Symfony RequestStack and RequestRegistry

RequestRegistry.php

<?php

namespace Symfony\Component\HttpFoundation;

/**
 * Registry for Requests.
 *
 * Facade for RequestStack that prevents modification of the stack,
 * so that users don't accidentily push()/pop() from the stack and
 * mess up the request cycle.
 */
class RequestRegistry
{
    private $stack;

    public function __construct(RequestStack $stack)
    {
        $this->stack = $stack;
    }

    /**
     * @return Request
     */
    public function getCurrentRequest()
    {
        return $this->stack->getCurrentRequest();
    }

    /**
     * @return Request
     */
    public function getMasterRequest()
    {
        return $this->stack->getMasterRequest();
    }
}

RequestStack.php

<?php

namespace Symfony\Component\HttpFoundation;

/**
 * Request stack that controls the lifecycle of requests.
 *
 * Notifies services of changes in the stack.
 */
class RequestStack
{
    /**
     * @var Request
     */
    private $masterRequest;

    /**
     * @var Request[]
     */
    private $requests = array();

    private $eventDispatcher;

    public function __construct(EventDispatcherInterface $eventDispatcher)
    {
        $this->eventDispatcher = $eventDispatcher;
    }

    public function push(Request $request)
    {
        if (HttpKernelInterface::MASTER_REQUEST === $request->getType()) {
            $this->masterRequest = $request;
        }

        $this->requests[] = $request;
        $this->dispatch('request.enter_scope', new RequestEnterScopeEvent($request));
    }

    /**
     * Pop the current request from the stack.
     *
     * This operation lets the current request go out of scope.
     *
     * @return Request
     */
    public function pop()
    {
        $previousRequest = array_pop($this->requests);

        $this->dispatch('request.leave_scope',
            new RequestLeaveScopeEvent(
                $previousRequest,
                $this->getCurrentRequest()
            )
        );

        return $request;
    }

    /**
     * @return Request
     */
    public function getCurrentRequest()
    {
        return end($this->requests);
    }

    /**
     * @return Request
     */
    public function getMasterRequest()
    {
        return $this->masterRequest;
    }
}

RequestStackAwareHttpKernel.php

<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\HttpKernel\DependencyInjection;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\HttpKernelInterface;
use Symfony\Component\HttpKernel\HttpKernel;
use Symfony\Component\HttpKernel\Controller\ControllerResolverInterface;
use Symfony\Component\EventDispatcher\EventDispatcherInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\DependencyInjection\Scope;

/**
 * Adds a managed request scope.
 *
 * @author Fabien Potencier <fabien@symfony.com>
 * @author Johannes M. Schmitt <schmittjoh@gmail.com>
 */
class RequestStackAwareHttpKernel extends HttpKernel
{
    protected $stack;

    /**
     * Constructor.
     *
     * @param EventDispatcherInterface    $dispatcher         An EventDispatcherInterface instance
     * @param ControllerResolverInterface $controllerResolver A ControllerResolverInterface instance
     */
    public function __construct(EventDispatcherInterface $dispatcher, ControllerResolverInterface $controllerResolver, RequestStack $stack)
    {
        parent::__construct($dispatcher, $controllerResolver);

        $this->stack = $stack;
    }

    /**
     * {@inheritdoc}
     */
    public function handle(Request $request, $type = HttpKernelInterface::MASTER_REQUEST, $catch = true)
    {
        $request->headers->set('X-Php-Ob-Level', ob_get_level());

        $this->stack->push($request);

        try {
            $response = parent::handle($request, $type, $catch);
        } catch (\Exception $e) {
            $this->stack->pop();

            throw $e;
        }

        $this->stack->pop();

        return $response;
    }
}

RouterListener.php

<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\HttpKernel\EventListener;

use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Routing\RequestContextAwareInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Initializes the locale based on the current request.
 *
 * @author Fabien Potencier <fabien@symfony.com>
 */
class LocaleListener implements EventSubscriberInterface
{
    private $router;
    private $defaultLocale;

    public function __construct($defaultLocale = 'en', RequestContextAwareInterface $router = null)
    {
        $this->defaultLocale = $defaultLocale;
        $this->router = $router;
    }

    public function onRequestLeaveScope(RequestLeaveScopeEvent $event)
    {
        $request = $event->getCurrentRequest();

        if (null === $request) {
            return;
        }

        if ($locale = $request->attributes->get('_locale')) {
            $request->setLocale($locale);
        }

        if (null !== $this->router) {
            $this->router->getContext()->setParameter('_locale', $request->getLocale());
        }
    }

    public function onRequestEnterScope(RequestEnterScopeEvent $event)
    {
        $request = $event->getRequest();
        $request->setDefaultLocale($this->defaultLocale);

        $this->setRequest($request);
    }

    public static function getSubscribedEvents()
    {
        return array(
            // TODO Adjust
        );
    }
}

This is a very rough prototype hack as an alternative to synchronized services symfony/symfony#7007

Synchronized services are just need for the "request" as a service.
But request is a value object and not a service, the extra complexity of scopes and synchronized services can be avoided by providing a "RequestRegistry" service that provides access to the current request instead.

More context: Igor wrote about stateless services in the context of DI: https://igor.io/2013/03/31/stateless-services.html

Very well done! And very much interested in what this whole discussion will lead to.

Added a RequestStackAwareHttpKernel that can replace ContainerAwareHttpKernel (except for the BC break with request scope actually, however this provides a "clean" approach how the code could look like)

The RequestStackAwareHttpKernel is probably not need, as HttpKernel depends on HttpFoundation and this code could just be part of the default HttpKernel.

I"m very interested in this concept. It's definitely going somewhere. I'd open a formal PR as an RFC

Wow nice idea. Looks very interesting and i think its more understandable as synchronized services.
I would let extend the RequestStack from the SplStack class.

@Baachi Why extend SplStack? it has a HUGE api where here we only need push()/pop(). This would create a big unnecessary API

@Baachi Why extend SplStack? it has a HUGE api where here we only need push()/pop(). This would create a big unnecessary API

@beberlei I agree with you

Please review symfony/symfony#7707 which is the pull request for this idea.