Joli\GifExceptionBundle\EventListener\ReplaceImageListener::onKernelResponse PHP Method

    public function onKernelResponse(FilterResponseEvent $event)
    {
        // $event->isMasterRequest() method was added in Symfony 2.4
        if (HttpKernelInterface::MASTER_REQUEST === $event->getRequestType() || $event->getRequest()->attributes->get('_controller') !== $this->exceptionController) {
            return;
        }
        // Status code is not set by the exception controller but only by the
        // kernel at the very end.
        // So lets use the status code from the flatten exception instead.
        $statusCode = $event->getRequest()->attributes->get('exception')->getStatusCode();
        $dir = $this->getGifDir($statusCode);
        $gif = $this->getRandomGif($dir);
        $url = $this->getGifUrl($dir, $gif);
        $content = $event->getResponse()->getContent();
        $content = preg_replace('/<img alt="Exception detected!" src=".*" \\/>/', sprintf('<img alt="Exception detected!" src="%s" data-gif style="width:145px" />', $url), $content);
        $event->getResponse()->setContent($content);
    }