code: private static int getWebSocketContentLength(HttpMessage message) {
          // WebSocket messages have constant content-lengths.
          HttpHeaders h = message.headers();
          if (message instanceof HttpRequest) {
              HttpRequest req = (HttpRequest) message;
              if (HttpMethod.GET.equals(req.method()) &&
                      h.contains(HttpHeaderNames.SEC_WEBSOCKET_KEY1) &&
                      h.contains(HttpHeaderNames.SEC_WEBSOCKET_KEY2)) {
                  return 8;
              }
          } else if (message instanceof HttpResponse) {
              HttpResponse res = (HttpResponse) message;
              if (res.status().code() == 101 &&
                      h.contains(HttpHeaderNames.SEC_WEBSOCKET_ORIGIN) &&
                      h.contains(HttpHeaderNames.SEC_WEBSOCKET_LOCATION)) {
                  return 16;
              }
          }
  
          // Not a web socket message
          return -1;
      }
docs: Returns the content length of the specified web socket message. If the
  specified message is not a web socket message, {@code -1} is returned.