[OASIS Issue Tracker] (MQTT-217) Deliver implementation guidance around overlapping subscriptions

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    [ https://issues.oasis-open.org/browse/MQTT-217?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=63907#comment-63907 ] 

Ken Borgendale commented on MQTT-217:
-------------------------------------

Overlapping subscriptions are commonly client application errors and they did not intend this function.  One way to deal with that is to add a return code value to Subscribe to indicate that the subscription overlaps an existing subscription.  Although we would return this as a non-error, the client might want to treat it as a error.

If we think the multiplex case is real, then we should add the subscription identifier in the publish.  This would save the client from having to run its own subscription matching logic to route such messages.  I would note that the multiplex case is a bit broken by the fact that exactly matching subscriptions replace each other.

For servers that keep the topic tree information separate from the session state, doing #4 is no easier than doing #2.  In reality the extra logic to implement this functionality would only need to be done in the case of overlapping subscriptions, so if the client does not use overlapping there is no extra overhead.

> Deliver implementation guidance around overlapping subscriptions
> ----------------------------------------------------------------
>
>                 Key: MQTT-217
>                 URL: https://issues.oasis-open.org/browse/MQTT-217
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: futures
>    Affects Versions: 5
>            Reporter: Richard Coppen
>            Assignee: Peter Niblett
>            Priority: Minor
>
> Following on from David Kemper's mqtt-comment on CSPRD02 the TC agreed to open this Jira to deliver implementation guidance around overlapping subscriptions.



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