March 16, 2004
By Dmitry Stogov
Intended AudienceThis article describes the new SOAP extension for PHP. It is intended for PHP developers who want to write their own Web Services servers, or use SOAP to access existing ones. It assumes some familiarity with Web Services, SOAP, and WSDL (Web Services Description Language).
SOAP (Simple Object Access Protocol) is a lightweight
XML-based protocol for exchanging structured information between distributed
applications over native web protocols, such as HTTP. SOAP specifies the formats
that XML messages should use, the way in which they should be processed, a set
of encoding rules for standard and application-defined data types, and a
convention for representing remote procedure calls and responses.
Web Services is a modern and very popular technology. The list
of protocols and technologies related to Web Services grows every day, but SOAP
is probably the most important. It is rapidly becoming the standard protocol for
accessing Web Services. It uses XML messages to exchange information across
endpoints, and provides several advantages over other binary protocols. RPC
(Remote Procedure Calls) support was originally a minor element in the design of
SOAP, but this feature is one of the most useful it has today.
PHP 5's SOAP extension is the first attempt to implement
the SOAP protocol for PHP in C. It has some advantages over the existing
implementations written in PHP itself, the main one being speed. The extension
is currently marked as experimental, but should gradually become more stable and
reliable as time progresses.
The SOAP extension implements a large subset of SOAP 1.1, SOAP
1.2 and WSDL 1.1 specifications. The key goal is to use the RPC feature of the
SOAP protocol. WSDL is used where possible in order to make the implementation
of Web Services more straightforward.
To demonstrate how to make a simple SOAP Client, we'll take the XMethods demo service, “Delayed Stock Quote”, as our target. Before we start to write any PHP code, we'll need to gather some information about this particular service:
| Method Name | getQuote |
| Endpoint URL | http://64.124.140.30:9090/soap |
| SOAPAction | urn:xmethods-delayed-quotes#getQuote |
| Method Namespace URI | urn:xmethods-delayed-quotes |
| Input Parameters |
Symbol String |
| Output Parameters |
Result float |
<?php
$client = new SoapClient(NULL,
array(
"location" => "http://64.124.140.30:9090/soap",
"uri" => "urn:xmethods-delayed-quotes",
"style" => SOAP_RPC,
"use" => SOAP_ENCODED
));
print($client->__call(
/* SOAP Method Name */
"getQuote",
/* Parameters */
array(
new SoapParam(
/* Parameter Value */
"ibm",
/* Parameter Name */
"symbol"
)),
/* Options */
array(
/* SOAP Method Namespace */
"uri" => "urn:xmethods-delayed-quotes",
/* SOAPAction HTTP Header for SOAP Method */
"soapaction" => "urn:xmethods-delayed-quotes#getQuote"
)). "\n");
?>
As you can see, this simple task required a lot of work
Fortunately, Web Services can describe themselves to the client using WSDL,
and generally they achieve this successfully. The location of the WSDL
document for the XMethods “Delayed Stock Quote” service is given
on the information page for that service at xmethods.com:
http://services.xmethods.net/soap/urn:xmethods-delayed-quotes.wsdl
Here is the same PHP SOAP client, rewritten using that WSDL
document. Now we don't need to specify the endpoint URI, namespace,
SOAPAction header, encoding style and parameter types. All the
information comes from the WSDL file.
<?php
$client = new
SoapClient(
"http://services.xmethods.net/soap/urn:xmethods-delayed-quotes.wsdl"
);
print($client->getQuote("ibm"));
?>
That's a little easier, isn't it?
What are the problems with WSDL? The only argument against using it is that the client has to load the relevant WSDL document
from the server before the RPC can be made, and this can take a significant amount of time in a Web environment. In order to
speed things up, PHP's ext/soap uses a WSDL caching feature that can be controlled through setting the
soap.wsdl_cache_enabled, soap.wsdl_cache_dir and soap.wsdl_cache_ttl configuration directives, either in your php.ini or by using ini_set()(see Example 4 ).
By default, WSDL caching is turned on and caches WSDL files for one day.
Here is the SOAP section for php.ini with default values. You can paste it into your php.ini.
[soap]
soap.wsdl_cache_enabled = "1"
; enables or disables WSDL caching feature
soap.wsdl_cache_dir = "/tmp"
; sets the directory name where SOAP extension will put cache files
soap.wsdl_cache_ttl = "86400"
; (time to live) sets the number of second while cached file will be used
; instead of original one
Let's try to write our own SOAP Web service that will do
the same as the XMethods “Delayed Stock Quote” service.
The first task is to create a WSDL document describing our
service in a format that client requests will understand. This requires minor
modifications to the original document taken from the Xmethods site, so
we'll start by taking a close look at that file.
The message section defines two messages. The first is
getQuoteRequest, which is a request to relay the getQuote message and takes
one string parameter called symbol. The other is getQuoteResponse, which is a
response to the getQuote message, containing one float value, named
Result.
The portType section defines one operation, getQuote,
which describes which of the messages listed in the message section will be used to
transmit the request and response.
The binding section defines how the messages must be transmitted and encoded.
Here it tells us that we will be sending an RPC request using SOAP encoding across HTTP. It also
specifies namespace and value of the SOAPAction header for the getQuote method.
Lastly, the service section defines the endpoint URL where the service is running.
<?xml version ='1.0' encoding ='UTF-8' ?>
<definitions name='StockQuote'
targetNamespace='http://example.org/StockQuote'
xmlns:tns=' http://example.org/StockQuote '
xmlns:soap='http://schemas.xmlsoap.org/wsdl/soap/'
xmlns:xsd='http://www.w3.org/2001/XMLSchema'
xmlns:soapenc='http://schemas.xmlsoap.org/soap/encoding/'
xmlns:wsdl='http://schemas.xmlsoap.org/wsdl/'
xmlns='http://schemas.xmlsoap.org/wsdl/'>
<message name='getQuoteRequest'>
<part name='symbol' type='xsd:string'/>
</message>
<message name='getQuoteResponse'>
<part name='Result' type='xsd:float'/>
</message>
<portType name='StockQuotePortType'>
<operation name='getQuote'>
<input message='tns:getQuoteRequest'/>
<output message='tns:getQuoteResponse'/>
</operation>
</portType>
<binding name='StockQuoteBinding' type='tns:StockQuotePortType'>
<soap:binding style='rpc'
transport='http://schemas.xmlsoap.org/soap/http'/>
<operation name='getQuote'>
<soap:operation soapAction='urn:xmethods-delayed-quotes#getQuote'/>
<input>
<soap:body use='encoded' namespace='urn:xmethods-delayed-quotes'
encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'/>
</input>
<output>
<soap:body use='encoded' namespace='urn:xmethods-delayed-quotes'
encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'/>
</output>
</operation>
</binding>
<service name='StockQuoteService'>
<port name='StockQuotePort' binding='StockQuoteBinding'>
<soap:address location='http://[insert real path here]/server1.php'/>
</port>
</service>
</definitions>
Note: The WSDL caching feature is on by default. During the
development of your WSDL file it should be turned off.
Now it's time to create our server.
First, we'll implement the getQuote() function, which will be
accessed as a service function by incoming request messages from the web. Next,
we'll create a SoapServer object and connect it with the service function using
SoapServer::addFunction() method. As you will see, the SoapServer()
constructor has only one parameter: the path of the WSDL document that describes the service.
<?php
$quotes = array(
"ibm" => 98.42
);
function getQuote($symbol) {
global $quotes;
return $quotes[$symbol];
}
ini_set("soap.wsdl_cache_enabled", "0"); // disabling WSDL cache
$server = new SoapServer("stockquote.wsdl");
$server->addFunction("getQuote");
$server->handle();
?>
The SoapServer can work without a WSDL document in much the same way that the
SoapClient can, but there are no obvious benefits to be had from setting it up in this way.
Were you to do so, you should ensure that the return values are special objects of the
SoapParam and SoapVar classes (as in the first example).
Here is a client for accessing our own SOAP server. Nothing
has changed from the previous example except the WSDL location. It assumes that
“stockquote.wsdl” is in the same directory as our SOAP
server.
<?php
$client = new SoapClient("stockquote.wsdl");
print($client->getQuote("ibm"));
?>
What are the problem areas with our server and client?
To start with, they don't handle errors. What happens when the server doesn't recognize the requested symbol?
The SOAP protocol specifies a special format of messages for reporting errors – SoapFault. To generate such messages
the server should throw an exception using the SoapFault object. The first parameter to the SoapFault()
constructor is a fault code string, and the second is a fault
description string. The client should be written in such a way as to
catch SoapFault exceptions.
Secondly, it would be better to encapsulate Web Service
functionality in a PHP class. In this case we wouldn't need to use
global variables and add each SOAP method to the server individually;
we could add an entire class, and all its methods would be accessible
through SOAP.
Save stockquote.wsdl as stockquote2.wsdl, and alter the
soap:address on line 43 to point to server2.php. A modified
version of our SOAP server and client follows:
<?php
class QuoteService {
private $quotes = array("ibm" => 98.42);
function getQuote($symbol) {
if (isset($this->quotes[$symbol])) {
return $this->quotes[$symbol];
} else {
throw new SoapFault("Server","Unknown Symbol '$symbol'.");
}
}
}
$server = new SoapServer("stockquote2.wsdl");
$server->setClass("QuoteService");
$server->handle();
?>
As you can see, I have used the SoapServer::setClass() method to connect the
SoapServer object with the QuoteService class.
<?php
$client = new SoapClient("stockquote2.wsdl");
try {
echo "<pre>\n";
print($client->getQuote("ibm"));
echo "\n";
print($client->getQuote("microsoft"));
echo "\n</pre>\n";
} catch (SoapFault $exception) {
echo $exception;
}
?>
Are you curious about the SOAP message format, or hoping to
debug a SOAP client of your own? If so, this section is for you.
The SoapClient()
constructor accepts an associative array as its second parameter, as you already
saw in the first example. Various options can be passed through this associative
array. Here are just two:
trace – allows the client to store SOAP requests and responses (turned off by default)
exceptions – allows the client to control the exception mechanism (turned on by default)
SoapClient methods __getLastRequest() and __getLastResponse().
<?php
$client = new SoapClient("stockquote.wsdl",array(
"trace" => 1,
"exceptions" => 0));
$client->getQuote("ibm");
print "<pre>\n";
print "Request :\n".htmlspecialchars($client->__getLastRequest()) ."\n";
print "Response:\n".htmlspecialchars($client->__getLastResponse())."\n";
print "</pre>";
?>
Here is the output of the script. It is modified a little, to make it more easily understood.
Request :
<?xml version="1.0" encoding="UTF-8" ?>
<SOAP-ENV:Envelope
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:ns1="urn:xmethods-delayed-quotes"
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/"
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<SOAP-ENV:Body>
<ns1:getQuote>
<symbol xsi:type="xsd:string">ibm</symbol>
</ns1:getQuote>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
Response:
<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:ns1="urn:xmethods-delayed-quotes"
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/"
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<SOAP-ENV:Body>
<ns1:getQuoteResponse>
<Result xsi:type="xsd:float">98.42</Result>
</ns1:getQuoteResponse>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
All the above are written in PHP, rather than in C.
In this article I have described only the basic functionality of the SOAP extension for PHP. In reality it can do significantly more, but it isn't possible to demonstrate all its features in a short article. The main ones are:
“Simple Object Access Protocol (SOAP) 1.1”
(http://www.w3.org/TR/2000/NOTE-SOAP-20000508/)
“SOAP 1.2 Part 0: Primer”
(http://www.w3.org/TR/2003/REC-soap12-part0-20030624/)
“SOAP 1.2 Part 1: Messaging Framework"
(http://www.w3.org/TR/2003/REC-soap12-part1-20030624/)
"SOAP 1.2 Part 2: Adjuncts"
(http://www.w3.org/TR/2003/REC-soap12-part2-20030624)
“Web Services Description Language (WSDL) 1.1”
(http://www.w3.org/TR/2001/NOTE-wsdl-20010315)
"XML Schema Part 1: Structures"
(http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/)
"XML Schema Part 2: Datatypes"
(http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/)
Dmitry Stogov is one of the authors of PHP's SOAP extension. He has also written the PECL/perl extension and Turck MMCache. He currently resides in St.Petersburg, Russia with his wife and one child. Please feel free to post any comments or questions below, or send them to dmitry@zend.com.
This article was last revised on December 6th 2004 [sf]