[OASIS Issue Tracker] Commented: (MQTT-74) What should happen to messages pending delivery once the client sends unsubscribe?

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    [ http://tools.oasis-open.org/issues/browse/MQTT-74?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=35192#action_35192 ] 

Raphael Cohen commented on MQTT-74:
-----------------------------------

OK, so to clarify I would:-

- change 'process' to deliver
- Add that a client that receives a message for a topic to which it is not currently subscribed MAY choose to discard the message
=> there's an impact here on QoS 1/2 handling for naive clients, but so be it

Add some non-normative text explaining the rationale of the final sentence, to make it clear that this might be for a few messages / only for the immediate future (ie not forever).

> What should happen to messages pending delivery once the client sends unsubscribe?
> ----------------------------------------------------------------------------------
>
>                 Key: MQTT-74
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-74
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 3.1.1
>            Reporter: Richard Coppen
>             Fix For: 3.1.1
>
>
> A client might be too busy to process any more work, so sends UNSUBSCRIBE to turn the flow off. 
> Alternatively, the client may be unaware that a backlog of messages exists and sends UNSUBSCRIBE. 
> There are at lesat three possible options:
> 1. The server delays sending the UNSUBACK until the backlog is cleared
> 2. Send the UNSUBACK and then send the messages
> 3. Send the UNSUBACK and then purge the messages 
> The client's last defense should it not want the messages is to disconnect and reconnect with cleanSession set to (1)

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