mqtt-packet

What is mqtt-packet?

The mqtt-packet npm package is a utility for encoding and decoding packets used in MQTT (Message Queuing Telemetry Transport), which is a lightweight messaging protocol for small sensors and mobile devices. It is designed for connections with remote locations where a small code footprint is required and/or network bandwidth is at a premium.

What are mqtt-packet's main functionalities?

Parsing MQTT Packets

This feature allows you to parse MQTT packets from a buffer. The code sample demonstrates how to create a parser instance, listen for 'packet' events, and parse a buffer containing an MQTT packet.

const mqttPacket = require('mqtt-packet');
const parser = mqttPacket.parser();
parser.on('packet', function(packet) {
  console.log(packet);
});
parser.parse(Buffer.from([0x30, 0x02, 0x00, 0x00]));

Generating MQTT Packets

This feature allows you to generate MQTT packets. The code sample shows how to create an MQTT packet object and then generate a buffer that can be sent over a network.

const mqttPacket = require('mqtt-packet');
const packet = {
  cmd: 'publish',
  messageId: 42,
  topic: 'test/topic',
  payload: 'test payload',
  qos: 0,
  retain: false
};
const buffer = mqttPacket.generate(packet);
console.log(buffer);

Other packages similar to mqtt-packet

mqtt

The 'mqtt' package is a client library for the MQTT protocol. It provides an API for connecting to an MQTT broker, publishing messages, and subscribing to topics. It is more feature-rich than mqtt-packet as it includes the full client functionality, not just packet encoding and decoding.

mqtt-connection

The 'mqtt-connection' package is a barebone connection package for MQTT that can be used when implementing an MQTT client or server. It provides a simple stream interface for sending and receiving MQTT packets over a network. It is similar to mqtt-packet but includes stream handling capabilities.

aedes-packet

The 'aedes-packet' package is a fork of mqtt-packet, which is used by the Aedes MQTT broker. It has similar functionalities to mqtt-packet but is tailored to work seamlessly with the Aedes broker ecosystem.

README

mqtt-packet

Encode and Decode MQTT 3.1.1, 5.0 packets the node way.

• Installation
• Examples
• Packets
• API
• Contributing
• License & copyright

This library is tested with node v6, v8, v10, v12 and v14. The last version to support older versions of node was mqtt-packet@4.1.2.

Installation

npm install mqtt-packet --save

Examples

Generating

const mqtt = require('mqtt-packet');
const object = {
  cmd: 'publish',
  retain: false,
  qos: 0,
  dup: false,
  length: 10,
  topic: 'test',
  payload: 'test' // Can also be a Buffer
};
const opts = { protocolVersion: 4 }; // default is 4. Usually, opts is a connect packet

console.log(mqtt.generate(object))
// Prints:
//
// <Buffer 30 0a 00 04 74 65 73 74 74 65 73 74>
//
// Which is the same as:
//
// Buffer.from([
//   48, 10, // Header (publish)
//   0, 4, // Topic length
//   116, 101, 115, 116, // Topic (test)
//   116, 101, 115, 116 // Payload (test)
// ])

Parsing

const mqtt = require('mqtt-packet');
const opts = { protocolVersion: 4 }; // default is 4. Usually, opts is a connect packet
const parser = mqtt.parser(opts);

// Synchronously emits all the parsed packets
parser.on('packet', packet => {
  console.log(packet)
  // Prints:
  //
  // {
  //   cmd: 'publish',
  //   retain: false,
  //   qos: 0,
  //   dup: false,
  //   length: 10,
  //   topic: 'test',
  //   payload: <Buffer 74 65 73 74>
  // }
})

parser.parse(Buffer.from([
  48, 10, // Header (publish)
  0, 4, // Topic length
  116, 101, 115, 116, // Topic (test)
  116, 101, 115, 116 // Payload (test)
]))
// Returns the number of bytes left in the parser

API

• mqtt#generate()
• mqtt#writeToStream()
• mqtt#parser()

mqtt.generate(object, [opts])

Generates a Buffer containing an MQTT packet. The object must be one of the ones specified by the packets section. Throws an Error if a packet cannot be generated.

mqtt.writeToStream(object, stream, [opts])

Writes the mqtt packet defined by object to the given stream. The object must be one of the ones specified by the packets section. Emits an Error on the stream if a packet cannot be generated. On node >= 0.12, this function automatically calls cork() on your stream, and then it calls uncork() on the next tick. By default cache for number buffers is enabled. It creates a list of buffers for faster write. To disable cache set mqtt.writeToStream.cacheNumbers = false. Should be set before any writeToStream calls.

mqtt.parser([opts])

Returns a new Parser object. Parser inherits from EventEmitter and will emit:

• packet, when a new packet is parsed, according to packets
• error, if an error happens

Parser.parse(buffer)

Parses a given Buffer and emits synchronously all the MQTT packets that are included. Returns the number of bytes left to parse.

If an error happens, an error event will be emitted, but no packet events will be emitted after that. Calling parse() again clears the error and previous buffer, as if you created a new Parser.

Packets

This section describes the format of all packets emitted by the Parser and that you can input to generate.

Connect

{
  cmd: 'connect',
  protocolId: 'MQTT', // Or 'MQIsdp' in MQTT 3.1 and 5.0
  protocolVersion: 4, // Or 3 in MQTT 3.1, or 5 in MQTT 5.0
  clean: true, // Can also be false
  clientId: 'my-device',
  keepalive: 0, // Seconds which can be any positive number, with 0 as the default setting
  username: 'matteo',
  password: Buffer.from('collina'), // Passwords are buffers
  will: {
    topic: 'mydevice/status',
    payload: Buffer.from('dead'), // Payloads are buffers
    properties: { // MQTT 5.0
      willDelayInterval: 1234,
      payloadFormatIndicator: false,
      messageExpiryInterval: 4321,
      contentType: 'test',
      responseTopic: 'topic',
      correlationData: Buffer.from([1, 2, 3, 4]),
      userProperties: {
        'test': 'test'
      }
    }
  },
  properties: { // MQTT 5.0 properties
      sessionExpiryInterval: 1234,
      receiveMaximum: 432,
      maximumPacketSize: 100,
      topicAliasMaximum: 456,
      requestResponseInformation: true,
      requestProblemInformation: true,
      userProperties: {
        'test': 'test'
      },
      authenticationMethod: 'test',
      authenticationData: Buffer.from([1, 2, 3, 4])
  }
}

If protocolVersion is 3, clientId is mandatory and generate will throw if missing.

If password or will.payload are passed as strings, they will automatically be converted into a Buffer.

Connack

{
  cmd: 'connack',
  returnCode: 0, // Or whatever else you see fit MQTT < 5.0
  sessionPresent: false, // Can also be true.
  reasonCode: 0, // reason code MQTT 5.0
  properties: { // MQTT 5.0 properties
      sessionExpiryInterval: 1234,
      receiveMaximum: 432,
      maximumQoS: 2,
      retainAvailable: true,
      maximumPacketSize: 100,
      assignedClientIdentifier: 'test',
      topicAliasMaximum: 456,
      reasonString: 'test',
      userProperties: {
        'test': 'test'
      },
      wildcardSubscriptionAvailable: true,
      subscriptionIdentifiersAvailable: true,
      sharedSubscriptionAvailable: false,
      serverKeepAlive: 1234,
      responseInformation: 'test',
      serverReference: 'test',
      authenticationMethod: 'test',
      authenticationData: Buffer.from([1, 2, 3, 4])
  }
}

The only mandatory argument is returnCode, as generate will throw if missing.

Subscribe

{
  cmd: 'subscribe',
  messageId: 42,
  properties: { // MQTT 5.0 properties
    subscriptionIdentifier: 145,
    userProperties: {
      test: 'test'
    }
  }
  subscriptions: [{
    topic: 'test',
    qos: 0,
    nl: false, // no Local MQTT 5.0 flag
    rap: true, // Retain as Published MQTT 5.0 flag
    rh: 1 // Retain Handling MQTT 5.0
  }]
}

All properties are mandatory.

Suback

{
  cmd: 'suback',
  messageId: 42,
  properties: { // MQTT 5.0 properties
    reasonString: 'test',
    userProperties: {
      'test': 'test'
    }
  }
  granted: [0, 1, 2, 128]
}

All the granted qos must be < 256, as they are encoded as UInt8. All properties are mandatory.

Unsubscribe

{
  cmd: 'unsubscribe',
  messageId: 42,
  properties: { // MQTT 5.0 properties
    userProperties: {
      'test': 'test'
    }
  }
  unsubscriptions: [
    'test',
    'a/topic'
  ]
}

All properties are mandatory.

Unsuback

{
  cmd: 'unsuback',
  messageId: 42,
  properties: { // MQTT 5.0 properties
    reasonString: 'test',
    userProperties: {
      'test': 'test'
    }
  }
}

All properties are mandatory.

Publish

{
  cmd: 'publish',
  messageId: 42,
  qos: 2,
  dup: false,
  topic: 'test',
  payload: Buffer.from('test'),
  retain: false,
  properties: { // optional properties MQTT 5.0
      payloadFormatIndicator: true,
      messageExpiryInterval: 4321,
      topicAlias: 100,
      responseTopic: 'topic',
      correlationData: Buffer.from([1, 2, 3, 4]),
      userProperties: {
        'test': 'test'
      },
      subscriptionIdentifier: 120, // can be an Array in message from broker, if message included in few another subscriptions
      contentType: 'test'
   }
}

Only the topic property is mandatory. Both topic and payload can be Buffer objects instead of strings. messageId is mandatory for qos > 0.

Puback

{
  cmd: 'puback',
  messageId: 42,
  reasonCode: 16, // only for MQTT 5.0
  properties: { // MQTT 5.0 properties
      reasonString: 'test',
      userProperties: {
        'test': 'test'
      }
  }
}

The only mandatory property is messageId, as generate will throw if missing.

Pubrec

{
  cmd: 'pubrec',
  messageId: 42,
  reasonCode: 16, // only for MQTT 5.0
  properties: { // properties MQTT 5.0
    reasonString: 'test',
    userProperties: {
      'test': 'test'
    }
  }
}

The only mandatory property is messageId, as generate will throw if missing.

Pubrel

{
  cmd: 'pubrel',
  messageId: 42,
  reasonCode: 16, // only for MQTT 5.0
  properties: { // properties MQTT 5.0
     reasonString: 'test',
     userProperties: {
       'test': 'test'
     }
  }
}

The only mandatory property is messageId, as generate will throw if missing.

Pubcomp

{
  cmd: 'pubcomp',
  messageId: 42,
  reasonCode: 16, // only for MQTT 5.0
  properties: { // properties MQTT 5.0
    reasonString: 'test',
    userProperties: {
       'test': 'test'
    }
  }
}

The only mandatory property is messageId, as generate will throw if missing.

Pingreq

{
  cmd: 'pingreq'
}

Pingresp

{
  cmd: 'pingresp'
}

Disconnect

{
  cmd: 'disconnect',
  reasonCode: 0, // MQTT 5.0 code
  properties: { // properties MQTT 5.0
     sessionExpiryInterval: 145,
     reasonString: 'test',
     userProperties: {
       'test': 'test'
     },
     serverReference: 'test'
  }
}

Auth

{
  cmd: 'auth',
  reasonCode: 0, // MQTT 5.0 code
  properties: { // properties MQTT 5.0
     authenticationMethod: 'test',
     authenticationData: Buffer.from([0, 1, 2, 3]),
     reasonString: 'test',
     userProperties: {
       'test': 'test'
     }
  }
}

Contributing

mqtt-packet is an OPEN Open Source Project. This means that:

Individuals making significant and valuable contributions are given commit-access to the project to contribute as they see fit. This project is more like an open wiki than a standard guarded open source project.

See the CONTRIBUTING.md file for more details.

Contributors

mqtt-packet is only possible due to the excellent work of the following contributors:

Matteo Collina	GitHub/mcollina	Twitter/@matteocollina
Adam Rudd	GitHub/adamvr	Twitter/@adam_vr
Peter Sorowka	GitHub/psorowka	Twitter/@psorowka
Siarhei Buntsevich	GitHub/scarry1992

License

MIT