why isnt the mqtt client subscriber displaying topic?

Question

I am new to MQTT. I have mosquitto and paho mqtt library installed in two computers. The computers are connected by a router in local network. I run publisher and mosquitto in one computer and subscriber in another.

# publisher.py code
# ===================================================================
#!/usr/local/bin/python3

import paho.mqtt.publish as publish

publish.single("paho/single", payload="boo", hostname="192.168.0.154")
# ===================================================================

And subscriber code

# subscriber.py

# =================================================================== 
#!/usr/local/bin/python3

import paho.mqtt.client as mqtt

mqttc = mqtt.Client("100")
mqttc.connect("192.168.0.154", 1883, 60)
mqttc.subscribe("paho/single", 0)

mqttc.loop_forever()
# ===================================================================

I can see both subscriber and publisher could be connected to mosquitto when they are run. But I cannot see topic being published displayed in subscriber terminal. Please help.

hardillb hardillb · Accepted Answer · 2015-12-10T13:15:09

You have subscribed to the topic but you haven't told the client code what to do with the message when it arrives.

The following update should print message and topic

# subscriber.py

# =================================================================== 
#!/usr/local/bin/python3

import paho.mqtt.client as mqtt

def on_message(client, userdata, msg):
  print(msg.topic+" "+str(msg.payload))


mqttc = mqtt.Client("100")
mqttc.on_message = on_message
mqttc.connect("192.168.0.154", 1883, 60)
mqttc.subscribe("paho/single", 0)

mqttc.loop_forever()
# ===================================================================

why isnt the mqtt client subscriber displaying topic?

1 Answers