anchor.diff:    // interface attributes
   
     final Uri url;
  +  final Map headers;
   
     EventSourceReadyState get readyState => _readyState;
   
  
positive.code: 
    /// Create a new EventSource by connecting to the specified url.
    static Future<EventSource> connect(url,
        {http.Client client, String lastEventId}) async {
      // parameter initialization
      url = url is Uri ? url : Uri.parse(url);
      client = client ?? new http.Client();
      lastEventId = lastEventId ?? "";
      EventSource es = new EventSource._internal(url, client, lastEventId);
      await es._start();
      return es;
    }
  
    EventSource._internal(this.url, this.client, this._lastEventId) {
      _decoder = new EventSourceDecoder(retryIndicator: _updateRetryDelay);
    }
  
  
negative.code:     request.headers["Accept"] = "text/event-stream";
      if (_lastEventId.isNotEmpty) {
        request.headers["Last-Event-ID"] = _lastEventId;
      }
      if (headers != null) {
        headers.forEach((k,v) {
          request.headers[k] = v;
        }); 
      }
      var response = await client.send(request);
      if (response.statusCode != 200) {
  