Minimal demonstration of shared subscriptions issue

Effects

• [✓] Bug exists Release Version 1.1.1 ( Master Branch)
• [?] Bug exists in Snapshot Version 1.1.2-SNAPSHOT (Develop Branch)

HEAD of develop branch appears to be broken wrt. my test program suggesting a regression wrt. 1.1.x API current exists, which may or may not be related.

Issue

Callbacks don't get called when subscribing to shared subscriptions, e.g. $share/group/topic, using the subscribe(String topicFilter, int qos, IMqttMessageListener messageListener)API (code).

However, shared subscriptions work as expected when using the setCallback(...) (code) API before invoking subscribe(String topicFilter, int qos).

This issue impacts downstream wrappers such as the Clojure library machine-head, which is what led me here...

Instructions

• Run a local MQTT broker localhost:1883 that supports shared subscriptions e.g. HiveMQ

In the root of this project:

• make build
• make run

Expected

Connecting to broker: tcp://localhost:1883
Published: 1
Received on [my/topic]: [1] for client: [subcriber1]
Received on [my/topic]: [2] for client: [subcriber2]
Published: 2
Published: 3
Received on [my/topic]: [3] for client: [subcriber1]
Published: 4
Received on [my/topic]: [4] for client: [subcriber2]
Published: 5
Received on [my/topic]: [5] for client: [subcriber1]
Published: 6
Received on [my/topic]: [6] for client: [subcriber2]
Published: 7
Received on [my/topic]: [7] for client: [subcriber1]
Published: 8
Received on [my/topic]: [8] for client: [subcriber2]
Disconnected
All done.

It's clear that the messages are load-balanced in a round-robin fashion across the two subscribers.

8 messages received in total.

For completeness, compare with normal subscription behaviour:

Connecting to broker: tcp://localhost:1883
Received on [my/topic]: [1] for client: [subcriber2]
Published: 1
Received on [my/topic]: [1] for client: [subcriber1]
Published: 2
Received on [my/topic]: [2] for client: [subcriber1]
Received on [my/topic]: [2] for client: [subcriber2]
Published: 3
Received on [my/topic]: [3] for client: [subcriber1]
Received on [my/topic]: [3] for client: [subcriber2]
Published: 4
Received on [my/topic]: [4] for client: [subcriber1]
Received on [my/topic]: [4] for client: [subcriber2]
Received on [my/topic]: [5] for client: [subcriber1]
Published: 5
Received on [my/topic]: [5] for client: [subcriber2]
Published: 6
Received on [my/topic]: [6] for client: [subcriber1]
Received on [my/topic]: [6] for client: [subcriber2]
Received on [my/topic]: [7] for client: [subcriber1]
Published: 7
Received on [my/topic]: [7] for client: [subcriber2]
Published: 8
Received on [my/topic]: [8] for client: [subcriber2]
Received on [my/topic]: [8] for client: [subcriber1]
Disconnected
All done.

16 messages received in total.

Received when executing BAD path

No messages arrive. Published messages are reported as unhandled.

Connecting to broker: tcp://localhost:1883
Published: 1
Published: 2
Published: 3
Published: 4
Published: 5
Published: 6
Published: 7
Published: 8
Disconnected
All done.