Symfony\Component\HttpFoundation\Response::prepare PHP Method

    public function prepare(Request $request)
    {
        $headers = $this->headers;

        if ($this->isInformational() || $this->isEmpty()) {
            $this->setContent(null);
            $headers->remove('Content-Type');
            $headers->remove('Content-Length');
        } else {
            // Content-type based on the Request
            if (!$headers->has('Content-Type')) {
                $format = $request->getRequestFormat();
                if (null !== $format && $mimeType = $request->getMimeType($format)) {
                    $headers->set('Content-Type', $mimeType);
                }
            }

            // Fix Content-Type
            $charset = $this->charset ?: 'UTF-8';
            if (!$headers->has('Content-Type')) {
                $headers->set('Content-Type', 'text/html; charset='.$charset);
            } elseif (0 === stripos($headers->get('Content-Type'), 'text/') && false === stripos($headers->get('Content-Type'), 'charset')) {
                // add the charset
                $headers->set('Content-Type', $headers->get('Content-Type').'; charset='.$charset);
            }

            // Fix Content-Length
            if ($headers->has('Transfer-Encoding')) {
                $headers->remove('Content-Length');
            }

            if ($request->isMethod('HEAD')) {
                // cf. RFC2616 14.13
                $length = $headers->get('Content-Length');
                $this->setContent(null);
                if ($length) {
                    $headers->set('Content-Length', $length);
                }
            }
        }

        // Fix protocol
        if ('HTTP/1.0' != $request->server->get('SERVER_PROTOCOL')) {
            $this->setProtocolVersion('1.1');
        }

        // Check if we need to send extra expire info headers
        if ('1.0' == $this->getProtocolVersion() && false !== strpos($this->headers->get('Cache-Control'), 'no-cache')) {
            $this->headers->set('pragma', 'no-cache');
            $this->headers->set('expires', -1);
        }

        $this->ensureIEOverSSLCompatibility($request);

        return $this;
    }

 public function onEventResponse(Application $app, Response $response)
 {
     if (null === $response->getCharset()) {
         $response->setCharset($app->getParameter('charset'));
     }
     $response->prepare($app->getRequest());
 }