[OASIS Issue Tracker] (MQTT-285) Subscribe options for retained messages

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

    [ https://issues.oasis-open.org/browse/MQTT-285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=62919#comment-62919 ] 

Jonathan Levell commented on MQTT-285:
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For a bridge application, the bridge would ideally be able to remake its durable subscriptions on each connect (to ensure that the server has not lost the state).

Retained messages are a problem because they'll be resent each time but the NoSendRetain doesn't fix the issue - the bridge would want to receive retained messages if the subscription is being made for the first time but not if it is being remade.

Would it not be better to have a flag that said NoRetainOnExistingSub on subscribe so the retained messages are sent if it a new subscription? 

> Subscribe options for retained messages
> ---------------------------------------
>
>                 Key: MQTT-285
>                 URL: https://issues.oasis-open.org/browse/MQTT-285
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: New Feature
>          Components: futures
>    Affects Versions: 5
>            Reporter: Ken Borgendale
>            Assignee: Ken Borgendale
>
> This issue came up when reviewing MQTT-235 (nolocal) as it affects the bridge use case along with others.
> The current setting of the retain flag on PUBLISH and the handling of retained messages on SUBSCRIBE is normally correct when the client really is a subscribing client, it is not correct behavior when the client is going to forward the message on in a bridge or filter use case.
> There are two issues here
> 1. In some case the subscriber does not want to get any messages which are retained at the time of the subscription.
> 2. If the subscriber is going to re-publish the message it needs to know if the messages was published with the retain flag, rather than that it came from a retained source



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