Zend_XmlRpc_Server

Introduction

Zend_XmlRpc_Server is intended as a fully-featured XML-RPC server, following » the specifications outlined at www.xmlrpc.com. Additionally, it implements the system.multicall() method, allowing boxcarring of requests.

Basic Usage

An example of the most basic use case:

  1. $server = new Zend_XmlRpc_Server();
  2. $server->setClass('My_Service_Class');
  3. echo $server->handle();

Server Structure

Zend_XmlRpc_Server is composed of a variety of components, ranging from the server itself to request, response, and fault objects.

To bootstrap Zend_XmlRpc_Server, the developer must attach one or more classes or functions to the server, via the setClass() and addFunction() methods.

Once done, you may either pass a Zend_XmlRpc_Request object to Zend_XmlRpc_Server::handle(), or it will instantiate a Zend_XmlRpc_Request_Http object if none is provided -- thus grabbing the request from php://input.

Zend_XmlRpc_Server::handle() then attempts to dispatch to the appropriate handler based on the method requested. It then returns either a Zend_XmlRpc_Response-based object or a Zend_XmlRpc_Server_Faultobject. These objects both have __toString() methods that create valid XML-RPC XML responses, allowing them to be directly echoed.

Anatomy of a webservice

General considerations

For maximum performance it is recommended to use a simple bootstrap file for the server component. Using Zend_XmlRpc_Server inside a Zend_Controller is strongly discouraged to avoid the overhead.

Services change over time and while webservices are generally less change intense as code-native APIs, it is recommended to version your service. Do so to lay grounds to provide compatibility for clients using older versions of your service and manage your service lifecycle including deprecation timeframes.To do so just include a version number into your URI. It is also recommended to include the remote protocol name in the URI to allow easy integration of upcoming remoting technologies. http://myservice.ws/1.0/XMLRPC/.

What to expose?

Most of the time it is not sensible to expose business objects directly. Business objects are usually small and under heavy change, because change is cheap in this layer of your application. Once deployed and adopted, web services are hard to change. Another concern is I/O and latency: the best webservice calls are those not happening. Therefore service calls need to be more coarse-grained than usual business logic is. Often an additional layer in front of your business objects makes sense. This layer is sometimes referred to as » Remote Facade. Such a service layer adds a coarse grained interface on top of your business logic and groups verbose operations into smaller ones.

Conventions

Zend_XmlRpc_Server allows the developer to attach functions and class method calls as dispatchable XML-RPC methods. Via Zend_Server_Reflection, it does introspection on all attached methods, using the function and method docblocks to determine the method help text and method signatures.

XML-RPC types do not necessarily map one-to-one to PHP types. However, the code will do its best to guess the appropriate type based on the values listed in @param and @return lines. Some XML-RPC types have no immediate PHP equivalent, however, and should be hinted using the XML-RPC type in the PHPDoc. These include:

  • dateTime.iso8601, a string formatted as 'YYYYMMDDTHH:mm:ss'

  • base64, base64 encoded data

  • struct, any associative array

An example of how to hint follows:

  1. /**
  2. * This is a sample function
  3. *
  4. * @param base64 $val1 Base64-encoded data
  5. * @param dateTime.iso8601 $val2 An ISO date
  6. * @param struct $val3 An associative array
  7. * @return struct
  8. */
  9. function myFunc($val1, $val2, $val3)
  10. {
  11. }

PhpDocumentor does no validation of the types specified for params or return values, so this will have no impact on your API documentation. Providing the hinting is necessary, however, when the server is validating the parameters provided to the method call.

It is perfectly valid to specify multiple types for both params and return values; the XML-RPC specification even suggests that system.methodSignature should return an array of all possible method signatures (i.e., all possible combinations of param and return values). You may do so just as you normally would with PhpDocumentor, using the '|' operator:

  1. /**
  2. * This is a sample function
  3. *
  4. * @param string|base64 $val1 String or base64-encoded data
  5. * @param string|dateTime.iso8601 $val2 String or an ISO date
  6. * @param array|struct $val3 Normal indexed array or an associative array
  7. * @return boolean|struct
  8. */
  9. function myFunc($val1, $val2, $val3)
  10. {
  11. }

Note: Allowing multiple signatures can lead to confusion for developers using the services; to keep things simple, a XML-RPC service method should only have a single signature.

Utilizing Namespaces

XML-RPC has a concept of namespacing; basically, it allows grouping XML-RPC methods by dot-delimited namespaces. This helps prevent naming collisions between methods served by different classes. As an example, the XML-RPC server is expected to server several methods in the 'system' namespace:

  • system.listMethods

  • system.methodHelp

  • system.methodSignature

Internally, these map to the methods of the same name in Zend_XmlRpc_Server.

If you want to add namespaces to the methods you serve, simply provide a namespace to the appropriate method when attaching a function or class:

  1. // All public methods in My_Service_Class will be accessible as
  2. // myservice.METHODNAME
  3. $server->setClass('My_Service_Class', 'myservice');
  4.  
  5. // Function 'somefunc' will be accessible as funcs.somefunc
  6. $server->addFunction('somefunc', 'funcs');

Custom Request Objects

Most of the time, you'll simply use the default request type included with Zend_XmlRpc_Server, Zend_XmlRpc_Request_Http. However, there may be times when you need XML-RPC to be available via the CLI, a GUI, or other environment, or want to log incoming requests. To do so, you may create a custom request object that extends Zend_XmlRpc_Request. The most important thing to remember is to ensure that the getMethod() and getParams() methods are implemented so that the XML-RPC server can retrieve that information in order to dispatch the request.

Custom Responses

Similar to request objects, Zend_XmlRpc_Server can return custom response objects; by default, a Zend_XmlRpc_Response_Http object is returned, which sends an appropriate Content-Type HTTP header for use with XML-RPC. Possible uses of a custom object would be to log responses, or to send responses back to STDOUT.

To use a custom response class, use Zend_XmlRpc_Server::setResponseClass() prior to calling handle().

Handling Exceptions via Faults

Zend_XmlRpc_Server catches Exceptions generated by a dispatched method, and generates an XML-RPC fault response when such an exception is caught. By default, however, the exception messages and codes are not used in a fault response. This is an intentional decision to protect your code; many exceptions expose more information about the code or environment than a developer would necessarily intend (a prime example includes database abstraction or access layer exceptions).

Exception classes can be whitelisted to be used as fault responses, however. To do so, simply utilize Zend_XmlRpc_Server_Fault::attachFaultException() to pass an exception class to whitelist:

  1. Zend_XmlRpc_Server_Fault::attachFaultException('My_Project_Exception');

If you utilize an exception class that your other project exceptions inherit, you can then whitelist a whole family of exceptions at a time. Zend_XmlRpc_Server_Exceptions are always whitelisted, to allow reporting specific internal errors (undefined methods, etc.).

Any exception not specifically whitelisted will generate a fault response with a code of '404' and a message of 'Unknown error'.

Caching Server Definitions Between Requests

Attaching many classes to an XML-RPC server instance can utilize a lot of resources; each class must introspect using the Reflection API (via Zend_Server_Reflection), which in turn generates a list of all possible method signatures to provide to the server class.

To reduce this performance hit somewhat, Zend_XmlRpc_Server_Cache can be used to cache the server definition between requests. When combined with __autoload(), this can greatly increase performance.

An sample usage follows:

  1. function __autoload($class)
  2. {
  3.     Zend_Loader::loadClass($class);
  4. }
  5.  
  6. $cacheFile = dirname(__FILE__) . '/xmlrpc.cache';
  7. $server = new Zend_XmlRpc_Server();
  8.  
  9. if (!Zend_XmlRpc_Server_Cache::get($cacheFile, $server)) {
  10.     require_once 'My/Services/Glue.php';
  11.     require_once 'My/Services/Paste.php';
  12.     require_once 'My/Services/Tape.php';
  13.  
  14.     $server->setClass('My_Services_Glue', 'glue');   // glue. namespace
  15.     $server->setClass('My_Services_Paste', 'paste'); // paste. namespace
  16.     $server->setClass('My_Services_Tape', 'tape');   // tape. namespace
  17.  
  18.     Zend_XmlRpc_Server_Cache::save($cacheFile, $server);
  19. }
  20.  
  21. echo $server->handle();

The above example attempts to retrieve a server definition from xmlrpc.cache in the same directory as the script. If unsuccessful, it loads the service classes it needs, attaches them to the server instance, and then attempts to create a new cache file with the server definition.

Usage Examples

Below are several usage examples, showing the full spectrum of options available to developers. Usage examples will each build on the previous example provided.

Example #1 Basic Usage

The example below attaches a function as a dispatchable XML-RPC method and handles incoming calls.

  1. /**
  2. * Return the MD5 sum of a value
  3. *
  4. * @param string $value Value to md5sum
  5. * @return string MD5 sum of value
  6. */
  7. function md5Value($value)
  8. {
  9.     return md5($value);
  10. }
  11.  
  12. $server = new Zend_XmlRpc_Server();
  13. $server->addFunction('md5Value');
  14. echo $server->handle();

Example #2 Attaching a class

The example below illustrates attaching a class' public methods as dispatchable XML-RPC methods.

  1. require_once 'Services/Comb.php';
  2.  
  3. $server = new Zend_XmlRpc_Server();
  4. $server->setClass('Services_Comb');
  5. echo $server->handle();

Example #3 Attaching a class with arguments

The following example illustrates how to attach a class' public methods and passing arguments to its methods. This can be used to specify certain defaults when registering service classes.

  1. class Services_PricingService
  2. {
  3.     /**
  4.      * Calculate current price of product with $productId
  5.      *
  6.      * @param ProductRepository $productRepository
  7.      * @param PurchaseRepository $purchaseRepository
  8.      * @param integer $productId
  9.      */
  10.     public function calculate(ProductRepository $productRepository,
  11.                               PurchaseRepository $purchaseRepository,
  12.                               $productId)
  13.     {
  14.         ...
  15.     }
  16. }
  17.  
  18. $server = new Zend_XmlRpc_Server();
  19. $server->setClass('Services_PricingService',
  20.                   'pricing',
  21.                   new ProductRepository(),
  22.                   new PurchaseRepository());

The arguments passed at setClass() at server construction time are injected into the method call pricing.calculate() on remote invokation. In the example above, only the argument $purchaseId is expected from the client.

Example #4 Passing arguments only to constructor

Zend_XmlRpc_Server allows to restrict argument passing to constructors only. This can be used for constructor dependency injection. To limit injection to constructors, call sendArgumentsToAllMethods and pass FALSE as an argument. This disables the default behavior of all arguments being injected into the remote method. In the example below the instance of ProductRepository and PurchaseRepository is only injected into the constructor of Services_PricingService2.

  1. class Services_PricingService2
  2. {
  3.     /**
  4.      * @param ProductRepository $productRepository
  5.      * @param PurchaseRepository $purchaseRepository
  6.      */
  7.     public function __construct(ProductRepository $productRepository,
  8.                                 PurchaseRepository $purchaseRepository)
  9.     {
  10.         ...
  11.     }
  12.  
  13.     /**
  14.      * Calculate current price of product with $productId
  15.      *
  16.      * @param integer $productId
  17.      * @return double
  18.      */
  19.     public function calculate($productId)
  20.     {
  21.         ...
  22.     }
  23. }
  24.  
  25. $server = new Zend_XmlRpc_Server();
  26. $server->sendArgumentsToAllMethods(false);
  27. $server->setClass('Services_PricingService2',
  28.                   'pricing',
  29.                   new ProductRepository(),
  30.                   new PurchaseRepository());

Example #5 Attaching a class instance

setClass() allows to register a previously instantiated object at the server. Just pass an instance instead of the class name. Obviously passing arguments to the constructor is not possible with pre-instantiated objects.

Example #6 Attaching several classes using namespaces

The example below illustrates attaching several classes, each with their own namespace.

  1. require_once 'Services/Comb.php';
  2. require_once 'Services/Brush.php';
  3. require_once 'Services/Pick.php';
  4.  
  5. $server = new Zend_XmlRpc_Server();
  6. $server->setClass('Services_Comb', 'comb');   // methods called as comb.*
  7. $server->setClass('Services_Brush', 'brush'); // methods called as brush.*
  8. $server->setClass('Services_Pick', 'pick');   // methods called as pick.*
  9. echo $server->handle();

Example #7 Specifying exceptions to use as valid fault responses

The example below allows any Services_Exception-derived class to report its code and message in the fault response.

  1. require_once 'Services/Exception.php';
  2. require_once 'Services/Comb.php';
  3. require_once 'Services/Brush.php';
  4. require_once 'Services/Pick.php';
  5.  
  6. // Allow Services_Exceptions to report as fault responses
  7. Zend_XmlRpc_Server_Fault::attachFaultException('Services_Exception');
  8.  
  9. $server = new Zend_XmlRpc_Server();
  10. $server->setClass('Services_Comb', 'comb');   // methods called as comb.*
  11. $server->setClass('Services_Brush', 'brush'); // methods called as brush.*
  12. $server->setClass('Services_Pick', 'pick');   // methods called as pick.*
  13. echo $server->handle();

Example #8 Utilizing custom request and response objects

Some use cases require to utilize a custom request object. For example, XML/RPC is not bound to HTTP as a transfer protocol. It is possible to use other transfer protocols like SSH or telnet to send the request and response data over the wire. Another use case is authentication and authorization. In case of a different transfer protocol, one need to change the implementation to read request data.

The example below instantiates a custom request object and passes it to the server to handle.

  1. require_once 'Services/Request.php';
  2. require_once 'Services/Exception.php';
  3. require_once 'Services/Comb.php';
  4. require_once 'Services/Brush.php';
  5. require_once 'Services/Pick.php';
  6.  
  7. // Allow Services_Exceptions to report as fault responses
  8. Zend_XmlRpc_Server_Fault::attachFaultException('Services_Exception');
  9.  
  10. $server = new Zend_XmlRpc_Server();
  11. $server->setClass('Services_Comb', 'comb');   // methods called as comb.*
  12. $server->setClass('Services_Brush', 'brush'); // methods called as brush.*
  13. $server->setClass('Services_Pick', 'pick');   // methods called as pick.*
  14.  
  15. // Create a request object
  16. $request = new Services_Request();
  17.  
  18. echo $server->handle($request);

Example #9 Specifying a custom response class

The example below illustrates specifying a custom response class for the returned response.

  1. require_once 'Services/Request.php';
  2. require_once 'Services/Response.php';
  3. require_once 'Services/Exception.php';
  4. require_once 'Services/Comb.php';
  5. require_once 'Services/Brush.php';
  6. require_once 'Services/Pick.php';
  7.  
  8. // Allow Services_Exceptions to report as fault responses
  9. Zend_XmlRpc_Server_Fault::attachFaultException('Services_Exception');
  10.  
  11. $server = new Zend_XmlRpc_Server();
  12. $server->setClass('Services_Comb', 'comb');   // methods called as comb.*
  13. $server->setClass('Services_Brush', 'brush'); // methods called as brush.*
  14. $server->setClass('Services_Pick', 'pick');   // methods called as pick.*
  15.  
  16. // Create a request object
  17. $request = new Services_Request();
  18.  
  19. // Utilize a custom response
  20. $server->setResponseClass('Services_Response');
  21.  
  22. echo $server->handle($request);

Performance optimization

Example #10 Cache server definitions between requests

The example below illustrates caching server definitions between requests.

  1. // Specify a cache file
  2. $cacheFile = dirname(__FILE__) . '/xmlrpc.cache';
  3.  
  4. // Allow Services_Exceptions to report as fault responses
  5. Zend_XmlRpc_Server_Fault::attachFaultException('Services_Exception');
  6.  
  7. $server = new Zend_XmlRpc_Server();
  8.  
  9. // Attempt to retrieve server definition from cache
  10. if (!Zend_XmlRpc_Server_Cache::get($cacheFile, $server)) {
  11.     $server->setClass('Services_Comb', 'comb');   // methods called as comb.*
  12.     $server->setClass('Services_Brush', 'brush'); // methods called as brush.*
  13.     $server->setClass('Services_Pick', 'pick');   // methods called as pick.*
  14.  
  15.     // Save cache
  16.     Zend_XmlRpc_Server_Cache::save($cacheFile, $server);
  17. }
  18.  
  19. // Create a request object
  20. $request = new Services_Request();
  21.  
  22. // Utilize a custom response
  23. $server->setResponseClass('Services_Response');
  24.  
  25. echo $server->handle($request);

Note: The server cache file should be located outside the document root.

Example #11 Optimizing XML generation

Zend_XmlRpc_Server uses DOMDocument of PHP extension ext/dom to generate it's XML output. While ext/dom is available on a lot of hosts it is not exactly the fastest. Benchmarks have shown, that XmlWriter from ext/xmlwriter performs better.

If ext/xmlwriter is available on your host, you can select a the XmlWriter-based generator to leaverage the performance differences.

  1. require_once 'Zend/XmlRpc/Server.php';
  2. require_once 'Zend/XmlRpc/Generator/XmlWriter.php';
  3.  
  4. Zend_XmlRpc_Value::setGenerator(new Zend_XmlRpc_Generator_XmlWriter());
  5.  
  6. $server = new Zend_XmlRpc_Server();
  7. ...

Note: Benchmark your application
Performance is determined by a lot of parameters and benchmarks only apply for the specific test case. Differences come from PHP version, installed extensions, webserver and operating system just to name a few. Please make sure to benchmark your application on your own and decide which generator to use based on your numbers.

Note: Benchmark your client
This optimization makes sense for the client side too. Just select the alternate XML generator before doing any work with Zend_XmlRpc_Client.

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