A simple JSONP filter for symfony web applications.

JsonpFilter.php

<?php

class JsonpFilter extends sfFilter
{
  public function execute($filterChain)
  {
    // nothing to do before the action is called
    $filterChain->execute();

    if (($response = $this->getContext()->getResponse()) instanceof sfWebResponse and ($request = $this->getContext()->getRequest()) instanceof sfWebRequest)
    {
      /* @var $request sfWebRequest */
      if ($request->getParameter('sf_format') === 'json' and $callback = $request->getGetParameter('callback'))
      {
        /* @var $response sfWebResponse */
        $response->setContentType('text/javascript');
        $response->setContent(sprintf('%s(%s);', $callback, $response->getContent()));
      }
    }
  }
}