Unable to connect to MQTT broker via ngx-mqtt in angular8 - mqtt

Question

No matter what i do i can't connect to a mqtt broker via websocket in my angular application (trying in chrome and firefox).
For simplicity i'm using HiveMQ broker, i've published on the topic /gat/38/openReservationRequests some data
I've followed this medium article on how to connect to mqtt in angular using ngx-mqtt but for me it is not working.
In my app:
I've installed the module
npm install ngx-mqtt --save
i've added the configuration and set the module forRoot in my app.module.ts
...
export const MQTT_SERVICE_OPTIONS: IMqttServiceOptions = {
connectOnCreate: true,
hostname: 'broker.hivemq.com',
port: 8000,
path: '/gat/38/openReservationRequests',
protocol: 'ws',
};
...
imports: [
...
MqttModule.forRoot(MQTT_SERVICE_OPTIONS),
...
],
...
i'm executing this function inside the ngOnInit of app.component.ts
...
import { IMqttMessage, MqttConnectionState, MqttService } from 'ngx-mqtt';
...
constructor(private mqttService: MqttService) {
this.mqttService.state.subscribe((s: MqttConnectionState) => {
const status = s === MqttConnectionState.CONNECTED ? 'CONNECTED' : 'DISCONNECTED';
this.status.push(`Mqtt client connection status: ${status}`);
});
}
ngOnInit() {
this.subscription = this.mqttService
.observe('/gat/38/openReservationRequests')
.subscribe((message: IMqttMessage) => {
this.msg = message;
console.log('msg: ', message);
console.log('Message: ' + message.payload.toString() + 'for topic: ' + message.topic);
console.log('subscribed to topic: ' + /gat/38/openReservationRequests);
});
}
but i am always getting this error:
core.js:6014 ERROR TypeError: Cannot read property 'resubscribe' of undefined
at MqttClient.subscribe (mqtt.min.js:1)
at mqtt.service.js:211
at Observable._subscribe (using.js:8)
at Observable._trySubscribe (Observable.js:42)
at Observable.subscribe (Observable.js:28)
at FilterOperator.call (filter.js:13)
at Observable.subscribe (Observable.js:23)
at Observable.connect (ConnectableObservable.js:30)
at RefCountOperator.call (refCount.js:17)
at Observable.subscribe (Observable.js:23)
mqtt.min.js:1 WebSocket connection to 'ws://broker.hivemq.com:8000/gat/38/openReservationRequests' failed: Connection closed before receiving a handshake response
if i specify the clientId inside the MQTT_SERVICE_OPTIONS i still get the same error.
if i change the protocol to wss i get a different error:
core.js:6014 ERROR TypeError: Cannot read property 'resubscribe' of undefined
at MqttClient.subscribe (mqtt.min.js:1)
at mqtt.service.js:211
at Observable._subscribe (using.js:8)
at Observable._trySubscribe (Observable.js:42)
at Observable.subscribe (Observable.js:28)
at FilterOperator.call (filter.js:13)
at Observable.subscribe (Observable.js:23)
at Observable.connect (ConnectableObservable.js:30)
at RefCountOperator.call (refCount.js:17)
at Observable.subscribe (Observable.js:23)
mqtt.min.js:1 WebSocket connection to 'wss://broker.hivemq.com:8000/gat/38/openReservationRequests' failed: Error in connection establishment: net::ERR_CONNECTION_CLOSED
If i try to connect manually inside my app.component.ts ngOnInit before observing the topic:
this.mqttService.connect({
hostname: 'broker.hivemq.com',
port: 8000,
path: '/gat/38/openReservationRequests',
clientId: '34er23qwrfq42w3' //those are just random digits
});
i still get the error above.
For me it would be ideal to connect in some inner component (accessible after the user is authenticated) because i will have my private mqtt broker and the topic will depend on the logged user information.
I've tried any combination of protocol with/without cliendId etc but at this point i don't know what is wrong. I've already fully recompiled my app lots of times, i've tried publishing it on my test-server which has a ssl certificate but nothing changed.
Resolved thanks to #Anant Lalchandani i set the correct path.
The other problem was that '/mytopic' and 'mytopic' are indeed two different topic and i was using it wrong too.
This is my code, updated:
app.module.ts
export const MQTT_SERVICE_OPTIONS: IMqttServiceOptions = {
connectOnCreate: false,
hostname: 'broker.hivemq.com',
port: 8000,
path: '/mqtt'
};
appcomponent.ts (inside ngOnInit for now)
this.mqttService.connect({
hostname: 'broker.hivemq.com',
port: 8000,
path: '/mqtt',
clientId: '1234e3qer23rf'
});
this.mqttService.onConnect
.subscribe(
connack=> {
console.log('CONNECTED');
console.log(connack);
}
);
this.mqttService.observe('gat/38/openReservationRequests')
.subscribe((message: IMqttMessage) => {
this.msg = message;
console.log(new TextDecoder('utf-8').decode(message.payload));
});

Answer 1

I have checked the code snippets you shared in question.
In your app.module.ts, the path value should be '/mqtt'. You have set the topic as the value of path here. The topic can only be subscribed/published. As you are using a topic as a path value at the time of connecting to a websocket, your application will not be able to connect to websocket at the first place.
The reason why we need to use /mqtt as a path is it specifies you are sending MQTT messages over the WebSocket protocol.
The documentation of HiveMQ itself stated to use the path as '/mqtt' in its example. You can check the documentation here.