Symfony: How does the HttpKernel work?

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In a nutshell

The HttpKernel component provides a structured process for converting an incoming HTTP request (encapsulated as a Request object) into a response (encapsulated as a Response object) using the EventDispatcher component.

The HttpKernel is driven by events

The HttpKernel::handle() method works internally by dispatching various events. This makes it flexible but also abstract because all the work of a framework/application using HttpKernel is done in event listeners.

Here’s an example application that uses HttpKernel:

use Symfony\Component\EventDispatcher\EventDispatcher;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\RequestStack;
use Symfony\Component\HttpKernel\Controller\ArgumentResolver;
use Symfony\Component\HttpKernel\Controller\ControllerResolver;
use Symfony\Component\HttpKernel\HttpKernel;

// create the Request object
$request = Request::createFromGlobals();

$dispatcher = new EventDispatcher();
// ... add some event listeners

// create your controller and argument resolvers
$controllerResolver = new ControllerResolver();
$argumentResolver = new ArgumentResolver();

// instantiate the kernel
$kernel = new HttpKernel($dispatcher, $controllerResolver, new RequestStack(), $argumentResolver);

// actually execute the kernel, which turns the request into a response
// by dispatching events, calling a controller, and returning the response
$response = $kernel->handle($request);

// send the headers and echo the content
$response->send();

// trigger the kernel.terminate event
$kernel->terminate($request, $response);

The steps for using HttpKernel are roughly as follows:

Create an event dispatcher
Create controller resolver
Create argument resolver
Instantiate the kernel with the event dispatcher, controller resolver, and argument resolver
Execute the kernel with HttpKernel::handle(). This will dispatch various events that resolve a controller and return a response.
Send the headers and content using the response.
Trigger the kerner.terminate event.

Sources

The HttpKernel Component – Symfony docs

Tagged: Symfony

In a nutshell

The HttpKernel is driven by events

Sources

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