code: private void logMqttFly(UnitRequest request, String msgStr) {
          long start = request.getContext().getSentTimestamp();
          LOG.debug(new JSONObject() {{
              put(Constant.COST, System.currentTimeMillis() - start);
              put("type", "mqttFly");//从发出到收到，主要用于监控内网间通信性能
              put("ssid", request.getContext().getSsid());
              put("from", request.getContext().getSourceNodeId());
              put("length", msgStr.length());
              put("msgType", request.getContext().getMessageType());
              put("payload", msgStr);
          }});
      }
docs: 打印mqtt消息传输耗时等信息:术语mqttFly