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Creating an AJAX-Friendly Web Service
For our example Web services, we'll be loosely adhering to the REST principle and creating Web services that are addressable through the service's Uniform Resource Identifier (URI).

Creating a PHP Web Service
This example requires JSON-PHP and assumes you have the XMLRPC extension installed. On Windows ensure that php_xmlrpc.dll is in your extensions folder and edit PHP.INI to uncomment the following line:

;extension=php_xmlrpc.dll

On Unix-based systems you'll have to compile PHP using the --with-xmlrpc[=DIR] configuration option.

In this example we'll create a basic Web service that will return the sum of the digits passed to it. This Web service will be used in the next section with AJAX JSON and XML requests.

The Code

Listing 6.5

<?php
// Only proceed if we were given numbers to sum
if( isset($_GET['numbers']) ) {
   // Split our string into an array using preg_split on any non-digit character.
   $numbers = preg_split("/[^\d]+/", $_GET['numbers']);

   // Force the types of the array values to integer
   array_walk($numbers, create_function('&$elem', 'settype($elem,"integer");') );
   // Set $sum to be the sum of all the digits in our $numbers array
   $sum = array_sum($numbers);

   // Build our response object.
   // We include the original request only to make our response more complex.
   $response = array(
     'numbers' => $numbers,
     'sum' => $sum
   );

   // Check to see if an output format was requested, and if it was JSON
   // Return XML output by default
   if( isset($_GET['output']) && !strcasecmp($_GET['output'], 'json') ) {
     require_once('JSON.php');
     $json = new Services_JSON();
     echo $json->encode($response);
   } else {
     // Send our XML content-type header
     header('Content-type: text/xml');
     // And print out our formatted response
     echo xmlrpc_encode_request(null,$response);
   }
}
?>

Dissecting the Code
This is an extremely simple Web service that can be accessed in a REST-like manner through the resources URI. It expects two variables in the query string: numbers and output. The variable numbers will contain a delimited list of numbers that this Web service will sum and return. To make our return object more complex, we'll return the original request as well as the sum. You can specify your desired output format by setting output to JSON or XML.

A normal GET request to http://yourserver/add.php?numbers=1+2+3&output=json will print the following:

{"numbers":["1","2","3"],"sum":6}

Changing output to XML (http://yourserver/add.php?numbers=1+2+3&output=xml) will return:

Listing 6.6

<?xml version="1.0" encoding="iso-8859-1"?>
  <methodResponse>
   <params>
    <param>
     <value>
      <struct>
       <member>
        <name>numbers</name>
        <value>
         <array>
          <data>
           <value>
            <int>1</int>
           </value>
           <value>
            <int>2</int>
           </value>
           <value>
            <int>3</int>
           </value>
          </data>
         </array>
        </value>
       </member>
       <member>
        <name>sum</name>
        <value>
         <int>6</int>
        </value>
       </member>
      </struct>
     </value>
    </param>
   </params>
  </methodResponse>

You can see that our original response, member name numbers, is there along with the three values we passed it. The second member, sum, has one value, and is the sum of the numbers array.

This content is reprinted from Real-World AJAX: Secrets of the Masters published by SYS-CON Books. To order the entire book now along with companion DVDs, click here to order.