Creating JSONP(adding) responses with Silex

Recently I had the need to extend a Silex application to be able to return JSONP responses when needed. I was looking for a generic approach and came across a blog post by Raphael Stolt who solved the problem with a clever "after middleware". This is the code you need to add to your app.php file:

<?php
use Symfony\Component\HttpFoundation\JsonResponse;

$app->after(function (Request $req, Response $res) {
  if ($req->get('jsonp_callback') !== null && $req->getMethod() === 'GET') {
    $contentType = $res->headers->get('Content-Type');
    $jsonpContentTypes = array(
      'application/json',
      'application/json; charset=utf-8',
      'application/javascript',
    );

    if (!in_array($contentType, $jsonpContentTypes)) {
      // Don't touch the response
      return;
    }

    if ($res instanceof JsonResponse) {
      $res->setCallBack($req->get('jsonp_callback'));
    } else {
      $res->setContent($req->get('jsonp_callback') 
          . '(' . $res->getContent() . ');'
      );
    }
  }
});

You just need to add the code above and everything else will work magically if your request contains a jsonp_callback variable and you returned JSON content in your controller function.