Django stops recieving/sending MQTT messages after raising any exception

Question

I am trying to implement Paho MQTT on Django but Django stops receiving/sending MQTT messages after raising any kind of exception.

I am using Paho MQTT client 1.3.0 along with Django 1.10.8, Python 3.6.2

Here are my MQTT settings:

mqtt.py

from django.conf import settings

import paho.mqtt.client as mqtt

SUB_TOPICS = ("device/vlt", "device/auth", "device/cfg", "device/hlt", "device/etracker", "device/pi")
RECONNECT_DELAY_SECS = 2


# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code " + str(rc))

    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    for topic in SUB_TOPICS:
        client.subscribe(topic, qos=0)


# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(msg.topic + " " + str(msg.qos) + " " + str(msg.payload))


def on_publish(mosq, obj, mid):
    print("mid: " + str(mid))


def on_subscribe(mosq, obj, mid, granted_qos):
    print("Subscribed: " + str(mid) + " " + str(granted_qos))


def on_log(mosq, obj, level, string):
    print(string)


def on_disconnect(client, userdata, rc):
    client.loop_stop(force=False)
    if rc != 0:
        print("Unexpected disconnection: rc:" + str(rc))
    else:
        print("Disconnected: rc:" + str(rc))


client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message
client.on_publish = on_publish
client.on_subscribe = on_subscribe
client.on_disconnect = on_disconnect

client.username_pw_set(username, password)
client.connect(<settings>)

apps.py

class CoreConfig(AppConfig):
    name = 'untitled.core'
    verbose_name = "Core"

    def ready(self):
        from . import mqtt
        mqtt.client.loop_start()

Code inspiration: Paho MQTT client connection reliability (reconnect on disconnection)

Answer 1

My team happen to face this problem as well and we solve it by creating a CustomMqttClient that inherit from mqtt.Client and override the _handle_on_message(self, message) function.

class CustomMqttClient(mqtt.Client):

    def _handle_on_message(self, message):
        try:
            super(ChatqMqttClient, self)._handle_on_message(message)
        except Exception as e:
            error = {"exception": str(e.__class__.__name__), "message": str(e)}
            self.publish("device/exception", json.dumps(error))

Then instead of using mqtt.Client(), we do this:

client = CustomMqttClient()
client.on_connect = on_connect
client.on_message = on_message

This catches all exception and actually publish it to our topic device/exception. Our other services can actually subscribe to it and actually get some useful information out of it.