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.
XML-RPC Method Call
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:
XML-RPC Method Call with Parameters
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.
Types and Conversions
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).
PHP Native Types as Parameters
Parameters may be passed to call() as native PHP variables, meaning as a String, Integer, Float, Boolean, Array, or an Object. In this case, each PHP native type will be auto-detected and converted into one of the XML-RPC types according to this table:
|PHP Native Type||XML-RPC Type|
What type do empty arrays get cast to?
Passing an empty array to an XML-RPC method is problematic, as it could represent either an array or a struct. Zend\XmlRpc\Client detects such conditions and makes a request to the server's system.methodSignature method to determine the appropriate XML-RPC type to cast to.
However, this in itself can lead to issues. First off, servers that do not support system.methodSignature will log failed requests, and Zend\XmlRpc\Client will resort to casting the value to an XML-RPC array type. Additionally, this means that any call with array arguments will result in an additional call to the remote server.
To disable the lookup entirely, you can call the setSkipSystemLookup() method prior to making your XML-RPC call:
Zend\XmlRpc\Value Objects as Parameters
Parameters may also be created as Zend\XmlRpc\Value instances to specify an exact XML-RPC type. The primary reasons for doing this are:
- When you want to make sure the correct parameter type is passed to the procedure (i.e. the procedure requires an integer and you may get it from a database as a string)
- When the procedure requires base64 or dateTime.iso8601 type (which doesn't exists as a PHP native type)
- When auto-conversion may fail (i.e. you want to pass an empty XML-RPC struct as a parameter. Empty structs are represented as empty arrays in PHP but, if you give an empty array as a parameter it will be auto-converted to an XML-RPC array since it's not an associative array)
There are two ways to create a Zend\XmlRpc\Value object: instantiate one of the Zend\XmlRpc\Value subclasses directly, or use the static factory method Zend\XmlRpc\AbstractValue::getXmlRpcValue().
|XML-RPC Type||Zend\XmlRpc\AbstractValue Constant||Zend\XmlRpc\Value Object|
When building a new Zend\XmlRpc\Value object, its value is set by a PHP type. The PHP type will be converted to the specified type using PHP casting. For example, if a string is given as a value to the Zend\XmlRpc\Value\Integer object, it will be converted using (int) $value.
Server Proxy Object
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.
Proxy the Default Namespace
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:
Proxy Any Namespace
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.
If any HTTP error occurs, such as the remote HTTP server returns a 404 Not Found, a Zend\XmlRpc\Client\Exception\HttpException will be thrown.
Handling HTTP Errors
Regardless of how the XML-RPC client is used, the Zend\XmlRpc\Client\Exception\HttpException will be thrown whenever an HTTP error occurs.
An XML-RPC fault is analogous to a PHP exception. It is a special type returned from an XML-RPC method call that has both an error code and an error message. XML-RPC faults are handled differently depending on the context of how the Zend\XmlRpc\Client is used.
When the call() method or the server proxy object is used, an XML-RPC fault will result in a Zend\XmlRpc\Client\Exception\FaultException being thrown. The code and message of the exception will map directly to their respective values in the original XML-RPC fault response.
Handling XML-RPC Faults
When the call() method is used to make the request, the Zend\XmlRpc\Client\Exception\FaultException will be thrown on fault. A Zend\XmlRpc\Response object containing the fault will also be available by calling getLastResponse().
When the doRequest() method is used to make the request, it will not throw the exception. Instead, it will return a Zend\XmlRpc\Response object returned will containing the fault. This can be checked with isFault() instance method of Zend\XmlRpc\Response.
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\XmlRpc\Client. It can then be used to perform introspection operations on the server.
The following methods are available for introspection:
- getSignatureForEachMethod: Returns the signature for each method on the server
- getSignatureForEachMethodByMulticall($methods=null): Attempt to get the method signatures in one request via system.multicall(). Optionally pass an array of method names.
- getSignatureForEachMethodByLooping($methods=null): Get the method signatures for every method by successively calling system.methodSignature. Optionally pass an array of method names
- getMethodSignature($method): Get the method's signature for $method
- listMethods: List all methods on the server
From Request to Response
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:
Processing Request to 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.
HTTP Client and Testing
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.