Rolling out an API for your cakePHP app Part ++1: The Solution

Router::connect('/:version/:controller/:action/*', array('prefix' => 'api', 'api' => true), array('version'=>'[0-9]+\.[0-9]+'));

var $components = array('Auth', 'Acl', 'RequestHandler', 'Api');
...
function api_get() {
    $this->Api->dispatch();
}

App::import('Vendor', 'Api_0_2', array('file' =>'api'.DS.'0.2'.DS.'api.php'));
class ApiComponent extends Object
{
    public $api = null;
 
    /**
     * Initialize API component.
     * Called before Controller::beforeFilter()
     *
     * @param $controller
     * @param $settings
     * @return void
     */
    function initialize(&$controller, $settings = array()) {
        $this->controller =& $controller;
    }
 
    /**
     * Dispatch the API request to the correct API class depending on version
     *
     * @return void
     */
    function dispatch() {
 
        //Want to dispatch to correct method in API class, get the name of the class
        $className = 'Api_'.str_replace('.', '_', $this->controller->params['version']);
 
        //Confirm class exists
        if (class_exists($className)) {
            $this->api = new $className();
        }
        else {
                //No need to worry about apiErrors just at the moment
            $this->cakeError('apiError', array('apiErrorCode'=>1001));
        }
 
        //Pass in controller
        $this->api->dispatch($this->controller);
    }
}

<?php
App::import('Inflector');
class Api extends Object
{
    public $controller;
    public $version = null;
    public $rendered = false;
 
    /**
     * Error codes for API errors
     */
    private $errorCodes = array(
        1001 => array('httpCode'=>500, 'errorMessage'=>'Version does not exist.'),
        1002 => array('httpCode'=>500, 'errorMessage'=>'Unknown output file.'),
        1003 => array('httpCode'=>500, 'errorMessage'=>'Unrecognised method.'),
    );
 
    /**
     * Retrieve data relating to an API error code
     * 
     * @param $errorCode Int API error code
     * @return Array Data associated with the error code.
     */
    public function getError($errorCode) {
        if (in_array($errorCode, array_keys($this->errorCodes))) {
        	return $this->errorCodes[$errorCode];
        }
    	return false;
    }
 
    /**
     * Render the API request using a version to select the view.
     * 
     * @return void
     */
    function render() {
 
        $controller = strtolower(Inflector::underscore($this->controller->name));
        $version = $this->version;
        $folder = $this->controller->RequestHandler->prefers();
        $view = str_replace('api_', '', $this->controller->action);
 
        //Check file exists before rendering
        $viewFile = new File(VIEWS . "/$controller/api/$version/$folder/$view.ctp");
 
        if ($viewFile->exists()) {
        	$this->controller->render("/$controller/api/$version/$folder/$view");
            $this->rendered = true;
        }
        else {
 
            /**
             * Try to get previous missing view from previous API version
             * Perhaps this is not the best approach? But allows us to reuse earlier API version 
             * views without duplicating files for new API releases.
             */
            $version = substr(strstr($version, '.'), 1);
 
            //NOTE: the version of our API actually started at 0.3, so you might need to edit some of the for loops in the code for your particular case
            for ($i = $version; $i >= 3; $i--) {
            	$viewFile = new File(VIEWS . "/$controller/api/0.$i/$folder/$view.ctp");
                if ($viewFile->exists()) {
                    $this->controller->render("/$controller/api/0.$i/$folder/$view");
                    $this->rendered = true;
                    break;
                }
            }
        }
        if (!$this->rendered) {
        	$this->cakeError('apiError', array('apiErrorCode'=>1002));
        }
    }
 
    /**
     * Dispatch the API request to the corresponding method.
     * 
     * @param $controller Object Controller of original request
     * @return void
     */
    function dispatch(&$controller) {
 
        $this->controller =& $controller;
 
        $controllerName = $this->controller->name;
        $actionName = $this->controller->action;
 
        $functionName = Inflector::variable(str_replace('api', Inflector::variable($controllerName), $actionName));
 
        //Check that method exists
        if (method_exists($this, $functionName)) {
        	$this->$functionName();
        }
        else {
        	$this->cakeError('apiError', array('apiErrorCode'=>1003));
        }
 
        //Render if it hasn't already done so
        if (!$this->rendered) {
            $this->render();
        }
    }
}
?>

<?php
App::import('Vendor', 'api/api');
class Api_0_3 extends Api  
{
    public $version = 0.3;
 
    function postsGet() {
        //Get posts, store them in an array and set them for the view?
        //Whatever code would go into the api_get() method in the posts controller, should go in here
        //With only one minor alteration, calls to $this-> should be replaced with $this->controller->
 
        $posts = $this->controller->Post->find('all', array(
            'contain'=>false
        ));
        $this->controller->set(compact('posts'));
    }
}