Unable to receive all MQTT messages in Python

Question

I am trying to send messages from one python script to another using MQTT. One script is a publisher. The second script is a subscriber. I send messages every 0.1 second.

Publisher:

client = mqtt.Client('DataReaderPub')
client.connect('127.0.0.1', 1883, 60)
print("MQTT parameters set.")

# Read from all files
count = 0
for i in range(1,51):
    payload = "Hello world" + str(count)
    client.publish(testtopic, payload, int(publisherqos))
    client.loop()
    count = count+1
    print(count, ' msg sent: ', payload)
    sleep(0.1)

Subscriber:

subclient = mqtt.Client("DynamicDetectorSub")
subclient.on_message = on_message
subclient.connect('127.0.0.1')

subclient.subscribe(testtopic, int(subscriberqos))

subclient.loop_forever()

mosquitto broker version - 3.1

mosquitto.conf has max inflight messages set to 0, persistence true.

publisher QOS = 2

subscriber QOS = 2

topic = 'test' in both scripts

When I run subscriber and publisher in the same script, the messages are sent and received as expected. But when they are in separate scripts, I do not receive all the messages and sometimes no messages. I run subscriber first and then publisher. I have tried subscriber with loop.start() and loop.stop() with waiting for few minutes.

I am unable to debug this problem. Any pointers would be great!

EDIT:

I included client.loop() after publish. -> Same output as before
When I printed out statements in 'on_connect' and 'on_disconnect', I noticed that client mqtt connection gets established and disconnects almost immediately. This happens every second. I even got this message once -

[WinError 10053] An established connection was aborted by the software in your host machine

Keep Alive = 60

Is there any other parameter I should look at?

Edit the question to include the FULL code for the publisher. Also if you have logs from the broker include those — hardillb
Also how many instances of the publisher are you running at once? — hardillb

hardillb hardillb · Accepted Answer · 2017-12-09T08:53:29

You need to call the network loop function in the publisher as well so the client actually gets some time to do the IO (And the dual handshake for the QOS2).

Add client.loop() after the call to client.publish() in the client:

import paho.mqtt.client as mqtt
import time

client = mqtt.Client('DataReaderPub')
client.connect('127.0.0.1', 1883, 60)
print("MQTT parameters set.")

# Read from all files
count = 0
for i in range(1,51):
    payload = "Hello world" + str(count)
    client.publish("test", payload, 2)
    client.loop()
    count = count+1
    print(count, ' msg sent: ', payload)
    time.sleep(0.1)

Subscriber code:

import paho.mqtt.client as mqtt

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

subclient = mqtt.Client("DynamicDetectorSub")
subclient.on_message = on_message
subclient.connect('127.0.0.1')

subclient.subscribe("test", 2)

subclient.loop_forever()

Unable to receive all MQTT messages in Python

3 Answers