code: func (s *rpcServer) writeHTTPResponseHeaders(req *http.Request, headers http.Header, code int, w io.Writer) error {
  	_, err := io.WriteString(w, s.httpStatusLine(req, code))
  	if err != nil {
  		return err
  	}
  
  	err = headers.Write(w)
  	if err != nil {
  		return err
  	}
  
  	_, err = io.WriteString(w, "\r\n")
  	return err
  }
docs: // writeHTTPResponseHeaders writes the necessary response headers prior to
  // writing an HTTP body given a request to use for protocol negotiation, headers
  // to write, a status code, and a writer.