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Subject: [OASIS Issue Tracker] Commented: (MQTT-19) How Retained publications are deleted.

    [ http://tools.oasis-open.org/issues/browse/MQTT-19?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=33581#action_33581 ] 

Nick O'Leary commented on MQTT-19:

Just to add some historical perspective on this.

Until 3.1, the spec said nothing about deleting retained messages. Implementations, such as Message Broker and MicroBroker had to provide an administrative API to do this out-of-band. This is a problem as it meant applications that relied on deleting retained messages were not portable between broker implementations - they had to use broker specific apis.

RSMB added this capability around the time 3.1 was being put together and it was decided to add the description of the behaviour to the spec so that new implementations would not have to come up with their own new scheme for handling it.

The reason most (non-IBM) brokers implement this behaviour is that they have only know the 3.1 version of the spec where the behaviour is described.

In terms of whether the zero-length payload should be sent to the subscribers; RSMB (and I believe mosquitto) do send the zero-length payload to the subscribers.

In terms of this specific JIRA item, I'm not clear what it's asking. The proposal suggests removing this capability altogether (which I don't support), but the description asks if the payload should be sent to the subscribers (a clarification I do support).

> How Retained publications are deleted.
> --------------------------------------
>                 Key: MQTT-19
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-19
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>            Reporter: Andrew Banks
> There specification suggests that a retained message published with a zero byte payload can be used to cause a retained message to be deleted by the server, although it
> leaves this behavior as optional. It is not clear whether the zero length message should be sent to subscribers.

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