Creating a Web Service with PEAR::XML-RPC

Several XML-RPC implementations are out there, but the one most widely used and also in active development is PEAR::XML-RPC, available at http://pear.php.net/package/XML_RPC/. It is a PEAR port of another XML-RPC library and adds some fixes that didn't make it in the original distribution.You can install it with pear upgrade XML_RPC, to get the latest and greatest version.

To provide such a Web Service, you have to instantiate the XML_RPC_Server class and provide some information about the service: which function to use, its description, and, of course, the signature (which parameter types are passed, which data type is returned). The preceding code contains this information for a simple "add two numbers" Web Service.

Information about the XML-RPC Web Service (xmlrpc-pear-server.php; excerpt)

 <?php   require_once 'XML/RPC/Server.php';   $description = 'adds two numbers';   $signature = array(     array('int', 'int', 'int')   );   $xmlrpc = new XML_RPC_Server(     array('phrasebook.php.add' =>       array(         'function' => 'add',         'docstring' => $description,         'signature' => $signature       )     )   ); ?> 

Note that the signature contains the data types of all input parameters plus the data type of the return value; that's why 'int' appears three times and not just twice.

Now the only thing missing is the actual business logic, the function to add. This is a bit tricky: First, the getParam() method returns all parameters provided to the function; then, the scalarval() retrieves the actual value of such a parameter. Then, the actual adding of the numbers can be done, by returning a suitable XML_RPC_Response object. For instance:

 function add($params) {   $a = $params->getParam(0);   $b = $params->getParam(1);   if (isset($a) && isset($b)) {     if ($a->scalartyp() == 'int' && $b->scalartyp()       == 'int') {        $a = $a->scalarval();        $b = $b->scalarval();        $c = new XML_RPC_Value($a + $b, 'int');        return new XML_RPC_Response($c);     } else {        global $XML_RPC_erruser;        return new XML_RPC_Response(0,          $XML_RPC_erruser,          'wrong parameters');     }   } }