As noted previously by myself and Davey, I've been working on Zend_XmlRpc_Server for some months now. In the past couple weeks, I've refactored it to push the class/function reflection into Zend_Server_Reflection, and, in doing so, noted that there were further areas for refactoring into additional helper classes. Currently, it now has classes for the Request, Response, and Faults, and all actual XML wrangling is done in those, making the server basically XML-agnostic.

One side benefit of this refactoring was that it allowed me to write tests much more quickly and easily. I no longer needed to worry about adding helper methods to the server in order to determine if it properly parsed the request to get the method call and arguments; I could simply test the public API for actually handling the requests. And I no longer needed to create XML in order to test the server; I could simply populate a request object in order to pass in the request, and check the response object to see if I received an appropriate value. No XML wrangling!

So, for an example, advanced case usage with all the bells and whistles:

<?php
require_once 'Zend/XmlRpc/Server.php';
require_once 'Zend/XmlRpc/Server/Fault.php';
require_once 'Zend/XmlRpc/Server/Cache.php';
require_once 'Services/Request.php';
require_once 'Services/Response.php';
require_once 'Services/Exception.php';

require_once 'Services/Comb.php';
require_once 'Services/Brush.php';
require_once 'Services/Pick.php';

// Specify a cache file
$cacheFile = dirname(__FILE__) . '/xmlrpc.cache';

// Allow Services_Exceptions to report as fault responses
Zend_XmlRpc_Server_Fault::attachFaultException('Services_Exception');

$server = new Zend_XmlRpc_Server();

// Attempt to retrieve server definition from cache
if (!Zend_XmlRpc_Server_Cache::get($cacheFile, $server)) {
    $server->setClass('Services_Comb', 'comb');   // methods called as comb.*
    $server->setClass('Services_Brush', 'brush'); // methods called as brush.*
    $server->setClass('Services_Pick', 'pick');   // methods called as pick.*

    // Save cache
    Zend_XmlRpc_Server_Cache::save($cacheFile, $server));
}

// Create a request object
$request = new Services_Request();

// Utilize a custom response
$server->setResponseClass('Services_Response');

echo $server->handle($request);

As an afterthought, something that hit me as I finished writing the Request, Response, and Fault classes is that, since the server doesn't need to do anything with XML, there's really no saying that these classes do, either. This means it could, theoretically, be used as a scaffold for other types of RPC web services — for instance, using compression or ssl-encoded transactions, YAML, JSON, etc. That will be a subject for another day.

If you're interested in testing the XML-RPC server, which is mostly complete at this stage (@todo items at this stage only include verifying arguments received in a request match one of the signatures and that reflection translates the signature parameter and return types to XML-RPC types), you can grab it from the Zend Framework subversion repository, in the incubator tree.