[OASIS Issue Tracker] (MQTT-328) WD9: Inconsistencies/Overlaps in Return Codes

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    [ https://issues.oasis-open.org/browse/MQTT-328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=64751#comment-64751 ] 

Ken Borgendale commented on MQTT-328:
-------------------------------------

We have made the return codes global and any case where the same return code is used for different purposes in different packets is an error.  

In the case of 144 what is invalid is a topic name or topic filter depending on what packet we are talking about.  It makes sense to call the return code "Topic Invalid" in all cases and specify in the description that when applied to a subscribe this is really the topic filter.

Several numbers are not currently used as they were assigned and then removed.  Before MQTTv5 goes out these can be reused.  Later versions of the spec should not reuse any return code which has been removed.

> WD9: Inconsistencies/Overlaps in Return Codes
> ---------------------------------------------
>
>                 Key: MQTT-328
>                 URL: https://issues.oasis-open.org/browse/MQTT-328
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Bug
>          Components: edits
>    Affects Versions: 5, wd09
>            Reporter: Brian Raymor
>            Assignee: Ed Briggs
>             Fix For: 5, wd10
>
>
> There is no statement in the WD that Return Code values are "global" rather than being specific to a particular control packet?
> From Roger Light on mqtt-comment:
> In table 3.13 for disconnect codes, the code 139 is "server shutting
> down". In table 3.6 for pubrec return codes, the code 139 is "topic
> invalid". This looks to be a typo in table 3.6 because code 144
> already exists for "topic invalid".
> The description of the return codes is a bit inconsistent. Sticking
> with the invalid topic case, it is variously described as
> Topic invalid : The topic is invalid
> Topic Filter not valid : The topic filter is correctly formed, but is
> not allowed for this client
> Topic name or filter not valid : The topic name or filter is valid,
> but it is not accepted by this client or server.
> I see that these apply to different scenarios, but the different
> descriptions are confusing. Should I take "the topic is invalid" to
> mean that it is not correctly formed? What is the difference between
> "is correctly formed" and "is valid"?
> I don't think descriptions of a term should just repeat the same words
> as the term itself, it doesn't clarify anything.
> I've spotted some more overlaps in return codes.
> Return code 154 is used by both pubrec and puback as "qos level not
> supported", and disconnect as "alias not supported".
> Return code 159 is used by subscribe as "subscription identifiers not
> supported" and connack as "connection rate exceeded".
> Some return codes aren't used - 141, 147, 148.



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