[OASIS Issue Tracker] (MQTT-563) Client Id format

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

    [ https://issues.oasis-open.org/browse/MQTT-563?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=82209#comment-82209 ] 

Simon Johnson commented on MQTT-563:
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So MQTT 5.0 suggest the broker MUST support 1-23 clientId space and CAN optionally support anything higher (interestingly this is unbounded in the specification even though in practise there is an upper limit according to the packet specification).

The Assigned Client Identifier in the CONNACK imposes no size requirements. I think it is reasonable to name the upper limits in the specification on the CONNECT (65521) for the client selected id; whilst adding a non-normative comment to suggest the practical size bounds are within a single non-variable length packet (which is 243 bytes). I have added this section along with a description in the CONNACK section which adds non-normative advice that the gateway should attempt where possible to follow this example (ie. restrict to a single fixed length packet size).

There is then the issue of where the broker supplies an Assigned Client Identifier that is larger than a single packet allows; in this case I have added a NORMATIVE statement that the gateway should provide a mapping of the broker side client identifiers to gateway side client Identifiers that have been generated at a more practical length.

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> Client Id format 
> -----------------
>
>                 Key: MQTT-563
>                 URL: https://issues.oasis-open.org/browse/MQTT-563
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Task
>          Components: MQTT-SN
>            Reporter: Simon Johnson [X]
>            Assignee: Allan Stockdill-Mander 
>            Priority: Major
>
> It was discussed that aligning the clientId format (23 UTF-8 bytes) to MQTT 5.0 was potentially dangerous in SN given the complexity of validation etc. However given ASCII is a subset of UTF-8 it is upon the broker & client implementation to enforce a more restrictive set if required. A note in implementation is required for this item.



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