Easy Web Services using PHP reflection API

phplondon, Dec 4th 2008

Reflection?

http://www.flickr.com/photos/bcnbits/368112752/

ReflectionIn computer science, reflection is the

process by which a computer program can observe and modify its own structure and behaviour.

Reflection in PHP5reverse-engineer• classes, • interfaces, • exceptions• functions• Methods• Parameters• properties• extensions

retrieve doc comments for • functions, • classes and • methods.

Eg. Reflection Methodclass ReflectionMethod extends […]{ public bool isFinal()    public bool isAbstract()    public bool isPublic()    public bool isPrivate()    public bool isProtected()    public bool isStatic()    public bool isConstructor()    public bool isDestructor()[…..]    public string getFileName()    public int getStartLine()    public int getEndLine()    public string getDocComment()    public array getStaticVariables()

Eg. Reflection Methodclass Randomizer{        /**     * Returns randomly 0 or 1       * @return  int     */     final public static function get()    {        return rand( 0, 1);    }}

// Create an instance of the ReflectionMethod class$method = new ReflectionMethod(‘Randomizer', get');

echo $method->isConstructor() ? 'the constructor' : 'a regular method‘;printf("---> Documentation:\n %s\n", var_export($method->getDocComment(), 1));

Reflection is useful for • Why reverse engineer comments in code?

Easy to generate documentation.• Unit tests framework: mockup objects, function

test*, etc.• Automatic serializations of object: your code

defines your data, your objects can be serialized automatically, converted in JSON, etc.

$reflectionClass = new ReflectionClass('ClassIsData');$properties = $reflectionClass->getProperties();

$property->getName(); $property->getValue( $instance );

Reflection is useful for • Annotations, eg. in PHP Unit

In this example the test will fail because it doesn’t throw the InvalidArgumentException

Easy Web Services Simple use case

Watch out, you will see code in slides!!!

class Users{ /** * @return array the list of all the users */ static public function getUsers($limit = 10) { // each API method can have different permission requirements Access::checkUserHasPermission('admin'); return Registry::get('db')->fetchAll(" SELECT * FROM users LIMIT $limit"); }}

Use case: you have this class in your system:

You want this class and the public methods to be automatically available in a REST service, so you can call: http://myService.net/?module=Users.getUsers&limit=100

And get the result (eg. in XML)

// simple call to the REST API via http$users = file_get_contents( "http://service/API/" . "?method=Users.getUsers&limit=100");

// we also want to call it from within our existing php code FrontController::getInstance()->init(); // init DB, logger, auth, etc.$request = new Request('method=Users.getUsers&limit=100');$result = $request->process();

How we want to call it (1/2)

// ResponseBuilder object can convert the data in XML, JSON, CSV// by converting your API returned value (from array, int, object, etc) $request = new Request(' method=Users.getUsers &limit=100 &format=JSON');$XmlResult = $request->process();

// possible to add token_based authentication: all API methods call helper// class that checks that the token has the right permissions $request = new Request('method=Users.getUsers&token_auth=puiwrtertwoc98');$result = $request->process();

How we want to call it (2/2)

The conceptRequest comes in, forwarded to Proxy that does the Reflection magic: calls the method on the right class, with the right parameters mapped.

class Request { protected $request; function __construct($requestString = null) { if(is_null($requestString)) { $request = $_REQUEST; } else { $request = parse_str($requestString); } $this->request = $request; } function process() { $responseBuilder = new ResponseBuilder($this->request); try { // eg. get the "Users.getUsers" $methodToCall = Helper::sanitizeInputVariable('method', $this->request); list($className, $method) = explode('.',$methodToCall); $proxy = Proxy::getInstance(); $returnedValue = $proxy->call($className, $method, $this->request ); // return the response after applying standard filters, converting format,.. $response = $responseBuilder->getResponse($returnedValue); } catch(Exception $e ) { // exception is forwarded to ResponseBuilder to be converted in XML/JSON,.. $response = $responseBuilder->getResponseException( $e ); } return $response; }}

$request = new Request( 'method=Users.getUsers&limit=100');

$result = $request->process();

class Proxy{ function call($className, $methodName, $request) { $this->setContext($className, $methodName, $request); $this->loadClassMetadata(); $this->checkMethodExists(); $this->checkParametersAreSet(); $parameterValues = $this->getParametersValues(); $object = call_user_func(array($className, "getInstance")); $timer = new Timer; $returnedValue = call_user_func_array( array($object, $methodName), $parameterValues); Registry::get('logger_api')->log($className, $methodName, $parameterValues $timer->getTimeMs(),$returnedValue); return $returnedValue; } function loadClassMetadata($className) { $reflectionClass = new ReflectionClass($className); foreach($reflectionClass->getMethods() as $method) { $this->loadMethodMetadata($className, $method); } } [...]}

Conclusion• Similar pattern as FrontController / Dispatcher• One entry point to your Models. You can then add:

– Caching– Logging– Authentication

• Eg. If your app is data-centric, the ResponseBuilder could apply set of filters.You could for example specify custom filters to be apply to API calls in the RequestString:

$request = new Request(' method=Analytics.getUsers &filter_sort=name-desc &filter_search=(pattern)');

... and use the Proxy class to generate your API documentation (from the code, and by reverse engineering your method comments)

Questions?

References• This pattern is used in the open source Piwik project

http://piwik.org• View the code on

http://dev.piwik.org/svn/trunk/core/API/• How to design an API: best practises, concepts

http://piwik.org/blog/2008/01/how-to-design-an-api-best-practises-concepts-technical-aspects/

• PHP: Reflection – Manual http://uk.php.net/oop5.reflection

• Declarative Development Using Annotations In PHPhttp://www.slideshare.net/stubbles/declarative-development-using-annotations-in-php

Presentation under license #cc-by-sa, by Matthieu Aubry