the ASN1XERDecodeBuffer and ASN1C_TypeName objects go out of scope.
A program fragment that could be used to decode an employee record is as follows:
int main (int argc, char* argv[])
{
const char* filename = "employee.xml";
int stat;
// steps 1, 2, and 3: instantiate an instance of the XER
// decoding classes. This example specifies an XML file
// as the message input source..
ASN1T_PersonnelRecord employee;
ASN1XERDecodeBuffer decodeBuffer (filename);
ASN1C_PersonnelRecord employeeC (decodeBuffer, employee);
// step 4: invoke the decode method
stat = employeeC.Decode ();
if (0 == stat) {
employeeC.Print ("employee");
}
else
decodeBuffer.printErrorInfo ();
// step 5: dynamic memory is released when employeeC and
// decode buffer objects go out of scope.
return (stat);
}
Procedure for Interfacing with Other C and C++ X ML
Parser Libraries
As mentioned previously, the Expat XML Parser library is the default XML parser library implementation used for
decoding XER messages. It is also possible to use the C++ SAX handlers generated by ASN1C with other XML parser
library implementations. The XER Run-Time Library (ASN1XER) provides a common interface to other parsers via
a common adapter interface layer. There is a special XML interface object file for each of the following supported
XML parsers:
• rtXmlLibxml2IF - interface to LIBXML2;
• rtXmlXercesIF - interface to XERCES;
• rtXmlExpatIF - interface to EXPAT.
• rtXmlMicroIF - interface to custom, small footprint, microparser
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Generated XML Functions
The XER Run-Time Library is completely independent from the XML readers because the adapter layer within these
libraries defines a common SAX API.
If an application is linked statically then the static variant of one of these interface objects (their names have suffix
“_a”) should be linked cooperatively with the XML parser, ASN1XER and ASN1RT libraries.
If the application is linked dynamically (using dynamically-linked libraries (DLL) in Windows or shared objects (SO
or SL in UNIX/Linux) then it is necessary to link the application with the dynamic variant of the interfaces (without
suffix “_a”), dynamic version of the XML parser, ASN1XER and ASN1RT dynamic libraries.
Tips for Upgrading to the New Style
• XmlDec_<Type>_PDU methods can be used to replace asn1XD_<Type> methods.
• Unlike the asn1XD_<Type> methods, the XmlDec_<Type> methods do not match an outer start tag but begin by
decoding the content of the type. You must use rtXmlpMatchStartTag to match the outer start tag yourself.
• Calls to rtInitContext should be replaced by calls to rtXmlInitContext
• If you are not using one of the XmlDec_<Type> methods, you must use rtxCtxtSetFlag to set the OSASN1XER
flag. This signals the generated and runtime code that XER, and not OSys-XER, rules apply.
• xerSetDecBufPtr is replaced by using one of the rtxStream methods. For example, if the buffer was read from a file,
you can use stat = rtxStreamFileOpen (pctxt, filename, OSRTSTRMF_INPUT);
• Use rtxCtxtSetFlag to set the OSXMLC14N flag if you want to encode using canonical-XER (the OSASN1XER
flag must still also be set).
• ASN1XERDecodeBuffer is replaced with OSXMLDecodeBuffer. Note that OSXMLDecodeBuffer can be created
on streams (there is no OSXMLDecodeStream corresponding to ASN1XERDecodeStream).
• OSXMLDecodeBuffer does not have a >> operator. Replace buffer
myObject.DecodeFrom(buffer)
>>
myObject with
Generated XML Encode Functions
Note
As of version 6.5.1, this section applies to XER encoding rules. See the Overview section above.
XML C encode and decode functions allow data in a populated variable to be formatted into an XML document.
For each ASN.1 production defined in the ASN.1 source file, a C XML encode function is generated. In the case
of XML schema, a C encode function is generated for each type and global element declaration. This function will
convert a populated C variable of the given type into an XML encoded message (i.e. an XML document).
If C++ code generation is specified, a control class is generated that contains an Encode method that wraps this function.
This function is invoked through the class interface to encode an ASN.1 message into the variable referenced in the
msgData component of the class.
Generated C Function Format and Calling Parameters
The format of the name of each generated XML encode function is as follows:
[<namespace>]XmlEnc_[<prefix>]<prodName>
231
Generated XML Functions
where <namespace> is an optional C namespace prefix, <prodName> is the name of the ASN.1 production for
which the function is being generated and <prefix> is an optional prefix that can be set via a configuration file
setting. The configuration setting used to set the prefix is the <typePrefix> element. This element specifies a prefix
that will be applied to all generated typedef names and function names for the production. <namespace> is set using
the ASN1C -namespace command-line argument. Note that this should not be confused with the notion of an XML
namespace.
The calling sequence for each encode function is as follows:
status = <ns>XmlEnc_<name> (OSCTXT* pctxt, <name>[*] value,
const OSUTF8CHAR* elemName,
const OSUTF8CHAR* nsPrefix);
In this definition, <ns> is short for <namespace> and <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program.
The value argument contains the value to be encoded or holds a pointer to the value to be encoded. This variable is of
the type generated from the ASN.1 production. The object is passed by value if it is a primitive ASN.1 data type such
as BOOLEAN, INTEGER, ENUMERATED, etc.. It is passed using a pointer reference if it is a structured ASN.1 type
value (in this case, the name will be pvalue instead of value). Check the generated function prototype in the header
file to determine how this argument is to be passed for a given function.
The elemName and nsPrefix arguments are used to pass the XML element name and namespace prefix respectively.
The two arguments are combined to form a qualified name (QName) of the form <nsPrefix:elemName>. If elemName
is null or empty, then no element tag is added to the encoded content. If nsPrefix is null or empty, the element name
is applied as a local name only without a prefix.
The function result variable stat returns the status of the encode operation. Status code zero indicates the function
was successful. A negative value indicates encoding failed. Return status values are defined in the rtxErrCodes.h
include file. The error text and a stack trace can be displayed using the rtxErrPrint function.
In addition to the XML encode function generated for types, a different type of encode function is generated for
Protocol Data Units (PDU’s). These are types in an ASN.1 specification that are not referenced by any other types.
In an XML schema specification, these are global elements that are not reference within any other types or global
elements.
The format of the a PDU encode function is the same name format as above with the suffix _PDU. This function does
not contain the elemName and nsPrefix arguments - these are built into the function as defined in the schema. For this
reason, calling PDU functions is usually more convenient than calling the equivalent function for the referenced type.
Procedure for Calling C Encode Functions
This section describes the step-by-step procedure for calling C XML encode functions. This procedure is similar to
that for the other encoding methods except that some of the functions used are specific to XML.
Before an XML encode function can be called, the user must first initialize an encoding context block structure. The
context block is initialized by calling rtXmlInitContext to initialize a context block structure. The user then must call the
rtXmlSetEncBufPtr function to specify a message buffer to receive the encoded message. Specification of a dynamic
message buffer is possible by setting the buffer address argument to null and the buffer size argument to zero.
An encode function can then be called to encode the message. If the return status indicates success, then the message
will have been encoded in the given buffer. XML encoding starts from the beginning of the buffer and proceeds from
low memory to high memory until the message is complete. This differs from BER where encoding was done from
232
Generated XML Functions
back-to-front. Therefore, the buffer start address is where the encoded XML message begins. If a dynamic message
buffer was used, the start address of the encoded message can be obtained by calling the rtXmlEncGetMsgPtr function.
Since the encoded XML message is nothing more than a null-terminated string in a memory buffer, the standard C
library function strlen can be used to obtain the length.
A program fragment that could be used to encode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
int main (int argc, char** argv)
{
PersonnelRecord employee;
OSCTXT
ctxt;
OSOCTET
msgbuf[4096];
int
stat;
/* Initialize context and set encode buffer pointer */
stat = rtXmlInitContext (&ctxt);
if (0 != stat) {
printf ("context initialization failed\n");
rtxErrPrint (&ctxt);
return stat;
}
rtXmlSetEncBufPtr (&ctxt, msgbuf, sizeof(msgbuf));
/* Populate variable with data to be encoded */
employee.name.givenName = “John”;
...
/* Encode data */
stat = XmlEnc_PersonnelRecord_PDU (&ctxt, &employee);
if (stat) == 0) {
/* Note: message can be treated as a null-terminated string
in memory */
printf ("encoded XML message:\n");
puts ((char*)msgbuf);
printf ("\n");
...
}
else
error processing...
}
rtFreeContext (&ctxt); /* release the context pointer */
Generated C++ Encode Method Format and Calling
Parameters
When C++ code generation is specified using the -xml switch, the generated EncodeTo and DecodeFrom methods in
the PDU control class are set up to encode complete XML documents including the start document header as well as
namespace attributes in the main element tag.
233
Generated XML Functions
Generated encode functions are invoked through the class interface by calling the base class Encode method. The
calling sequence for this method is as follows:
stat = <object>.Encode ();
In this definition, <object> is an object of the class generated for the given production. The function result variable
stat returns the status value from the XML encode function. This status value will be zero if encoding was successful
or a negative error status value if encoding fails. Return status values are defined in the rtxErrCodes.h include file.
The user must call the encode buffer class methods getMsgPtr and getMsgLen to obtain the starting address and length
of the encoded message component.
Procedure for Using the C++ Control Class Encode
Method
The procedure to encode a message using the C++ class interface is as follows:
1. Instantiate an XML encode buffer object (OSXMLEncodeBuffer) to describe the buffer into which the message will
be encoded. Constructors are available that allow a static message buffer to be specified. The default constructor
specifies use of a dynamic encode buffer.
2. Instantiate an ASN1T_<type> object and populate it with data to be encoded.
3. Instantiate an ASN1C_<type> object to associate the message buffer with the data to be encoded.
4. Invoke the ASN1C_<type> object Encode or EncodeTo method.
5. Check the return status. The return value is a status value indicating whether encoding was successful or not.
Zero indicates success. If encoding failed, the status value will be a negative number. The encode buffer method
printErrorInfo can be invoked to get a textual explanation and stack trace of where the error occurred.
6. If encoding was successful, get the start-of-message pointer and message length. The start-of-message pointer is
obtained by calling the getMsgPtr method of the encode buffer object. If static encoding was specified (i.e., a
message buffer address and size were specified to the XML Encode Buffer class constructor), the start-of-message
pointer is the buffer start address. The message length is obtained by calling the getMsgLen method of the encode
buffer object.
A program fragment that could be used to encode an employee record is as follows:
#include employee.h
// include file generated by ASN1C
main ()
{
OSOCTET msgbuf[4096];
int
msglen, stat;
// step 1: instantiate an instance of the XML encode
// buffer class. This example specifies a static
// message buffer..
OSXMLEncodeBuffer encodeBuffer (msgbuf, sizeof(msgbuf));
// step 2: populate msgData with data to be encoded
234
Generated XML Functions
ASN1T_PersonnelRecord msgData;
msgData.name.givenName = "SMITH";
...
// step 3: instantiate an instance of the ASN1C_<ProdName>
// class to associate the encode buffer and message data..
ASN1C_PersonnelRecord employee (encodeBuffer, msgData);
// steps 4 and 5: encode and check return status
if ((stat
{
printf
printf
printf
= employee.Encode ()) == 0)
("encoded XML message:\n");
((const char*)msgbuf);
(“\n”);
// step 6: get start-of-message pointer and message length.
// start-of-message pointer is start of msgbuf
// call getMsgLen to get message length..
msgptr = encodeBuffer.getMsgPtr (); // will return &msgbuf
len = encodeBuffer.getMsgLen ();
}
else
{
printf ("Encoding failed\n");
encodeBuffer.printErrorInfo ();
exit (0);
}
// msgptr and len now describe fully encoded message
...
Generated XML Decode Functions
Note
As of version 6.5.1, this section applies also to XER encoding rules. See the Overview section above.
A major difference between generated XER decode functions and generated XML decode functions in ASN1C version
6.0 and later is that the XML functions no longer use the Simple API for XML (SAX) interface. Instead, the XML
runtime now uses an XML pull-parser developed in-house for improved efficiency. The pull-parser also provides a
similar interface to that of binary encoding rules such as BER or PER meaning easier integration with existing encoding
rules. Finally, the pull-parser interface does not require integration with any 3rd-party XML parser software.
For each ASN.1 production defined in the ASN.1 source file, a C XML decode function is generated. This function
will parse the data contents from an XML message of the corresponding ASN.1 or XML schema type and populate
a variable of the C type with the data.
If C++ code generation is specified, a control class is generated that contains a DecodeFrom method that wraps this
function. This function is invoked through the class interface to encode an ASN.1 message into the variable referenced
in the msgData component of the class.
235
Generated XML Functions
Generated C Function Format and Calling Parameters
The format of the name of each generated XML decode function is as follows:
[<namespace>]XmlDec_[<prefix>]<prodName>
where <namespace> is an optional C namespace prefix, <prodName> is the name of the ASN.1 production for
which the function is being generated and <prefix> is an optional prefix that can be set via a configuration file
setting. The configuration setting used to set the prefix is the <typePrefix> element. This element specifies a prefix
that will be applied to all generated typedef names and function names for the production. <namespace> is set using
the ASN1C -namespace command-line argument. Note that this should not be confused with the notion of an XML
namespace.
The calling sequence for each decode function is as follows:
status = <ns>XmlDec_<name> (OSCTXT* pctxt, <name>* pvalue);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of decode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program.
The pvalue argument is a pointer to a variable to hold the decoded result. This variable is of the type generated from
the ASN.1 production. The decode function will automatically allocate dynamic memory for variable length fields
within the structure. This memory is tracked within the context structure and is released when the context structure
is freed.
The function returns the status of the decode operation. Status code zero indicates the function was successful. A
negative value indicates decoding failed. Return status values are defined in the rtxErrCodes.h include file. The reason
text and a stack trace can be displayed using the rtxErrPrint function.
Procedure for Calling C Decode Functions
This section describes the step-by-step procedure for calling a C XML decode function. This method must be used
if C code generation was done. This method can also be used as an alternative to using the control class interface if
C++ code generation was done.
These are the steps involved calling a compiler-generated decode function:
1. Prepare a context variable for decoding
2. Open an input stream for the XML document to be decoded
3. Decode the initial tag value to figure out what type of message was received (optional).
4. Call the appropriate compiler-generated decode function to decode the message
5. Free the context after use of the decoded data is complete to free allocated memory structures
Before a C XML decode function can be called, the user must first initialize a context block structure. The context
block structure is initialized by calling the rtXmlInitContext function.
An input stream is then opened using one of the rtxStream functions. If the data is to be read from a file, the
rtxStreamFileCreateReader function can use used. Similar functions exist for opening a memory or socket-based
stream.
236
Generated XML Functions
If the user knows the type of XML message that is to be processed, he can directly call the decode function at this
point. If not, the user may call the rtXmlpMatchStartTag method to match the initial tag in the message with a known
start tag. The user can continue to do this until a match is found with one of the expected message types. Note that the
rtXmlpMarkLastEvent function must be called if the tag is to be reparsed to attempt another match operation.
A decode function can then be called to decode the message. If the return status indicates success (0), then the message
will have been decoded into the given ASN.1 type variable. The decode function may automatically allocate dynamic
memory to hold variable length variables during the course of decoding. This memory will be tracked in the context
structure, so the programmer does not need to worry about freeing it. It will be released when the context is freed.
The final step of the procedure is to free the context block. The function to free the context is rtFreeContext.
A program fragment that could be used to decode an employee record is as follows:
#include employee.h
/* include file generated by ASN1C */
main ()
{
PersonnelRecord data;
OSCTXT ctxt;
OSBOOL trace = TRUE, verbose = FALSE;
const char* filename = "message.xml";
int i, stat;
.. logic to read message into msgbuf ..
/* This example uses a static context block */
/* step 1: initialize the context block */
stat = rtXmlInitContext (&ctxt);
if (stat != 0) {
rtxErrPrint (&ctxt);
return stat;
}
/* step 2: open an input stream */
stat = rtxStreamFileCreateReader (&ctxt, filename);
if (stat != 0) {
rtxErrPrint (&ctxt);
return -1;
}
/* step 3: attempt to match the start tag to a known value */
if (0 == rtXmlpMatchStartTag (&ctxt, OSUTF8(“Employee”)) {
/* Note that it is necessary to mark the last event active in
the pull-parser to that it can be parsed again in the PDU
decode function. */
rtXmlpMarkLastEventActive (&ctxt);
/* step 4: call the decode function */
237
Generated XML Functions
stat = XmlDec_PersonnelRecord_PDU (&ctxt, &data);
if (stat == 0)
{
process received data..
}
else {
/* error processing... */
rtxErrPrint (&ctxt);
}
}
/* can check for other possible tag matches here.. */
/* step 5: free the context */
rtFreeContext (&ctxt);
}
Generated C++ Decode Method Format and Calling
Parameters
Generated decode functions are invoked through the class interface by calling the base class Decode or DecodeFrom
methods. The calling sequence for this method is as follows:
status = <object>.Decode ();
In this definition, <object> is an object of the class generated for the given production.
An OSXMLDecodeBuffer object must be passed to the <object> constructor prior to decoding. This is where the
message stream containing the XML document to be decoded is specified. Several constructors are available allowing
the specification of XML input from a file, memory buffer, or another stream.
The function result variable status returns the status of the decode operation. The return status will be zero if
decoding is successful or a negative value if an error occurs. Return status values are documented in the C/C++
Common Functions Reference Manual and in the rtxErrCodes.h include file.
Procedure for Using the C++ Control Class Decode
Method
The following are the steps are involved in decoding an XML message using the generated C++ class:
1. Instantiate an XML decode buffer object (OSXMLDecodeBuffer) to describe the message to be decoded. There are
several choices of constructors that can be used including one that takes the name of a file which contains the XML
message, one the allows a memory buffer to be specified, and one that allows an existing stream object to be used.
2. Instantiate an ASN1T_<ProdName> object to hold the decoded message data.
3. Instantiate an ASN1C_<ProdName> object to decode the message. This class associates the message buffer object
with the object that is to receive the decoded data. The results of the decode operation will be placed in the variable
declared in step 2.
4. Invoke the ASN1C_<ProdName> object Decode or DecodeFrom method.
238
Generated XML Functions
5. Check the return status. The return value is a status value indicating whether decoding was successful or not.
Zero indicates success. If decoding failed, the status value will be a negative number. The decode buffer method
printErrorInfo can be invoked to get a textual explanation and stack trace of where the error occurred.
6. Release dynamic memory that was allocated by the decoder. All memory associated with the decode context is
released when both the OSXMLDecodeBuffer and ASN1C_<ProdName> objects go out of scope.
A program fragment that could be used to decode an employee record is as follows:
#include employee.h
// include file generated by ASN1C
main ()
{
const char* filename = "message.xml";
OSBOOL verbose = FALSE, trace = TRUE;
int i, stat;
.. logic to read message into msgbuf ..
// step 1: instantiate an XML decode buffer object
OSXMLDecodeBuffer decodeBuffer (filename);
// step 2: instantiate an ASN1T_<ProdName> object
ASN1T_PersonnelRecord msgData;
// step 3: instantiate an ASN1C_<ProdName> object
ASN1C_PersonnelRecord employee (decodeBuffer, msgData);
// step 4: decode the record
stat = employee.Decode ();
// step 5: check the return status
if (stat == 0)
{
process received data..
}
else {
// error processing..
decodeBuffer.PrintErrorInfo ();
}
// step 6: free dynamic memory (will be done automatically
// when both the decodeBuffer and employee objects go out
// of scope)..
}
239
Chapter 12. Generated JavaScript Object
Notation (JSON) Functions
JavaScript Object Notation (JSON) is a minimal format for exchanging data. In version 6.6, ASN1C introduces the
capability of targeting JSON for encoding and decoding. This marries a well-known simple text format (JSON) with
a robust and mature schema language (ASN.1) and provides a possible interchange between JSON and ASN.1 binary
formats like BER or PER.
To generate encoding and decoding functions, use the -json switch on the command-line or select the appropriate
option in the GUI. The following sections describe the generated encoding and decoding functions. Descriptions of the
JSON run time functions may be found in our C JSON Runtime Library Reference Manual. C++ classes are described
in the C++ JSON Runtime Libarary Reference Manual.
Generated JSON Encode Functions
Generated C Function Format and Calling Parameters
The format of the name of each generated encode function is as follows:
asn1JsonEnc_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each encode function follows:
stat = asn1JsonEnc_<name> (OSCTXT* pctxt,
<name>* pvalue);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application.
The user is required to supply a pointer to a variable of this type declared somewhere in his or her program. The
variable should be initialized using the rtInitContext run-time library function (see the C JSON Runtime Library
Reference Manual for a complete description of this function).
The pvalue argument holds a pointer to the data to be encoded and is of the type generated from the ASN.1
production.
The function result variable stat returns an error status code if encoding fails. Return status values are defined in
the asn1type.h include file.
Procedure for Calling C Encode Functions
This section describes the step-by-step procedure for calling a C JSON encode function.
Before any encode function can be called; the user must first initialize an encoding context. This is a variable of type
OSCTXT. This variable holds all of the working data used during the encoding of a message. The context variable is
declared as a normal automatic variable within the top-level calling function. It must be initialized before use. This
can be accomplished by using the rtInitContext function as follows:
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Generated JavaScript Object Notation (JSON) Functions
OSCTXT ctxt;
if (rtInitContext (&ctxt) != 0) {
/* initialization failed, could be a license problem */
printf ("context initialization failed (check license)\n");
return -1;
}
After initializing the context and populating a variable of the structure to be encoded, an encode function can be called
to encode the message.
A complete example may be found in the employee sample program, here edited for brevity:
stat = rtInitContext (&ctxt);
stat = rtxStreamFileCreateWriter (&ctxt, filename);
if (stat != 0) {
printf ("Unable to create file stream.\n");
rtxErrPrint(&ctxt);
return stat;
}
rtxSetDiag (&ctxt, verbose);
asn1Init_PersonnelRecord (&employee);
/* populate employee structure */
stat = asn1JsonEnc_PersonnelRecord (&ctxt, &employee);
Encoding a Series of Messages
Encoding a series of messages in JSON is similar to encoding a series of messages in any other set of encoding rules:
iterate through the input data using a loop, using rtxMemReset to improve performance by reusing memory:
/* initialize context, et c. */
for ( ; ; ) {
/* initialize / populate message structure to be encoded */
/* call MDEREnc_<messageType> (...); */
/* call rtxMemReset when finished encoding: */
rtxMemReset (pctxt);
}
Generated C++ Encoding Methods
Generated C++ encoding methods use the control classes and the OSJSONEncodeBuffer and
OSJSONOutputStream classes to accomplish encodings, as in the following code snippet:
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Generated JavaScript Object Notation (JSON) Functions
OSJSONEncodeBuffer encodeBuffer (0, 0);
encodeBuffer.setDiag (verbose);
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (encodeBuffer, msgData);
/* Populate structure of generated type here */
// Encode
if ((stat = employee.Encode ()) == 0) {
if (trace) {
printf ("Encoding was successful\n");
printf ("%s\n", (const char *)encodeBuffer.getMsgPtr());
}
}
The generated control class (ASN1C_PersonnelRecord) contains methods for encoding (Encode). It unites the
message data (held in ASN1T_PersonnelRecord) and the encoding buffer (OSJSONEncodeBuffer) to encode
the JSON message.
Encoding a Series of Messages using the C++ Control
Class
Encoding a series of messages is virtually identical in the C++ case as it is with C:
for ( ; ; ) {
// logic for populating the data type
stat = employee.Encode();
if (stat == 0) {
// encoding was successful
}
else {
// error handling
}
encodeBuffer.init()
}
The major difference in this case is that the init method is called at the end of the loop rather than the C runtime
function rtxMemReset. The init method serves the same purpose.
Generated JSON Decode Functions
Generated C Function Format and Calling Parameters
The format of the name of each decode function generated is as follows:
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Generated JavaScript Object Notation (JSON) Functions
asn1JsonDec_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each decode function is as follows:
status = asn1JsonDec_<name> (OSCTXT* pctxt, <name> *pvalue);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of decode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program. The variable
must be initialized using the rtInitContext run-time function before use.
The pvalue argument is a pointer to a variable of the generated type that will receive the decoded data.
The function result variable status returns the status of the decode operation. The return status will be greater
than or equal to zero if decoding is successful or negative if an error occurs. Return status values are defined in the
"asn1type.h" include file.
Procedure for Calling C Decode Functions
This section describes the step-by-step procedure for calling a C JSON decode function. This method must be used
if C code generation was done. This method can also be used as an alternative to using the control class interface if
C++ code generation was done.
Before any decode function can be called; the user must first initialize a context variable. This is a variable of type
OSCTXT. This variable holds all of the working data used during the decoding of a message. The context variable
is declared as a normal automatic variable within the top-level calling function. It must be initialized before use.
This can be accomplished as follows:
OSCTXT ctxt;
int stat;
stat = rtInitContext (&ctxt);
if (stat != 0) {
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return stat;
}
The next step is to create a reader that will read from the given source. In our example, we read from a file, but it is
also possible to read data from a socket or other source as well. Alternatively, a decode buffer may also be used.
A decode function can then be called to decode the message. If the return status indicates success, the C variable
that was passed as an argument will contain the decoded message contents. Note that the decoder may have allocated
dynamic memory and stored pointers to objects in the C structure. After processing on the C structure is complete, the
run-time library function rtxMemFree should be called to free the allocated memory.
A program fragment that could be used to decode a simple PDU type follows:
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Generated JavaScript Object Notation (JSON) Functions
/* Init context structure */
if (rtInitContext (&ctxt) != 0) {
printf ("Error initializing context\n");
return -1;
}
stat = rtxStreamFileCreateReader (&ctxt, filename);
if (stat != 0) {
printf ("Unable to open %s for reading.\n", filename);
rtxErrPrint(&ctxt);
rtFreeContext(&ctxt);
return stat;
}
rtxSetDiag (&ctxt, verbose);
/* Decode */
asn1Init_PersonnelRecord (&employee);
stat = asn1JsonDec_PersonnelRecord (&ctxt, &employee);
This example follows the employee sample in the distribution kit.
Decoding a Series of Messages Using the C Decode
Functions
Decoding a series of messages is very similar to the method used for other encoding rules.
Short pseudo-code is shown below. As in the encoding example, rtxMemReset is used at the end of the loop to
avoid allocating new memory for dynamic data structures. This helps to improve performance.
/* initialize context, et c. */
for ( ; ; ) {
/* initialize data structure */
/* call asn1JsonDec_<name> function */
/* perform operations on decoded structure */
/* reset memory: */
stat = rtxMemReset (&ctxt);
}
More details may be found in the sample programs included in the ASN1C software development kit.
Generated C++ Encoding Methods
Generated C++ decoding methods use the control classes and the OSJSONDecodeBuffer and
OSJSONInputStream classes to accomplish decoding, as in the following code snippet:
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Generated JavaScript Object Notation (JSON) Functions
OSJSONDecodeBuffer encodeBuffer (filename);
decodeBuffer.setDiag (verbose);
ASN1T_PersonnelRecord msgData;
ASN1C_PersonnelRecord employee (decodeBuffer, msgData);
/* Populate structure of generated type here */
// Decode
if ((stat = employee.Decode ()) == 0) {
if (trace) {
printf ("Encoding was successful\n");
printf ("%s\n", (const char *)decodeBuffer.getMsgPtr());
}
}
The generated control class (ASN1C_PersonnelRecord) contains methods for encoding (Encode). It unites the
message data (held in ASN1T_PersonnelRecord) and the encoding buffer (OSJSONEncodeBuffer) to encode
the JSON message.
Decoding a Series of Messages using the C++ Control
Class
Decoding a series of messages is virtually identical in the C++ case as it is with C:
for ( ; ; ) {
stat = employee.Decode();
if (stat == 0) {
// decoding was successful
}
else {
// error handling
}
decodeBuffer.init()
}
The major difference in this case is that the init method is called at the end of the loop rather than the C runtime
function rtxMemReset. The init method serves the same purpose.
245
Chapter 13. Generated 3GPP Layer 3
(3GL3) Functions
Generated 3GPP Layer 3 Encode Functions
3GPP Layer 3 encode/decode functions are generated when the -3gl3 switch is specified on the command line. For
each ASN.1 production defined in the ASN.1 source file, a C 3GPP Layer 3 encode function is generated. This function
will convert a populated C variable of the given type into a 3GPP layer 3 encoded message.
C++ is not directly supported for 3GPP Layer 3; however, it is possible to call the generated C functions from a C
++ program.
Generated C Function Format and Calling Parameters
The format of the name of each generated 3GPP layer 3 encode function is as follows:
x3GL3Enc_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
It is also possible to change the 'x3GL3' prefix at the beginning of the function name by using the <protocol>
configuration setting. For example, an API was generated for the Non-Access Stratum (NAS) protocol within the
ASN1C package. A protocol setting of NAS was used for this, so all encode function names begin with 'NASEnc_'
instead of 'x3GL3Enc_'.
The calling sequence for each encode function is as follows:
status = x3GL3Enc_<name> (OSCTXT* pctxt, <name>[*] value);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program.
The value argument contains the value to be encoded or holds a pointer to the value to be encoded. This variable is
of the type generated from the ASN.1 production. The object is passed by value if it is a primitive ASN.1 data type
such as BOOLEAN, INTEGER, ENUMERATED, etc.. It is passed using a pointer reference if it is a structured ASN.1
type value. Check the generated function prototype in the header file to determine how the value argument is to be
passed for a given function.
The function result variable stat returns the status of the encode operation. Status code 0 (0) indicates the function
was successful. Note that this return value differs from that of BER encode functions in that the encoded length of
the message component is not returned – only an OK status indicating encoding was successful. A negative value
indicates encoding failed. Return status values are defined in the "asn1type.h" include file. The error text and a stack
trace can be displayed using the rtxErrPrint function.
It is possible to add extra arguments to 3GPP Layer 3 encode functions through the use of the <addarg> configuration
setting. This is normally done to pass data from container type member variables into an encode function.
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Generated 3GPP Layer 3 (3GL3) Functions
Populating Generated Structure Variables for Encoding
See the section Populating Generated Structure Variables for Encoding for a discussion on how to populate variables
for encoding.
The only difference in populating encode member variables for the general case and for 3GPP layer 3 has to do with
an element configured to be a length variable via the <is3GLength/> configuration setting. A value populated in
this field will be ignored and replaced with the actual length of the encoded data.
Procedure for Calling C Encode Functions
This section describes the step-by-step procedure for calling a C 3GL3 encode function.
Before a 3GL3 encode function can be called, the user must first initialize an encoding context block structure. The
context block is initialized by calling the rtInitContext function.
Only memory-buffer based encoding is supported for 3GPP layer 3 because the message sizes are generally small
(normally less than 256 bytes).
To do memory-based encoding, the rtxInitContextBuffer function would be called. This can be used to specify use of a
static or dynamic memory buffer. Specification of a dynamic buffer is possible by setting the buffer address argument
to null and the buffer size argument to zero.
An encode function can then be called to encode the message. If the return status indicates success (0), then the
message will have been encoded in the given buffer or written to the given stream. 3GL3 encoding starts from the
beginning of the buffer and proceeds from low memory to high memory until the message is complete. This differs
from definite-length BER where encoding was done from back-to-front. Therefore, the buffer start address is where the
encoded 3GL3 message begins. The length of the encoded message can be obtained by calling the rtxCtxtGetMsgLen
run-time function. If dynamic encoding was specified (i.e., a buffer start address and length were not given), the
rtxCtxtGetMsgPtr run-time function can be used to obtain the start address of the message. This routine will also return
the length of the encoded message.
A program fragment that could be used to encode a 3G NAS Identity Request message is as follows:
#include "rt3gppsrc/TS24008Msgs.h"
/* include file generated by ASN1C */
main ()
{
TS24008Msg_PDU pdu;
TS24008Msg_IdentityRequest idReq;
OSCTXT
ctxt;
OSOCTET
msgbuf[256], *msgptr;
int
i, len, stat;
const char* filename = "message.dat";
/* Initialize context structure */
stat = rtInitContext (&ctxt);
if (0 != stat) {
printf ("rtInitContext failed; status = %d\n", ret);
rtxErrPrint (&ctxt);
return ret;
}
247
Generated 3GPP Layer 3 (3GL3) Functions
/* Populate C structure */
pdu.l3HdrOpts.t = T_TS24007L3_L3HdrOptions_skipInd;
pdu.l3HdrOpts.u.skipInd = 0;
asn1SetTC_TS24008Msg_PDU_obj_IdentityRequest (&ctxt, &pdu, &idReq);
OSCRTLMEMSET (&idReq, 0, sizeof(idReq));
idReq.value.typeOfIdent = TS24008IE_IdentityTypeValue_typeOfIdent_imei;
/* Encode */
rtxCtxtSetBufPtr (&ctxt, msgbuf, sizeof(msgbuf));
stat = NASEnc_TS24008Msg_PDU (&ctxt, &pdu);
if (0 != stat) {
printf ("encode PDU failed; status = %d\n", ret);
rtxErrPrint (&ctxt);
return ret;
}
msgptr = rtxCtxtGetMsgPtr (&ctxt);
len = rtxCtxtGetMsgLen (&ctxt);
...
}
In general, static buffers should be used for encoding messages where possible as they offer a substantial performance
benefit over dynamic buffer allocation. In the case of L3 messages, most are small because the length field is sized to
hold a single octet. It is therefore possible to size the buffer at 256 bytes which is the maximum size.
Generated 3GPP Layer 3 Decode Functions
3GPP Layer 3 decode functions are generated when the -3gl3 switch is specified on the command line. For each ASN.1
production defined in the ASN.1 source file, a C 3GL3 decode function is generated. This function will parse the data
contents from a 3GPP layer 3 binary message and populate a variable of the corresponding type with the data.
Generated C Function Format and Calling Parameters
The format of the name of each generated decode function is as follows:
x3GL3Dec_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
It is also possible to change the 'x3GL3' prefix at the beginning of the function name by using the <protocol>
configuration setting. For example, an API was generated for the Non-Access Stratum (NAS) protocol within the
ASN1C package. A protocol setting of NAS was used for this, so all decode function names begin with 'NASDec_'
instead of 'x3GL3Dec_'.
The calling sequence for each decode function is as follows:
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Generated 3GPP Layer 3 (3GL3) Functions
status = x3GL3Dec_<name> (OSCTXT* pctxt, <name>* pvalue);
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold a context pointer to keep track of decode parameters. This is a basic "handle"
variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The
user is required to supply a pointer to a variable of this type declared somewhere in his or her program.
The pvalue argument is a pointer to a variable to hold the decoded result. This variable is of the type generated from
the ASN.1 production. The decode function will automatically allocate dynamic memory for variable length fields
within the structure. This memory is tracked within the context structure and is released when the context structure
is freed.
The function result variable stat returns the status of the decode operation. Status code 0 (0) indicates the function
was successful. A negative value indicates decoding failed. Return status values are defined in the "asn1ErrCodes.h"
and "rtxErrCodes.h" header files. The reason text and a stack trace can be displayed using the rtxErrPrint function
described later in this document.
It is possible to add extra arguments to 3GPP Layer 3 decode functions through the use of the <addarg> configuration
setting. This is normally done to pass data from container type member variables into a decode function.
Procedure for Calling C Decode Functions
This section describes the step-by-step procedure for calling a C 3GL3 decode function.
A Protocol Data Unit (PDU) function is normally defined that includes all of the message that make up a given protocol.
These are grouped together using an Information Object Set that sets up a relation between the protocol discriminator/
message type field combination and the associated message data type. This PDU function is then called to decode both
the header and payload data in one call.
The following are the basic steps in calling the PDU decode function:
1. Prepare a context variable for decoding
2. Initialize the data structure to receive the decoded data
3. Call the PDU decode function to decode the message
4. Free the context after use of the decoded data is complete to free allocated memory structures
Before a 3GL3 decode function can be called, the user must first initialize a context block structure. The context block
is initialized by calling the rtInitContext function.
Only memory-buffer based encoding is supported for 3GPP layer 3 because the message sizes are generally small
(normally less than 256 bytes).
To do memory-based decoding, the rtxInitContextBuffer function would be called. The message to be decoded must
reside in memory. The arguments to this function would then specify the message buffer in which the data to be
decoded exists.
The PDU variable that is to receive the decoded data must then be initialized. This can be done by either initializing
the variable to zero using memset, or by calling the ASN1C generated initialization function.
The PDU decode function can then be called to decode the message. If the return status indicates success (0), then the
message will have been decoded into the PDU type variable. The decode function may automatically allocate dynamic
memory to hold variable length variables during the course of decoding. This memory will be tracked in the context
249
Generated 3GPP Layer 3 (3GL3) Functions
structure, so the programmer does not need to worry about freeing it. It will be released when the either the context is
freed or explicitly when the rtxMemFree or rtxMemReset function is called.
The final step of the procedure is to free the context block. This must be done regardless of whether the block is static
(declared on the stack and initialized using rtInitContext), or dynamic (created using rtNewContext). The function to
free the context is rtFreeContext.
A program fragment that could be used to decode a 3G NAS PDU is as follows:
#include "rt3gppsrc/TS24008Msgs.h"
/* include file generated by ASN1C */
main ()
{
TS24008Msg_PDU data;
OSCTXT
ctxt;
OSOCTET*
msgbuf;
const char* filename = "message.dat";
int
stat;
OSSIZE
len;
/* step 1: initialize context */
stat = rtInitContext (&ctxt);
if (stat != 0) {
printf (“rtInitContext failed (check license)\n“);
rtErrPrint (&ctxt);
return stat;
}
/* step 2: read input file into a memory buffer */
stat = rtxFileReadBinary (&ctxt, filename, &pMsgBuf, &len);
if (0 == stat) {
stat = rtxInitContextBuffer (&ctxt, pMsgBuf, len);
}
if (0 != stat) {
rtxErrPrint (&ctxt);
rtFreeContext (&ctxt);
return stat;
}
/* step 3: set protocol version number */
rtxCtxtSetProtocolVersion (&ctxt, 8);
/* step 4: call the decode function */
stat = NASDec_TS24008Msg_PDU (&ctxt, &data);
if (stat == 0)
{
process received data..
}
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Generated 3GPP Layer 3 (3GL3) Functions
else {
/* error processing... */
rtxErrPrint (&ctxt);
}
/* step 4: free the context */
rtFreeContext (&ctxt);
}
251
Chapter 14. Additional Generated
Functions
Generated Initialization Functions
As of ASN1C version 6.0, initialization functions are automatically generated (in previous versions, it was necessary to
use the -genInit option to force this action). If for some reason, a user does want initialization functions to be generated,
the -noInit switch can be used to turn initialization function generation off.
The use of initialization functions are optional - a variable can be initialized by simply setting its contents to zero
(for example, by using the C run-time memset function). The advantage of initialization function is that they provide
smarter initialization which can lead to improved application performance. For example, it is not necessary to set
a large byte array to zero prior to its receiving a populated value. The use of memset in this situation can result in
degraded performance.
Generated initialization functions are written to the main <module>.c file. This file contains common constants, global
variables, and functions that are generic to all type of encode/decode functions. If the -cfile command-line option is
used, the functions are written to the specified .c or .cpp file along with all other generated functions. If -maxcfiles is
specified, each generated initialization function is written to a separate .c file.
The format of the name of each generated initialization function is as follows:
asn1Init_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each generated initialization function is as follows:
asn1Init_<name> (<name>* pvalue)
In this definition, <name> denotes the prefixed production name defined above.
The pvalue argument is used to pass a pointer to a variable of the item to be initialized.
Generated Memory Free Functions
The -genFree option causes functions to be generated that free dynamic memory allocated using the ASN1C run-time
memory management functions and macros (rtxMem). By default, all memory held within a context is freed using the
rtxMemFree run-time function. It is also possible to free an individual memory item using the rtMemFreePtr function.
But it is not possible to free all memory held within a specific generated type container. For example, a SEQUENCE
type could contain elements that require dynamic memory. These elements in turn can reference other types that require
dynamic memory. The generated memory free functions make it possible to release all memory held within a variable
of the type with a single call.
Generated memory free functions are written to the main <module>.c file. This file contains common constants, global
variables, and functions that are generic to all type of encode/decode functions. If the -cfile command-line option is
used, the functions are written to the specified .c or .cpp file along with all other generated functions. If -maxcfiles is
specified, each generated function is written to a separate .c file.
252
Additional Generated Functions
The format of the name of each generated memory free function is as follows:
asn1Free_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each generated memory free function is as follows:
asn1Free_<name> (OSCTXT* pctxt, <name>* pvalue)
In this definition, <name> denotes the prefixed production name defined above.
The pctxt argument is used to hold the context pointer that the memory to be freed was allocated with. This is a
basic "handle" variable that is used to make the function reentrant so it can be used in an asynchronous or threaded
application. The user is required to supply a pointer to a variable of this type declared somewhere in his or her or
her program.
The pvalue argument is used to pass a pointer to a variable of the item that contains the dynamic memory to be freed.
Generated Print Functions
The following options are available for generating code to print the contents of variables of generated types:
-print - This is the standard print option that causes print functions to be generated that output data to the standard
output device (stdout).
-genPrtToStr - This option causes print functions to be generated that write their output to a memory buffer.
-genPrtToStrm - This option causes print functions to be generated that write their output to an output stream via a
user-defined print callback function.
Print to Standard Output
The -print option causes functions to be generated that print the contents of variables of generated types to the standard
output device. It is possible to specify the name of a .c or .cpp file as an argument to this option to specify the name
of the file to which these functions will be written. This is an optional argument. If not specified, the functions are
written to separate files for each module in the source file. The format of the name of each file is <module>Print.c. If
an output filename is specified after the –print qualifier, all functions are written to that file.
The format of the name of each generated print function is as follows:
asn1Print_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each generated print function is as follows:
asn1Print_<name> (const char* name, <name>* pvalue)
In this definition, <name> denotes the prefixed production name defined above.
253
Additional Generated Functions
The name argument is used to hold the top-level name of the variable being printed. It is typically set to the same
name as the pvalue argument in quotes (for example, to print an employee record, a call to asn1Print_Employee
(“employee”, &employee) might be used).
The pvalue argument is used to pass a pointer to a variable of the item to be printed.
If C++ code generation is specified, a Print method is added to the ASN1C control class for the type. This method
takes only a name argument; the pvalue argument is obtained from the msgData reference contained within the class.
Print to String
The -genPrtToStr option causes functions to be generated that print the contents of variables of generated types to a
given text buffer. This buffer can then be used to output the information to other mediums such as a file or window
display.
It is possible to specify the name of a .c or .cpp file as an argument to this option to specify the name of the file to which
these functions will be written. This is an optional argument. If not specified, the functions are written to separate files
for each module in the source file. The format of the name of each file is <module>PrtToStr.c. If an output filename
is specified after the –genPrtToStr qualifier, all functions are written to that file.
The calling sequence for each generated print-to-string function is as follows:
asn1PrtToStr_<name> (const char* name, <name>* pvalue,
char* buffer, int bufSize)
The name and pvalue arguments are the same as they were in the -print case.
The buffer and bufSize arguments are used to describe the memory buffer the text is to be written into. These arguments
specify a fixed-size buffer. If the generated text is larger than the given buffer size, as much text as possible is written
to the buffer and a –1 status value is returned. If the buffer is large enough to hold the text output, all text is written
to the buffer and a zero status is returned. If there is text already in the buffer, the function will append to this text,
rather than overwrite it, starting at the first null character. So in this case there must be enough space in the buffer
starting from the first null character to hold all of the generated text; otherwise, a status of -1 is returned. For this
reason initializing a newly allocated buffer with zeroes before passing it to the function is a good idea.
For C++, two toString methods are generated in the control class that call the generated print-to-string function. With
the first signature, in addition to the name argument, the method also takes a buffer and bufSize argument to describe
the buffer to which the text is to be written. The second signature does not take a name argument; instead, the name
of the item that the control class instance describes is defaulted.
Print to Stream
The -genPrtToStrm option causes functions to be generated that print the contents of variables of generated types to an
output stream via a user-defined callback function. The advantage of these functions is that a user can register a callback
function, and then the print stream is automatically directed to the callback function. This makes it easier to support
print-to-file or print-to-window type of functionalities. It also make it possible to create an optimized print-to-string
capability by maintaining a structure that keeps track of the current end-of-string position in the output buffer. The
generated print-to-string functions always must use the strlen run-time function to find the end position, an operation
that becomes compute intensive in large string buffers that are constantly appended to.
It is possible to specify the name of a .c or .cpp file as an argument to this option to specify the name of the file to which
these functions will be written. This is an optional argument. If not specified, the functions are written to separate files
for each module in the source file. The format of the name of each file is <module>PrtToStrm.c. If an output filename
is specified after the –genPrtToStrm qualifier, all functions are written to that file.
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Additional Generated Functions
Before calling generated print-to-stream functions, a callback function should be registered. Otherwise, a default
callback function will be used that directs the print stream to the standard output device.
The callback function is declared as:
void (*rtxPrintCallback)
void* pPrntStrmInfo, const char* fmtspec, va_list arglist);
The first parameter is user-defined data which will be passed to each invocation of the callback function. This parameter
can be used to pass print stream specific data, for example, a file pointer if the callback function is to output data to a
file. The second and third parameters to the callback function constitute the data to be printed, in the form of format
specification followed by list of arguments. A simple callback function for printing to file can be defined as follows:
void writeToFile (void* pPrntStrmInfo, const char* fmtspec, va_list arglist)
{
FILE * fp = (FILE*) pPrntStrmInfo;
vfprintf (fp, fmtspec, arglist);
}
Once the callback function is defined, it has to be registered with the runtime library. There are two types of registrations
possible: 1. global, which applies to all print streams and, 2. context level, which applies to print streams associated
with a particular context.
For registering a global callback use:
rtxSetGlobalPrintStream (rtxPrintCallback myCallback, void* pStrmInfo);
For registering a context level callback use:
rtxSetPrintStream (OSCTXT *pctxt, rtxPrintCallback myCallback, void* pStrmInfo);
Once the callback function is registered, the calling of each generated print-to-stream function will result in output
being directed to the callback function.
The print to stream functions are declared as follows:
asn1PrtToStrm_<name> (OSCTXT *pctxt, const char* name, <name>* pvalue);
The name and pvalue arguments are the same as they were in the -print case.
The pctxt argument is used to specify an ASN1C context. If a valid context argument is passed and there is a context
level callback registered, then that callback will be used. If there is no context level callback registered, or the pctxt
argument is NULL, then the global callback will be used. If there is no global callback registered, the default callback
will be used which writes the print output to stdout.
If C++ code generation is specified, setPrintStream and toStream methods are added to the ASN1C control class for
the type. The setPrintStream method takes only myCallback and pStrmInfo arguments; the pctxt argument is obtained
from the context pointer reference contained within the class. The toStream method takes only a name argument; the
pctxt argument is derived from the context pointer reference within the class and the pvalue argument is obtained from
the msgData reference contained within the class.
Print Format
The -prtfmt option can be used in conjunction with any of the -genPrint options documented above to alter the format
of the printed data. There are two possible print formats: details and bracetext.
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Additional Generated Functions
The details format prints a line-by-line display of every item in the generated structure. For example, the following
is an excerpt from a details display:
Employee.name.givenName = 'John'
Employee.name.initial = 'P'
Employee.name.familyName = 'Smith'
Employee.number = 51
Employee.title = 'Director'
...
The alternative format - bracetext - provides a C-like structure printout. This is a more concise format that will omit
optional fields that are not present in the decoded data. An example of this is as follows:
Employee {
name {
givenName = 'John'
initial = 'P'
familyName = 'Smith'
}
number = 51
title = 'Director'
...
As of ASN1C version 6.0 and higher, bracetext is the default format used if -prtfmt is not specified on the commandline.
Previous versions of ASN1C had details as the default setting.
Generated Compare Functions
The -genCompare option causes comparison functions to be generated. These functions can be used to compare the
contents of two generated type variables.
If an output file is not specified with the –genCompare qualifier, the functions are written to separate .c files for each
module in the source file. The format of the name of each file is <module>Compare.c. If an output filename is specified
after the –genCompare qualifier, all functions are written to that file.
The format of the name of each generated compare function is as follows:
asn1Compare_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each generated compare function is as follows:
OSBOOL asn1Compare_<name> (const char* name,
<name>* pvalue, <name>* pCmpValue,
char* errBuff, int errBufSize);
In this definition, <name> denotes the prefixed production name defined above.
The name argument is used to hold the top-level name of the variable being compared. It is typically set to the same
name as the pvalue argument in quotes (for example, to compare employee records, a call to ‘asn1Compare_Employee
(“employee”, &employee, etc.)’ might be used).
256
Additional Generated Functions
The pvalue argument is used to pass a pointer to a variable of the item to the first item to be compared. The pCmpValue
argument is used to pass the second value. The two items are then compared field-by-field for equality.
The errBuff and errBuffSize arguments are used to describe a text buffer into which information on what fields the
comparison failed on is written. These arguments specify a fixed-size buffer – if the generated text is larger than the
given buffer size, the text is terminated. These arguments may be omitted by passing null (0) values if you only care
to know if the structures are different and not concerned with the details.
The return value of the function is a Boolean value that is true if the variables are equal and false if they are not.
Generated Copy Functions
The -genCopy option causes copy functions to be generated. These functions can be used to copy the content of one
generated type variable to another.
If no output file is specified with the –genCopy qualifier, the functions are written to separate .c/.cpp files for each
module in the source file. The format of the name of each file is <module>Copy.c/.cpp where <module> would be
replaced with the name of the ASN.1 module. If an output filename is specified after the –genCopy qualifier, all
functions are written to that file.
The format of the name of each generated copy function is as follows:
asn1Copy_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names
and function names for the production.
The calling sequence for each generated copy function is as follows:
void asn1Copy_<name> (OSCTXT* pctxt,
<name>* pSrcValue,
<name>* pDstValue);
In this definition, <name> denotes the prefixed production name defined above.
The pointer to the context structure (pctxt) provides a storage area for the function to store all variables that have
been copied
The pSrcValue argument is used to pass a pointer to a variable to be copied. The pDstValue argument is used to pass
the pointer to the destination value. The source value is then copied to the destination value field-by-field. Memory
will be allocated for dynamic fields using calls to the rtxMemAlloc function.
If C++ is used (-cpp option is specified) and PDU generation is not disabled (<noPDU> config option is not used)
then the control class ASN1C_<name> additionally will contain:
• A copy constructor that can be used to create an exact copy of the class instance.
The calling sequence is as follows:
ASN1C_<name> (ASN1C_<name>& orginal);
For example:
ASN1C_PersonnelRecord (ASN1C_PersonnelRecord& original);
257
Additional Generated Functions
• A getCopy method that creates a copy of the ASN1T_<name> variable:
ASN1T_<name>& getCopy (ASN1T_<name>* pDstData = 0);
For example:
ASN1T_PersonnelRecord& getCopy (ASN1T_PersonnelRecord* pDstData = 0);
The pDstData argument is used to pass the pointer to a destination variable where the value will be copied. It may
be null, in this case the new ASN1T_<name> variable will be allocated via a call to the rtxMemAlloc function.
• A newCopy method that will create a new, dynamically allocated copy of the referenced ASN1T_ data member
variable.
• An assignment operator. This is used to copy one instance of a control class to another one:
inline ASN1C_<name>& operator= (ASN1C_<name>& srcData)
{
srcData.getCopy (&msgData);
return *this;
}
For example:
inline ASN1C_PersonnelRecord& operator=
(ASN1C_PersonnelRecord& srcData)
{
srcData.getCopy (&msgData);
return *this;
}
Finally, the class declaration might look as follows:
class EXTERN ASN1C_PersonnelRecord :
public ASN1CType
{
protected:
ASN1T_PersonnelRecord& msgData;
public:
ASN1C_PersonnelRecord (
ASN1MessageBuffer& msgBuf, ASN1T_PersonnelRecord& data);
ASN1C_PersonnelRecord (ASN1C_PersonnelRecord& original);
...
ASN1T_PersonnelRecord& getCopy (ASN1T_PersonnelRecord*
pDstData = 0);
ASN1T_PersonnelRecord* newCopy ();
inline ASN1C_PersonnelRecord&
operator= (ASN1C_PersonnelRecord& srcData)
{
srcData.getCopy (&msgData);
return *this;
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Additional Generated Functions
}
} ;
The generated ASN1T<name> structure will also contain an additional copy constructor if C++ is used and PDU
generation is not disabled. A destructor is also generated if the type contains dynamic memory fields. This destructor
will free the dynamic memory upon destruction of the type instance.
For example:
typedef struct EXTERN ASN1T_PersonnelRecord : public ASN1TPDU {
...
ASN1T_PersonnelRecord () {
m.uniPresent = 0;
m.seqOfseqPresent = 0;
}
ASN1T_PersonnelRecord (ASN1C_PersonnelRecord& srcData);
~ASN1T_PersonnelRecord();
} ASN1T_PersonnelRecord;
This constructor is used to create an instance of the ASN1T_<name> type from an ASN1C_<name> control class
object.
Memory Management of Copied Items
Prior to ASN1C version 5.6, dynamic memory of decoded or copied items would only be available as long as the
control class instance and/or the message buffer object used to decode or copy the item remained in scope or was not
deleted. This restriction no longer exists as long as the type being copied is a Protocol Data Unit (PDU). The copied
item will now hold a reference to the context variable used to create the item and will increment the item’s reference
count. This reference is contained in the ASN1TPDU base class variable from which PDU data types are now derived.
The dynamic memory within the item will persist until the item is deleted.
Generated Test Functions
The -genTest option causes test functions to be generated. These functions can be used to populate variables of
generated types with random test data. The main purpose is to provide a code template to users for writing code to
populate variables. This is quite useful to users because generated data types can become very complex as the ASN.1
schemas become more complex. It is sometimes difficult to figure out how to navigate all of the lists and pointers.
Using –genTest can provide code that simply has to be modified to accomplish the population of a data variable with
any type of data.
The generated test functions are written to a .c or .cpp file with a name of the following format:
<asn1ModuleName>Test.c
where <asn1ModuleName> is the name of the ASN.1 module that contains the type definitions. The format of the
name of each generated test function is as follows:
asn1Test_[<prefix>]<prodName>
where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix>
is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix
is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and
function names for the production.
The calling sequence for each generated test function is as follows:
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Additional Generated Functions
<typeName>* pvalue = <testFunc> (OSCTXT* pctxt)
In this definition, <testFunc> denotes the formatted function name defined above.
The pctxt argument is used to hold a context pointer to keep track of dynamic memory allocation parameters. This
is a basic "handle" variable that is used to make the function reentrant so that it can be used in an asynchronous or
threaded application. The user is required to supply a pointer to a variable of this type declared somewhere in his or
her program. The variable must have been previously initialized using the rtInitContext run-time function.
The pvalue argument is a pointer to hold the populated data variable. This variable is of the type generated for
the ASN.1 production. The test function will automatically allocate dynamic memory using the run-time memory
management for the main variable as well as variable length fields within the structure. This memory is tracked within
the context structure and is released when the context structure is freed.
In the case of C++, a method is added to the generated control class for test code generation. The name of this method
is genTestInstance. The prototype is as follows:
<typeName>* pvalue = <object>.genTestInstance();
where <typeName> is the ASN1T_<name> type name of the generated type and <object> is an instance of the
ASN1C_<name> generated control class.
Generated Sample Programs
In addition to test functions, it is possible to generate writer and reader sample programs. These programs contain
sample code to populate and encode an instance of ASN.1 data and then read and decode this data respectively. These
programs are generated using the -genwriter and -genreader command-line switches.
260
Chapter 15. Event Handler Interface
The –events command line switch causes hooks for user-defined event handlers to be inserted into the generated decode
functions. What these event handlers do is up to the user. They fire when key message-processing events or errors
occur during the course of parsing an ASN.1 message. They are similar in functionality to the Simple API for XML
(SAX) that was introduced to provide a simple interface for parsing XML messages.
The -notypes option can be used in conjunction with the -events option to generate pure parsing functions. In this case,
no C types or encode or decode functions are generated for the productions within the given ASN.1 source file. Instead,
only a set of parser functions are generated that invoke the event handler callback functions. This gives the user total
control over what is done with the message data. Data that is not needed can be discarded and only the parts of the
message needed for a given application need to be saved.
How it Works
Users of XML parsers are probably already quite familiar with the concepts of SAX. Significant
events are defined that occur during the parsing of a message. As a parser works through a message,
these events are ‘fired’ as they occur by invoking user defined callback functions. These callback
functions are also known as event handler functions. A diagram illustrating this parsing process is as
follows:
The events are defined to be significant actions that occur during the parsing process. We will define the following
events that will be passed to the user when an ASN.1 message is parsed:
1. startElement – This event occurs when the parser moves into a new element. For example, if we have a
SEQUENCE { a, b, c } construct (type names omitted), this event will fire when we begin parsing a, b, and c. The
name of the element is passed to the event handling callback function.
2. endElement – This event occurs when the parser leaves a given element space. Using the example above, these
would occur after the parsing of a, b, and c are complete. The name of the element is once again passed to the
event handling callback function.
3. contents methods – A series of virtual methods are defined to pass all of the different types of primitive values that
might be encountered when parsing a message (see the event handler class definition below for a complete list).
4. error – This event will be fired when a parsing error occurs. It will provide fault-tolerance to the parsing process
as it will give the user the opportunity to fix or ignore errors on the fly to allow the parsing process to continue.
261
Event Handler Interface
In C++, these events are defined as unimplemented virtual methods in two base classes: Asn1NamedEventHandler (the
first 3 events) and Asn1ErrorHandler (the error event). These classes are defined in the asn1CppEvtHndlr.h header file.
In C, the first 3 event types are contained within a struct, Asn1NamedCEventHandler, defined in asn1CEvtHndlr.h, as
consisting of function pointers. The error event, however, is not part of this struct and must be defined separately.
The start and end element methods are invoked when an element is parsed within a constructed type. The start method
is invoked as soon as the tag/length is parsed in a BER message or the preamble/length is parsed in a PER message.
The end method is invoked after the contents of the field are processed. The signature of these methods, in C++, is
as follows:
virtual void startElement (const char* name, int index) = 0;
virtual void endElement (const char* name, int index) = 0;
and in C:
typedef void (*rtxStartElement) (const char* name, int idx) ;
typedef void (*rtxEndElement) (const char* name, int idx) ;
The name argument is used pass the element name. The index argument is used for SEQUENCE OF/SET OF constructs
only. It is used to pass the index of the item in the array. This argument is set to –1 for all other constructs.
There is one contents method for passing each of the ASN.1 data types. Some methods are used to handle several
different types. For example, the charValue method is used for values of all of the different character string types
(IA5String, NumericString, PrintableString, etc.) as well as for big integer values. Note that this method is overloaded.
The second implementation is for 16-bit character strings. These strings are represented as an array of unsigned short
integers in ASN1C. All of the other contents methods correspond to a single equivalent ASN.1 primitive type.
The C++ error handler base class has a single virtual method that must be implemented. This is the error method and
this has the following signature:
virtual int error (OSCTXT* pCtxt, ASN1CCB* pCCB, int stat) = 0;
The C error handler function, unlike the other events in C, is not contained within a struct. Its signature is as follows:
typedef int (*rtErrorHandler) (OSCTXT *pctxt, ASN1CCB *pCCB, int stat);
In these definitions, pCtxt and pctxt are pointers to the standard ASN.1 context block that should already be familiar.
The pCCB structure is known as a “Context Control Block”. This can be thought of as a sub-context used to control
the parsing of nested constructed types within a message. It is included as a parameter to the error method mainly to
allow access to the “seqx” field. This is the sequence element index used when parsing a SEQUENCE construct. If
parsing a particular element is to be retried, this item must be decremented within the error handler.
How to Use It
In both C and C++, two things must be done to define event handlers:
1. In C++, one or more new classes must be derived from the Asn1NamedEventHandler and/or the Asn1ErrorHandler
base classes. All pure virtual methods must be implemented.
In C, a function with an appropriate signature must be created for each function pointer in the struct; the behavior
of null function pointers is undefined. The error handler function, if one is desired, must also be defined.
2. Objects of these classes (or in C, an instance of the Asn1NamedCEventHandler struct) must be created and registered
prior to calling the generated decode method or function.
262
Event Handler Interface
The best way to illustrate this procedure is through examples. We will first show a C++ and then a C version of a
simple event handler application to provide a customized formatted printout of the fields in a PER message. Then we
will show a simple error handler that will ignore unrecognized fields in a BER message.
Example 1: A Formatted Print Handler (C++)
The ASN1C evaluation and distribution kits include a sample program for doing a formatted print of parsed data.
This code can be found in the cpp/sample_per/eventHandler directory. Parts of the code will be reproduced here for
reference, but refer to this directory to see the full implementation.
The format for the printout will be simple. Each element name will be printed followed by an equal sign (=) and an
open brace ({) and newline. The value will then be printed followed by another newline. Finally, a closing brace (})
followed by another newline will terminate the printing of the element. An indentation count will be maintained to
allow for a properly indented printout.
A header file must first be created to hold our print handler class definition (or the definition could be added to an
existing header file). This file will contain a class derived from the Asn1NamedEventHandler base class as follows:
class PrintHandler : public Asn1NamedEventHandler {
protected:
const char* mVarName;
int mIndentSpaces;
public:
PrintHandler (const char* varName);
~PrintHandler ();
void indent ();
virtual void startElement (const char* name, int index = -1);
virtual void endElement (const char* name, int index = -1);
virtual void boolValue (OSBOOL value);
... other virtual contents method declarations
}
In this definition, we chose to add the mVarName and mIndentSpaces member variables to keep track of these items.
The user is free to add any type of member variables he or she wants. The only firm requirement in defining this
derived class is the implementation of the virtual methods.
We implement these virtual methods as follows:
In startElement, we print the name, equal sign, and opening brace:
void PrintHandler::startElement (const char* name, int index)
{
indent();
printf (“%s = {\n”, name);
mIndentLevel++;
}
In this simplified implementation, we simply indent (this is another private method within the class) and print out the
name, equal sign, and opening brace. We then increment the indent level. Note that this is a highly simplified form.
We don’t even bother to check if the index argument is greater than or equal to zero. This would determine if a ‘[x]’
should be appended to the element name. In the sample program that is included with the compiler distribution, the
implementation is complete.
In endElement, we simply terminate our brace block as follows:
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Event Handler Interface
void PrintHandler::endElement (const char* name, int index)
{
mIndentLevel--;
indent();
printf (“}\n”);
}
Next, we need to create an object of our derived class and register it prior to invoking the decode method. In the
reader.cpp program, the following lines do this:
// Create and register an event handler object
PrintHandler* pHandler = new PrintHandler ("employee");
decodeBuffer.addEventHandler (pHandler);
The addEventHandler method defined in the Asn1MessageBuffer base class is the mechanism used to do this. Note
that event handler objects can be stacked. Several can be registered before invoking the decode function. When this is
done, the entire list of event handler objects is iterated through and the appropriate event handling callback function
invoked whenever a defined event is encountered.
The implementation is now complete. The program can now be compiled and run. When this is done, the resulting
output is as follows:
employee = {
name = {
givenName = {
"John"
}
initial = {
"P"
}
familyName = {
"Smith"
}
}
...
This can certainly be improved. For one thing it can be changed to print primitive values out in a “name = value”
format (i.e., without the braces). But this should provide the general idea of how it is done.
Example 2: A Formatted Print Handler (C)
As with the C++ version, a C version of the sample is available in the c/sample_per/eventHandler directory.
A header file containing all function declaratios must be created. In this example, an
initializePrintHandler(Asn1NamedCEventHandler *printHandler, const char* varname) function is also declared,
which will be used to populate the Asn1NamedCEventHandler struct:
Asn1NamedCEventHandler printHandler;
void initializePrintHandler
(Asn1NamedCEventHandler *printHandler, const char* varname);
void finishPrint();
void indent ();
void printStartElement (const char* name, int index );
void printEndElement (const char* name, int index );
264
Event Handler Interface
void printBoolValue (OSBOOL value);
void printIntValue (OSINT32 value);
...
A corresponding *.c file (printHandler.c, in this case) contains the definitions of these functions:
static int gs_IndentSpaces;
void initializePrintHandler
(Asn1NamedCEventHandler *printHandler, const char* varname)
{
printHandler->startElement = &printStartElement;
printHandler->endElement = &printEndElement;
printHandler->boolValue = &printBoolValue;
printHandler->intValue = &printIntValue;
...
}
...
void printStartElement (const char* name, int index)
{
indent ();
printf (name);
if (index >= 0) printf ("[%d]", index);
printf (" = {\n");
gs_IndentSpaces += 3;
}
void printEndElement (const char* name, int index)
{
gs_IndentSpaces -= 3;
indent ();
printf ("}\n");
}
As in Example 1, a variable gs_IndentSpaces is used to keep track of indentation.
Next, the reader program will need to create an Asn1NamedCEventHandler variable, populate it (via
initializePrintHandler), and add it to the decode context:
int main (int argc, char** argv)
{
PersonnelRecord employee;
OSCTXT ctxt;
...
int i, len, stat;
265
Event Handler Interface
Asn1NamedCEventHandler printHandler;
ASN1TAG tag;
...
/* initialize print handler */
initializePrintHandler(&printHandler, "employee");
...
/* Add event handler to list */
rtAddEventHandler (&ctxt, &printHandler);
/* Call compiler generated decode function */
stat = asn1D_PersonnelRecord (&ctxt, &employee, ASN1EXPL, 0);
...
}
The rtAddEventHandler function used to push the event handler into the decode context is defined in asn1CEvtHndlr.h.
This can be done multiple times, as with C++, and every event will trigger the appropriate callback function of each
event handler.
Example 3: An Error Handler
Despite the addition of things like extensibility and version brackets, ASN.1 implementations get out-of-sync. For
situations such as this, the user needs some way to intervene in the parsing process to set things straight. This is
faulttolerance – the ability to recover from certain types of errors.
The error handler interface is provided for this purpose. The concept is simple. Instead of throwing an exception and
immediately terminating the parsing process, a user defined callback function is first invoked to allow the user to check
the error. If the user can fix the error, all he or she needs to do is apply the appropriate patch and return a status of 0.
The parser will be none the wiser. It will continue on thinking everything is fine.
This interface is probably best suited for recovering from errors in BER or DER instead of PER. The reason is the
TLV format of BER makes it relatively easy to skip an element and continue on. It is much more difficult to find
these boundaries in PER.
Our example can be found in the cpp/sample_ber/errorHandler subdirectory. In this example, we have purposely
added a bogus element to one of the constructs within an encoded employee record. The error handler will be invoked
when this element is encountered. Our recovery action will simply be to print out a warning message, skip the element,
and continue.
As before, the first step is to create a class derived from the Asn1ErrorHandler base class. This class is as follows:
class MyErrorHandler : public Asn1ErrorHandler {
public:
// The error handler callback method. This is the method
// that the user must override to provide customized
// error handling..
virtual int error (OSCTXT* pCtxt, ASN1CCB* pCCB, int stat);
} ;
Simple enough. All we are doing is providing an implementation of the error method.
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Event Handler Interface
Implementing the error method requires some knowledge of the run-time internals. In most cases, it will be necessary
to somehow alter the decoding buffer pointer so that the same field isn’t looked at again. If this isn’t done, an
infinite loop can occur as the parser encounters the same error condition over and over again. The run-time functions
xd_NextElement or xd_OpenType might be useful in the endeavor as they provide a way to skip the current element
and move on to the next item.
Our sample handler corrects the error in which an unknown element is encountered within a SET construct. This will
cause the error status ASN_E_NOTINSET to be generated. When the error handler sees this status, it prints information
on the error that was encountered to the console, skips to the next element, and then returns an 0 status that allows the
decoder to continue. If some other error occurred (i.e., status was not equal to ASN_E_NOTINSET), then the original
status is passed out which forces the termination of the decoding process.
The full text of the handler is as follows:
int MyErrorHandler::error (OSCTXT* pCtxt, ASN1CCB* pCCB, int stat)
{
// This handler is set up to look explicitly for ASN_E_NOTINSET
// errors because we know the SET might contain some bogus elements..
if (stat == ASN_E_NOTINSET) {
// Print information on the error that was encountered
printf ("decode error detected:\n");
rtErrPrint (pCtxt);
printf ("\n");
// Skip element
xd_NextElement (pCtxt);
// Return an OK status to indicate parsing can continue
return 0;
}
else return stat; // pass existing status back out
}
Now we need to register the handler. Unlike event handlers, only a single error handler can be registered. The method
to do this in the message buffer class is setErrorHandler. The following two lines of code in the reader program
register the handler:
MyErrorHandler errorHandler;
decodeBuffer.setErrorHandler (&errorHandler);
The error handlers can be as complicated as you need them to be. You can use them in conjunction with event handlers
in order to figure out where you are within a message in order to look for a specific error at a specific place. Or you
can be very generic and try to continue no matter what.
It should be noted that implementing an error handler in C does not involve a struct at all. It is only necessary to
implement a function with the appropriate signature (specified above) and to pass a pointer to it to the decode buffer.
So, with a error handler function:
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Event Handler Interface
static int myErrorHandler (OSCTXT *pctxt, ASN1CCB *pCCB, int stat) {
// Error-handling code goes here...
}
the function is set in the decode context by calling:
rtSetErrorHandler(&ctxt, &myErrorHandler);
where ctxt is an OSCTXT.
Also, just as in C++, there can be only one error handler set at a time.
Example 4: A Pure Parser to Convert PER-encoded Data to XML
A pure-parser is created by using the -notypes option along with the -events option. In this case, no backing data types
to hold decoded data are generated. Instead, parsing functions are generated that store the data internally within local
variables inside the parsing functions. This data is dispatched to the callback functions and immeditely disposed of
upon return from the function. It is up to the user to decide inside the callback handler what they want to keep and they
must make copies at that time. The result is a very fast and low-memory consuming parser that is ideal for parsing
messages in which only select parts of the messages are of interest.
Another use case for pure-parser functions is validation. These functions can be used to determine if a PER message
is valid without going through the high overhead operation of decoding. They can be used on the front-end of an
application to reject invalid messages before processing of the messages is done. In some cases, this can result in
significantly increased performance.
An example of a pure-parser can be found in the cpp/sample_per/per2xmlEH directory. This program uses a pureparser to convert PER-encoded data into XML. The steps in creating an event handler are the same as in Example 1
above. An implementation of the Asn1NamedEventHandler interface must be created. This is done in the xmlHandler.h
and xmlHandler.cpp files. A detailed discussion of this code will not be provided here. What it does in a nutshell
is adds the angle brackets (< >) around the element names in the startElement and endElement callbacks. The data
callbacks simply output a textual representation of the data as they do in the print handler case.
The only difference in reader.cpp from the other examples is that:
1. There is no declaration of an employee variable to hold decoded data because no type for this variable was generated,
and
2. The Parse method is invoked instead of the Decode method. This is the generated method definition for a pureparser.
If one examines the generated class definitions, they will see that no Encode or Decode methods were generated.
Compiling and running this program will show the encoded PER message written to stdout as an XML message. The
resulting message is also saved in the message.xml file.
268
Chapter 16. IMPORT/EXPORT of Types
ASN1C allows productions to be shared between different modules through the ASN.1 IMPORT/EXPORT
mechanism. The compiler parses but ignores the EXPORTS declaration within a module. As far as it is concerned,
any type defined within a module is available for import by another module.
When ASN1C sees an IMPORT statement, it first checks its list of loaded modules to see if the module has already
been loaded into memory. If not, it will attempt to find and parse another source file containing the module. The logic
for locating the source file is as follows:
1. The configuration file (if specified) is checked for a <sourceFile> element containing the name of the source file for
the module. Note that the <oid> configuration item can be used to distinguish modules that have the same names
but different object identifiers.
2. If this element is not present, the compiler looks for a file with the name <ModuleName>.asn where module name
is the name of the module specified in the IMPORT statement.
In both cases, the –I command line option can be used to tell the compiler where to look for the files.
The other way of specifying multiple modules is to include them all within a single ASN.1 source file. It is possible to
have an ASN.1 source file containing multiple module definitions in which modules IMPORT definitions from other
modules. An example of this would be the following:
ModuleA DEFINITIONS ::= BEGIN
IMPORTS B From ModuleB;
A ::= B
END
ModuleB DEFINITIONS ::= BEGIN
B ::= INTEGER
END
This entire fragment of code would be present in a single ASN.1 source file.
269
Chapter 17. ROSE and SNMP Macro
Support
The ASN1C compiler has a special processing mode that contains extensions to handle items in the older 1990 version
of ASN.1 (i.e. the now deprecated X.208 and X.209 standards). This mode is activated by using the -asnstd x208
command-line option.
Although the X.208 and X.209 standards are no longer supported by the ITU-T, they are still in use today. This version
of ASN1C contains logic to parse some common MACRO definitions that are still in widespread use despite the fact
that MACRO syntax was retired with this version of the standard. The types of MACRO definitions that are supported
are ROSE OPERATION and ERROR and SNMP OBJECT-TYPE.
ROSE OPERATION and ERROR
ROSE stands for "Remote Operations Service Element" and defines a request/response transaction protocol in which
requests to a conforming entity must be answered with the result or errors defined in operation definitions. Variations
of this are used in a number of protocols in use today including CSTA and TCAP.
The definition of the ROSE OPERATION MACRO that is built into the ASN1C is as follows:
OPERATION MACRO ::=
BEGIN
TYPE NOTATION
VALUE NOTATION
Parameter
ArgKeyword
Result
Errors
LinkedOperations
ResultType
ErrorNames
ErrorList
Error
::=
::=
::=
::=
::=
::=
::=
::=
::=
::=
::=
LinkedOperationNames ::=
OperationList
::=
Operation
::=
NamedType
::=
Parameter Result Errors LinkedOperations
value (VALUE INTEGER)
ArgKeyword NamedType | empty
"ARGUMENT" | "PARAMETER"
"RESULT" ResultType | empty
"ERRORS" "{"ErrorNames"}" | empty
"LINKED" "{"LinkedOperationNames"}" | empty
NamedType | empty
ErrorList | empty
Error | ErrorList "," Error
value(ERROR) -- shall reference an error value
| type
-- shall reference an error type
-- if no value is specified
OperationList | empty
Operation | OperationList "," Operation
value(OPERATION) -- shall reference an op value
| type
-- shall reference an op type
-- if no value is specified
identifier type | type
END
This MACRO does not need to be defined in the ASN.1 specification to be parsed. In fact, any attempt to redefine this
MACRO will be ignored. Its definition is hard-coded into the compiler.
The compiler uses this definition to parse types and values out of OPERATION definitions. An example of an
OPERATION definition is as follows:
login OPERATION
ARGUMENT SEQUENCE { username IA5String, password IA5String }
270
ROSE and SNMP Macro Support
RESULT SEQUENCE { ticket OCTET STRING, welcomeMessage IA5String }
ERRORS { authenticationFailure, insufficientResources }
::= 1
In this case, there are two embedded types (an ARGUMENT type and a RESULT type) and an integer value (1) that
identifies the OPERATION. There are also error definitions.
The ASN1C compiler generates two types of items for the OPERATION:
1. It extracts the type definitions from within the OPERATION definitions and generates equivalent C/C++ structures
and encoders/decoders, and
2. It generates value constants for the value associated with the OPERATION (i.e., the value to the right of the '::='
in the definition).
The compiler does not generate any structures or code related to the OPERATION itself (for example, code to encode
the body and header in a single step). The reason is because of the multi-layered nature of the protocol. It is assumed
that the user of such a protocol would be most interested in doing the processing in multiple stages, hence no single
function or structure is generated.
Therefore, to encode the login example the user would do the following:
1. At the application layer, the Login_ARGUMENT structure would be populated with the username and password
to be encoded.
2. The encode function for Login_ARGUMENT would be called and the resulting message pointer and length would
be passed down to the next layer (the ROSE layer).
3. At the ROSE layer, the Invoke structure would be populated with the OPERATION value, invoke identifier, and
other header parameters. The parameter.numocts value would be populated with the length of the message passed
in from step 2. The parameter.data field would be populated with the message pointer passed in from step 2.
4. The encode function for Invoke would be called resulting in a fully encoded ROSE Invoke message ready for
transfer across the communications link.
The following is a picture showing this process:
On the decode side, the process would be reversed with the message flowing up the stack:
1. At the ROSE layer, the header would be decoded producing information on the OPERATION type (based on the
MACRO definition) and message type (Invoke, Result, etc..). The invoke identifier would also be available for use
in session management. In our example, we would know at this point that we got a login invoke request.
271
ROSE and SNMP Macro Support
2. Based on the information from step 1, the ROSE layer would know that the Open Type field contains a pointer
and length to an encoded Login_ARGUMENT component. It would then route this information to the appropriate
processor within the Application Layer for handling this type of message.
3. The Application Layer would call the specific decoder associated with the Login_ARGUMENT. It would then have
available to it the username/password the user is logging in with. It could then do whatever applicationspecific
processing is required with this information (database lookup, etc.).
4. Finally, the Application Layer would begin the encoding process again in order to send back a Result or Error
message to the Login Request.
A picture showing this is as follows:
The login OPERATION also contains references to ERROR definitions. These are defined using a separate MACRO
that is built into the compiler. The definition of this MACRO is as follows:
ERROR MACRO ::=
BEGIN
TYPE NOTATION
::= Parameter
VALUE NOTATION
::= value (VALUE INTEGER)
Parameter
::= "PARAMETER" NamedType | empty
NamedType
::= identifier type | type
END
In this definition, an error is assigned an identifying number as well as on optional parameter type to hold parameters
associated with the error. An example of a reference to this MACRO for the authenticationFailure error in
the login operation defined earlier would be as follows:
applicationError ERROR
PARAMETER SEQUENCE {
errorText IA5String
}
}
::= 1
The ASN1C compiler will generate a type definition for the error parameter and a value constant for the error value.
The format of the name of the type generated will be "<name>_PARAMETER" where <name> is the ERROR name
272
ROSE and SNMP Macro Support
(applicationError in this case) with the first letter set to uppercase. The name of the value will simply be the ERROR
name.
SNMP OBJECT-TYPE
The SNMP OBJECT-TYPE MACRO is one of several MACROs used in Management Information Base (MIB)
definitions. It is the only MACRO of interest to ASN1C because it is the one that specifies the object identifiers and
data that are contained in the MIB.
The version of the MACRO currently supported by this version of ASN1C can be found in the SMI Version 2 RFC
(RFC 2578). The compiler generates code for two of the items specified in this MACRO definition:
1. The ASN.1 type that is specified using the SYNTAX command, and
2. The assigned OBJECT IDENTIFIER value
For an example of the generated code, we can look at the following definition from the UDP MIB:
udpInDatagrams OBJECT-TYPE
SYNTAX
Counter32
MAX-ACCESS read-only
STATUS
current
DESCRIPTION
"The total number of UDP datagrams delivered to UDP users."
::= { udp 1 }
In this case, a type definition is generated for the SYNTAX element and an Object Identifier value is generated for
the entire item. The name used for the type definition is "<name>_SYNTAX" where <name> would be replaced
with the OBJECT-TYPE name (i.e., udpInDatagrams). The name used for the Object Identifier value constant is the
OBJECTTYPE name. So for the above definitions, the following two C items would be generated:
typedef Counter32 udpInDatagrams_SYNTAX;
ASN1OBJID udpInDatagrams = {
8,
{ 1, 3, 6, 1, 2, 1, 7, 1 }
} ;
273
Appendix A. Runtime Status Codes
This appendix describes status code messages returned by the ASN1C C/C++ runtime libraries. When deploying
applications linked against optimized runtime libraries, ASN1C by default does not include a stacktrace; instead only
an error code is provided. These codes are described more fully in this appendix.
The descriptions are derived from the contents of rtxsrc/rtxErrCodes.h and rtsrc/asn1ErrCodes.h.
Users may always look at these two files or the documentation generated from them for a fully updated list of error
messages and their descriptions.
ASN1C Error Messages
The following table describes error messages that ASN1C may report during the course of code generation, not during
runtime. These include syntax errors, import warnings, type resolution failures, and others.
Users should note that there are several classes of status messages in this list: errors (ASN-E messages), warnings
(ASN-W messages), and informational notices (ASN-I messages).
Error Code
Error Description
ASN-E-NOTYPE
No type was defined for the referenced element in a SEQUENCE or
SET.
ASN-E-UNDEFTYPE
The type referenced was not defined within the context of this module.
ASN-E-NOTAG
The object must be tagged in this context. This usually occurs when
context-specific tags are required to disambiguate elements in a
SEQUENCE or SET.
ASN-W-DUPLICATE
The referenced type or value was previously defined.
ASN-W-DUPLTAG
The referenced tag was previously defined in a CHOICE or SET; this
happens when an contextual tag is provided more than once.
ASN-E-UNRECTYP
The type described is not recognized by the compiler.
ASN-E-MULTDEF
A choice tag has multiple definitions.
ASN-E-UNDEFVAL
The referenced value is not defined or cannot be found.
ASN-E-INVTYPNAM
Invalid type name. This is a parsing failure; all type names must begin
with an uppercase letter.
ASN-E-UNDEFTAG
The referenced type must be tagged in this context.
ASN-E-UNKNOWN
Undocumented error occurred in routine. A status value is provided
with this error message to help locate the cause of the failure.
ASN-I-NOCASE
A case statement for the named object was not generated.
ASN-E-IMPFILOPN
The compiler was unable to open the named import file.
ASN-E-IMPFILPAR
The compiler was unable to parse the named imported module.
ASN-E-IMPNOTFOU
The named type was not found in the import module as specified in
the IMPORT statement.
ASN-E-INVCNSTRNT
Invalid constraint specification.
ASN-W-INVOBJNAM
Invalid object name. The object name must begin with a lowercase
letter.
ASN-E-SETTOOBIG
Set contains more than 32 elements.
ASN-E-DUPLCASE
This tag was used in a previous switch case statement.
274
Runtime Status Codes
Error Code
Error Description
ASN-E-AMBIGUOUS
This indicates a general ambiguity in the specification such as multiple
embedded extensible elements.
ASN-E-VALTYPMIS
This indicates the value specified does not match the type it is
associated with.
ASN-E-RANGERR
This indicates the value is not within defined range for its associated
type.
ASN-E-VALPARSE
This indicates a general failure to parse a value definition. It would
be raised, for example, if a floating point number was used as part of
a SIZE constraint.
ASN-E-INVRANGE
This indicates an invalid range specification, for example when the
lower bound is greater than the upper bound.
ASN-E-IMPORTMOD
This indicates that the specified import module object was not found.
ASN-E-NOTSUPP
This indicates that the requested functionality is not supported by the
compiler. Most often the error is raised when generating test code for
complex value definitions.
ASN-E-IDNOTFOU
This indicates the compiler was unable to look up the specified
identifier.
ASN-E-NOFIELD
This indicates that the specified field could not be found in the named
class.
ASN-E-DUPLNAME
This indicates the specified name is already defined.
ASN-W-UNNAMED
This warning is raised when specifications use unnamed fields. These
fields not allowed in X.680, but ASN1C supports them for purposes
of backwards compatibility with X.208.
ASN-E-UNDEFOBJ
This indicates that the named object is not defined within context of
the requested module.
ASN-E-ABSCLSFLD
This indicates that the specified field is absent in an information object
definition.
ASN-E-UNDEFCLAS
This indicates that the specified class is not defined within context of
the module that uses it.
ASN-E-INVFIELD
This indicates the specified class field is not valid; it must be defined.
ASN-E-UNDEFOSET
This indicates that ASN1C was unable to find the specified object set
in the context of the module in which it's used.
ASN-E-INVVALELM
An invalid value was supplied for an element in a type.
ASN-E-MISVALELM
This indicates that a non-optional element is missing a value when it
should have one.
ASN-E-INVLIDENT
This indicates that an invalid identifier was specified in an
enumeration.
ASN-E-FILNOTFOU
This indicates that the requested file was not found.
ASN-E-INVSIZE
This indicates that an invalid size specification for a type was
provided; check size constraints for base types.
ASN-E-UNRESOBJ
This indicates that the specified information object could not be
resolved within the context of the named module.
ASN-E-TOOMANY
This indicates that too many sub-elements for the specified type were
provided.
275
Runtime Status Codes
Error Code
Error Description
ASN-E-LOOPDETECTED
This indicates a loop was detected in the course of code generation;
typically this is raised during test code generation.
ASN-E-INVXMLATTR
This indicates that the specified attribute type must be a simple type.
ASN-E-INTERNAL
This indicates that internal structures used for generating code are
inconsistent.
ASN-E-NOPDU
This indicates that a PDU type was not found for generating a reader
or writer program.
General Status Messages
The following table contains both system and validation failures that may occur during program execution. These
failures do not arise from ASN.1-specific features (such as an invalid PER encoding), but instead comprehend such
failures as buffer overflows, invalid socket options, or closed streams.
Error Code
Error Name
Description
0
RT_OK
Normal completion status.
2
RT_OK_FRAG
Message fragment return status. This is returned when a
part of a message is successfully decoded. The application
should continue to invoke the decode function until a zero
status is returned.
-1
RTERR_BUFOVFLW
Encode buffer overflow. This status code is returned when
encoding into a static buffer and there is no space left for
the item currently being encoded.
-2
RTERR_ENDOFBUF
Unexpected end-of-buffer. This status code is returned
when decoding and the decoder expects more data to be
available but instead runs into the end of the decode buffer.
-3
RTERR_IDNOTFOU
Expected identifier not found. This status is returned when
the decoder is expecting a certain element to be present
at the current position and instead something different
is encountered. An example is decoding a sequence
container type in which the declared elements are expected
to be in the given order. If an element is encountered that
is not the one expected, this error is raised.
-4
RTERR_INVENUM
Invalid enumerated identifier. This status is returned when
an enumerated value is being encoded or decoded and
the given value is not in the set of values defined in the
enumeration facet.
-5
RTERR_SETDUPL
Duplicate element in set. This status code is returned when
decoding an ASN.1 SET or XSD xsd:all construct. It is
raised if a given element defined in the content model
group occurs multiple times in the instance being decoded.
-6
RTERR_SETMISRQ
Missing required element in set. This status code is
returned when decoding an ASN.1 SET or XSD xsd:all
construct and all required elements in the content model
group are not found to be present in the instance being
decoded.
276
Runtime Status Codes
Error Code
Error Name
Description
-7
RTERR_NOTINSET
Element not in set. This status code is returned when
encoding or decoding an ASN.1 SET or XSD xsd:all
construct. When encoding, it occurs when a value in the
generated _order member variable is outside the range of
indexes of items in the content model group. It occurs on
the decode side when an element is received that is not
defined in the content model group.
-8
RTERR_SEQOVFLW
Sequence overflow. This status code is returned when
decoding a repeating element (ASN.1 SEQUENCE OF or
XSD element with minmaxOccurs > 1) and more instances
of the element are received the content model group.
-9
RTERR_INVOPT
Invalid option in choice. This status code is returned
when encoding or decoding an ASN.1 CHOICE or XSD
xsd:choice construct. When encoding, it occurs when a
value in the generated 't' member variable is outside the
range of indexes of items in the content model group. It
occurs on the decode side when an element is received that
is not defined in the content model group.
-10
RTERR_NOMEM
No dynamic memory available. This status code is
returned when a dynamic memory allocation request is
made and an insufficient amount of memory is available
to satisfy the request.
-11
RTERR_INVHEXS
Invalid hexadecimal string. This status code is returned
when decoding a hexadecimal string value and a character
is encountered in the string that is not in the valid
hexadecimal character set ([0-9A-Fa-f] or whitespace).
-12
RTERR_INVREAL
Invalid real number value. This status code is returned
when decoding a numeric floating-point value and an
invalid character is received (i.e. not numeric, decimal
point, plus or minus sign, or exponent character).
-13
RTERR_STROVFLW
String overflow. This status code is returned when a
fixed-sized field is being decoded as specified by a size
constraint and the item contains more characters or bytes
then this amount. It can occur when a run-time function
is called with a fixed-sixed static buffer and whatever
operation is being done causes the bounds of this buffer
to be exceeded.
-14
RTERR_BADVALUE
Bad value. This status code is returned anywhere where
an API is expecting a value to be within a certain range
and it not within this range. An example is the encoding or
decoding date values when the month or day value is not
within the legal range (1-12 for month and 1 to whatever
the max days is for a given month).
-15
RTERR_TOODEEP
Nesting level too deep. This status code is returned when a
preconfigured maximum nesting level for elements within
a content model group is exceeded.
-16
RTERR_CONSVIO
Constraint violation. This status code is returned when
constraints defined the schema are violated. These include
XSD facets such as minmaxOccurs, minmaxLength,
277
Runtime Status Codes
Error Code
Error Name
Description
patterns, etc.. Also ASN.1 value range, size, and permitted
alphabet constraints.
-17
RTERR_ENDOFFILE
Unexpected end-of-file error. This status code is returned
when an unexpected end-of-file condition is detected
on decode. It is similar to the ENDOFBUF error code
described above except that in this case, decoding is being
done from a file stream instead of from a memory buffer.
-18
RTERR_INVUTF8
Invalid UTF-8 character encoding. This status code is
returned by the decoder when an invalid sequence of bytes
is detected in a UTF-8 character string.
-19
RTERR_OUTOFBND
Array index out-of-bounds. This status code is returned
when an attempt is made to add something to an array and
the given index is outside the defined bounds of the array.
-20
RTERR_INVPARAM
Invalid parameter passed to a function of method. This
status code is returned by a function or method when it
does an initial check on the values of parameters passed in.
If a parameter is found to not have a value in the expected
range, this error code is returned.
-21
RTERR_INVFORMAT
Invalid value format. This status code is returned when a
value is received or passed into a function that is not in
the expected format. For example, the time string parsing
function expects a string in the form "nn:nn:nn" where
n's are numbers. If not in this format, this error code is
returned.
-22
RTERR_NOTINIT
Context not initialized. This status code is returned when
the run-time context structure (OSCTXT) is attempted to
be used without having been initialized. This can occur
if rtxInitContext is not invoked to initialize a context
variable before use in any other API call. It can also occur
is there is a license violation (for example, evaluation
license expired).
-23
RTERR_TOOBIG
Value will not fit in target variable. This status is returned
by the decoder when a target variable is not large enough
to hold a a decoded value. A typical case is an integer
value that is too large to fit in the standard C integer
type (typically a 32-bit value) on a given platform. If this
occurs, it is usually necessary to use a configuration file
setting to force the compiler to use a different data type
for the item. For example, for integer, the <isBigInteger>
setting can be used to force use of a big integer type.
-24
RTERR_INVCHAR
Invalid character. This status code is returned when a
character is encountered that is not valid for a given data
type. For example, if an integer value is being decoded and
a non-numeric character is encountered, this error will be
raised.
-25
RTERR_XMLSTATE
XML state error. This status code is returned when the
XML parser
278
Runtime Status Codes
Error Code
Error Name
Description
-26
RTERR_XMLPARSE
XML parser error. This status code in returned when the
underlying XML parser application (by default, this is
Expat) returns an error code. The parser error code or text
is returned as a parameter in is not in the correct state to
do a certain operation.
-27
RTERR_SEQORDER
Sequence order error. This status code is returned when
decoding an ASN.1 SEQUENCE or XSD xsd:sequence
construct. It is raised if the elements were received in
an order different than that specified the errInfo structure
within the context structure.
-28
RTERR_FILNOTFOU
File not found. This status code is returned if an attempt
is made to open a file input stream for decoding and the
given file does not exist.
-29
RTERR_READERR
Read error. This status code if returned if a read IO error is
encountered when reading from an input stream associated
with a physical device such as a file or socket.
-30
RTERR_WRITEERR
Write error. This status code if returned if a write IO error
is encountered when attempting to output data to an output
stream associated with a physical device such as a file or
socket.
-31
RTERR_INVBASE64
Invalid Base64 encoding. This status code is returned
when an error is detected in decoding base64 data.
-32
RTERR_INVSOCKET
Invalid socket. This status code is returned when an
attempt is made to read or write from a scoket and the
given socket handle is invalid. This may be the result of
not having established a proper connection before trying
to use the socket handle variable.
-33
RTERR_INVATTR
Invalid attribute. This status code is returned by the
decoder when an attribute is encountered in an XML
instance that was not defined in the XML schema.
-34
RTERR_REGEXP
Invalid regular expression. This status code is returned
when a syntax error is detected in a regular expression
value. Details of the syntax error can be obtained by
invoking rtxErrPrint to print the details of the error
contained within the context variable.
-35
RTERR_PATMATCH
Pattern match error. This status code is returned by the
decoder when a value in an XML instance does not match
the pattern facet defined in the XML schema. It can also be
returned by numeric encode functions that cannot format a
numeric value to match the pattern specified for that value.
-36
RTERR_ATTRMISRQ
Missing required attribute. This status code is returned by
the decoder when an XML instance is missing a required
attribute value as defined in the XML schema.
-37
RTERR_HOSTNOTFOU
Host name could not be resolved. This status code is
returned from run-time socket functions when they are
unable to connect to a given host computer.
279
Runtime Status Codes
Error Code
Error Name
Description
-38
RTERR_HTTPERR
HTTP protocol error. This status code is returned by
functions doing HTTP protocol operations such as SOAP
functions. It is returned when a protocol error is detected.
Details on the specific error can be obtained by calling
rtxErrPrint.
-39
RTERR_SOAPERR
SOAP error. This status code when an error is detected
when tryingto execute a SOAP operation.
-40
RTERR_EXPIRED
Evaluation license expired. This error is returned from
evaluation versions of the run-time library when the hardcoded evaluation period is expired.
-41
RTERR_UNEXPELEM
Unexpected element encountered. This status code is
returned when an element is encountered in a position
where something else (for example, an attribute) was
expected.
-42
RTERR_INVOCCUR
Invalid number of occurrences. This status code is
returned by the decoder when an XML instance contains
a number of occurrences of a repeating element that is
outside the bounds (minOccursmaxOccurs) defined for
the element in the XML schema.
-43
RTERR_INVMSGBUF
Invalid message buffer has been passed to decode
or validate method. This status code is returned
by decode or validate method when the used
message buffer instance has type different from
OSMessageBufferIF::XMLDecode.
-44
RTERR_DECELEMFAIL
Element decode failed. This status code and parameters
are added to the failure status by the decoder to allow the
specific element on which a decode error was detected to
be identified.
-45
RTERR_DECATTRFAIL
Attribute decode failed. This status code and parameters
are added to the failure status by the decoder to allow the
specific attribute on which a decode error was detected to
be identified.
-46
RTERR_STRMINUSE
Stream in-use. This status code is returned by stream
functions when an attempt is made to initialize a stream or
create a reader or writer when an existing stream is open
in the context. The existing stream must first be closed
before initializaing a stream for a new operation.
-47
RTERR_NULLPTR
Null pointer. This status code is returned when a null
pointer is encountered in a place where it is expected that
the pointer value is to be set.
-48
RTERR_FAILED
General failure. Low level call returned error.
-49
RTERR_ATTRFIXEDVAL
Attribute fixed value mismatch. The attribute contained a
value that was different than the fixed value defined in the
schema for the attribute.
-50
RTERR_MULTIPLE
Multiple errors occurred during an encode or decode
operation. See the error list within the context structure for
a full list of all errors.
280
Runtime Status Codes
Error Code
Error Name
Description
-51
RTERR_NOTYPEINFO
This error is returned when decoding a derived type
definition and no information exists as to what type of
data is in the element content. When decoding XML, this
normally means that an xsi:type attribute was not found
identifying the type of content.
-52
RTERR_ADDRINUSE
Address already in use. This status code is returned when
an attempt is made to bind a socket to an address that is
already in use.
-53
RTERR_CONNRESET
Remote connection was reset. This status code is returned
when the connection is reset by the remote host (via
explicit command or a crash).
-54
RTERR_UNREACHABLE
Network failure. This status code is returned when the
network or host is down or otherwise unreachable.
-55
RTERR_NOCONN
Not connected. This status code is returned when an
operation is issued on an unconnected socket.
-56
RTERR_CONNREFUSED
Connection refused. This status code is returned when an
attempt to communicate on an open socket is refused by
the host.
-57
RTERR_INVSOCKOPT
Invalid option. This status code is returned when an
invalid option is passed to socket.
-58
RTERR_SOAPFAULT
This error is returned when the decoded SOAP envelope
is a fault message.
-59
RTERR_MARKNOTSUP
This error is returned when an attempt is made to mark a
stream position on a stream type that does not support it.
-60
RTERR_NOTSUPP
Feature is not supported. This status code is returned when
a feature that is currently not supported is encountered.
-61
RTERR_CODESETCONVFAIL
This status code is returned when transcoding from one
character set to another one (for example, from UTF-8 to
UTF-16) and a conversion error occurs.
ASN.1-specific Status Messages
The following table describes status messages that may arise during the course of encoding or decoding an ASN.1
message. The errors below indicate that while the system was able to read the data successfully, it was unable to
decode it properly.
Error Code
Error Name
Description
2
ASN_OK_FRAG
Fragment decode success status. This is returned when
decoding is successful but only a fragment of the item was
decoded. User should repeat the decode operation in order
to fully decode message.
-100
ASN_E_BASE
Error base. ASN.1 specific errors start at this base number
to distinguish them from common and other error types.
(ASN_E_BASE)
ASN_E_INVOBJID
Invalid object identifier. This error code is returned when
an object identifier is encountered that is not valid.
Possible reasons for being invalid include invalid first and
281
Runtime Status Codes
Error Code
Error Name
Description
second arc identifiers (first must be 0, 1, or 2; second must
be less than 40), not enough subidentifier values (must be
2 or more), or too many arc values (maximum number is
128).
(ASN_E_BASE-1)
ASN_E_INVLEN
Invalid length. This error code is returned when a length
value is parsed that is not consistent with other lengths in
a BER or DER message. This typically happens when an
inner length within a constructed type is larger than the
outer length value.
(ASN_E_BASE-2)
ASN_E_BADTAG
Bad tag value. This error code is returned when a tag value
is parsed with an identifier code that is too large to fit in
a 32-bit integer variable.
(ASN_E_BASE-3)
ASN_E_INVBINS
Invalid binary string. This error code is returned when
decoding XER data and a bit string value is received that
contains something other than '1' or '0' characters.
(ASN_E_BASE-4)
ASN_E_INVINDEX
Invalid table constraint index. This error code is returned
when a value is provided to index into a table and the value
does not match any of the defined indexes.
(ASN_E_BASE-5)
ASN_E_INVTCVAL
Invalid table constraint value. This error code is returned
when a the value for an element in a table-constrained
message instance does not match the value for the element
defined in the table.
(ASN_E_BASE-6)
ASN_E_CONCMODF
Concurrent list modification error. This error is returned
from within a list iterator when it is detected that the list
was modified outside the control of the iterator.
(ASN_E_BASE-7)
ASN_E_ILLSTATE
Illegal state for operation. This error is returned in places
where an operation is attempted but the object is not in a
state that would allow the operation to be completed. One
example is in a list iterator class when an attempt is made
to remove a node but the node does not exist.
(ASN_E_BASE-8)
ASN_E_NOTPDU
This error is returned when a control class Encode or
Decode method is called on a non-PDU. Only PDUs have
implementations of these methods.
(ASN_E_BASE-9)
ASN_E_UNDEFTYP
Element type could not be resolved at run-time. This
error is returned when the run-time parser module is used
(Asn1RTProd) to decode a type at run-time and the type
of the element could not be resolved.
(ASN_E_BASE-10)
ASN_E_INVPERENC
Invalid PER encoding. This occurs when a given element
within an ASN.1 specification is configured to have an
expected PER encoding and the decoded value does not
match this encoding.
282
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