Reading subscribed MQTT messages after reconnect

Question

I am trying to read messages on a MQTT server. In some cases, the connection is unstable and requires to reconnect. But after reconnect, I am not able to receive any message from the topic that I previously subscribed to. I am using paho's python package to handle MQTT connection. Here is some code I am using

TopicName='some/topic/name'

class Counter:
    def __init__(self, mqttClient):
        self.messages_recieved = 0
        self.mqttClient = mqttClient
        self.mqttClient.subscribe(TopicName)
        self.mqttClient.on_message = self.on_message
        self.mqttClient.on_disconnect = self.on_disconnect
        self.mqttClient.loop_start()

    def on_message(self, client, userdata, message):
        self.messages_received += 1

    def on_disconnect(self, client, userdata, rc):
        if rc != 0:
            print("Trying to reconnect")
            while not self.mqttClient.is_connected():
                try:
                    self.mqttClient.reconnect()
                except OSError:
                    pass

If my internet goes down, I am no longer able to receive messages. I have tried to subscribe again to the topic, also I have tried to call loop_start in the on_disconnect method, neither of those worked. Any solution would be helpful. Also to point out messages are being sent, I can see them in the browser on MQTT wall

self.mqttClient.subscribe(TopicName) will default to QOS 0 and the spec does not require that brokers retain messages at this QOS level. Try QOS 1/2 (e.g. subscribe(TopicName, qos=1)) . — Brits

hardillb hardillb · Accepted Answer · 2020-12-03T08:37:51

You have not shown where you are calling connect, but the usual safe pattern is to put the calls to subscribe() in the on_connect() callback attached to the client.

This means that calls to subscribe will

Always wait until the connection has completed
Get called again automatically when a reconnect had happend

Reading subscribed MQTT messages after reconnect

2 Answers