python paho-mqtt - Not receiving mqtt messages

Question

I am developing a python app that should receive mqtt messages. I'm using paho-mqtt library.

After setting the username/password and the callback function on_message , I subscribe to the topic and make the connection to the broker. Then I start the loop_forever().

Here is my code:

import paho.mqtt.client as mqtt

MQTT_TOPIC = "my_topic"
BROKER_ENDPOINT = "my_broker_url"
BROKER_PORT = my_port
BROKER_USERNAME = "my_username"
BROKER_PASSWORD = "my_password"

mqtt_client = mqtt.Client()

def on_message(client, userdata, message):
   print("Message Recieved from broker: " + message.payload)

def main():
    mqtt_client.username_pw_set(username=BROKER_USERNAME, password=BROKER_PASSWORD)
    mqtt_client.on_message = on_message
    mqtt_client.connect(BROKER_ENDPOINT, BROKER_PORT)
    mqtt_client.subscribe(MQTT_TOPIC)
    mqtt_client.loop_forever()

if __name__ == '__main__':
    main()

I'm testing this code with the mosquitto_pub command:

mosquitto_pub -h my_broker_url -p my_port -u my_username -P my_password -t 'my_topic' -m "Hello World"

But I cannot see any messages received by my application.

What am i doing wrong ? Thanks for helping

What does mosquitto_sub give you with the same BROKER_* and MQTT_TOPIC parameters? — Gambit Support

iAmoric iAmoric · Accepted Answer · 2019-08-19T14:27:04

I finally found the error:

def on_message(client, userdata, message):
   print("Message Recieved from broker: " + message.payload.decode())

.decode() was missing

Messages are received correctly now

python paho-mqtt - Not receiving mqtt messages

1 Answers