class NegotiationMiddleware

class NegotiationMiddleware implements HttpKernelInterface {
    
    /**
     * The wrapped HTTP kernel.
     *
     * @var \Symfony\Component\HttpKernel\HttpKernelInterface
     */
    protected $app;
    
    /**
     * Contains a hashmap of format as key and mimetype as value.
     *
     * @var array
     */
    protected $formats = [];
    
    /**
     * Constructs a new NegotiationMiddleware.
     *
     * @param \Symfony\Component\HttpKernel\HttpKernelInterface $app
     *   The wrapper HTTP kernel
     */
    public function __construct(HttpKernelInterface $app) {
        $this->app = $app;
    }
    
    /**
     * {@inheritdoc}
     */
    public function handle(Request $request, $type = self::MAIN_REQUEST, $catch = TRUE) : Response {
        // Register available mime types.
        foreach ($this->formats as $format => $mime_type) {
            $request->setFormat($format, $mime_type);
        }
        // Determine the request format using the negotiator.
        if ($requested_format = $this->getContentType($request)) {
            $request->setRequestFormat($requested_format);
        }
        return $this->app
            ->handle($request, $type, $catch);
    }
    
    /**
     * Registers a format for a given MIME type.
     *
     * @param string $format
     *   The format.
     * @param string $mime_type
     *   The MIME type.
     *
     * @return $this
     */
    public function registerFormat($format, $mime_type) {
        $this->formats[$format] = $mime_type;
        return $this;
    }
    
    /**
     * Gets the normalized type of a request.
     *
     * The normalized type is a short, lowercase version of the format, such as
     * 'html', 'json' or 'atom'.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object from which to extract the content type.
     *
     * @return string
     *   The normalized type of a given request.
     */
    protected function getContentType(Request $request) {
        // AJAX iframe uploads need special handling, because they contain a JSON
        // response wrapped in <textarea>.
        if ($request->request
            ->get('ajax_iframe_upload', FALSE)) {
            return 'iframeupload';
        }
        if ($request->query
            ->has('_format')) {
            return $request->query
                ->get('_format');
        }
        // No format was specified in the request.
        return NULL;
    }

}