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mqtt_connection.md

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MOSQUITTO SETUP

INDEX:

INSTALLATION:

CLIENT

First of all you have to install mosquitto library on the device where you'll run the telemetry, using

sudo apt install libmosquitto-dev
sudo apt install mosquitto-dev

BROKER

On the broker device you have to install the mosquitto broker service by

sudo snap install mosquitto

or, if you'll run the broker on 32-bit devices or if you don't have snap installed

sudo apt install mosquitto

TEST THE BROKER

Before using the telemetry test if the broker work by installing also mosquito-clients, so

sudo snap install mosquitto-clients

or, as for the broker installation,

sudo apt install mosquitto-clients

Once you had installed mosquitto-clients, you can run a subscriber by

mosquitto_sub -h localhost -p 1883 -t [TOPIC_TO_SUBSCRIBE] {-u [USERNAME] -P [PASSWORD]}

and, on another terminal, run a publisher by

mosquitto_pub -h localhost -p 1883 -t [TOPIC_TO_PUBLISH] -m [MESSAGE] {-u [USERNAME] -P [PASSWORD]}

where the username and the password had been set on the broker (not mandatory, but raccommended). If there's no users or if you want to add some, you can follow the Documentation.

EXAMPLE:

Create a password's file passwords and run

sudo mosquitto_passwd -c [FILE_NAME] [USERNAME]

You'll be asked to choose a password and to repeat it.

COMPILE & TEST:

To use the mosquitto library you also have to append the -lmosquitto flag. There's a test in scripts/testMQTT folder.

USAGE:

Broker's Configuration File

You can find the .conf file in the /etc/mosquitto/ folder.

# Place your local configuration in /etc/mosquitto/conf.d/
#
# A full description of the configuration file is at
# /usr/share/doc/mosquitto/examples/mosquitto.conf.example

#allow_anonymous true

listener 1883 0.0.0.0

pid_file /run/mosquitto/mosquitto.pid

persistence true
persistence_location /var/lib/mosquitto/

log_dest topic
log_type error
log_type warning
log_type notice
log_type information
connection_messages true
log_timestamp true

password_file /etc/mosquitto/passwords

log_dest file /var/log/mosquitto/mosquitto.log

include_dir /etc/mosquitto/conf.d
  • allow_anonymous true: can be useful while testing, to avoid creating new users or to don't add corresponging flags while executing the code.
  • listener 1883 0.0.0.0: must be insert to make the broker listen on all its addresses.
  • include_dir /etc/mosquitto/conf.d: it's the folder where you can add your custom configuration files.
  • log_dest file /var/log/mosquitto/mosquitto.log: here you can find the log about your last broker session.

Start the Broker

Before starting the broker, remember to stop the service that is enabled by default on the device. To do so, you can run

sudo systemctl stop mosquitto.service

After the setup, you can start the broker by

./run_broker.sh

that will execute the following line

sudo mosquitto --verbose --config-file ./mosquitto.conf

If you don't have the ./run_broker.sh file you can write it by yourself.

If you would like to modify the configuration of the broker just add a new .conf file inside the conf.d/ folder.

For the documentation about writing .conf files visit the Mosquitto Documentation.

Start the Telemetry

For this part just have a look at the Telemetry Documentation and, if you want to create a new type of connection, at the Connection Documentation.

Setup the Connection

Before setting up the connection, here's a thing you have to know: the topic field can be used to create a tree of topics, so you can subscribe to a topic and receive all the messages published on that topic and on all its subtopics. For example, if you subscribe to the topic home/sensors/temperature you'll receive all the messages published on home/sensors/temperature, home/sensors/temperature/1 and home/sensors/temperature/2.

  1. To setup the connection you have to create a new MQTTConnection object and, if needed, pass the username and the password to it.

  2. Add all callbacks you want to use to the MQTTConnection object by using the addOn[CALLBACK] method.

  3. Init the connection by calling the init method (view Connection Documentation to see which parameters it will need and for other information about connections).

  4. Start the connection by calling the start method and storing the return thread.

  5. Subscribe/unsubscribe to/from a topic or set data.

    name.subscribe("topic");

// or

name.unsubscribe("topic");

// or

name.setData("topic", "data");

  6. Close the connection.

    name.closeConnection();

EXAMPLES:

The MQTT example is in the script/testMQTT/ folder. The .cpp and the .h files are in the src/connection/ and in the inc/connection folder. The user must check the pending messages counter before publishing by calling getPendingMessages().