4. Interacting with Sensors in Java | MQTT Essentials - A Lightweight IoT Protocol

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MQTT Essentials - A Lightweight IoT Protocol

By : Gaston C. Hillar

4.1 (7)

MQTT Essentials - A Lightweight IoT Protocol

4.1 (7)

By: Gaston C. Hillar

Overview of this book

This step-by-step guide will help you gain a deep understanding of the lightweight MQTT protocol. We’ll begin with the specific vocabulary of MQTT and its working modes, followed by installing a Mosquitto MQTT broker. Then, you will use best practices to secure the MQTT Mosquitto broker to ensure that only authorized clients are able to publish and receive messages. Once you have secured the broker with the appropriate configuration, you will develop a solution that controls a drone with Python. Further on, you will use Python on a Raspberry Pi 3 board to process commands and Python on Intel Boards (Joule, Edison and Galileo). You will then connect to the MQTT broker, subscribe to topics, send messages, and receive messages in Python. You will also develop a solution that interacts with sensors in Java by working with MQTT messages. Moving forward, you will work with an asynchronous API with callbacks to make the sensors interact with MQTT messages. Following the same process, you will develop an iOS app with Swift 3, build a website that uses WebSockets to connect to the MQTT broker, and control home automation devices with HTML5, JavaScript code, Node.js and MQTT messages

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

1. Lightweight Messaging with MQTT 3.1.1 and Mosquitto

1. Lightweight Messaging with MQTT 3.1.1 and Mosquitto

Understanding convenient scenarios for the MQTT protocol

Working with the publish-subscribe pattern

Working with message filtering

Understanding the MQTT puzzle -- clients, servers, and connections

Installing a Mosquitto broker on Ubuntu Linux

Installing a Mosquitto broker on macOS

Installing a Mosquitto broker on Windows

Subscribing to topics

Publishing messages

Unsubscribing from topics

Working with best practices when creating topics

Understanding wildcards

Learning about the different Quality of Service levels

Working with at least once delivery

Working with exactly once delivery

Test your knowledge

Summary

2. Securing an MQTT Mosquitto Server

2. Securing an MQTT Mosquitto Server

Securing a Mosquitto server

Generating a private certificate authority to use TLS with Mosquitto

Creating a certificate for the Mosquitto server

Configuring TLS transport security in Mosquitto

Testing the MQTT TLS configuration with MQTT.fx

Testing the MQTT TLS configuration with MQTT-spy

Creating a certificate for each MQTT client

Configuring TLS client certificate authentication in Mosquitto

Testing the MQTT TLS client authentication with MQTT.fx

Testing the MQTT TLS configuration with MQTT-spy

Forcing the TLS protocol version

Test your knowledge

Summary

3. Controlling a Drone with Python

3. Controlling a Drone with Python

Understanding the requirements to control a drone with MQTT

Defining the topics and commands

Installing paho-mqtt for Python

Connecting the client to the MQTT server with Python

Understanding callbacks

Subscribing to topics with Python

Creating a class to represent a drone

Receiving messages with Python

Processing commands with Python

Sending messages with Python

Working with the network loop with Python

Test your knowledge

Summary

4. Interacting with Sensors in Java

4. Interacting with Sensors in Java

Understanding the requirements

Defining the topics and commands

Installing the Eclipse Paho Java Client

Creating a security helper class to establish a TLS secured connection

Configuring a TLS secured connection in Java

Working with asynchronous notifications and callbacks in Java

Subscribing to topics and understanding notification events in Java

Processing commands that interact with sensors in Java

Working with last will and testament in Java

Publishing messages with commands to target sensors

Test your knowledge

Summary

5. Controlling Home Automation in JavaScript

5. Controlling Home Automation in JavaScript

Understanding the requirements

Defining the topics and commands to control home automation

Enabling WebSockets for a Mosquitto server

Testing WebSockets with the Eclipse Paho client JavaScript utility

Understanding the Eclipse Paho JavaScript asynchronous client

Creating an HTML 5 web page to control LEDs

Publishing messages to target remote devices in JavaScript

Processing the received messages in JavaScript

Working with WebSockets to connect to the MQTT server

Subscribing to topics in JavaScript

Processing commands that interact with LEDs in Node.js

Running the home automation web application

Debugging asynchronous code with Chrome Developer Tools (CDT) in JavaScript

Securing MQTT over WebSockets with TLS

Test your knowledge

Summary

6. Interacting with Actuators in Swift

6. Interacting with Actuators in Swift

Understanding the requirements

Defining topics and commands

Enabling connections without TLS for a Mosquitto server

Installing the CocoaMQTT client library to create a new iOS app

Building the UI for the iOS app that will control an actuator

Understanding the CocoaMQTT client in Swift 3

Connecting to the MQTT server and subscribing to topics in Swift

Publishing messages to target actuators in Swift

Processing commands that interact with actuators in Node.js

Running the iOS app that controls an actuator with MQTT

Debugging events in Swift

Test your knowledge

Summary

A. Exersise Answers

Chapter 1, Lightweight Messaging with MQTT 3.1.1 and Mosquitto

Chapter 2, Securing an MQTT Mosquitto Server

Chapter 3, Controlling a Drone with Python

Chapter 4, Interacting with Sensors in Java

Chapter 5, Controlling Home Automation in JavaScript

Chapter 6, Interacting with Actuators in Swift

Subscribing to topics and understanding notification events in Java

The onSuccess method prints a message indicating that the client has successfully connected with the MQTT server and then calls the mqttAsyncClient.subscribe method with topic_for_led01 as the argument that specifies the topic filter to subscribe to 0 for the argument that specifies the desired QoS level, null for the userContext argument, and another anonymous class that implements the IMqttActionListener interface as the value for the callback argument. As happened with the connect method, the subscribe method requires the callback argument of the org.eclipse.paho.client.mqttv3.IMqttActionListener type. The anonymous class provides implementations for the previously explained two methods required by the IMqttActionListener interface: onSuccess and onFailure.

The code in the onSuccess method prints a message indicating that the client has subscribed to the topic filter and the granted QoS level. The asyncActionToken.getGrantedQoS...

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