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

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    [ https://issues.oasis-open.org/browse/MQTT-285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=63767#comment-63767 ] 

Jonathan Levell commented on MQTT-285:
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I like the two bits for retain options on subscribe but I think there is a usecase for knowing for a given message  BOTH whether it was published as retained AND whether the subscriber is receiving it "live":

A new bridge between a system that has a large, static collection of retained messages and a target system may want to copy the existing retained messages, but take different actions depending on whether a message was an old retained message or receiving it live and if it uses RetainAsPublished it won't be able to find out.

I don't feel very strongly about this usecase. If the general feeling is that this is not important then I don't want to hold up this JIRA issue for it.

> 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: core
>    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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