PHP and Web Services

PHP and Web Services
Programmer to Programmer
TM
Professional
Open Source
Web Services
Dietrich Ayala, Christopher Browne, Vivek Chopra,
Dr. Poornachandra Sarang, Kapil Apshankar, Tim McAllister
Wrox technical support at: support@wrox.com
Updates and source code at: www.wrox.com
Peer discussion at: p2p.wrox.com
Summary of Contents
Introduction
1
Chapter 1:
Web Services – An Introduction
Chapter 2:
Web Services Architecture
27
Chapter 3:
Exploring SOAP, WSDL, and UDDI
57
Chapter 4:
Java Web Services from Apache
111
Chapter 5:
Web Services Security
171
Chapter 6:
Perl and SOAP::Lite
199
Chapter 7:
Python and Web Services
267
Chapter 8:
PHP and Web Services
305
Chapter 9:
Web Services with C++
329
Chapter 10:
Other SOAP Implementations
391
Chapter 11:
Case Study – Designing Web Services from Legacy Modules
435
Appendix A:
Configuring Tomcat with Apache
487
Appendix B:
server.xml Attributes for Tomcat Configuration
495
Appendix C:
TcpTunnelGui and Tcpmon
499
Appendix D:
JBoss Installation
501
Appendix E:
WSDL2Java Options
505
Appendix F:
Java2WSDL Options
507
Appendix G:
SOAP::Lite Classes
509
Appendix H:
kSOAP API Reference
515
Index
7
523
8
PHP and Web Services
PHP Hypertext Processor (PHP) is a widely-used general-purpose scripting language that is specially
suited for web development as it was designed to work on the Web and can be embedded into
HTML. It is a procedural language, with some object-oriented capabilities and has syntax similar to
C, Perl, and Java. PHP was first released on June 8, 1995. PHP version 4, which was released in May
2000, was a major milestone, with its explosive performance increase and many features, such as
native session support.
In this chapter, we will first present PHP with its advantages for Web Services development. Then we
will cover the installation and configuration of PHP on a Unix system.
The second section will concentrate on SOAP usage in PHP. We'll look at the NuSOAP toolkit, and
learn how to use it for both consumption and deployment of SOAP Web Services. We'll also explore
NuSOAP's functionality for several advanced Web Services scenarios such as using HTTP proxy,
SOAP over HTTPS, and document style messaging. We'll discuss some of the issues facing Web
Service development in PHP, such as security and language to data type mapping, and how NuSOAP
solves them.
The final section covers XML-RPC in PHP. We'll explore the particular features of XML-RPC, as well
as discuss scenarios for using XML-RPC versus using SOAP. We will then use the Useful, Inc.
implementation to create XML-RPC client and server applications.
Chapter 8
PHP Features
Several of PHP's features are advantageous for Web Service development. The first would be its objectoriented programming capabilities. This may be limited in comparison to other natively object-oriented
languages, but it provides the support needed to create extendable and reusable tools for PHP. It also
allows SOAP and XML-RPC toolkits to be split into a group of classes each supporting parts of the
entire Web Service transaction, but which on its own can be reused to accomplish the plethora of
different kinds of transactions that are possible and tasks that may be necessary, such as native type
serialization, network operations, XML parsing, and XML generation.
Another advantage of PHP is its XML support. The Expat parser is bundled with PHP, providing SAX
capability out of the box. There are several PHP extensions available for expanded XML functionality,
such as the domxml extension that use the libxml library to provide DOM, Xpath, and Xlink support.
The xslt extension is a wrapper for different third-party XSLT libraries such as Sablotron and libxslt.
There are also experimental extensions for XML-RPC and SOAP.
A very helpful PHP extension for Web Service development is the CURL extension, described as a
Client URL Library. CURL allows you to communicate via various different protocols such as HTTP,
HTTPS, FTP, telnet, and LDAP. The HTTPS support is particularly helpful for Web Service usage in
PHP as it allows a (Web Service) client to make a secure connection with the server.
PHP and Web Services
PHP Web Service newbies can experiment with Web Services using PHP by writing only a few lines of
code, without having to set up a special environment, and without needing to know anything about how
Web Services actually work. But this ease-of-use is a double-edged sword and general advice is to know
as much as possible about the technologies used, to stay abreast of security issues especially, considering
that by nature Web Services are exposed to the network.
PHP is already broadly deployed for data-centric web applications. If you are planning to develop Web
Services using PHP, your PHP-driven web sites may have components that may be reused by exposing
their methods using XML-RPC or SOAP. The conversion from wrapping your data in HTML to serving
it as SOAP messages is trivial using the tools available today.
An excellent reason to use PHP for Web Services is that sometimes it's the only choice you've got. Web
sites that are hosted by PHP hosting services and want to use Web Services to share data with their
partners to access services cannot do so, since they have no control over their PHP installation. They
cannot install Java, don't have compiler access, and have no permissions to restart Apache if assuming
they could install new software on the server. Now users in such a scenario can easily consume and
deploy Web Services in short order if the server has PHP.
Currently PHP does not have standard SOAP or XML-RPC support. There are several different
implementations each of SOAP and XML-RPC and the stable ones are written in pure PHP. There has
been a recent push by developers to create standard support for SOAP in PHP. Several of the PHP core
developers have expressed interest in seeing this happen, and a PHP-SOAP mailing list was started to
pursue the effort. Hopefully, this activity will culminate in a SOAP extension that will be compiled into
PHP by default, thereby being available out of the box to developers everywhere, regardless of systemrelated limitations such as permissions or compiler access.
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The XML-RPC support in PHP has increased with Epinions opening the source to their XML-RPC
extension. The extension has been in the main PHP CVS repository for quite some time, yet is still
marked experimental and is not recommended for production use.
There are several advantages and disadvantages in using SOAP against XML-RPC for Web Services:
Strong and extensible typing – SOAP allows user- and schema-defined types to be passed in
SOAP message bodies. XML-RPC is very limited in the types of data it supports.
Character set – SOAP allows the user to define the character set used in the message (like
US-ASCII, UTF-8, UTF-16) while XML-RPC does not.
Specifies recipient – SOAP can specify the recipient of a message, as well as can be routed
through intermediaries.
Failure if not understood – SOAP allows the sender to force a recipient to fail if the recipient
cannot understand its message.
Ease of use – Both PHP and XML-RPC have a short learning curve. It is easy for users new to
PHP and Web Services to consume and deploy Web Services quickly and easily.
Simplicity by design – XML-RPC was designed to be simple; to accomplish remote procedure
calls with a minimum of infrastructure. SOAP is overkill for many Web Services that pass only
simple or complex values.
Configuring PHP
Installing and configuring PHP for the examples in this chapter requires the Apache web server. To compile
and configure PHP for Apache, we first download the PHP source from http://www.php.net/downloads.php
and unpack it. Then change your directory to the root directory of the PHP source distribution. To run the
configure script type ./configure on the command line. You can add options to this command to compile
PHP with non-standard functionality. Some useful options are listed below:
Apache
To enable PHP to be run as an Apache module, use the --with-apxs option, adding the path
to your APXS binary as is appropriate for your server. For example:
--with-apxs=/www/bin/apxs
DOMXML
This extension provides XML DOM, Xpath, and Xlink functionality. Currently, this extension
is not required in Web Services, but is useful for reading and manipulation XML documents.
Domxml support requires a version of the libxml libraries to be present on the system (with a
version number greater than or equal to 2.4.2). For example, --with-dom=DIR. Here DIR is
the libxml install directory, which defaults to /usr.
XSLT
This extension is also not necessary for using Web Services with PHP, but is useful for
transforming XML data returned in Web Service messages into other types of documents. The
configure option for this extension is --enable-xslt --with-xslt-sablot. The
Sablotron XSLT library from Gingerall (http://www.gingerall.com/) must be installed in a
location where your compiler can find it, usually /usr/lib or /usr/local/lib.
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CURL
The CURL extension provides the ability to initiate secure socket connections using SSL. This is
a necessary extension if you want to conduct SOAP client operations using SSL. The configure
option is --with-curl=DIR where DIR is the location of the CURL libraries on your system.
The CURL extension requires version 7.0.2-beta or higher of the CURL libraries.
Finally, run make and then make install on the command line, and the installation is complete. The
final installation process on the command line using the previous options would look like this:
> cd PHP-xxx
> ./configure --with-apxs=/www/bin/apxs --with-dom=/usr/local/lib --enable-xslt
--with-xslt-sablot --with-curl=/usr/local/lib
> make
> make install
The PHP web site at http://www.php.net/manual/en/installation.php provides instructions for installing
PHP with many other options on a variety of platforms.
PHP Web Services Using NuSOAP
NuSOAP is a collection of PHP classes that allow users to send and receive SOAP messages over HTTP.
NuSOAP, formerly known as SOAPx4, is distributed by the NuSphere Corporation
(http://www.nusphere.com/). It is open source, licensed under the GNU LGPL. SOAPx4 has been used
as the core of several Web Services toolkits for PHP, including PEAR-SOAP and Active State software's
simple Web Services API project.
One of the benefits of NuSOAP is that it's not a PHP extension, but is written in pure PHP. This
means that nearly all PHP developers, regardless of the web server or permissions restrictions, can
use NuSOAP.
NuSOAP is a component-based Web Services toolkit. It employs a base class that provides utility
methods such as variable and envelope serialization, as well as namespace information and mappings of
different types to different namespaces. Web Service interaction is achieved through a high-level client
class called soapclient. This high-level class allows users to specify options such as HTTP
authorization credentials, HTTP proxy information, as well as managing the actual sending and
receiving of the SOAP message itself. It uses several helper classes to accomplish the sending and
receiving of SOAP messages.
SOAP operations may be executed by passing the name of the operation you'd like to execute to the
call() method. If the service to be consumed provides a WSDL file, the soapclient class takes the
URL of the WSDL file as an argument to its constructor, and uses the wsdl class to parse the WSDL file
and extract all the data. The WSDL class has methods that extract data on a per-operation or
per-binding basis.
The soapclient uses this data from the WSDL file to encode parameters and create the SOAP
envelope when the user executes a call to a service. When the call is executed, the soapclient class
uses the soap_transport_http class to send the outgoing message and receive the incoming message.
The incoming message is parsed using soap_parser class. The diagram opposite describes the process
of consuming a SOAP Web Service using NuSOAP.
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PHP and Web Services
xmlschema class
soapclient
class
wsdl class
WSDL file
soap_parser class
soap_transport_http
class
SOAP Service
nusoap_base class
If the Web Service to be consumed does not provide a WSDL file, then the process is different. The
URL of the service is passed to the soapclient class constructor. Operations are still executed using
the call method of the soapclient object, but details that are otherwise provided by the WSDL file
must be passed as arguments. Parameters that are custom types can be represented using the soapval
class, which allow users to customize a parameter's serialization.
Installation and Configuration
The installation of NuSOAP is a pretty straightforward process. It can be achieved in a few steps
as follows:
Download the files from http://dietrich.ganx4.com/nusoap/.
Extract the file nusoap.php from its zip.
For easy access, copy the classes to a location in your include path, or into the directory in
which you'll be using the classes.
Include the class in your script. The path to nusoap.php can be relative or absolute:
include('nusoap.php');
In this example, we have used the include() function to include the NuSOAP classes in our script.
This function will generate a warning if the path to nusoap.php is incorrect, but will continue to
process the rest of the script. There are several other alternatives:
require()
This function is identical to include(), but handles failure by emitting a fatal error, which
will halt processing of the script
require_once()
Identical to require(), except that if the file to be included is already included in the script,
it will not repeat the inclusion
include_once()
Identical to include(), except that if the file to be included has been previously included in
the script, it will not include it again
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Language to Data Mapping
SOAP and WSDL both make heavy use of the data types described in the XML Schema specification.
This can be problematic since PHP does not natively support most of the data types defined in the
specification. Also, the XML Schema data types are fine-grained and explicitly defined, whereas PHP is
a loosely-typed language and will convert data types automatically when deemed appropriate. NuSOAP
solves this problem at three different levels:
In WSDL, NuSOAP's soapclient class will encode a value's type according to the type
specified in the WSDL document.
The NuSOAP soapval class allows users to explicitly define a value's type.
If no type is explicitly declared when instantiating a soapval object, NuSOAP will analyze the
value passed to it using PHP's built-in variable introspection functions as well as regular
expressions and other means where necessary, and classify it as a valid XML Schema data
type, or a valid type as described in Section 5 of the SOAP 1.1 specification.
A Simple PHP SOAP Client Example
In this example we will pass a string to a SOAP server that echoes the same string back. This example
demonstrates the basic process of creating a SOAP client, calling a SOAP service and passing it
parameters, and receiving the response. We will name this file echoStringClient.php.
In this chapter to start a script in a standard way would be to include the NuSOAP classes first. We'll
use the require() function in our examples because we'd like the script to halt execution if it cannot
find the NuSOAP file:
<?php
require('nusoap.php');
Let's create a variable for the string we'd like to send.
$myString = 'Dietrich Ayala';
Our parameters must be passed as an array to the SOAP client, so let's create one:
$parameters = array($myString);
Now we can instantiate the soapclient object. It takes the URL of the server as an argument to
its constructor:
$s = new soapclient('http://localhost/wrox/nusoap/echoStringServer.php');
This step is where all the magic takes place. Using the call() method, we tell the soapclient object
which service we'd like to access, then pass our array of parameters, and the method then returns the
response from the server. This response is a PHP native type, such as a string, integer, or array. It is the
result of the decoding that takes place when NuSOAP parses the response message:
$result = $s->call('echoString',$parameters);
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NuSOAP offers error detection through the getError() method. If an error has occurred this method
returns a string describing the error, and returns false otherwise. In our example, we print our result
after checking for errors if there are none. If there are errors, we'll print the error message:
if(!$err = $s->getError()){
echo 'Result: '.$result;
} else {
echo 'Error: '.$err;
}
This final bit of code is very helpful for debugging SOAP operations. The request and response
properties of the soapclient class contain strings of the respective messages, including the HTTP
headers sent with each:
echo '<xmp>'.$s->request.'</xmp>';
echo '<xmp>'.$s->response.'</xmp>';
?>
SOAP Request and SOAP Response
Here is the request message from the previous example:
POST /wrox/nusoap/echoStringServer.php HTTP/1.0
User-Agent: NuSOAP v0.6.1
Host: localhost
Content-Type: text/xml
Content-Length: 569
SOAPAction: ""
<?xml version="1.0" encoding="ISO-8859-1"?>
<SOAP-ENV:Envelope
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:si="http://soapinterop.org/xsd">
<SOAP-ENV:Body>
<nu:echoString xmlns:nu="http://testuri.org">
<soapVal xsi:type="xsd:string">Dietrich Ayala</soapVal>
</nu:echoString>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
This is the server's response message from the previous example. Notice that the first element in the
body of the message is the name of the operation we called, with Response appended to it. Also, the
element name of the return value is called return. Both of these are standard practice for serializing
SOAP responses:
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HTTP/1.1 200 OK
Server: Microsoft-IIS/5.0
Date: Tue, 04 Jun 2002 18:47:53 GMT
X-Powered-By: PHP/4.1.2
Status: 200 OK
Server: NuSOAP Server v0.6.1
Connection: Close
Content-Type: text/xml; charset=UTF-8
Content-Length: 1525
<?xml version="1.0" encoding="ISO-8859-1"?>
<SOAP-ENV:Envelope
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:si="http://soapinterop.org/xsd">
<SOAP-ENV:Body>
<echoStringResponse>
<soapVal xsi:type="xsd:string">Dietrich Ayala</soapVal>
</echoStringResponse>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
A Simple PHP SOAP Server Example
This example is the server that was accessed by our client example. It implements the echoString service.
The first step as usual is to include the NuSOAP classes:
<?php
require('nusoap.php');
Now we can instantiate the server object, provided by the soap_server class:
$s = new soap_server;
To allow our function to be called remotely, we must register it with the server object. If this is not
done, the server will generate a fault indicating that the service is not available if a client accesses the
service. In the absence of such a registration process, any PHP functions would be remotely available,
which would present a serious security risk:
$s->register('echoString');
Now we can define our function that we are exposing as a service. Notice that we first check to make
sure a string was passed. If the parameter is not a string, we use the soap_fault class to return an error
to the client indicating that they must pass a string value as the parameter to this function:
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PHP and Web Services
function echoString($inputString){
if(is_string($inputString)){
return $inputString;
} else {
return new soap_fault('Client','','The parameter to this service must be a
string.');
}
}
The final step is to pass any incoming posted data to the SOAP server's service method. This method
processes the incoming request, and calls the appropriate function. It will then formulate the response,
and print it:
$s->service($HTTP_RAW_POST_DATA);
?>
Fault Handling
The soap_fault class provides a way to specify errors and return them when developing services with NuSOAP.
The properties of the soap_fault class are below. These are also the arguments to the soap_fault
constructor, in the same order as below:
Fault
Description
faultcode
This property must have a value. The values available to the user are
Client and Server. Client class errors indicate that the message didn't
contain the information required for the operation to succeed. Server class
errors indicate processing problems on the server.
faultactor
This property is not functional yet in NuSOAP, and can be left empty. Its
purpose is to indicate the location of the fault among multiple actors in a
message path.
faultstring
This is a human-readable error message. This is the best place for you to
describe errors.
faultdetail
The value of the faultdetail property is XML data used to detail the
application-specific errors related strictly to the Body element of the SOAP
message. You can insert your own XML markup here.
The soap_fault class has only one method besides the constructor that is serialize(). The
serialize() method takes the fault information and serializes it, returning a complete SOAP message.
An example of using the soap_fault class is shown here:
$fault = new soap_fault(
'Client','','The inputString parameter must not be empty');
echo $fault->serialize();
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The SOAP message below is what is returned by the serialize() method of the soap_fault object
instantiated above:
<?xml version="1.0"?>
<SOAP-ENV:Envelope
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:si="http://soapinterop.org/xsd">
<SOAP-ENV:Body>
<SOAP-ENV:Fault>
<faultcode>Client</faultcode>
<faultactor></faultactor>
<faultstring>The inputString parameter must not be empty</faultstring>
<detail></detail>
</SOAP-ENV:Fault>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
Using Arrays
Transmitting and receiving arrays is transparently done in NuSOAP. You can pass PHP arrays in the
parameters array argument to the soapclient class's call method, and NuSOAP will detect the type of
the array contents, and serialize accordingly. This script uses a service called echoArray that accepts
an array and returns the same array. While running this example, try modifying the parameter array by
adding different data types, and see how the serialization changes.
First, include the NuSOAP classes:
<?php
require('nusoap.php');
Create the array we'd like to send:
$arr = array('string1','string2');
Create the array of parameters:
$parameters = array($arr);
Instantiate the soapclient object, passing it the endpoint URL:
$s = new soapclient('http://localhost/wrox/nusoap/echoArrayServer.php');
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PHP and Web Services
Now we call the echoArray operation, passing it our array of parameters, and receive the result. Then
print the result on the screen, and view the request and response messages, as follows:
$result = $s->call('echoArray',$parameters);
if(!$err = $s->getError()){
echo 'Result: '.$result;
} else {
echo 'Error: '.$err;
}
echo '<xmp>'.$s->request.'</xmp>';
echo '<xmp>'.$s->response.'</xmp>';
?>
Creating Complex Types
SOAP allows users to define their own types, called "general compound types" in the specification.
NuSOAP provides the soapval class for defining custom types, or for situations where you want to
override NuSOAP's default serialization behavior. An example of overriding NuSOAP's behaviors
would be where let's say NuSOAP would type the value 2.3433 as a float, but the service requires it to
be typed as a double. You could create the parameter like:
$param = new soapval('','double',2.3433);
NuSOAP would then serialize the parameter like this:
<soapVal xsi:type="xsd:double">2.3433</soapVal>
Here is an example of using the soapval class to create a custom type for some contact information:
<?php
include('nusoap.php');
$address = array(
'street' => '123 Freezing Lane',
'city' => 'Nome',
'state' => 'Alaska',
'zip' => 12345,
'phonenumbers' => array('home'=>'1234567890','mobile'=>'0987654321')
);
$s =new soapval('myAddress','address',$address,'','http://myNamespace.com');
print "<xmp>".$s->serialize()."</xmp>";
?>
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Here is the result of running the above code:
<myAddress xmlns:ns8467="http://myNamespace.com" xsi:type="ns8467:address">
<street xsi:type="xsd:string">123 Freezing Lane</street>
<city xsi:type="xsd:string">Nome</city>
<state xsi:type="xsd:string">Alaska</state>
<zip xsi:type="xsd:int">12345</zip>
<phonenumbers>
<home xsi:type="xsd:string">1234567890</home>
<mobile xsi:type="xsd:string">0987654321</mobile>
</phonenumbers>
</myAddress>
Using WSDL and soap_proxy
WSDL is an XML language used to describe a Web Service. It is a machine-readable format that provides
Web Service clients with all the information necessary to access the service. NuSOAP provides a class for
parsing WSDL files, and extracting data from them. The soapclient object uses the wsdl class to ease the
burden of the developer calling a service. With the help of the WSDL data to create messages, a programmer
only needs to know the name of the operation to call, and the parameters required by the operation.
Using WSDL with NuSOAP provides several benefits:
All service meta data such as namespaces, endpoint URLs, parameter names, and much more
are read from the WSDL, allowing the client to dynamically cope with changes from the
server. This information no longer needs to be hard-coded into the user's script since it's on the
server.
It allows us to use the soap_proxy class. This class is an extended soapclient class with
new methods for each of the operations detailed in the WSDL file. Now the user can call these
methods directly. This process is described below.
The soapclient class contains a method called getProxy(). This method returns an object of the
class soap_proxy. The soap_proxy class extends the soapclient class with methods that
correspond to the operations defined in the WSDL document, and allows users to call the remote
methods of an endpoint as if they were local to the object. This is only functional when the
soapclient object has been instantiated using a WSDL file and has the advantage of easy access for a
user. The disadvantage though is the performance – object creation is expensive in PHP – and this
functionality serves no utilitarian purpose.
Here is an example of using WSDL to call a stock quotes service from Xmethods, using the
soap_proxy class. We start by including the NuSOAP classes:
<?php
include('nusoap.php');
When instantiating the client object using WSDL, we pass the URL or path to the WSDL file as an
argument to the constructor, as well as an argument that lets the client know we've passed it WSDL and
not a SOAP endpoint:
$s = new soapclient(
'http://services.xmethods.net/soap/urn:xmethods-delayed-quotes.wsdl', 'wsdl');
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PHP and Web Services
Now we'll generate the proxy class. This is achieved by invoking the getProxy() method of the
soapclient class:
$p = $s->getProxy();
We can now invoke the remote method as a method of the proxy class, and pass our parameters
directly. The proxy object will handle the details such as matching up parameter values to their names,
assigning namespaces, and types:
$sq = $p->getQuote('ibm');
Lastly let's check for errors, and if none are present print out the results:
if(!$err = $p->getError()){
print "IBM current stock price: $sq.";
} else {
print "ERROR: $err";
}
print '<xmp>'.$p->request.'</xmp>';
print '<xmp>'.str_replace('><',">\n<",$p->response).'</xmp>';
?>
Using an HTTP Proxy Server
The soapclient class has a method called setHTTPProxy(), which allows you to use an HTTP
proxy server. It takes two arguments: the proxy hostname and the port address. For example:
$s = new soapclient('http://www.remoteserver.com/soap_server.php');
$s->setHTTPProxy('proxy.myCompany.com',8080);
You can then continue your SOAP calls as we did above. Calling this method will force all requests to
be sent to the specified proxy server, which then forwards the request to its intended recipient.
HTTP Authentication
The soapclient object provides a method called setCredentials(). This method is used when
HTTP authentication is needed to access a SOAP server. The two arguments to the method are a
username and password. Its functionality is shown in the example below:
$s = new soapclient(
'http://www.remoteserver.com/protected_directory/soap_server.php');
$s->setCredentials('myUsername','myPassword');
You can then continue your SOAP calls, as you would normally do. The most common way of
implementing this level of security on the server is to use Apache's .htaccess files to implement
required authorization to protect a directory or file.
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SSL
Using SSL with the NuSOAP client requires the CURL extension, which was discussed earlier in the
chapter, to be installed. The CURL functions provide a way to make a secure connection to a URL.
Standard PHP doesn't provide this functionality. If you have the CURL extension, and you would like
to connect to a secure Web Service using SSL, you need do nothing other than enter the URL as you
normally would. If the URL is secure, you'll notice it starts with https instead of the normal http:
$s = new soapclient('https://mySecureServer.com');
Implementing SSL on the server side is outside the scope of PHP's abilities. Check your web server's
documentation for instructions on how to achieve this.
Using Document Style Messaging
All of the examples we have seen so far were remote procedure calls, or SOAP RPC, in which we call
remote methods, and pass them, encoded parameters. There is another style of message exchange in
SOAP, which is known as document style. Document style messaging involves the exchange of literal
XML documents. This means that the message bodies are not modeled after procedure calls, and the
elements in the message bodies do not have attributes containing type information.
This section provides two examples of document/literal usage using NuSOAP: one using WSDL and
one without WSDL. The more common scenario would be to use a WSDL document, but it is useful
being able to send arbitrary XML documents and document fragments via SOAP. The service used in
the examples is a simple service that allows users to pass a ZIP code, and it returns a listing of 10 ATM
cash machines in the ZIP code. The service is listed on Xmethods (http://www.xmethods.net/), and is
provided by ServiceObjects (http://www.serviceobjects.com/).
The initial step, as usual, is to include the NuSOAP classes:
<?php
require('nusoap.php');
Next let's set the URL or path to the WSDL file:
$wsdlfile = 'http://ws.serviceobjects.net/gc/GeoCash.asmx?WSDL';
Now we'll create the XML document to be sent to the service. This document can be created manually
by examining the schema defined in the WSDL document, or by using an XML writing tool, or a PHP
class that supports the generation of document skeletons from an XML Schema:
// set parameters
$msg =
'<GetATMLocations xmlns="http://www.serviceobjects.com/">
<strInput>32804</strInput>
<strLicenseKey>0</strLicenseKey>
</GetATMLocations>';
We can now instantiate our soapclient object, and pass it the WSDL location:
$s = new soapclient($wsdlfile,'wsdl');
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Finally, we make the call and get the result (which will be an XML document). When using document
style messaging with NuSOAP, the document is available as a string via the document property of the
soapclient class. Here we are printing out the document, and the request and response messages:
$s->call('GetATMLocations',array($msg));
print 'RESULT:<xmp>';
var_dump($s->document);
print '</xmp>';
print 'REQUEST:<xmp>'.$s->request.'</xmp>';
print 'RESPONSE:<xmp>'.$s->response.'</xmp>';
?>
Sometimes no WSDL is available for a service, or you just need to send arbitrary XML documents via
SOAP. The method for sending arbitrary documents is described below:
<?php
require('nusoap.php');
First we create the XML messages we would like to send:
$body =
'<GetATMLocations xmlns="http://www.serviceobjects.com/">
<strInput>32804</strInput>
<strLicenseKey>0</strLicenseKey>
</GetATMLocations>';
Now we will instantiate the soapclient object by passing the service endpoint to the constructor, like this:
$s = new soapclient('http://ws.serviceobjects.net/gc/GeoCash.asmx');
The serializeEnvelope() method can be used to wrap a SOAP envelope around XML content:
$msg = $s->serializeEnvelope($body);
Use the send() method to actually send the message. The method takes two arguments: the message
content, and the SOAPAction header value. Once again, we can examine the result via the document
property of the soapclient class, and we'll print out our request and response messages:
$s->send($msg,'http://www.serviceobjects.com/GetATMLocations');
print 'RESULT:<xmp>';
var_dump($s->document);
print '</xmp>';
print 'REQUEST:<xmp>'.$s->request.'</xmp>';
print 'RESPONSE:<xmp>'.$s->response.'</xmp>';
?>
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Other PHP SOAP Implementations
The following are PHP Web Services toolkits for sending and receiving SOAP messages.
Active State SWSAPI
Active State, a software company in Vancouver, Canada, used SOAPx4 as the core for their SOAP and
WSDL toolkit for PHP, which is Web Service API called the Simple Web Services API (SWSAPI). It is
a unified API for Web Service programming for Active State's Perl, Python, and PHP distributions.
PEAR
PHP Extension and Add-on Repository or PEAR is a group of classes bundled with the PHP
distribution. PEAR is a community effort to create a set of tools that provide functionality common to
the many uses of PHP. Shane Caraveo recently converted the SOAPx4 classes to meet the PEAR
standards, and the toolkit was added to the repository. He also added many new features, such as
HTTPS, SMTP support, and function overloading.
Krysalis
Krysalis is an application development platform for PHP from Interakt. It is similar in design to the
Cocoon Application Framework, and was inspired by it. In the latest version of Krysalis, 1.0.4, Interakt
has implemented a simple SOAP client and SOAP server. Until now, much of the message creation is
done manually. Use of Krysalis requires PHP's XSLT Sablotron extension, and access to the PEAR
classes. http://www.interakt.ro/products/Krysalis/.
PHP Web Services and XML-RPC
XML-RPC in PHP provides a simple and accessible alternative to SOAP. It is widely used, and there
are several implementations to choose from. For many PHP developers, XML-RPC serves their RPC
needs, without the complexity and infrastructure required by other RPC methods.
XML-RPC Data Types
As discussed above, XML-RPC specification defines a limited number of supported data types. The
supported types are listed below with their PHP equivalents and examples:
XML-RPC
PHP
Example
i4
Integer
23
int
Integer
23
boolean
Boolean
true, false
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XML-RPC
PHP
Example
string
String
'Dietrich Ayala'
double
Double or float
23.3
dateTime.Iso860
1
no native PHP equivalent
-
base64
Base64 encoded string
base64 ('Dietrich Ayala')
array
Array
array ( 1, 2, 'red', 'blue');
struct
Associative array
array ('color' => 'red',
'number'=> 2)
Useful Inc. XML-RPC Implementation
The XML-RPC toolkit that we'll be using for our examples is a set of PHP classes authored by Edd
Dumbill of Useful, Inc. The code and documentation can be found at Sourceforge.net
(http://phpxmlrpc.sourceforge.net/). The toolkit contains both client and server implementations of
XML-RPC.
The toolkit comes with two important classes: the xmlrpc_client class for the client and the
xmlrpc_server class for server-side programming. These classes are mainly used for sending and
receiving the XML-RPC messages. An xmlrpcval class is used to encode the PHP variables into their
XML-RPC equivalents and is used to pass parameters to a remote method. The reverse process of
decoding back into the PHP equivalent is done using the xmlrpc_decode() function. An XML-RPC
message is created using the xmlrpcmsg class by passing a parameter list to it.
The xmlrpc_client class sends XML-RPC messages that are created by the xmlrpcmsg class. On
the server side, the xmlrpc_server class parses these incoming messages back into an xmlrpcmsg
object. This message object is then passed as the single argument to the user's deployed function. This
function must return a response in the form of an xmlrpcresp object that the xmlrpc_server class
uses to serialize and return back to the client. This basic architecture of the toolkit is shown in the
diagram below:
xmlrpc_client
class
xmlrpcresp
class
xmlrpcval
class
xmlrpc_server
class
xmlrpcmsg
class
xmlrpcresp
class
xmlrpcval
class
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Installation and Configuration
The installation can be achieved in a few steps as follows:
Download XML-RPC for PHP from http://phpxmlrpc.sourceforge.net/
Unpack it
Move xmlrpc.inc and xmlrpcs.inc to a location in your include path, or save them to the
same directory as the script(s) in which you expect to use them
To use the XML-RPC client you must include the client code that is done by adding the following line at
the top of your script. Here, the argument to the include() function is the path to the xmlrpc.inc file:
include('xmlrpc.inc');
To use the XML-RPC server class – to create and deploy your own XML-RPC Web Services – you
must include the client and the server code:
include('xmlrpc.inc');
include('xmlrpcs.inc'); //server code
A Simple XML-RPC Client Example
This example demonstrates an XML-RPC client that passes a string variable to an XML-RPC server
that echoes the string back to the client.
The first step is to include the XML-RPC client code:
<?php
// include the xml-rpc classes
require('xmlrpc.inc');
Now we can create a client object, and pass it our connection information. The xmlrpc_client class is
a high-level class that serializes parameters and messages. It is also responsible for sending the messages
to the server. Its constructor takes three arguments: the path, hostname, and port address of the server:
$s = new xmlrpc_client('/wrox/xmlrpc/xmlrpc_server.php','localhost',80);
The next step is to create the string variable that we would like to send to the echoString service. We
do this using the xmlrpcval class. It allows us to create abstractions of PHP variables into XML
elements according to the XML-RPC specification:
// create xmlrpcval object, which allows the encoding of our variable
$inputString = new xmlrpcval('Dietrich Ayala','string');
Let's add our parameter to an array that can hold multiple parameters. We do this because the
xmlrpcmsg object constructor takes a parameter list as its second argument:
// create an array of parameters
$parameters = array($inputString);
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The final preparatory step is to create the XML-RPC message using the xmlrpcmsg object. Its constructor
takes the method name we are calling as its first argument, and our array of parameters as its second:
// create the message object
$msg = new xmlrpcmsg('echoString',$parameters);
Now we are ready to send our message. To do this we use the send() method of the xmlrpc_client
object. It takes our xmlrpcmsg object as an argument and returns an xmlrpcresp object. The
xmlrpcresp object has three methods of use to the client:
faultCode()
This method returns the code associated with any errors returned
faultString()
This method returns a string description of the error
value()
This method returns the value contained in the response in the form of an xmlrpcval object
If no errors occur, the faultCode() method will return a zero. This is an easy way to check for errors
and this is what we'll do in our example:
// send the message, get the response
$rsp = $s->send($msg);
// check for errors
if($rsp->faultcode() == 0){
If no errors occurred, we can go ahead and retrieve the value returned by the server. To do this, we will first call
the value() method of the response object, which returns an xmlrpcval object. To convert this into its
equivalent PHP type, we use the xmlrpc_decode() function that returns the value converted into a PHP type:
// decode the response to a PHP type
$response = xmlrpc_decode($rsp->value());
Let's print the result, or any errors, and view the messages:
// print results
print '<pre>';
var_dump($response);
print '</pre>';
} else {
// print errors
print 'Error: '.$rsp->faultcode().', '.$rsp->faultstring().'<br>';
}
// show messages
$msg->createpayload();
print 'REQUEST:<xmp>'.$msg->payload.'</xmp>';
print 'RESPONSE:<xmp>'.$rsp->serialize().'</xmp>';
?>
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XML-RPC Request and Response
This is the request message generated in the previous code sample. Notice the readability of the
message. Though verbose, it is intuitive and easy to decipher its meaning:
<?xml version="1.0"?>
<methodCall>
<methodName>echoString</methodName>
<params>
<param>
<value><string>Dietrich Ayala</string></value>
</param>
</params>
</methodCall>
Here is the response message from the server:
<methodResponse>
<params>
<param>
<value><string>Dietrich Ayala</string></value>
</param>
</params>
</methodResponse>
A Simple XML-RPC Server Example
This example implements the service that we used in our client example that is the echoString
service. Here we'll see how to use the xmlrpc_server class to create and deploy a service and then
serve requests using the xmlrpcresp class to encapsulate and return responses.
We must first include the XML-RPC files. Note the inclusion of xmlrpcs.inc, which provides the
code necessary for the server:
<?php
// include the client and server classes
require('xmlrpc.inc');
require('xmlrpcs.inc');
Let's define our function that will handle the incoming request. The function to be deployed must take
only one argument, which is an xmlrpcmsg object:
// service that echoes a string
function echoString($msg){
The first step in our function is to take the parameters from the message object and decode them into
PHP types. The decoding is done using the xmlrpc_decode() function that we discussed above:
// decode parameters into native types
$inputString = xmlrpc_decode(array_shift($msg->params));
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PHP and Web Services
Here we check the parameter's type to see that it is valid. If it is, we return it using the xmlrpcresp
object. To return a value, the xmlrpcresp class constructor takes one argument of type xmlrpcval.
Thus, any returned value must first be encoded as an xmlrpcval:
// check for input parameter validity
if(is_string($inputString)){
return new xmlrpcresp( new xmlrpcval($inputString, 'string') );
}
If the parameter is invalid, we may use the xmlrpcresp object again to return a fault. This is done by
passing zero to the xmlrpcresp constructor as its first argument followed by the error code. The
XML-RPC specification says that fault codes are to be user-defined. XML-RPC for PHP defines a
constant named $xmlrpcerruser, which sets an error level. For errors taking place outside of the
XML-RPC classes themselves, the standard convention recommended by the author of these classes is
to increment the value of this variable by one. The last argument is the fault code, which is a
human-readable string describing the error:
else {
// or return a fault
return new xmlrpcresp(0, $xmlrpcerruser+1,
"Parameter type ".gettype($inputString)." mismatched expected type.");
}
}
The final step in the process is to instantiate the server class, and register our function in it. The
xmlrpc_server constructor takes an associative array as its first argument. This array is what is called
the "dispatch map." It is an associative array of associative arrays. The key values of the outer array are
the public names of the functions being deployed that are the names by which XML-RPC clients would
call them. The inner array contains three members:
function
This is a mandatory entry and its value is the name of the PHP function you've defined to
handle this service. In our example above this is the same as the service name that is
echoString. For example, you could deploy a service called reverser that maps to a PHP
function strrev() that takes a string as an argument and returns the string reversed. The
most important point to note is that the value of function must be a valid function in the
global scope.
signature
This is an optional member. A signature is defined by creating an array of parameter types for
each input and output parameters. It is an array of possible signatures to validate requests against.
The value of this member takes an array in which each member is a possible signature. Here, the
last one is the output parameter while all the previous ones are input parameters.
docstring
This is an optional member that may contain the documentation for your service, and may
even have HTML contents.
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Instantiating the server class initiates the processing of any incoming requests. The second parameter to
the xmlrpc_server constructor is optional. When this is set to zero, the server will not immediately
process requests. The processing can be executed later by using the server's service() method:
// instantiate the server object and register our functions
$s = new xmlrpc_server(array(
'echoString' => array(
'function' => 'echoString',
'signature' => array( array('string','string') ),
'docstring' => 'This service echoes the input string back to the
client.'
)
));
?>
Other PHP XML-RPC Implementations
The other open source implementations of the XML-RPC protocol for PHP are either experimental or
not well documented. Here we list a couple of them.
XMLRPC-EPI
XMLRPC-EPI is an XML-RPC implementation written in C. It was originally developed for internal
use at Epinions (hence the -EPI). Epinions (http://epinions.com/) released XMLRPC-EPI as open source
in March 2000. Since then the project has been hosted and managed on Sourceforge.net. Epinions also
donated a PHP module for the code, written by Dan Libby. This module has since been folded into the
PHP core distribution and has been available in PHP since version 4.1.0. It is currently labeled
experimental in the PHP manual.
Noyade
This is a pure PHP implementation by Matt Bean. It has no documentation available. The source is
available at http://rpc.lemurpants.com/noyrpc.phps. The script for testing the implementation against
Userland Software's Validator is provided at http://rpc.lemurpants.com/rpc-validator1.phps.
Future of PHP Web Services
The momentum of Web Services in PHP is growing rapidly. The core PHP developers are discussing
the possibility of having standard SOAP support bundled with the main PHP distribution. This would
enable Web Service usage in PHP to explode by making it available in every new PHP installation.
Brad LaFountain has recently released the first version of a SOAP extension for PHP. It looks very
promising, and will probably end up being PHP's standard SOAP extension. It uses the libxml library,
which provides implementations of XML DOM, Xpath, and XLink. If it were bundled with PHP it
would be a double win for PHP developers who use XML.
Other Web Services activity in PHP is the creation of PEAR-SOAP. PEAR (PHP Extension and
Application Repository) is a collection of reusable PHP components. Shane Caraveo, primary developer
of the initial port of PHP to Windows, ported SOAPx4 (NuSOAP's predecessor) to PEAR, which
became PEAR-SOAP.
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PHP and Web Services
Summary
With NuSOAP we've been able to create a client that retrieves content by consuming services offered
by remote servers using SOAP, and guided by WSDL. We've also deployed our own service that is
accessible by a multiplicity of clients of all different platforms and languages. These basic operations
are boilerplates for your imagination as you can use them to create robust interoperable Web
Services for yourself.
We have also seen how to use XML-RPC for PHP to create a client that can pass encoded data to a
server and detect success or failure from the response. We have seen how to create an XML-RPC server
and deploy services using it. These examples demonstrate how PHP and XML-RPC can be used
together to access remote applications, as well as to create your own.
Though the question that arises is "which is a better choice: SOAP or XML-RPC?", actually there is
no black-and-white answer to this question. The best solution is the one that solves the stated
problem best, or achieves the goals of your application. Both XML-RPC and SOAP have different
abilities, different strengths and weaknesses. You should weigh these against the needs of your
application to make your decision.
XML-RPC is designed for simplicity. It contains limitations that some developers might welcome, such
as a small number of types to support and a small XML vocabulary. It may perform faster as it requires
much less infrastructure than SOAP.
SOAP is designed to accomplish much more complex messaging problems than XML-RPC. It allows
users to define a near limitless amount of types, as well as different styles of messaging. You can specify
the character set of the message, as well as specify a recipient, and force the recipient to reply with a
fault if it can't understand the message. All in all, SOAP provides a much richer set of features than
XML-RPC, but at the cost of more complexity. The final decision of which is better will be decided by
the needs of your application or project.
This chapter has demonstrated the use of PHP tools to consume and deploy Web Services with
XML-RPC and SOAP, which is not only possible, but robust and interoperable as well. The examples in
this chapter have shown that PHP and Web Services can turn your web applications into distributed
systems that can provide interoperable services to others.
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328
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