[OASIS Issue Tracker] (MQTT-256) Message Format indication and message metadata in general.

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

    [ https://issues.oasis-open.org/browse/MQTT-256?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=62914#comment-62914 ] 

Stefan Vaillant commented on MQTT-256:
--------------------------------------

Agree to item 2 and 3 from Ken.
In addition, my proposal is to remove the complete sentence including " A server MUST send the Payload Format Indicator unaltered to all subscribers receiving the publication":
I understand the sentence in such a way that it goes beyond the pure MQTT protocol (one client - one server), but specifies a behaviour of a broker which is IMHO implementation dependent., i.e. out of scope of a protocol specification. Why shouldn't a broker do modifications of metadata?

> Message Format indication and message metadata in general.
> ----------------------------------------------------------
>
>                 Key: MQTT-256
>                 URL: https://issues.oasis-open.org/browse/MQTT-256
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Bug
>          Components: futures
>    Affects Versions: 5
>            Reporter: Peter Niblett
>            Priority: Critical
>
> MQTT 3.1.1 does not provide an architected way of indicating the format of the payload that is passed in a PUBLISH packet. We need to avoid the risk of spec or data bloat, and I'm not advocating adding a complicated header structure that passes schemas, messageType indicators, MIME type strings or the like, but at the moment there is no standard way for a receiver even to be able to tell whether the payload is binary or string. 
> There are three ways that this can be dealt with today:
> 1. The Receiver already knows. It's implementing some bigger standard or program design which has dictated the encoding format (e.g. someone decides that all messages will be JSON)
> 2. There is an indicator embedded somewhere in the Topic name (The Topic name is  the only header we have in MQTT 3.1.1). There isn't a standard convention for this, so topic space designers have to choose their own way of doing it.
> 3. The Receiver assumes one format and has a go parsing it. If that doesn't look right it tries another



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