如何关闭与 mqtt 客户端 node.js 的连接

Question

I'm doing a method that works as follows: When I press a button, I want to be continuously getting messages from the topic I'm subscribed to, and when I press another button I want to close connection and not receive any more messages. I think the connection closes correctly because the client.on('close') event is executed, however I continue receiving messages from the topic. What should I do to not receive any more messages?

startStop is a boolean, it is true when I want to receive messages and false when I want to stop receiving them. What am I doing wrong?

Here's my code:

mqttClientSubscribeToTraceability(reguladorId, startStop) {
    const tls = (Meteor.settings.mqttConfigClient.mqtt.port === 8883) || Meteor.settings.mqttConfigClient.mqtt.ca;

    const client = mqtt.connect(`${tls ? 'mqtts' : 'mqtt'}://${Meteor.settings.mqttConfigClient.mqtt.host}:${Meteor.settings.mqttConfigClient.mqtt.port}`, 
 { keyPath: Meteor.settings.mqttConfigClient.mqtt.key, 
certPath: Meteor.settings.mqttConfigClient.mqtt.cert, 
ca: [Meteor.settings.mqttConfigClient.mqtt.ca], 
rejectUnauthorized: false 
});

    const topic = `in/1.0/trafficLights/${global.region}/${reguladorId}`;

    const json = {};

    if (startStop) {
      client.on('connect', () => {
        client.subscribe(topic);
      });
      client.on('message', (topic, message) => {
        const msg = JSON.parse(message);
        console.log('msg', msg);
      });   
    } else {
      client.end();
      client.on('close', () => {
        client.unsubscribe(topic);
      });
    }
 }

Answer 1

The problem is that you are creating the connection object every time you call the function and not keeping a persistent reference to it.

This means when you call the function with startstop equal to true, you will create a new client object, subscribe to the topic and then attach the message callback. You then throw away the reference to the client object so there is no way to get it back.

When you call the function with startstop set to false, you still create a new client object, but then immediately close it. (Also calling unsubscribe after the client has been closed will achieve nothing except maybe throwing an error).

Given you have another variable (the reguladorId ) you probably need to use an object which uses that as the key to hold separate client instances.