Zend Framework provides support for consuming remote XML-RPC services as a client in the Zend_XmlRpc_Client package. Its major features include automatic type conversion between PHP and XML-RPC, a server proxy object, and access to server introspection capabilities.

The constructor of Zend_XmlRpc_Client receives the URL of the remote XML-RPC server endpoint as its first parameter. The new instance returned may be used to call any number of remote methods at that endpoint.

To call a remote method with the XML-RPC client, instantiate it and use the call() instance method. The code sample below uses a demonstration XML-RPC server on the Zend Framework website. You can use it for testing or exploring the Zend_XmlRpc components.

$client = new Zend_XmlRpc_Client('http://framework.zend.com/xmlrpc');

echo $client->call('test.sayHello');

// hello

The XML-RPC value returned from the remote method call will be automatically unmarshaled and cast to the equivalent PHP native type. In the example above, a PHP String is returned and is immediately ready to be used.

The first parameter of the call() method receives the name of the remote method to call. If the remote method requires any parameters, these can be sent by supplying a second, optional parameter to call() with an Array of values to pass to the remote method:

$client = new Zend_XmlRpc_Client('http://framework.zend.com/xmlrpc');

$arg1 = 1.1;
$arg2 = 'foo';

$result = $client->call('test.sayHello', array($arg1, $arg2));

// $result is a native PHP type

If the remote method doesn't require parameters, this optional parameter may either be left out or an empty array() passed to it. The array of parameters for the remote method can contain native PHP types, Zend_XmlRpc_Value objects, or a mix of each.

The call() method will automatically convert the XML-RPC response and return its equivalent PHP native type. A Zend_XmlRpc_Response object for the return value will also be available by calling the getLastResponse() method after the call.

Some remote method calls require parameters. These are given to the call() method of Zend_XmlRpc_Client as an array in the second parameter. Each parameter may be given as either a native PHP type which will be automatically converted, or as an object representing a specific XML-RPC type (one of the Zend_XmlRpc_Value objects).

$client->setSkipSystemLookup(true);
$result = $client->call('foo.bar', array(array()));

Another way to call remote methods with the XML-RPC client is to use the server proxy. This is a PHP object that proxies a remote XML-RPC namespace, making it work as close to a native PHP object as possible.

To instantiate a server proxy, call the getProxy() instance method of Zend_XmlRpc_Client. This will return an instance of Zend_XmlRpc_Client_ServerProxy. Any method call on the server proxy object will be forwarded to the remote, and parameters may be passed like any other PHP method.

$client = new Zend_XmlRpc_Client('http://framework.zend.com/xmlrpc');

$service = $client->getProxy();           // Proxy the default namespace

$hello = $service->test->sayHello(1, 2);  // test.Hello(1, 2) returns "hello"

The getProxy() method receives an optional argument specifying which namespace of the remote server to proxy. If it does not receive a namespace, the default namespace will be proxied. In the next example, the 'test' namespace will be proxied:

$client = new Zend_XmlRpc_Client('http://framework.zend.com/xmlrpc');

$test  = $client->getProxy('test');     // Proxy the "test" namespace

$hello = $test->sayHello(1, 2);         // test.Hello(1,2) returns "hello"

If the remote server supports nested namespaces of any depth, these can also be used through the server proxy. For example, if the server in the example above had a method test.foo.bar(), it could be called as $test->foo->bar().

Two kinds of errors can occur during an XML-RPC method call: HTTP errors and XML-RPC faults. The Zend_XmlRpc_Client recognizes each and provides the ability to detect and trap them independently.

$client = new Zend_XmlRpc_Client('http://foo/404');

try {

    $client->call('bar', array($arg1, $arg2));

} catch (Zend_XmlRpc_Client_HttpException $e) {

    // $e->getCode() returns 404
    // $e->getMessage() returns "Not Found"

}

$client = new Zend_XmlRpc_Client('http://framework.zend.com/xmlrpc');

try {

    $client->call('badMethod');

} catch (Zend_XmlRpc_Client_FaultException $e) {

    // $e->getCode() returns 1
    // $e->getMessage() returns "Unknown method"

}

Some XML-RPC servers support the de facto introspection methods under the XML-RPC system. namespace. Zend_XmlRpc_Client provides special support for servers with these capabilities.

A Zend_XmlRpc_Client_ServerIntrospection instance may be retrieved by calling the getIntrospector() method of Zend_XmlRpcClient. It can then be used to perform introspection operations on the server.

Under the hood, the call() instance method of Zend_XmlRpc_Client builds a request object (Zend_XmlRpc_Request) and sends it to another method, doRequest(), that returns a response object (Zend_XmlRpc_Response).

The doRequest() method is also available for use directly:

$client = new Zend_XmlRpc_Client('http://framework.zend.com/xmlrpc');

$request = new Zend_XmlRpc_Request();
$request->setMethod('test.sayHello');
$request->setParams(array('foo', 'bar'));

$client->doRequest($request);

// $client->getLastRequest() returns instanceof Zend_XmlRpc_Request
// $client->getLastResponse() returns instanceof Zend_XmlRpc_Response

Whenever an XML-RPC method call is made by the client through any means, either the call() method, doRequest() method, or server proxy, the last request object and its resultant response object will always be available through the methods getLastRequest() and getLastResponse() respectively.

In all of the prior examples, an HTTP client was never specified. When this is the case, a new instance of Zend_Http_Client will be created with its default options and used by Zend_XmlRpc_Client automatically.

The HTTP client can be retrieved at any time with the getHttpClient() method. For most cases, the default HTTP client will be sufficient. However, the setHttpClient() method allows for a different HTTP client instance to be injected.

The setHttpClient() is particularly useful for unit testing. When combined with the Zend_Http_Client_Adapter_Test, remote services can be mocked out for testing. See the unit tests for Zend_XmlRpc_Client for examples of how to do this.