[OASIS Issue Tracker] (MQTT-504) No way to tell when a retained message was set

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

    [ https://issues.oasis-open.org/browse/MQTT-504?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=67447#comment-67447 ] 

Ken Borgendale commented on MQTT-504:
-------------------------------------

I see three possible dispositions for this:

1. Do nothing

2. Say that the server is allowed to add a user property to a forwarded message.  We should need to talk about the server being allowed to modify such a property when forwarding.

3. Define a property on the PUBLISH which represents a timestamp, and say the the server is allowed to add or modify this property when the message is forwarded.

If we go with solution 3, we need to further define the type and semantics of the timestamp.  I will throw out three suggestions for this:

1. Define an Eight byte integer as the type, and the value as milliseconds into the Unix epoch (1970-01-01T00Z ignoring leap seconds).  This is the Java tiemstamp.  Alternately,  a resolution of microseconds or nanoseconds could be used.

2. Define the value as a string in ISO8601 format and require that it start with the year.  The resolution could be arbitrary as the decimal places after the seconds.  The time zone could be specified or default to UTC.

3. Two Four byte integers, the first representing seconds into the Unix epoch, and the second nanoseconts beyond that second.  This is pure Unix time format.

> No way to tell when a retained message was set 
> -----------------------------------------------
>
>                 Key: MQTT-504
>                 URL: https://issues.oasis-open.org/browse/MQTT-504
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: New Feature
>          Components: core
>    Affects Versions: 5, CSD01
>            Reporter: Ian Craggs
>            Priority: Minor
>
> I implemented this feature in a broker specific way myself some years back, so I know it's useful.  It was raised on Twitter to me here: https://twitter.com/MichMich/status/903283262415568898
> Maybe expiry would be enough for some use cases.
> We could allow the server to set a property with the received timestamp on the retained message.



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