[Solved] You wrote this code to publish a message with QoS 2: client.publish('home/lights', 'ON', qos=2) But the message is sometimes duplicated on the subscriber side. What is the likely cause? | Raspberry Pi

Raspberry Pi - MQTT for IoT

You wrote this code to publish a message with QoS 2:

client.publish('home/lights', 'ON', qos=2)

But the message is sometimes duplicated on the subscriber side. What is the likely cause?

AThe client.publish syntax is incorrect

BQoS 2 does not guarantee no duplicates

CQoS 2 is not supported by the broker

DThe subscriber is not handling duplicate messages properly

Step-by-Step Solution

Solution:

Step 1: Understand QoS 2 guarantees
QoS 2 guarantees exactly once delivery, so duplicates should not occur in transmission.
Step 2: Identify cause of duplicates
If duplicates appear, likely the subscriber application is not filtering duplicates properly.
Final Answer:
The subscriber is not handling duplicate messages properly -> Option D
Quick Check:
QoS 2 = no duplicates in network, subscriber must handle duplicates [OK]

Quick Trick: Duplicates often come from subscriber logic, not QoS 2 itself [OK]

Common Mistakes:

MISTAKES

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