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MQTT QoS

作者資料

原始 MD by 綱庭

網路不穩?QoS 網路服務品質

回顧 上上次的MQTT​

通訊協定 MQTT之淺入深出

物聯網 Internet Of Thing​

當訊息是很重要的不可遺失的呢?​

例如前途的瓦斯爐訊號

遺失1 Pub -> Broker​

遺失2 Broker -> Sub​

額外補充 遺失3 Broker -> Storage(AMQP協議中才有)​

補充資料AMQP Transaction機制

解決方案 QoS​

Quality of Service(網路服務品質)

在MQTT中是用來設置訊息傳輸的規則

QoS 0​

最多一次(不管有沒有送到就是送一次)

QoS 1​

最少一次(類似郵件掛號，必須被確認packetId封包ID) 過一段時間都沒收到確認會補送訊息

QoS 2​

確認一次(避免重複丟出訊息)

實作環節​

新增帶有QoS等級的發送訊息方法​

import express from 'express';
import mqtt, { QoS } from 'mqtt';

const app = express();

const mqttClient = mqtt.connect('mqtt://localhost');

app.get('/publish', (req, res) => {
  const message = req.query.message as string;
  const qosLevel = parseInt(req.query.qos as string);

  if (![0, 1, 2].includes(qosLevel)) {
    res.status(400).send('Invalid QoS level');
    return;
  }

  mqttClient.publish('topic', message, { qos: qosLevel as QoS }, (err) => {
    if (err) {
      console.error(`Error publishing message: ${err}`);
      res.status(500).send('Error publishing message');
      return;
    }

    console.log(`Published message "${message}" with QoS ${qosLevel}`);
    res.status(200).send('Message published');
  });
});

app.listen(3000, () => {
  console.log('Express server started on port 3000');
});

去處理QoS 訊息​

import express from 'express';
import mqtt, { QoS } from 'mqtt';

const app = express();

const mqttClient = mqtt.connect('mqtt://localhost');

mqttClient.on('connect', () => {
  mqttClient.subscribe('topic', { qos: 2 }, (err) => {
    if (err) {
      console.error(`Error subscribing to topic: ${err}`);
    } else {
      console.log('Subscribed to topic with QoS 2');
    }
  });
});

mqttClient.on('message', (topic, message, packet) => {
  console.log(`Received message "${message.toString()}" on topic "${topic}" with QoS ${packet.qos}`);
});

app.listen(3000, () => {
  console.log('Express server started on port 3000');
});

參考文章