一、简述

​ MQTT（消息队列遥测传输协议），是一种基于发布/订阅（publish/subscribe）模式的通讯协议，该协议构建于TCP/IP协议上。MQTT最大优点在于，可以以极少的代码和有限的带宽，为连接远程设备提供实时可靠的消息服务。MQTT 协议的应用场景包括物联网、移动应用、车联网、智能家居、即时聊天等。

二、特性

使用发布/订阅消息模式。

对负载内容屏蔽的消息传输。

使用TCP/IP提供网络连接。

有三种消息发布服务质量：

“至多一次”，消息发布完全依赖底层TCP/IP网络。会发生消息丢失或重复。这一级别可用于如下情况，环境传感器数据，丢失一次读记录无所谓，因为不久后还会有第二次发送。这一种方式主要普通APP的推送，倘若你的智能设备在消息推送时未联网，推送过去没收到，再次联网也就收不到了。

“至少一次”，确保消息到达，但消息重复可能会发生。

“只有一次”，确保消息到达一次。在一些要求比较严格的计费系统中，可以使用此级别。在计费系统中，消息重复或丢失会导致不正确的结果。这种最高质量的消息发布服务还可以用于即时通讯类的APP的推送，确保用户收到且只会收到一次。

小型传输，开销很小（固定长度的头部是2字节），协议交换最小化，以降低网络流量。

使用Last Will和Testament特性通知有关各方客户端异常中断的机制。

Last Will：即遗言机制，用于通知同一主题下的其他设备发送遗言的设备已经断开了连接。

Testament：遗嘱机制，功能类似于Last Will。

三、MQTT协议中的订阅、主题、会话

1.订阅（Subscription）

订阅包含主题筛选器（Topic Filter）和最大服务质量（QoS）。订阅会与一个会话（Session）关联。一个会话可以包含多个订阅。每一个会话中的每个订阅都有一个不同的主题筛选器。

2.会话（Session）

每个客户端与服务器建立连接后就是一个会话，客户端和服务器之间有状态交互。会话存在于一个网络之间，也可能在客户端和服务器之间跨越多个连续的网络连接。

3.主题名（Topic Name）

连接到一个应用程序消息的标签，该标签与服务器的订阅相匹配。服务器会将消息发送给订阅所匹配标签的每个客户端。

4.主题筛选器（Topic Filter）

一个对主题名通配符筛选器，在订阅表达式中使用，表示订阅所匹配到的多个主题。

5.负载（Payload）

消息订阅者所具体接收的内容。

四、MQTT协议中的方法

Connect。等待与服务器建立连接。Disconnect。等待MQTT客户端完成所做的工作，并与服务器断开TCP/IP会话。Subscribe。等待完成订阅。UnSubscribe。等待服务器取消客户端的一个或多个topics订阅。Publish。MQTT客户端发送消息请求，发送完成后返回应用程序线程。

五、前端使用mqtt

1. mqtt服务器的部署

使用 EMQX CLOUD 进行mqtt服务的部署

EMQX Cloud: 全托管的 MQTT 消息云服务

部署教程：https://www.bilibili.com/video/BV1Bx4y1K7hN/

使用Serverless版本每月有免费额度

2. 安装js的mqtt包

<code>npm i mqtt

3. 前端代码

完整代码已上传至github

https://github.com/void00013/8.mqtt_vue3_test/tree/main

请自行下载依赖后运行

// Home.vue

<template>

<div class="home-container">code>

<el-card shadow="always" style="margin-bottom:30px;">code>

<div class="emq-title">code>

Configuration

</div>

<el-form ref="configForm" hide-required-asterisk size="small" label-position="top" :model="connection">code>

<el-row :gutter="20">code>

<el-col :span="8">code>

<el-form-item prop="host" label="Host">code>

<el-row :gutter="10">code>

<el-col :span="7">code>

<el-select v-model="connection.protocol" @change="handleProtocolChange">code>

<el-option label="ws://" value="ws"></el-option>code>

<el-option label="wss://" value="wss"></el-option>code>

</el-select>

</el-col>

<el-col :span="17">code>

<el-input v-model="connection.host"></el-input>code>

</el-col>

</el-row>

</el-form-item>

</el-col>

<el-col :span="8">code>

<el-form-item prop="port" label="Port">code>

<el-input v-model.number="connection.port" type="number" placeholder="8083/8084"></el-input>code>

</el-form-item>

</el-col>

<el-col :span="8">code>

<el-form-item prop="endpoint" label="Mountpoint">code>

<el-input v-model="connection.endpoint" placeholder="/mqtt"></el-input>code>

</el-form-item>

</el-col>

<el-col :span="8">code>

<el-form-item prop="clientId" label="Client ID">code>

<el-input v-model="connection.clientId"> </el-input>code>

</el-form-item>

</el-col>

<el-col :span="8">code>

<el-form-item prop="username" label="Username">code>

<el-input v-model="connection.username"></el-input>code>

</el-form-item>

</el-col>

<el-col :span="8">code>

<el-form-item prop="password" label="Password">code>

<el-input v-model="connection.password"></el-input>code>

</el-form-item>

</el-col>

<el-col :span="24">code>

<el-button type="success" size="small" class="conn-btn" style="margin-right: 20px;" :disabled="client.connected" @click="createConnection" :loading="connecting">code>

{ { client.connected ? 'Connected' : 'Connect' }}

</el-button>

<el-button v-if="client.connected" type="danger" size="small" class="conn-btn" @click="destroyConnection">code>

Disconnect

</el-button>

</el-col>

</el-row>

</el-form>

</el-card>

<el-card shadow="always" style="margin-bottom:30px;">code>

<div class="emq-title">code>

Subscribe

</div>

<el-form ref="subscription" hide-required-asterisk size="small" label-position="top" :model="subscription">code>

<el-row :gutter="20">code>

<el-col :span="8">code>

<el-form-item prop="topic" label="Topic">code>

<el-input v-model="subscription.topic"></el-input>code>

</el-form-item>

</el-col>

<el-col :span="8">code>

<el-form-item prop="qos" label="QoS">code>

<el-select v-model="subscription.qos">code>

<el-option v-for="qos in qosList" :key="qos" :label="qos" :value="qos"></el-option>code>

</el-select>

</el-form-item>

</el-col>

<el-col :span="8">code>

<el-button :disabled="!client.connected" type="success" size="small" class="subscribe-btn" @click="doSubscribe">code>

{ { subscribeSuccess ? 'Subscribed' : 'Subscribe' }}

</el-button>

<el-button :disabled="!client.connected" type="success" size="small" class="subscribe-btn" style="margin-left:20px" @click="doUnSubscribe" v-if="subscribeSuccess">code>

Unsubscribe

</el-button>

</el-col>

</el-row>

</el-form>

</el-card>

<el-card shadow="always" style="margin-bottom:30px;">code>

<div class="emq-title">code>

Publish

</div>

<el-form ref="publish" hide-required-asterisk size="small" label-position="top" :model="publish">code>

<el-row :gutter="20">code>

<el-col :span="8">code>

<el-form-item prop="topic" label="Topic">code>

<el-input v-model="publish.topic"></el-input>code>

</el-form-item>

</el-col>

<el-col :span="8">code>

<el-form-item prop="payload" label="Payload">code>

<el-input v-model="publish.payload"></el-input>code>

</el-form-item>

</el-col>

<el-col :span="8">code>

<el-form-item prop="qos" label="QoS">code>

<el-select v-model="publish.qos">code>

<el-option v-for="qos in qosList" :key="qos" :label="qos" :value="qos"></el-option>code>

</el-select>

</el-form-item>

</el-col>

</el-row>

</el-form>

<el-col :span="24">code>

<el-button :disabled="!client.connected" type="success" size="small" class="publish-btn" @click="doPublish">code>

Publish

</el-button>

</el-col>

</el-card>

<el-card shadow="always" style="margin-bottom:30px;">code>

<div class="emq-title">code>

Receive

</div>

<el-col :span="24">code>

<el-input type="textarea" :rows="3" style="margin-bottom: 15px" v-model="receiveNews" readOnly></el-input>code>

</el-col>

</el-card>

</div>

</template>

<script>

import mqtt from 'mqtt'

export default {

name: 'Home',

data() {

return {

connection: {

protocol: 'wss',

host: '你的mqtt服务器地址',

// server less服务器只有两种协议：mqtts: 8883; wss: 8084

port: 8084,

endpoint: '/mqtt',

clean: true,

connectTimeout: 30 * 1000, // ms

reconnectPeriod: 4000, // ms

clientId: 'emqx_vue_' + Math.random().toString(16).substring(2, 8),

// auth

username: 'void',

password: '123',

},

subscription: {

topic: 'topic/mqttx',

qos: 0,

},

publish: {

topic: 'topic/browser',

qos: 0,

payload: '{ "msg": "Hello, I am browser." }',

},

receiveNews: '',

qosList: [0, 1, 2],

client: {

connected: false,

},

subscribeSuccess: false,

connecting: false,

retryTimes: 0,

}

},

methods: {

initData() {

this.client = {

connected: false,

}

this.retryTimes = 0

this.connecting = false

this.subscribeSuccess = false

},

handleOnReConnect() {

this.retryTimes += 1

if (this.retryTimes > 5) {

try {

this.client.end()

this.initData()

this.$message.error('Connection maxReconnectTimes limit, stop retry')

} catch (error) {

this.$message.error(error.toString())

}

}

},

createConnection() {

try {

this.connecting = true

const { protocol, host, port, endpoint, ...options } = this.connection

const connectUrl = `${protocol}://${host}:${port}${endpoint}`

this.client = mqtt.connect(connectUrl, options)

if (this.client.on) {

this.client.on('connect', () => {

this.connecting = false

console.log('Connection succeeded!')

})

this.client.on('reconnect', this.handleOnReConnect)

this.client.on('error', (error) => {

console.log('Connection failed', error)

})

this.client.on('message', (topic, message) => {

this.receiveNews = this.receiveNews.concat(message)

console.log(`Received message ${message} from topic ${topic}`)

})

}

} catch (error) {

this.connecting = false

console.log('mqtt.connect error', error)

}

},

// subscribe topic

doSubscribe() {

const { topic, qos } = this.subscription

this.client.subscribe(topic, { qos }, (error, res) => {

if (error) {

console.log('Subscribe to topics error', error)

return

}

this.subscribeSuccess = true

console.log('Subscribe to topics res', res)

})

},

// unsubscribe topic

doUnSubscribe() {

const { topic } = this.subscription

this.client.unsubscribe(topic, (error) => {

if (error) {

console.log('Unsubscribe error', error)

}

})

},

// publish message

doPublish() {

const { topic, qos, payload } = this.publish

this.client.publish(topic, payload, { qos }, (error) => {

if (error) {

console.log('Publish error', error)

}

})

},

// disconnect

destroyConnection() {

if (this.client.connected) {

try {

this.client.end(false, () => {

this.initData()

console.log('Successfully disconnected!')

})

} catch (error) {

console.log('Disconnect failed', error.toString())

}

}

},

handleProtocolChange(value) {

this.connection.port = value === 'wss' ? '8084' : '8083'

},

},

}

</script>

<style lang="scss">code>

@import url('../assets/style/home.scss');

.home-container {

max-width: 1100px;

margin: 0 auto;

.conn-btn {

color: #fff;

background-color: #00b173;

font-size: 14px;

}

.publish-btn {

margin-bottom: 20px;

float: right;

}

.el-button--success {

background-color: #34c388 !important;

border-color: #34c388 !important;

font-size: 14px !important;

}

.el-button--danger {

background-color: #f5222d !important;

border-color: #f5222d !important;

}

.el-form-item {

&.is-error {

.el-input__inner,

.el-textarea__inner {

box-shadow: 0 0 0 2px rgba(245, 34, 45, 0.2);

}

}

&.is-success {

.el-input__inner,

.el-textarea__inner {

border-color: #34c388 !important;

}

}

}

}

</style>

// home.scss

body {

background-color: #f0f2f5;

padding: 0;

margin: 0;

color: rgba(0, 0, 0, 0.65);

font-size: 14px;

font-family: -apple-system, BlinkMacSystemFont, Segoe UI, PingFang SC, Hiragino Sans GB, Microsoft YaHei,

Helvetica Neue, Helvetica, Arial, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol;

}

.emq-title {

font-size: 16px;

color: #333333;

font-weight: bolder;

margin-bottom: 15px;

&.h3 {

font-size: 14px;

}

&[size='small'] {code>

font-size: 14px;

}

.sub-title {

font-weight: normal;

display: block;

font-size: 12px;

color: #8f9297;

margin-top: 12px;

}

&.required-title {

&:before {

content: '*';

color: #f5222d;

margin-right: 4px;

}

}

}

.el-select {

width: 100%;

}

.subscribe-btn {

margin-top: 42px !important;

}

.publish-btn {

margin-bottom: 30px;

}

4. EMQX官方示例