How to Register a new Request Format and Mime Type

Every Request has a “format” (e.g. html, json), which is used to determine what type of content to return in the Response. In fact, the request format, accessible via getRequestFormat(), is used to set the MIME type of the Content-Type header on the Response object. Internally, Symfony contains a map of the most common formats (e.g. html, json) and their associated MIME types (e.g. text/html, application/json). Of course, additional format-MIME type entries can easily be added. This document will show how you can add the jsonp format and corresponding MIME type.

Create a kernel.request Listener

The key to defining a new MIME type is to create a class that will “listen” to the kernel.request event dispatched by the Symfony kernel. The kernel.request event is dispatched early in Symfony’s request handling process and allows you to modify the request object.

Create the following class, replacing the path with a path to a bundle in your project:

// src/AppBundle/EventListener/RequestListener.php
namespace AppBundle\EventListener;

use Symfony\Component\HttpKernel\HttpKernelInterface;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;

class RequestListener
    public function onKernelRequest(GetResponseEvent $event)
        $event->getRequest()->setFormat('jsonp', 'application/javascript');

Registering your Listener

As with any other listener, you need to add it in one of your configuration files and register it as a listener by adding the kernel.event_listener tag:

  • YAML
    # app/config/services.yml
            class: AppBundle\EventListener\RequestListener
                - { name: kernel.event_listener, event: kernel.request, method: onKernelRequest }
  • XML
    <!-- app/config/services.xml -->
    <?xml version="1.0" ?>
    <container xmlns=""
            <service id="app.listener.request"
                <tag name="kernel.event_listener"
  • PHP
    # app/config/services.php
    $definition = new Definition('AppBundle\EventListener\RequestListener');
    $definition->addTag('kernel.event_listener', array(
        'event'  => 'kernel.request',
        'method' => 'onKernelRequest',
    $container->setDefinition('app.listener.request', $definition);

At this point, the app.listener.request service has been configured and will be notified when the Symfony kernel dispatches the kernel.request event.


You can also register the listener in a configuration extension class (see Importing Configuration via Container Extensions for more information).