events.rst

Built-in Symfony Events

During the handling of an HTTP request, the Symfony framework (or any application using the :doc:`HttpKernel component </components/http_kernel>`) dispatches some :doc:`events </event_dispatcher>` which you can use to modify how the request is handled.

Kernel Events

Each event dispatched by the HttpKernel component is a subclass of :class:`Symfony\\Component\\HttpKernel\\Event\\KernelEvent`, which provides the following information:

:method:`Symfony\\Component\\HttpKernel\\Event\\KernelEvent::getRequestType`

Returns the type of the request (HttpKernelInterface::MASTER_REQUEST or HttpKernelInterface::SUB_REQUEST).

:method:`Symfony\\Component\\HttpKernel\\Event\\KernelEvent::getKernel`

Returns the Kernel handling the request.

:method:`Symfony\\Component\\HttpKernel\\Event\\KernelEvent::getRequest`

Returns the current Request being handled.

:method:`Symfony\\Component\\HttpKernel\\Event\\KernelEvent::isMasterRequest`

Checks if this is a master request.

kernel.request

Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\RequestEvent`

This event is dispatched very early in Symfony, before the controller is determined. It's useful to add information to the Request or return a Response early to stop the handling of the request.

.. seealso::

    Read more on the :ref:`kernel.request event <component-http-kernel-kernel-request>`.

Execute this command to find out which listeners are registered for this event and their priorities:

$ php bin/console debug:event-dispatcher kernel.request

kernel.controller

Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\ControllerEvent`

This event is dispatched after the controller to be executed has been resolved but before executing it. It's useful to initialize things later needed by the controller, such as param converters, and even to change the controller entirely:

use Symfony\Component\HttpKernel\Event\ControllerEvent;

public function onKernelController(ControllerEvent $event)
{
    // ...

    // the controller can be changed to any PHP callable
    $event->setController($myCustomController);
}

.. seealso::

    Read more on the :ref:`kernel.controller event <component-http-kernel-kernel-controller>`.

Execute this command to find out which listeners are registered for this event and their priorities:

$ php bin/console debug:event-dispatcher kernel.controller

kernel.controller_arguments

Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\ControllerArgumentsEvent`

This event is dispatched just before a controller is called. It's useful to configure the arguments that are going to be passed to the controller. Typically, this is used to map URL routing parameters to their corresponding named arguments; or pass the current request when the Request type-hint is found:

use Symfony\Component\HttpKernel\Event\ControllerArgumentsEvent;

public function onKernelControllerArguments(ControllerArgumentsEvent $event)
{
    // ...

    // get controller and request arguments
    $namedArguments = $event->getRequest()->attributes->all();
    $controllerArguments = $event->getArguments();

    // set the controller arguments to modify the original arguments or add new ones
    $event->setArguments($newArguments);
}

Execute this command to find out which listeners are registered for this event and their priorities:

$ php bin/console debug:event-dispatcher kernel.controller_arguments

kernel.view

Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\ViewEvent`

This event is dispatched after the controller has been executed but only if the controller does not return a :class:`Symfony\\Component\\HttpFoundation\\Response` object. It's useful to transform the returned value (e.g. a string with some HTML contents) into the Response object needed by Symfony:

use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\Event\ViewEvent;

public function onKernelView(ViewEvent $event)
{
    $value = $event->getControllerResult();
    $response = new Response();

    // ... somehow customize the Response from the return value

    $event->setResponse($response);
}

.. seealso::

    Read more on the :ref:`kernel.view event <component-http-kernel-kernel-view>`.

Execute this command to find out which listeners are registered for this event and their priorities:

$ php bin/console debug:event-dispatcher kernel.view

kernel.response

Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\ResponseEvent`

This event is dispatched after the controller or any kernel.view listener returns a Response object. It's useful to modify or replace the response before sending it back (e.g. add/modify HTTP headers, add cookies, etc.):

use Symfony\Component\HttpKernel\Event\ResponseEvent;

public function onKernelResponse(ResponseEvent $event)
{
    $response = $event->getResponse();

    // ... modify the response object
}

.. seealso::

    Read more on the :ref:`kernel.response event <component-http-kernel-kernel-response>`.

Execute this command to find out which listeners are registered for this event and their priorities:

$ php bin/console debug:event-dispatcher kernel.response

kernel.finish_request

Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\FinishRequestEvent`

This event is dispatched after the kernel.response event. It's useful to reset the global state of the application (for example, the translator listener resets the translator's locale to the one of the parent request):

use Symfony\Component\HttpKernel\Event\FinishRequestEvent;

public function onKernelFinishRequest(FinishRequestEvent $event)
{
    if (null === $parentRequest = $this->requestStack->getParentRequest()) {
        return;
    }

    // reset the locale of the subrequest to the locale of the parent request
    $this->setLocale($parentRequest);
}

Execute this command to find out which listeners are registered for this event and their priorities:

$ php bin/console debug:event-dispatcher kernel.finish_request

kernel.terminate

Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\TerminateEvent`

This event is dispatched after the response has been sent (after the execution of the :method:`Symfony\\Component\\HttpKernel\\HttpKernel::handle` method). It's useful to perform slow or complex tasks that don't need to be completed to send the response (e.g. sending emails).

.. seealso::

    Read more on the :ref:`kernel.terminate event <component-http-kernel-kernel-terminate>`.

Execute this command to find out which listeners are registered for this event and their priorities:

$ php bin/console debug:event-dispatcher kernel.terminate

kernel.exception

Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\ExceptionEvent`

This event is dispatched as soon as an error occurs during the handling of the HTTP request. It's useful to recover from errors or modify the exception details sent as response:

use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\Event\ExceptionEvent;

public function onKernelException(ExceptionEvent $event)
{
    $exception = $event->getThrowable();
    $response = new Response();
    // setup the Response object based on the caught exception
    $event->setResponse($response);

    // you can alternatively set a new Exception
    // $exception = new \Exception('Some special exception');
    // $event->setThrowable($exception);
}

Note

The TwigBundle registers an :class:`Symfony\\Component\\HttpKernel\\EventListener\\ExceptionListener` that forwards the Request to a given controller defined by the exception_listener.controller parameter.

Symfony uses the following logic to determine the HTTP status code of the response:

• If :method:`Symfony\\Component\\HttpFoundation\\Response::isClientError`, :method:`Symfony\\Component\\HttpFoundation\\Response::isServerError` or :method:`Symfony\\Component\\HttpFoundation\\Response::isRedirect` is true, then the status code on your Response object is used;
• If the original exception implements :class:`Symfony\\Component\\HttpKernel\\Exception\\HttpExceptionInterface`, then getStatusCode() is called on the exception and used (the headers from getHeaders() are also added);
• If both of the above aren't true, then a 500 status code is used.

Note

If you want to overwrite the status code of the exception response, which you should not without a good reason, call ExceptionEvent::allowCustomResponseCode() first and then set the status code on the response:

$event->allowCustomResponseCode();
$response = new Response('No Content', 204);
$event->setResponse($response);

The status code sent to the client in the above example will be 204. If $event->allowCustomResponseCode() is omitted, then the kernel will set an appropriate status code based on the type of exception thrown.

.. seealso::

    Read more on the :ref:`kernel.exception event <component-http-kernel-kernel-exception>`.

Execute this command to find out which listeners are registered for this event and their priorities:

$ php bin/console debug:event-dispatcher kernel.exception