ruby-mqtt

Pure Ruby gem that implements the MQTT protocol, a lightweight protocol for publish/subscribe messaging.

Also includes a class for parsing and generating MQTT-SN packets.

Table of Contents

• Installation
• Quick Start
• Library Overview
• Resources
• License
• Contact

Installation

You may get the latest stable version from Rubygems:

$ gem install mqtt

Alternatively, to use a development snapshot from GitHub using Bundler, add this to your Gemfile:

    gem 'mqtt', :github => 'njh/ruby-mqtt'

Quick Start

require 'mqtt'

# Publish example
MQTT::Client.connect('test.mosquitto.org') do |c|
  c.publish('test', 'message')
end

# Subscribe example
MQTT::Client.connect('test.mosquitto.org') do |c|
  # If you pass a block to the get method, then it will loop
  c.get('test') do |topic,message|
    puts "#{topic}: #{message}"
  end
end

Library Overview

Connecting

A new client connection can be created by passing either a MQTT URI, a host and port or by passing a hash of attributes.

client = MQTT::Client.connect('mqtt://myserver.example.com')
client = MQTT::Client.connect('mqtts://user:pass@myserver.example.com')
client = MQTT::Client.connect('myserver.example.com')
client = MQTT::Client.connect('myserver.example.com', 18830)
client = MQTT::Client.connect(:host => 'myserver.example.com', :port => 1883 ... )

TLS/SSL is not enabled by default, to enabled it, pass :ssl => true:

client = MQTT::Client.connect(
  :host => 'test.mosquitto.org',
  :port => 8883,
  :ssl => true
)

Alternatively you can create a new Client object and then configure it by setting attributes. This example shows setting up client certificate based authentication:

client = MQTT::Client.new
client.host = 'myserver.example.com'
client.ssl = true
client.cert_file = path_to('client.pem')
client.key_file  = path_to('client.key')
client.ca_file   = path_to('root-ca.pem')
client.connect()

The connection can either be made without the use of a block:

client = MQTT::Client.connect('test.mosquitto.org')
# perform operations
client.disconnect()

Or, if using a block, with an implicit disconnection at the end of the block.

MQTT::Client.connect('test.mosquitto.org') do |client|
  # perform operations
end

For more information, see and list of attributes for the MQTT::Client class and the MQTT::Client.connect method.

Publishing

To send a message to a topic, use the publish method:

client.publish(topic, payload, retain=false)

The method will return once the message has been sent to the MQTT server.

For more information see the MQTT::Client#publish method.

Subscribing

You can send a subscription request to the MQTT server using the subscribe method. One or more Topic Filters may be passed in:

client.subscribe( 'topic1' )
client.subscribe( 'topic1', 'topic2' )
client.subscribe( 'foo/#' )

For more information see the MQTT::Client#subscribe method.

Receiving Messages

To receive a message, use the get method. This method will block until a message is available. The topic is the name of the topic the message was sent to. The message is a string:

topic,message = client.get

Alternatively, you can give the get method a block, which will be called for every message received and loop forever:

client.get do |topic,message|
  # Block is executed for every message received
end

For more information see the MQTT::Client#get method.

Parsing and serialising of packets

The parsing and serialising of MQTT and MQTT-SN packets is a separate lower-level API. You can use it to build your own clients and servers, without using any of the rest of the code in this gem.

# Parse a string containing a binary packet into an object
packet_obj = MQTT::Packet.parse(binary_packet)
    
# Write a PUBACK packet to an IO handle
ios << MQTT::Packet::Puback(:id => 20)
    
# Write an MQTT-SN Publish packet with QoS -1 to a UDP socket
socket = UDPSocket.new
socket.connect('localhost', MQTT::SN::DEFAULT_PORT)
socket << MQTT::SN::Packet::Publish.new(
  :topic_id => 'TT',
  :topic_id_type => :short,
  :data => "The time is: #{Time.now}",
  :qos => -1
)
socket.close

Limitations

• QoS 2 is not currently supported by client
• Automatic re-connects to the server are not supported
• No local persistence for packets

Resources

• API Documentation: http://rubydoc.info/gems/mqtt
• Protocol Specification v3.1.1: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html
• Protocol Specification v3.1: http://public.dhe.ibm.com/software/dw/webservices/ws-mqtt/mqtt-v3r1.html
• MQTT-SN Protocol Specification v1.2: http://mqtt.org/new/wp-content/uploads/2009/06/MQTT-SN_spec_v1.2.pdf
• MQTT Homepage: http://www.mqtt.org/
• GitHub Project: http://github.com/njh/ruby-mqtt

License

The mqtt ruby gem is licensed under the terms of the MIT license. See the file LICENSE for details.

Contact

• Author: Nicholas J Humfrey
• Email: njh@aelius.com
• Twitter: @njh
• Home Page: http://www.aelius.com/njh/