Creating and Consuming Web Services With PHP
by Jean-Luc David |

Finally, the web service responds with the result of our query wrapped in a SOAP message. The result of the exchange rate between Canada and the US is 1.3267. The result is displayed on the screen without the SOAP headers.

HTTP/1.1 200 OK

Date: Tue, 10 Feb 2004 11:45:27 GMT

Server: Electric/1.0

Content-Type: text/xml

Content-Length: 492

X-Cache: MISS from www.xmethods.net

Connection: close



<?xml version='1.0' encoding='UTF-8'?>

<soap:Envelope xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/' 

      xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' 

      xmlns:xsd='http://www.w3.org/2001/XMLSchema' 

      xmlns:soapenc='http://schemas.xmlsoap.org/soap/encoding/' 

      soap:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'>

<soap:Body>

<n:getRateResponse xmlns:n='urn:xmethods-CurrencyExchange'>

<Result xsi:type='xsd:float'>1.3267</Result></n:getRateResponse>

</soap:Body>

</soap:Envelope>

Creating a NuSOAP Web service

The next example will demonstrate how to create a web service using NuSOAP. One of the nice features of NuSOAP is the web service summary information and the dynamically generated WSDL files. Here is an example of a web service summary:

We will now create a web service called CanadaTaxCalculator which will calculate the Provincial & Federal sales tax for Ontario Canada just like the XML-RPC example. Let's look at the code:

<?

require_once("nusoap.php");

$ns="http://localhost/nusoap";

First we must include our NuSOAP library and define the namespace of the service. It is usually recommended that you designate a distinctive URI for each one of your Web services.

$server = new soap_server();

$server->configureWSDL('CanadaTaxCalculator',$ns);

$server->wsdl->schemaTargetNamespace=$ns;

Next step, we instantiate the SOAP server and define the settings for our WSDL file such as the service name and the namespace.

$server->register('CalculateOntarioTax',

array('amount' => 'xsd:string'),

array('return' => 'xsd:string'),

$ns);

Then we register our PHP tax calculation function. This step will make the server "aware" of the existence of the CalculateOntarioTax method and the values that will pass to and from the method. If you have several methods, you must register each one separately.

function CalculateOntarioTax($amount){

$taxcalc=$amount*.15;

return new soapval('return','string',$taxcalc);

}

Then we invoke the service using the following line of code:

$server->service($HTTP_RAW_POST_DATA);

?>

That's it. Save your code in a file called "server.php", place the file on your web server and voila! You can now view dynamic WSDL formatted data by typing the following URL (be sure to substitute "localhost" with your own server name):

http://localhost/server.php?wsdl

In fact, appending "?wsdl" to the end of any PHP NuSOAP server file will dynamically produce WSDL code. Here's how our CanadaTaxCalculator Web service is described using WSDL:

 <?xml version="1.0" encoding="ISO-8859-1" ?> 

    <definitions 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" 

                 xmlns:tns="http://localhost/nusoap" 

                 xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" 

                 xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" 

                 xmlns="http://schemas.xmlsoap.org/wsdl/" 

                 targetNamespace="http://localhost/nusoap">

     <types>

      <xsd:schema targetNamespace="http://localhost/nusoap">

        <xsd:import namespace="http://schemas.xmlsoap.org/soap/encoding/" /> 

        <xsd:import namespace="http://schemas.xmlsoap.org/wsdl/" /> 

      </xsd:schema>

  </types>

  <message name="CalculateOntarioTaxRequest">

    <part name="amount" type="xsd:string" /> 

  </message>

  <message name="CalculateOntarioTaxResponse">

    <part name="return" type="xsd:string" /> 

  </message>

  <portType name="CanadaTaxCalculatorPortType">

   <operation name="CalculateOntarioTax">

    <input message="tns:CalculateOntarioTaxRequest" /> 

    <output message="tns:CalculateOntarioTaxResponse" /> 

   </operation>

  </portType>

  <binding name="CanadaTaxCalculatorBinding" type="tns:CanadaTaxCalculatorPortType">

    <soap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http" /> 

  <operation name="CalculateOntarioTax">

    <soap:operation 

     soapAction="http://localhost/nusoap/onttaxws.php/CalculateOntarioTax" 

     style="rpc" /> 

      <input>

       <soap:body use="encoded" 

        namespace="http://localhost/nusoap" 

        encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" /> 

      </input>

      <output>

       <soap:body use="encoded" 

        namespace="http://localhost/nusoap" 

        encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" /> 

      </output>

  </operation>

  </binding>

  <service name="CanadaTaxCalculator">

   <port 

    name="CanadaTaxCalculatorPort" 

    binding="tns:CanadaTaxCalculatorBinding">

   <soap:address location="http://localhost/nusoap/onttaxws.php" /> 

  </port>

 </service>

</definitions>

Creating a NuSOAP Web Service Client

What if we want to consume the web service we just created? Not a problem at all. Let's build a client from scratch. First, we must instantiate the NuSOAP client object and pass the WSDL file with the relevant web service definitions into the client.

<?php

require_once('nusoap.php'); 

$wsdl="http://localhost/server.php?wsdl";

$client=new soapclient($wsdl, 'wsdl'); 

Next step, we create a set of parameters to pass into the Web service and then remotely call the CalculateOntarioTax method. The example shows us sending an amount of $15.00 into the web service to find out how much tax we would have to pay in Ontario.

$param=array(

'amount'=>'15.00',

); 

echo $client->call('CalculateOntarioTax', $param);

?>

REST

REST differs a great deal from SOAP and XML-RPC. First, it's not a standard, whether formal or informal. Second, there is no standardized toolkit or pre-built client and server classes in PHP. The strength of REST is that you won't need special extensions or tools to develop web services. The HTTP protocol specifications contains everything you would need to transmit and receive XML messages.

REST, which stands for "Representational State Transfer", is a simpler approach than XML-RPC or SOAP, using standard HTTP methods such as GET, POST and PUT to send and retrieve XML data. You can then use tools like PHP DOM, SAX, or even XSL to do the parsing. The downside is that everything has to be built by hand (though REST toolkits and frameworks are starting to appear in some languages). If you want to develop REST web services, you must thoroughly understand XML and HTTP. Expect to have to write a little more code yourself.

Consuming an XML Web service using REST

To pass XML data from one server to another, we will be using the cURL PHP extensions. The Client URL Request Library is a versatile set of classes that enable PHP to transmit and receive files via HTTP. The data that is transmitted is a simple XML file, therefore you are not required to create an elaborate server. No custom wrappers or APIs are needed either. REST is increasing in popularity: in fact, Amazon.com has created a popular web service designed around the REST concept.

Let's look at the code for our REST web service client. First, we define the file location and the name of the XML file; if you want to dynamically generate the XML file, all you need to do is design a custom PHP script that accepts parameters (through the query string), incorporates your processing functions and outputs an XML file with the "result":

<?

$rs="http://localhost/xmldata.xml";

$qs="";

Then we create an array which will contain the parameters we will pass in the query string. Each one of the parameters is then urlencoded so that it may pass without problems in the HTTP header:

$parray=array('amount'=>"15.00");

foreach($parray as $par=>$value){ 

$qs=$qs."$par=".urlencode($value)."&";}

$uri="$rs?$qs";

Then we instantiate the cURL object. The CURLOPT_RETURNTRANSFER parameter specifies that we want the data to transmit even if errors are encountered. We then execute the transfer and pass the resulting data into a variable called $xml:

$cobj=curl_init($uri);

curl_setopt($cobj,CURLOPT_RETURNTRANSFER,1);

$xml=curl_exec($cobj);

curl_close($cobj);

echo $xml;

?>

Here is the code for the REST server. The program grabs the dollar amount from the query string, executes the tax calculation then outputs XML with the result:

<?

$amount=$_GET["amount"];

$taxcalc=$amount*.15;

echo "<?xml version=\"1.0\"?>";

echo "<taxinfo>";

echo "<result>".$taxcalc."</result>";

echo "</taxinfo>";

?>

Conclusion

With three different methods of consuming and producing web services and tons of toolkits at your disposal, there is simply no reason why you can't use PHP to develop web based XML applications. Be sure to download our sample code and good luck.

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