[tipatterson-dev]

Fixes lost subscriptions in the HiveMQ extension: after a handler module restarted, clients that were already subscribed got no more messages.

Closes #269. Part of #249. Needs #262, which is merged: this branch starts from it. The PR targets master.

Problem

When a module that registers an MQTT handler restarts while the MQTT Server runs, HiveMQ and OshExtension keep the client subscriptions. The new handler never got onSubscribe for them, so it published nothing to those clients. A new SUBSCRIBE to the same topic was accepted but did not help, because the topic was already recorded. The client had to unsubscribe and subscribe again, or reconnect. This affects every module that registers a handler.

Fix

• OshExtension keeps the user of each client subscription.
• registerHandler calls onSubscribe for the existing subscriptions under the prefix of the new handler.
• If onSubscribe fails (for example, the resource is gone or the user lost the permission), the subscription is removed from the client in HiveMQ.
• Module version 0.1.1 to 0.1.2.

Testing

• New tests in TestOshExtension:
  • a restarted handler gets the existing subscriptions with the correct users, and a new SUBSCRIBE to the same topic does not count the client twice
  • a subscription that the handler refuses is removed from the client
  • only the topics of the new handler are restored

Merge order

1. mqtt-hivemq: re-check permissions when a rejected subscribe is retried #262 re-check permissions on a retried subscribe (merged)
2. This PR

[tipatterson-dev]

Closed in favor of #267. That PR contains the same fix for #269 (the same changes to OshExtension and TestOshExtension), and its wildcard check for restored subscriptions needs it. #267 now closes #269. The module version there is 0.2.0, so the 0.1.2 of this PR is not used.