mqtt

What is mqtt?

The mqtt npm package is a client library for the MQTT protocol, which is a lightweight messaging protocol designed for small sensors and mobile devices. It allows you to connect to an MQTT broker, publish messages to topics, and subscribe to topics to receive messages.

What are mqtt's main functionalities?

Connect to an MQTT broker

This feature allows you to connect to an MQTT broker. The code sample demonstrates how to connect to a public MQTT broker (HiveMQ) and log a message upon successful connection.

const mqtt = require('mqtt');
const client = mqtt.connect('mqtt://broker.hivemq.com');
client.on('connect', () => {
  console.log('Connected to broker');
});

Publish messages to a topic

This feature allows you to publish messages to a specific topic. The code sample shows how to publish a message 'Hello MQTT' to the topic 'test/topic' after connecting to the broker.

const mqtt = require('mqtt');
const client = mqtt.connect('mqtt://broker.hivemq.com');
client.on('connect', () => {
  client.publish('test/topic', 'Hello MQTT');
  console.log('Message published');
});

Subscribe to a topic

This feature allows you to subscribe to a specific topic and receive messages published to that topic. The code sample demonstrates subscribing to 'test/topic' and logging any received messages.

const mqtt = require('mqtt');
const client = mqtt.connect('mqtt://broker.hivemq.com');
client.on('connect', () => {
  client.subscribe('test/topic', (err) => {
    if (!err) {
      console.log('Subscribed to topic');
    }
  });
});
client.on('message', (topic, message) => {
  console.log(`Received message: ${message.toString()} on topic: ${topic}`);
});

Other packages similar to mqtt

mqttjs

mqttjs is another popular MQTT client library for Node.js. It offers similar functionalities to the mqtt package, including connecting to brokers, publishing, and subscribing to topics. It is known for its simplicity and ease of use.

aedes

aedes is a barebone MQTT broker that can be embedded in Node.js applications. While it serves as a broker rather than a client, it can be used in conjunction with mqtt to create a complete MQTT solution. It is lightweight and highly performant.

mosca

mosca is an MQTT broker that can be used with Node.js. It is designed to be fast and scalable, making it suitable for IoT applications. Like aedes, it can be used alongside mqtt to provide a full MQTT ecosystem.

README

mqtt.js

Important note for existing users

v0.2.0 has brough some API breaking changes to mqtt.js. Please consult the migration guide for information or open an issue if you need any help.

Introduction

mqtt.js is a library for the MQTT protocol, written in javascript.

Installation

npm install mqtt

Documentation

Detailed documentation can be found in the wiki

Client API usage

A basic publish client, the basis for bin/mqtt_pub:

var mqtt = require('mqtt');
var argv = process.argv;

for (var i = 2; i <= 5; i++) {
  if(!argv[i]) process.exit(-1);
}

var port = argv[2],
  host = argv[3],
  topic = argv[4],
  payload = argv[5];

var client = mqtt.createClient(port, host)
client.on('connect', function() {
  client.publish(topic, payload);
  client.end();
});

Server API usage

A broadcast server example, included in examples/broadcast.js:

var mqtt = require('mqtt');

mqtt.createServer(function(client) {
  var self = this;

  if (!self.clients) self.clients = {};

  client.on('connect', function(packet) {
    client.connack({returnCode: 0});
    client.id = packet.client;
    self.clients[client.id] = client;
  });

  client.on('publish', function(packet) {
    for (var k in self.clients) {
      self.clients[k].publish({topic: packet.topic, payload: packet.payload});
    }
  });

  client.on('subscribe', function(packet) {
    var granted = [];
    for (var i = 0; i < packet.subscriptions.length; i++) {
      granted.push(packet.subscriptions[i].qos);
    }

    client.suback({granted: granted});
  });

  client.on('pingreq', function(packet) {
    client.pingresp();
  });

  client.on('disconnect', function(packet) {
    client.stream.end();
  });

  client.on('close', function(err) {
    delete self.clients[client.id];
  });

  client.on('error', function(err) {
    client.stream.end();
    console.log('error!');
  });
}).listen(1883);