[OASIS Issue Tracker] (MQTT-324) Consolidate list of optional server capabilities and review how they are signaled to the client

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

    [ https://issues.oasis-open.org/browse/MQTT-324?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=64650#comment-64650 ] 

Shawn McAllister commented on MQTT-324:
---------------------------------------

What i suggest we do as the next step is:
a) List the major features that are optional (in progress with other comments and I will provide mine later). Not fields, packets but major capabilities of the protocol that we agree is optional for implementations to support
b) Explain how with the current draft a client "discovers" that this feature is not supported - eg:
      - Looks at a field in ConnAck
      - Receives an error on a PUBLISH request
      - Connection is closed with an error

(a) allows us clarity in the specification & with what client implementers and MQTT apps can expect to potentially not be supported by their MQTT broker/service

(b) gives us a view of whether we are currently "notifying" clients in a convenient / consistent manner which may or may not cause us to make changes to the current draft.

> Consolidate list of optional server capabilities and review how they are signaled to the client
> -----------------------------------------------------------------------------------------------
>
>                 Key: MQTT-324
>                 URL: https://issues.oasis-open.org/browse/MQTT-324
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Task
>          Components: core
>    Affects Versions: 5
>            Reporter: Shawn McAllister
>            Assignee: Rahul Gupta
>
> This jira is raised as a result of a decision from the Nov 17 TC:
> The action is to perform the following analysis to then determine if there should be technical changes to the specification::
> - create a consolidated list of optional server capabilities (eg. support for Retain, wildcard subscriptions, QoS2, subscription identifiers, etc)
> - document the current method by which a client learns of these capabilities for a given connection.
> - determine if the manner in which the client learns of these is adequate or should be changed to be more uniform, consistent, simple
> The intent is to ensure we do not have what appear to be randomly different ways of notifying the client of what is and is not supported for a given connection.
> Depending on the outcome of this analysis, normative or non-normative sections may be added to the specification



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