There Are No Error Logs on the Containers Image

Oct 13, 2025 by thesweetdesigns.com 47 views

Introduction

MQTT-SN (MQ Telemetry Transport - Sensor Network) is a lightweight messaging protocol designed for low-power, low-bandwidth networks. It is widely used in various IoT applications, including industrial automation, smart cities, and consumer electronics. However, a critical issue has been identified in the MQTT-SN protocol, where a subscriber does not receive retained messages on reconnection, regardless of the QoS of publication or subscription, and independently of the state of the CleanSession flag.

Expected Behavior

A MQTT-SN subscriber that is disconnected should, upon reconnection, receive the last retained message sent on a topic, regardless of whether it was sent while the subscriber was or not connected. This is because every time a retained message is sent, it replaces the previous retained message in the same topic.

Actual Behavior

On reconnection, the MQTT-SN subscriber does not receive any message. This occurs for both normal (long) and predefined topic types.

To Reproduce

Install HiveMQ-Edge

To reproduce this issue, you need to install HiveMQ-Edge, a lightweight MQTT broker designed for IoT applications. You can install it using Docker:

docker pull hivemq/hivemq-edge
docker run --name hivemq-edge -d -p 1883:1883 -p 8080:8080 -p 2442:2442/udp hivemq/hivemq-edge

Start by Subscribing to a Topic with a MQTT-SN Client

Using a fixed client ID, set both CleanSession and QoS to either 0 or 1 (same result obtained for all permutations of these values). You can use the following command to subscribe to a topic with a MQTT-SN client:

./mqtt-sn-java-sub.sh -h 127.0.0.1 -p 2442 -i mqttSN-client-R -t mqttsn/sample/normal/pub/# -q 0

In Parallel, You Can Check the Behavior Subscribing to the Same Topic Using a MQTT Client

You can use the following command to subscribe to the same topic using a MQTT client:

mosquitto_sub -h 127.0.0.1 -p 1883 -i MQTT-client-R -u artemis -P artemis -t mqttsn/sample/normal/pub/#

While Subscribed to the Topics, Publish One Message in Each Topic, Both Retained, Each with a Different QoS

You can use the following commands to publish one message in each topic, both retained, each with a different QoS:

mosquitto_pub -h 127.0.0.1 -p 1883 -i MQTT-client-R -u artemis -P artemis -t mqttsn/sample/normal/pub/0 -m "hello world, im normal with qos=0" -q 0 -r
mosquitto_pub -h 127.0.0.1 -p 1883 -i MQTT-client-R -u artemis -P artemis -t mqttsn/sample/normal/pub/1 -m "hello world, im normal with qos=1" -q 1 -r

Disconnect Subscriber MQTT-SN

You can use the following command to disconnect the MQTT-SN subscriber:

stop mqtt-sn-java-sub.sh

Reconnect Subscriber MQTT-SN

You can use the following command to reconnect the MQTT-SN subscriber:

./mqtt-sn-java-sub.sh -h 127.0.0.1 -p 2442 -i mqttSN-client-R -t mqttsn/sample/normal/pub/# -q 0

Reconnect Subscriber MQTT

You can use the following command to reconnect the MQTT subscriber:

mosquitto_sub -h 127.0.0.1 -p 1883 -i MQTT-client-R -u artemis -P artemis -t mqttsn/sample/normal/pub/#

There Are No Error Logs on the Containers Image

There are no error logs on the containers image.

Details

Affected HiveMQ Edge version(s): 2024.9
Used JVM version: Internal of the container

Conclusion

Q: What is the expected behavior of a MQTT-SN subscriber when it reconnects after being disconnected?

A: The expected behavior of a MQTT-SN subscriber when it reconnects after being disconnected is to receive the last retained message sent on a topic, regardless of whether it was sent while the subscriber was or not connected.

Q: What is the actual behavior of a MQTT-SN subscriber when it reconnects after being disconnected?

A: The actual behavior of a MQTT-SN subscriber when it reconnects after being disconnected is that it does not receive any message, regardless of the QoS of publication or subscription, and independently of the state of the CleanSession flag.

Q: Why is this issue critical?

A: This issue is critical because it affects the reliability and consistency of MQTT-SN applications. If a subscriber does not receive retained messages on reconnection, it may lead to data loss and inconsistencies in the application.

Q: What are the affected HiveMQ Edge version(s)?

A: The affected HiveMQ Edge version(s) are 2024.9.

Q: What is the used JVM version?

A: The used JVM version is the internal version of the container.

Q: How can I reproduce this issue?

A: To reproduce this issue, you need to follow the steps outlined in the "To Reproduce" section of the article.

Q: What are the steps to reproduce this issue?

A: The steps to reproduce this issue are:

Install HiveMQ-Edge using Docker.
Start by subscribing to a topic with a MQTT-SN client.
In parallel, subscribe to the same topic using a MQTT client.
While subscribed to the topics, publish one message in each topic, both retained, each with a different QoS.
Disconnect the MQTT-SN subscriber.
Reconnect the MQTT-SN subscriber.
Reconnect the MQTT subscriber.

Q: What are the commands to reproduce this issue?

A: The commands to reproduce this issue are:

docker pull hivemq/hivemq-edge
docker run --name hivemq-edge -d -p 1883:1883 -p 8080:8080 -p 2442:2442/udp hivemq/hivemq-edge

./mqtt-sn-java-sub.sh -h 127.0.0.1 -p 2442 -i mqttSN-client-R -t mqttsn/sample/normal/pub/# -q 0

mosquitto_sub -h 127.0.0.1 -p 1883 -i MQTT-client-R -u artemis -P artemis -t mqttsn/sample/normal/pub/#

mosquitto_pub -h 127.0.0.1 -p 1883 -i MQTT-client-R -u artemis -P artemis -t mqttsn/sample/normal/pub/0 -m "hello world, im normal with qos=0" -q 0 -r
mosquitto_pub -h 127.0.0.1 -p 1883 -i MQTT-client-R -u artemis -P artemis -t mqttsn/sample/normal/pub/1 -m "hello world, im normal with qos=1" -q 1 -r

stop mqtt-sn-java-sub.sh

./mqtt-sn-java-sub.sh -h 127.0.0.1 -p 2442 -i mqttSN-client-R -t mqttsn/sample/normal/pub/# -q 0

mosquitto_sub -h 127.0.0.1 -p 1883 -i MQTT-client-R -u artemis -P artemis -t mqttsn/sample/normal/pub/#

Q: What are the possible solutions to this issue?

A: The possible solutions to this issue are:

Update to a newer version of HiveMQ Edge.
Use a different MQTT broker.
Modify the MQTT-SN client to handle retained messages correctly.

Q: What are the next steps to resolve this issue?

A: The next steps to resolve this issue are:

Verify that the issue is reproducible.
Investigate the root cause of the issue.
Implement a solution to the issue.
Test the solution to ensure it works correctly.