ngx-mqtt

ngx-mqtt

This library isn't just a wrapper around MQTT.js for angular >= 2. It uses observables and takes care of subscription handling and message routing.

• Description
• Installation
• Usage
• Test

Description

ngx-mqtt is well suited for applications with many components and many subscribers. The problem is, if you regulary subscribe to mqtt with client libraries like MQTT.js, still every message is handled with an on-message-eventhandler, so you have to dispatch the received messages for yourself. So, if you have multiple components using mqtt in your code, you just want to only receive the messages for your local filter. Furthermore, if you destroy a component, you want to unsubscribe from mqtt, but only if no other component uses the same filter.

This library exposes a method observe(filter), which returns an Observable. If you subscribe to this observable, the actual mqtt subscription is executed. The topic filter is used to only add matching mqtt messages to the observable. Every other execution of observe(filter) with an already used filter will return the same observable. The observable keeps track of the subscribers and executes an mqtt unsubscribe method, if all subscribers have unsubscribed from the observable.

Installation

Simply install it from npm:

npm install ngx-mqtt --save

Usage

import { Observable } from 'rxjs/Observable';

import {
  MqttMessage,
  MqttModule,
  MqttService
} from 'ngx-mqtt';

export const MQTT_SERVICE_OPTIONS = {
  hostname: 'localhost',
  port: 9001,
  path: '/mqtt'
};

export function mqttServiceFactory() {
  return new MqttService(MQTT_SERVICE_OPTIONS);
}

@NgModule({
  imports: [
    ...
    MqttModule.forRoot({
      provide: MqttService,
      useFactory: mqttServiceFactory
    })
  ]
  ...
})

export class AppModule { }

@Component({
  template: `
    <h1>{{mesage}}</h1>
    <h1>{{(myOtherMessage$ | async)?.payload.toString()}}</h1>
  `
})
export class ExampleComponent {
  public myOtherMessage$: Observable<MqttMessage>;

  constructor(private _mqttService: MqttService) { 
    this._mqttService.observe('my/topic').subscribe((message: MqttMessage) => {
      this.myMessage = message.payload.toString();
    });
    this.myOtherMessage$ = this._mqttService.observe('my/other/topic');
  }

  public unsafePublish(topic: string, message: string): void {
    this._mqttService.unsafePublish(topic, message, {qos: 1, retain: true});
  }
}

For further usage use this module, see demo.module.ts and index.html. To see the demo in action use

npm install && npm run start

Test

$ npm test