Make an MQTT Publisher box

Introduction

• What is MQTT? For details, please check the following sites, but a brief explanation is the lightweight protocol of the Pub / Sub messaging model. Since it is assumed to be operated by a weak device that can be connected by IoT and WoT, various low-cost processing is possible.

• MQTT

• Summary about MQTT

• I think Pepper can use it, so I'll give it a try.

• MQTT I'm studying.

MQTT Publisher Box

The following libraries are used as the MQTT library for Python.

• Paho - Open Source messaging for M2M

Create a Python box and change the input Type from "bang" to "string".

Setting items

The setting items are like this.

Allows you to specify the MQTT broker host, port, KeepAlive value, and the topic to send the message to, the QOS value, and the Retain value.

Python code

The code looks like this. Get various parameters, connect to MQTT broker and send a message.

For how to use the library in the box, I referred to the following article.

• Make a Tweet box for Pepper

class MyClass(GeneratedClass):
    def __init__(self):
        GeneratedClass.__init__(self)

    def onLoad(self):
        self.framemanager = ALProxy("ALFrameManager")
        self.folderName = None
        
    def onUnload(self):
        import sys
        
        if self.folderName and self.folderName in sys.path:
            sys.path.remove(self.folderName)
        self.folderName = None

    def onInput_onStart(self, payload):
        import sys, os
        
        self.folderName = os.path.join(
            self.framemanager.getBehaviorPath(self.behaviorId), "../lib")
        if self.folderName not in sys.path:
            sys.path.append(self.folderName)
            
        import paho.mqtt.client as paho

        host       = self.getParameter("Broker Host")
        port       = self.getParameter("Broker Port")
        keep_alive = self.getParameter("KeepAlive")
        topic      = self.getParameter("Topic")
        qos        = self.getParameter("Qos") 
        retain     = self.getParameter("Retain")
        
        mqttc = paho.Client()
        mqttc.connect(host, port, keep_alive)
        mqttc.publish(topic, payload, qos, retain)

    def onInput_onStop(self):
        self.onUnload()
        self.onStopped()

Connect with Choregraphe

Connect the "Text Edit" box for setting the message content and the "MQTT" box you created.

Subscriber side

Prepare a Subscriber that will receive messages sent from the MQTT Publisher side. It uses the same Paho library as the Pub side.

sub.py

import paho.mqtt.client as paho

def on_message(mqttc, obj, msg):
    print("topic: " + msg.topic + ", payload: " + str(msg.payload) + ", qos: \
" + str(msg.qos) + ", retain: " + str(msg.retain))

if __name__ == '__main__':
    mqttc = paho.Client()

    mqttc.on_message = on_message
    mqttc.connect("test.mosquitto.org", 1883, 60)
    mqttc.subscribe("my/topic/pepper", 0)

    mqttc.loop_forever()

Operation check

Run Subscriber

Run on your PC and wait to receive a message for the topic.

$ python sub.py

Run Publisher

Run the program in Choregraphe and send a message.

Result display

The message Publisher-> Broker-> Subscriber was transmitted and displayed on the Subscriber side.

$ python sub.py
topic: my/topic/pepper, payload: Hello World from Pepper, qos: 0, retain: 0

Impressions

• I wondered if the Publisher side could use it, but I felt that it would be interesting for the Subscriber side as well.