code: function parserOnHeaders(headers, url) {
    // Once we exceeded headers limit - stop collecting them
    if (this.maxHeaderPairs <= 0 ||
        this._headers.length < this.maxHeaderPairs) {
      this._headers = this._headers.concat(headers);
    }
    this._url += url;
  }
docs: Only called in the slow case where slow means that the request headers were either fragmented across multiple TCP packets or too large to be processed in a single run. This method is also called to process trailing HTTP headers.