Demo of publishing MQTT messages to local RabbitMQ broker. Scenario is a fleet of networked cars that continually transmit telemetry data back to the manufacturer for diagnostic purposes.

mqtt_message_publisher.rb

#!/usr/bin/ruby
require 'rubygems'
require 'mqtt'

# Credits:
# https://github.com/njh/ruby-mqtt

# How many vehicles we've sold
num_vehicles = 100

# What things are transmitting MQTT messages
sensor_types = [
  "/brakes/front/left/",
  "/brakes/front/right/",
  "/brakes/rear/left/",
  "/brakes/rear/right/",
  "/engine/battery/",
  "/headlight/left/",
  "/headlight/right/",
  "/airconditioning/",
  ]

status_topics = [
    "ok",
    "error",
    "warning",
    "nodata"
]

# Publish example
MQTT::Client.connect('localhost') do |c|
  # Do the following forever...
  while true do
    # Pick a random vehicle to report on...
    vehicle_number = rand(num_vehicles)

    # For each sensor type in that vehicle...
    sensor_types.each do |sensor|
      # Choose which status topic to publish to
      status_topic = status_topics[rand(status_topics.length)]

      # Compose our MQTT topic string
      topic = "vehicle/" + vehicle_number.to_s + sensor + status_topic

      # Compose our diagnostic message
      message = topic + "\t\t Diagnostic message " + rand(1000).to_s

      # ... publish the name of the sensor plus a randomly chosen status message.
      c.publish(topic, message)

      # Throttle a bit
      # sleep 0.1
    end
  end
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