code: func httpError(w http.ResponseWriter, body string, code int) {
  	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
  	w.Header().Set("Content-Length", strconv.Itoa(len(body)))
  	w.WriteHeader(code)
  	w.Write([]byte(body))
  }
docs: // httpError is like the http.Error with WebSocket context exception.