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<h2>Middlewares</h2>

<p>Creating a new middleware is generally quite easy. The hardest part is grasping the decorator pattern.</p>

<p>A decorator is simply an object that wraps around an other object. In this case a middleware is a decorator for <code>HttpKernelInterface</code>. The decorator wraps around a kernel, and exposes the same interface.</p>

<p>Let's take a look at an <code>PoweredByStack</code> middleware, that adds a `X-Powered-By` header to all responses.</p>

<pre><code class="php">{%- filter escape -%}use Symfony\Component\HttpFoundation\Request;

use Symfony\Component\HttpKernel\HttpKernelInterface;

class PoweredByStack implements HttpKernelInterface

{

private $app;

public function __construct(HttpKernelInterface $app)

{

$this->app = $app;

}

public function handle(Request $request, $type = HttpKernelInterface::MASTER_REQUEST, $catch = true)

{

$response = $this->app->handle($request, $type, $catch);

$response->headers->set('X-Powered-By', 'Stack');

return $response;

}

}{%- endfilter -%}</code></pre>

<p>This middleware takes a kernel in the constructor and delegates to this kernel from within <code>handle</code>. Then it augments the response. It <em>decorates</em> the <code>handle</code> call.</p>

<p>Here is an example of how you could use this middleware with Silex. Note that you can replace Silex with any kernel implementation.</p>

<pre><code class="php">{%- filter escape -%}$app = new Silex\Application();

$app->get('/', function () {

return 'Hello World!';

});

$app = new PoweredByStack($app);

Stack\run($app);{%- endfilter -%}</code></pre>

<p>This will return a "Hello World" body, but have the extra `X-Powered-By: Stack` header.</p>

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