anchor.diff:  
     void addNotFoundView(RequestHandler handler) {
       router.defaultStream.listen((HttpRequest httpRequest) {
  -      HttpBodyHandler.processRequest(httpRequest).then((HttpBody body) {
  -        Request request = new Request(body.type, body.body, httpRequest.response, httpRequest.headers, httpRequest);
  -        return handler(request);
  -      });
  +      _prepareRequestHandler(httpRequest, handler);
       });
     }
   
  
positive.code:   Router router;
    List _defaulHttpHeaders = new List();
  
    Stream<Request> onPrepareRequest;
  
    Backend({String host: "0.0.0.0", int port: 8080}) {
      this.host = host;
  
negative.code:     _defaulHttpHeaders.add({'name': name, 'value': value});
    }
  
    void _prepareRequestHandler(HttpRequest httpRequest, RequestHandler handler) {
      HttpBodyHandler.processRequest(httpRequest).then((HttpBody body) {
        Request request = new Request(body.type, body.body, httpRequest.response, httpRequest.headers, httpRequest);
        _onPrepareRequestController.add(request);
        handler(request);
      });
    }
  
    void addView(Pattern url,RequestHandler handler) {
      router.serve(url).listen((HttpRequest httpRequest) {
        if (_defaulHttpHeaders != null) {
          _defaulHttpHeaders.forEach((header) => httpRequest.response.headers.add(header['name'],header['value']));
        }
        _prepareRequestHandler(httpRequest, handler);
      });
    }
  
  
  
    void addStaticView(Pattern url, String path) {
      StaticFileHandler fileHandler = new StaticFileHandler.serveFolder(path);
  