Angular is a development platform built on top of TypeScript. It consists of a component-based framework for building scalable Web applications; a set of perfectly integrated libraries covering routing, form management, client-server communication and other functions; and a set of development tools to help users develop, build, test, and update codes.

MQTT is a lightweight IoT message transfer protocol based on publish/subscribe mode, providing one-to-many message distribution and application decoupling with small transmission consumption, which can minimize network traffic. At the same time, it can meet various delivery requirements thanks to its three QoS (Quality of Service) levels for messages.

This article will introduce how to use MQTT protocol in Angular projects to connect, subscribe, send/receive messages, unsubscribe and perform other functions between clients and MQTT Broker.

Project Initialization

Create a new project

The reference is as follows: Create an Angular project with the Angular CLI

Example:

ng new my-app

Installation of MQTT client library

The library used in this case is ngx-mqtt, which isn’t just a wrapper around MQTT.js for angular >= 2. It uses observables and takes care of subscription handling and message routing. ngx-mqtt is well suited for applications with many components and many subscribers.

To install ngx-mqtt via the command line, you can use the npm or yarn command (either one)

npm install ngx-mqtt --save 
yarn add ngx-mqtt

Use of MQTT

Connecting to MQTT Broker

We use the free public MQTT Broker provided by EMQX in this article, which is built on top of the MQTT cloud service - EMQX Cloud. EMQX is a large-scale distributed IoT MQTT message broker that can efficiently and reliably connect massive IoT devices, process and distribute messages and event flow data in real-time, and help customers build business-critical IoT platforms and applications.

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The server access information is as follows:

Broker: broker.emqx.io
TCP Port: 1883
WebSocket Port: 8083

Key codes for connection:

import {
 IMqttMessage,
 IMqttServiceOptions,
 MqttService,
 IPublishOptions,
} from 'ngx-mqtt';
import { IClientSubscribeOptions } from 'mqtt-browser';
import { Subscription } from 'rxjs';

@Component({
 selector: 'app-root',
 templateUrl: './app.component.html',
 styleUrls: ['./app.component.scss'],
})
export class AppComponent {
 constructor(private _mqttService: MqttService) {
   this.client = this._mqttService;
}
 private curSubscription: Subscription | undefined;
 connection = {
   hostname: 'broker.emqx.io',
   port: 8083,
   path: '/mqtt',
   clean: true, // Retain session
   connectTimeout: 4000, // Timeout period
   reconnectPeriod: 4000, // Reconnect period
   // Authentication information
   clientId: 'mqttx_597046f4',
   username: 'emqx_test',
   password: 'emqx_test',
   protocol: 'ws',
  }
 subscription = {
   topic: 'topic/mqttx',
   qos: 0,
};
 publish = {
   topic: 'topic/browser',
   qos: 0,
   payload: '{ "msg": "Hello, I am browser." }',
};
 receiveNews = '';
 qosList = [
  { label: 0, value: 0 },
  { label: 1, value: 1 },
  { label: 2, value: 2 },
];
 client: MqttService | undefined;
 isConnection = false;
 subscribeSuccess = false;

 // Create a connection
 createConnection() {
   // Connection string, which allows the protocol to specify the connection method to be used
   // ws Unencrypted WebSocket connection
   // wss Encrypted WebSocket connection
   // mqtt Unencrypted TCP connection
   // mqtts Encrypted TCP connection
   try {
     this.client?.connect(this.connection as IMqttServiceOptions)
  } catch (error) {
     console.log('mqtt.connect error', error);
  }
   this.client?.onConnect.subscribe(() => {
     this.isConnection = true
     console.log('Connection succeeded!');
  });
   this.client?.onError.subscribe((error: any) => {
     this.isConnection = false
     console.log('Connection failed', error);
  });
   this.client?.onMessage.subscribe((packet: any) => {
     this.receiveNews = this.receiveNews.concat(packet.payload.toString())
     console.log(`Received message ${packet.payload.toString()} from topic ${packet.topic}`)
  })
}
}

Upon connecting to the MQTT Broker successfully, call the subscribe method of the current MQTT instance and pass in the Topic and QoS parameters for the successful subscription.

doSubscribe() {
 const { topic, qos } = this.subscription
 this.curSubscription = this.client?.observe(topic, { qos } as IClientSubscribeOptions).subscribe((message: IMqttMessage) => {
   this.subscribeSuccess = true
   console.log('Subscribe to topics res', message.payload.toString())
})
}

Unsubscribe

The unsubscribe method can release the resources held by the subscription.

doUnSubscribe() {
 this.curSubscription?.unsubscribe()
 this.subscribeSuccess = false
}

Message publishing

The usafePublish publishes messages on topics with optional options, such as QoS and Retain, as shown below.

doPublish() {
 const { topic, qos, payload } = this.publish
 console.log(this.publish)
 this.client?.unsafePublish(topic, payload, { qos } as IPublishOptions)
}

Disconnect

The disconnect will disconnect the MQTT client. The parameter true is passed in to force a disconnection from the MQTT client.

destroyConnection() {
 try {
   this.client?.disconnect(true)
   this.isConnection = false
   console.log('Successfully disconnected!')
} catch (error: any) {
   console.log('Disconnect failed', error.toString())
}
}

Test

We create the following simple browser application with Angular, which has the following functions: Establish a connection, Subscribe to topics, Send & receive messages, Unsubscribe, Disconnect, and so on. For the complete code, see: https://github.com/emqx/MQTT-Client-Examples/tree/master/mqtt-client-Angular.js

Use MQTT 5.0 client tool - MQTTX as another client to test message sending & receiving.

Before MQTTX sends a second message, unsubscribe at the browser side, and the browser side will not receive subsequent messages sent by MQTTX.

Summary

We have successfully created an MQTT connection in an Angular project and simulated the scenarios of subscription, message sending and receiving, unsubscription, and disconnection between the client and the MQTT.

As one of the three mainstream front-end frameworks, Angular can be used both on the browser and the mobile side. Various interesting applications can be developed by combining MQTT protocol and MQTT cloud service, such as the chat system for customer service or management system for real-time monitoring of IoT device information.

Resources

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