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I like the way the framework “distributes” the logic of the web application between different controllers (i.e. Posts, Comments, and so on). But when I want to develop an XML-RPC server, I prefer to place all the code into a single controller so I can maintain consistency and have a single place to look for errors. The other advantage of this solution is that you don’t need to add logic in the single controllers to handle XML-RPC calls.

For the implementation of the XML-RPC protocol I decided to go with the Inutio XML-RPC Library (http://scripts.incutio.com/xmlrpc/). This library is completely object oriented, easy to use and works with both PHP 4 and PHP 5.

You can download a little modified version from the following URL:

http://www.creativepark.it/downloads/xmlrpc.zip

The 2 changes I made are described in the header of the file.

Here are the steps to build your XML-RPC server with CakePHP:

1. Download the xmlrpc.zip archive and extract its content into your app/vendors folder.
2. Create the app/controllers/xml_rpc_controller.php file as follows:

File: app/controllers/xml_rpc_controller.php

Controller Class:

Download code <?php 

// Import the app/vendor/xmlrpc.php library
App::import('Vendor', 'xmlrpc');

class XmlRpcController extends AppController {

    // This demo doesn't need models
    var $uses = array();
    
    // The XML-RPC server object
    var $server = null;

    function index() {

        // Disable debug information
        // Required to generate valid XML output
        Configure::write('debug', 0); 

        // Avoids render() call
        $this->autoRender = false;

        // XML-RPC callbacks settings
        // Use this parameter to map XML-RPC methods to your protected or private controller methods
        $callbacks = array();
        $callbacks['demo.sayHello'] = array(&$this, '_sayHello');

        // Handle XML-RPC request
        $this->server = new IXR_Server($callbacks);
    }
    
    // Protected Method
    function _sayHello($name, $country) {
        return "Hi {$name}! You come from {$country}!";
    }
    
}

?>
That’s all. You have created your first, simple XML-RPC server.
To test its behavior, you can use the following client script:

Download code <?php

// Include the XML-RPC class
require_once(dirname(__FILE__) . '/xmlrpc.php');

// Set here your XML-RPF control url
$url = 'http://cake.local/xml_rpc';

// Create the client object
$client = new IXR_Client($url);

// Set the debug property to true during development to see both request and response data
// $client->debug = true;

// Call the demo.sayHello method passing 'Filippo' and 'Italy' as first and second parameter
if (!$client->query('demo.sayHello', 'Filippo', 'Italy')) {
    die('Something went wrong - '.$client->getErrorCode().' : '.$client->getErrorMessage());
}

// Display the result
echo '<pre>';
print_r($client->getResponse());
echo '</pre>';

?>
Of course this isn’t very useful, but it’s a starting point.

Here is the another controller that exposes some functions of the Blog sample application (requires the Post table and model).

File: app/controllers/xml_rpc_controller.php

Controller Class:

Download code <?php 

// Import the app/vendor/xmlrpc.php library
App::import('Vendor', 'xmlrpc');

class XmlRpcController extends AppController {

    // This time we need the Post model
    var $uses = array('Post');
    
    // The XML-RPC server object
    var $server = null;
    
    // XML-RPC access point
    function index() {

        // Disable debug information
        // Required to generate valid XML output
        Configure::write('debug', 0); 

        // Avoids render() call
        $this->autoRender = false;

        // XML-RPC callbacks settings
        // Use this parameter to map XML-RPC methods to your protected or private controller methods
        $callbacks = array();
        $callbacks['post.view']   = array(&$this, '_postView');
        $callbacks['post.add']    = array(&$this, '_postAdd');
        $callbacks['post.edit']   = array(&$this, '_postEdit');
        $callbacks['post.delete'] = array(&$this, '_postDelete');

        // Handle XML-RPC request
        $this->server = new IXR_Server($callbacks);
    }

    function _postView($id = null) {
        if (!$id) {
            return new IXR_Error(2, 'Invalid Post');
        }
        return $this->Post->read(null, $id);
    }

    function _postAdd($data = array()) {
        if (!empty($data)) {
            $this->Post->create();
            if ($this->Post->save($data)) {
                return (int)$this->Post->id;
            } else {
                return new IXR_Error(1, 'Post not saved');
            }
        }
        return false;
    }
    
    function _postEdit($data = array()) {
        if (empty($data)) {
            return new IXR_Error(2, 'Invalid Post');
        } elseif (!$this->Post->save($data)) {
            return new IXR_Error(1, 'Post not saved');
        }
        return true;
    }    
    
    function _postDelete($id = null) {
        if (!$id) {
            return new IXR_Error(2, 'Invalid Post');
        } elseif (!$this->Post->del($id)) {
            return new IXR_Error(3, 'Post not deleted');
        }        
        return true;
    }    
    
}

?>
And this is a simple client that uses all the methods exposed by the controller:

Download code <?php

// Include the XML-RPC class
require_once(dirname(__FILE__) . '/xmlrpc.php');

// Set here your XML-RPF control url
$url = 'http://cake.local/xml_rpc';

// Create the client object
$client = new IXR_Client($url);

// Set the debug property to true during development to see both request and response data
// $client->debug = true;

echo('<pre>');

// ####################### Let's create a new Post ####################### //

// Set Post data
$post = array ('Post' => 
  array (
    'title' => 'My First XML-RPC Post',
    'body' => 'This is the post body.',
  ),
);

// Call post.add
if (!$client->query('post.add', $post)) {
    die('Something went wrong - ' . $client->getErrorCode() . ' : ' . $client->getErrorMessage());
}

// Get new Post ID
$post_id = (int)$client->getResponse();

echo("New Post ID: {$post_id}\r\n");

// ####################### Let's display the new Post ####################### //

// Call post.view
if (!$client->query('post.view', $post_id)) {
    die('Something went wrong - ' . $client->getErrorCode() . ' : ' . $client->getErrorMessage());
}

// Get the Post data
$data = $client->getResponse();

// Display the Post data
print('Post data: ');
print_r($data);

// ####################### Let's edit the Post ####################### //

// Change Post data
$data['Post']['title']    = 'My First Edited XML-RPC Post';
$data['Post']['modified'] =  date('Y-m-d H:i:s');

// Call post.edit
if (!$client->query('post.edit', $data)) {
    die('Something went wrong - ' . $client->getErrorCode() . ' : ' . $client->getErrorMessage());
}

echo("Post Modified\r\n");

// ####################### Let's delete the Post ####################### //

// Call post.delete
if (!$client->query('post.delete', $data['Post']['id'])) {
    die('Something went wrong - ' . $client->getErrorCode() . ' : ' . $client->getErrorMessage());
}

echo("Post Deleted\r\n");

echo('</pre>');

?>
As you can seen, there’s a bit of redundance of code between the XmlRpcController and the PostsController of the Blog sample application.

Creating an XML-RPC server with CakePHP is straight forward. You can easily build an API for external developers using a common protocol and the power of CakePHP.