Concepts

• SOAP methods will be implemented as model class methods. Models that will handle SOAP calls will have suffix Service, for example BookService
• The Soap component will provide function to generate WSDL from the model class definition and to handle SOAP calls to the model class methods.
• A controller will act as a SOAP proxy to the service models using the SOAP component

Requirements

• PHP Soap extension
• CakePHP 1.2 (haven't tested it in CakePHP 1.1)

Webservice Handler library

Download Webservice Handler library from jool.nl site and extract the contents into app/vendors/wshelper.

Create the SOAP component

Save the code below into app/controllers/components/soap.php.
The generated WSDL will be cached into app/tmp/cache directory. If DEBUG configuration
is greater than 0, the cache file modified time will be compared the model file
modified time and updated appropriately.

Component Class:

<?php 
vendor('wshelper/lib/soap/IPReflectionClass.class');
vendor('wshelper/lib/soap/IPReflectionCommentParser.class');
vendor('wshelper/lib/soap/IPXMLSchema.class');
vendor('wshelper/lib/soap/IPReflectionMethod.class');
vendor('wshelper/lib/soap/WSDLStruct.class');
vendor('wshelper/lib/soap/WSDLException.class');

/**
 * Class SoapComponent
 *
 * Generate WSDL and handle SOAP calls
 */
class SoapComponent extends Component
{
    var $params = array();

    function initialize(&$controller)
    {
        $this->params = $controller->params;
    }
    
    /**
     * Get WSDL for specified model.
     *
     * @param string $modelClass : model name in camel case
     * @param string $serviceMethod : method of the controller that will handle SOAP calls
     */
    function getWSDL($modelId, $serviceMethod = 'call')
    {
        $modelClass = $this->__getModelClass($modelId);
        $expireTime = '+1 year';
        $cachePath = $modelClass . '.wsdl';
        
        // Check cache if exist
        $wsdl = cache($cachePath, null, $expireTime);

        // If DEBUG > 0, compare cache modified time to model file modified time
        if ((Configure::read() > 0) && (! is_null($wsdl))) {

            $cacheFile = CACHE . $cachePath;
            if (is_file($cacheFile)) {
                $modelMtime = filemtime($this->__getModelFile($modelId));
                $cacheMtime = filemtime(CACHE . $cachePath);
                if ($modelMtime > $cacheMtime) {
                    $wsdl = null;
                }
            }

        }
        
        // Generate WSDL if not cached
        if (is_null($wsdl)) {
        
            $refl = new IPReflectionClass($modelClass);
            
            $controllerName = $this->params['controller'];
            $serviceURL = Router::url("/$controllerName/$serviceMethod", true);

            $wsdlStruct = new WSDLStruct('http://schema.example.com', 
                                         $serviceURL . '/' . $modelId, 
                                         SOAP_RPC, 
                                         SOAP_LITERAL);
            $wsdlStruct->setService($refl);
            try {
                $wsdl = $wsdlStruct->generateDocument();
                // cache($cachePath, $wsdl, $expireTime);
            } catch (WSDLException $exception) {
                if (Configure::read() > 0) {
                    $exception->Display();
                    exit();
                } else {
                    return null;
                }
            }
        }

        return $wsdl;
    }

    /**
     * Handle SOAP service call
     *
     * @param string $modelId : underscore notation of the called model
     *                          without _service ending
     * @param string $wsdlMethod : method of the controller that will generate the WSDL
     */
    function handle($modelId, $wsdlMethod = 'wsdl')
    {
        $modelClass = $this->__getModelClass($modelId);
        $wsdlCacheFile = CACHE . $modelClass . '.wsdl';

        // Try to create cache file if not exists
        if (! is_file($wsdlCacheFile)) {
            $this->getWSDL($modelId);
        }

        if (is_file($wsdlCacheFile)) {
            $server = new SoapServer($wsdlCacheFile);
        } else {
            $controllerName = $this->params['controller'];
            $wsdlURL = Router::url("/$controllerName/$wsdlMethod", true);
            $server = new SoapServer($wsdlURL . '/' . $modelId);
        }
        $server->setClass($modelClass);
        $server->handle();
    }

    /**
     * Get model class for specified model id
     *
     * @access private
     * @return string : the model id
     */
    function __getModelClass($modelId)
    {
        $inflector = new Inflector;
        return ($inflector->camelize($modelId) . 'Service');
    }

    /**
     * Get model id for specified model class
     *
     * @access private
     * @return string : the model id
     */
    function __getModelId($modelClass)
    {
        $inflector = new Inflector;
        return $inflector->underscore(substr($class, 0, -7));
    }

    /**
     * Get model file for specified model id
     *
     * @access private
     * @return string : the filename
     */
    function __getModelFile($modelId)
    {
        $modelDir = dirname(dirname(dirname(__FILE__))) . DS . 'models';
        return $modelDir . DS . $modelId . '_service.php';
    }
}
?>

Create the controller that will handle SOAP calls

This is an example controller. You can change the method name
that will handle SOAP calls and provide WSDL definition as you wish.
But don't forget to change the arguments to the handle and
getWSDL methods.
Save the file into app/controllers/service_controller.php

Controller Class:

<?php 
class ServiceController extends AppController
{
    public $name = 'Service';
    public $uses = array('TestService');
    public $helpers = array();
    public $components = array('Soap');

    /**
     * Handle SOAP calls
     */
    function call($model)
    {
        $this->autoRender = FALSE;
        $this->Soap->handle($model, 'wsdl');
    }

    /**
     * Provide WSDL for a model
     */
    function wsdl($model)
    {
        $this->autoRender = FALSE;
        header('Content-Type: text/xml'); // Add encoding if this doesn't work e.g. header('Content-Type: text/xml; charset=UTF-8'); 
        echo $this->Soap->getWSDL($model, 'call');
    }
}
?>

Create the service model

This is a test model. Save it into app/models/test_service.php. Note that the webservice handler library parses the method comments to create the WSDL, so you'll need to make sure that all the function parameters and return value are documented in the function docblock. Make sure that you specify the type of each parameters and make sure the ordering matches the order of the parameters in the function. (Thanks to Brett Nemeroff for pointing this).

Model Class:

<?php 
class TestService extends AppModel
{
    var $name = 'TestService';
    var $useTable = false;

    /**
     * Divide two numbers
     *
     * @param float $a
     * @param float $b
     * @return float
     */
    function divide($a, $b)
    {
        if ($b != 0) {
            return $a / $b;
        }
        return 0;
    }
}
?>

Testing the service

My favorite tool for testing SOAP services is SoapUI. You can use it or your
favorite tool to test the service. To access the WSDL, direct your tool to
http://yourhost/service/wsdl/test. The SOAPAction URL will be
http://yourhost/service/call/test.