How to use MQTT in the Electron project

Electron is an open-source software framework developed and maintained by GitHub. It allows for the development of desktop GUI applications using web technologies: it combines the Chromium rendering engine and the Node.js runtime. Electron is the main GUI framework behind several notable open-source projects including Atom, GitHub Desktop, Light Table, Visual Studio Code, and WordPress Desktop.¹

A basic Electron includes three files: package.json (metadata) main.js (code) and index.html (graphical user interface). The frame is provided by the Electron executable file (electron.exe on Windows, electron.app on macOS, electron on Linux). Developers are free to add flags, customize icons, rename or edit Electron executable files.

This article mainly introduces how to use MQTT in Electron projects, and complete a simple MQTT desktop client, and implement the connection, subscription, unsubscribe, messaging and other functions between the client and MQTT broker.

Project initialization

New project

There are many ways to build a new project, but here is a brief list of a few:

• To create manually, do the following in the self-built project directory

  cd your-project
  
  npm init
  
  npm i -D electron@lates
  

  Also, refer to the following documentation for the steps to build the project.

  Address: https://www.electronjs.org/docs/tutorial/first-app

• Rapid development with the official template projects electron-qucik-start.

  Address: https://github.com/electron/electron-quick-start

    # Clone this repository
    git clone https://github.com/electron/electron-quick-start
    # Go into the repository
    cd electron-quick-start
    # Install dependencies
    npm install
    # Run the app
    npm start
  

• Rapid development builds with the template project electron-react-bolierplate, which can be developed using React.js.

  Address: https://github.com/electron-react-boilerplate/electron-react-boilerplate

  git clone --depth 1 --single-branch https://github.com/electron-react-boilerplate/electron-react-boilerplate.git your-project-name
  cd your-project-name
  yarn
  

• The rapid development build of the project via electron-vue will be coupled with project initialization using the vue-cli tool, which can be developed using Vue.js.

  Address: https://github.com/SimulatedGREG/electron-vue

  # Install vue-cli and scaffold boilerplate
  npm install -g vue-cli
  vue init simulatedgreg/electron-vue my-project
  
  # Install dependencies and run your app
  cd my-project
  yarn # or npm install
  yarn run dev # or npm run dev
  

In this article, the official electron quick start project template will be used to initialize the project in order to quickly build the example project.

Installation dependencies

Installation through the command line

npm install mqtt --save

After the dependencies are installed, if you want to open the console for debugging, you need to modify the code in main.js and uncomment win.webContents.openDevTools().

// Open the DevTools.
mainWindow.webContents.openDevTools()

In this case, the locally installed MQTT.js module cannot be loaded directly into renderer.js without using the front-end builder to package the front-end page. In addition to using the build tool method, there are two other ways to solve this:

1. nodeIntegration can be set to true in webPreferences. When this property is present, webview will have Node integration in it, and node APIs like require and process can be used to access low-level system resources. Node integration is disabled by default.

   const mainWindow = new BrowserWindow({
     width: 800,
     height: 600,
     webPreferences: {
       nodeIntegration: true,
       preload: path.join(__dirname, 'preload.js'),
     },
   })
   

2. The MQTT.js module can be imported in preload.js. When there is no node integration, this script still can access all Node APIs. However, when this script execution completes, global objects injected via Node will be removed.

3. The MQTT.js module can be imported in main process and connected. In Electron, processes communicate by passing messages through developer-defined "channels" with the ipcMain and ipcRenderer modules. These channels are arbitrary (you can name them anything you want) and bidirectional (you can use the same channel name for both modules). For usage examples, check out the IPC tutorial.

   For example, in the main process, ipcMain listens for connection operations. When the user clicks the connection, the corresponding configuration information collected in the render process is transferred to the main process through ipcRenderer to connect:

   • Receive the connection data sent by the rendering process in the main process and make MQTT connection:

   // main.js
   ipcMain.on('onConnect', (event, connectUrl, connectOpt) => {
     client = mqtt.connect(connectUrl, connectOpt)
     client.on('connect', () => {
       console.log('Client connected:' + options.clientId)
     })
     client.on('message', (topic, message) => {
       console.log(`${message.toString()}\nOn topic: ${topic}`)
     })
   })
   

   • Click to connect in the rendering process, get the connection data from the page and send it to the main process:

   // render.js
   function onConnect() {
     const { host, port, clientId, username, password } = connection
     const connectUrl = `mqtt://${host.value}:${port.value}`
     const options = {
       keepalive: 30,
       protocolId: 'MQTT',
       clean: true,
       reconnectPeriod: 1000,
       connectTimeout: 30 * 1000,
       rejectUnauthorized: false,
       clientId,
       username,
       password,
     }
     console.log('connecting mqtt client')
     window.electronAPI.onConnect(connectUrl, options)
   }
   

   • In preload.js, the API method for interprocess IPC communication is implemented, and the channel is established:

   // preload.js
   contextBridge.exposeInMainWorld('electronAPI', {
     onConnect: (data) => ipcRenderer.send('onConnect', data),
   })
   

The use of MQTT

Connect to the MQTT broker

This article will use the free public MQTT broker provided by EMQX. This service was created based on the EMQX MQTT IoT cloud platform. The information about broker access is as follows:

• Broker: broker.emqx.io
• TCP Port: 1883
• Websocket Port: 8083

A Practical Guide to MQTT Broker Selection

Download this practical guide and learn what to consider when choosing an MQTT broker.

Get the eBook →

To illustrate more intuitive, the key connection code for the example will be written in the renderer.js file. With the consideration of security, the installed MQTT module will be loaded via the require method of the Node.js API, in the preload.js file (using method 2 above). Also, this method injecting it in the global window object.

Note: Context isolation (contextIsolation) has been enabled by default since Electron 12, Although preload scripts share a window global with the renderer they're attached to, you cannot directly attach any variables from the preload script to window because of the contextIsolation default.

Therefore, we need to set contextIsolation: false in webPreferences to close:

const mainWindow = new BrowserWindow({
    width: 800,
    height: 600,
    webPreferences: {
      preload: path.join(__dirname, 'preload.js'),
      contextIsolation: false; // Version 12.0.0 above are enabled by default
    }
  })

So that the loaded module can be accessed directly in renderer.js:

• Import MQTT module

// preload.js
const mqtt = require('mqtt')
window.mqtt = mqtt

• Configure and test MQTT module

// renderer.js
const clientId = 'mqttjs_' + Math.random().toString(16).substr(2, 8)

const host = 'mqtt://broker.emqx.io:1883'

const options = {
  keepalive: 30,
  clientId: clientId,
  protocolId: 'MQTT',
  protocolVersion: 4,
  clean: true,
  reconnectPeriod: 1000,
  connectTimeout: 30 * 1000,
  will: {
    topic: 'WillMsg',
    payload: 'Connection Closed abnormally..!',
    qos: 0,
    retain: false,
  },
  rejectUnauthorized: false,
}

// Information about the mqtt module is available
console.log(mqtt)

console.log('connecting mqtt client')
const client = mqtt.connect(host, options)

client.on('error', (err) => {
  console.log('Connection error: ', err)
  client.end()
})

client.on('reconnect', () => {
  console.log('Reconnecting...')
})

client.on('connect', () => {
  console.log('Client connected:' + clientId)
  client.subscribe('testtopic/electron', {
    qos: 0,
  })
  client.publish('testtopic/electron', 'Electron connection demo...!', {
    qos: 0,
    retain: false,
  })
})

client.on('message', (topic, message, packet) => {
  console.log(
    'Received Message: ' + message.toString() + '\nOn topic: ' + topic
  )
})

We can see the following output on the console after writing the above code and running the project:

The MQTT module works fine. After setting up the module, we can write a simple UI interface to manually enter the configuration required for the MQTT connection, and click the connect button to connect to the MQTT server, as well as disconnect, subscribe to topics, send and receive messages, and so on.

Interface of application

The complete code is available here: https://github.com/emqx/MQTT-Client-Examples/tree/master/mqtt-client-Electron.

Key code

Connect

let client = null

const options = {
  keepalive: 30,
  protocolId: 'MQTT',
  protocolVersion: 4,
  clean: true,
  reconnectPeriod: 1000,
  connectTimeout: 30 * 1000,
  will: {
    topic: 'WillMsg',
    payload: 'Connection Closed abnormally..!',
    qos: 0,
    retain: false,
  },
}

function onConnect() {
  const { host, port, clientId, username, password } = connection
  const connectUrl = `mqtt://${host.value}:${port.value}`
  options.clientId =
    clientId.value || `mqttjs_${Math.random().toString(16).substr(2, 8)}`
  options.username = username.value
  options.password = password.value
  console.log('connecting mqtt client')
  client = mqtt.connect(connectUrl, options)
  client.on('error', (err) => {
    console.error('Connection error: ', err)
    client.end()
  })
  client.on('reconnect', () => {
    console.log('Reconnecting...')
  })
  client.on('connect', () => {
    console.log('Client connected:' + options.clientId)
    connectBtn.innerText = 'Connected'
  })
}

Subscribe to the topic

function onSub() {
  if (client.connected) {
    const { topic, qos } = subscriber
    client.subscribe(
      topic.value,
      { qos: parseInt(qos.value, 10) },
      (error, res) => {
        if (error) {
          console.error('Subscribe error: ', error)
        } else {
          console.log('Subscribed: ', res)
        }
      }
    )
  }
}

Unsubscribe

function onUnsub() {
  if (client.connected) {
    const { topic } = subscriber
    client.unsubscribe(topic.value, (error) => {
      if (error) {
        console.error('Unsubscribe error: ', error)
      } else {
        console.log('Unsubscribed: ', topic.value)
      }
    })
  }
}

Publish messages

function onSend() {
  if (client.connected) {
    const { topic, qos, payload } = publisher
    client.publish(topic.value, payload.value, {
      qos: parseInt(qos.value, 10),
      retain: false,
    })
  }
}

Receive messages

// In the onConnect function
client.on('message', (topic, message) => {
  const msg = document.createElement('div')
  msg.setAttribute('class', 'message-body')
  msg.innerText = `${message.toString()}\nOn topic: ${topic}`
  document.getElementById('article').appendChild(msg)
})

Disconnect

function onDisconnect() {
  if (client.connected) {
    client.end()
    client.on('close', () => {
      connectBtn.innerText = 'Connect'
      console.log(options.clientId + ' disconnected')
    })
  }
}

Client test

At this point, we test the sending and receiving of messages with a MQTT 5.0 client tool - MQTTX, also written in Electron.

When using MQTTX to send a message to the client, you can see that the message is received properly:

Send a message to MQTTX using the client you wrote yourself, and now you can see that MQTTX is also receiving the message properly:

Summary

So far, we have completed that use Electron to create a simple MQTT desktop client, and simulate the connection, messaging, unsubscribe and disconnect scenarios between the client and MQTT broker. It is also worth noting that since the Electron project includes both a browser environment and a Node.js environment, it is possible to use the browser's WebSocket API to implement an MQTT over WebSocket connection by modifying the connection protocol and port number in the above code.

Resources

• How to Use MQTT in Vue
• How to Use MQTT in React
• How to Use MQTT in Angular
• How to Use MQTT in Node.js
• A Quickstart Guide to Using MQTT over WebSocket