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MQTT client
===================

.. contents:: :local:


Description
===========

For Python, we use the client library *paho-mqtt*.
It is pretty easy to use and provides several examples to start with on their `github repo <https://github.com/eclipse/paho.mqtt.python/tree/master/examples>`_.

A basic example that subscribes to */in* and publishes to */out*:

   .. code-block:: python

      import paho.mqtt.client as mqtt

      # connection callback
      def on_connect(client, userdata, flags, rc):
         print("Connected with result code " + str(rc))

      # message received callback
      def on_message(client, userdata, msg):
         print(msg.topic + " " + str(msg.payload))
         client.publish("/out", "received an input...")

      # set up the client
      client = mqtt.Client()
      client.on_connect = on_connect
      client.on_message = on_message
      client.connect("mqtt.eclipse.org", 1883, 60) # address ip, port number, keep alive

      # subscribe
      client.subscribe("/in")

      # process the MQTT business
      client.loop_forever()

Ressources
==========

The documentation of the *paho-mqtt* library can be found `here <https://pypi.org/project/paho-mqtt/>`_.

The `repo <https://gitlab.hevs.ch/SPL/digital-twin/mqtt-clients>`_ with our own clients can be used as a base to start.

:tag:`Python`
:tag:`MQTT`