server.js.sample

// FileSystem
var fs = require('fs');

// MQTT
var mqtt = require('mqtt');
// In case of MQTTS (TLS):
// var connectOptions = {
//     host: "<MQTT_server_IP_or_hostname>",
//     port: 8883,
//     protocol: "mqtts",
//     keepalive: 10,
//     clientId: "test_client_01",
//     protocolId: "MQTT",
//     protocolVersion: 4,
//     clean: true,
//     reconnectPeriod: 2000,
//     connectTimeout: 2000,
//     cert: fs.readFileSync("ca.crt"),
//     rejectUnauthorized: false,
// };

// In case of MQTT:
var connectOptions = {
    host: "<MQTT_server_IP_or_hostname>",
    port: 1883,
    protocol: "mqtt",
    keepalive: 10,
    clientId: "test_client_01",
    protocolId: "MQTT",
    protocolVersion: 4,
    clean: true,
    reconnectPeriod: 2000,
    connectTimeout: 2000
};

// Express HTTP Server =================================================
var express = require('express');
var app = express();
var server = require('http').createServer(app);

// Socket.io ===========================================================
var io = require('socket.io')(server);

app.get('/', function(req, res,next) {
    res.sendFile(__dirname + '/public/index.html');
});

// MQTT ================================================================
var client = mqtt.connect(connectOptions);
var topic="<topic_to_subscribe>";

io.on('connection', function(socket) {
    console.log('Client connected...');

    socket.on('join', function(data) {
        console.log('Browser says: ' + data);
        socket.emit('messages', 'Hello from server');
        client.subscribe(topic);
    });

    //handle incoming messages
    client.on('message',(topic, message, packet) => {
      // console.log("Topic: " + topic + " | Message: " + message);
      var raw_decoded = (JSON.parse(message.toString())).object;
      console.log(raw_decoded);
      console.log("Topic: " + topic + " | Message: " + String(raw_decoded));
      socket.emit('messages', raw_decoded);
    });
});

client.on("connect",() => {
  if (client.connected) {
    client.publish("test", "I'm connected!");
    console.log("MQTT client connected to " + connectOptions.host + ":" + connectOptions.port)
  }
})

//handle errors
client.on("error",(error) => {
  console.log("Can't connect" + error);
  process.exit(1)
});

server.listen(4200, () => {
  console.log('Server listening on *:4200');
});