RabbitMQ sends MQTT messages on connect to the client without a subscription.

[Kremr]

Describe the bug

RabbitMQ sends MQTT messages on connect to the client without a subscription.

Reproduction steps

1. Connect to RabbitMQ via MQTT 3.1.1 and TLS → client_id = test123
2. Subscribe to a topic (test/#) with clean_session false and QoS 1.
3. Disconnect from RabbitMQ.
4. Connect to RabbitMQ via MQTT 3.1.1 and TLS → client_id = test-sender
5. Send 10 messages to topic test/123
6. Disconnect from Broker.
7. Now check if, in the dynamically created queue (mqtt-subscription-test123qos1 in the RabbitMQ Server), are 10 messages queued.
8. Connect to RabbitMQ via MQTT 3.1.1 and TLS → client_id = test123 without a subscription.
9. Now check the number of messages in if the dynamically created queue (mqtt-subscription-test123qos1) in RabbitMQ is 0.

...

Expected behavior

Intended behavior should be, only if the client subscribes to the topic, the messages are sent to the client.

Additional context

No response

[lukebakken]

Hello, thanks for using RabbitMQ.

Team RabbitMQ has a community support policy that specifies that, in order to receive free support, you must "provide detailed and well researched issue reports".

Please provide a client application we can clone, compile, and run to observe this behavior. By doing so, you save us time in reproducing this behavior so we can focus on analyzing it.

@ansd may be able to make sense of what is going on by reading the prose description here.

[ansd]

@lukebakken @Kremr in step 8. does the client connect with clean_session=true or clean_session=false ? One way or the other, RabbitMQ behaves correctly because if clean_session=false, the old subscriptions are intact and therefore RabbitMQ sends the messages, and if clean_session=true the old session state including messages must be discarded.