code: func (w *gzipResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
  	if hj, ok := w.ResponseWriter.(http.Hijacker); ok {
  		return hj.Hijack()
  	}
  	return nil, nil, httpserver.NonHijackerError{Underlying: w.ResponseWriter}
  }
docs: // Hijack implements http.Hijacker. It simply wraps the underlying
  // ResponseWriter's Hijack method if there is one, or returns an error.