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Subject: [OASIS Issue Tracker] Commented: (MQTT-16) Reserve $SYS topic name


    [ http://tools.oasis-open.org/issues/browse/MQTT-16?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=34501#action_34501 ] 

Nick O'Leary commented on MQTT-16:
----------------------------------

Following today's TC call, it was agreed to remove mention of SYS from the normative part of the proposal to avoid any question of us attempting to prescribe topic spaces as per the charter. The 'MUSTs' have been downgraded to 'SHOULD NOTs' for the same reason.

---------- 
Topics beginning with $ 
  1. Applications SHOULD NOT define any topic names that start with a leading $ character
  2. MQTT server implementations MAY define topic names that start with a leading $ character

  non-normative: 
    $SYS/ has been widely adopted as a prefix to topics that contain server-specific information or control APIs.

Subscription handling 
  1. A topic filter that starts with a wildcard character (# or +) does not match topic names that begin with a $ character 

  non-normative examples: 
  1. A subscription to # will not receive any messages published to a topic beginning with a $ 
  2. A subscription to +/monitor/clients will not receive any messages published to $SYS/monitor/clients 
  3. A subscription to $SYS/# will receive messages published to topics beginning with $SYS/ 
  4. A subscription to $SYS/monitor/+ will receive messages published to $SYS/monitor/clients 
  5. For a client to receive messages from topics that begin with $SYS/ and from topics that don't begin with a $, it must subscribe to both # and $SYS/# 
----------

> Reserve $SYS topic name
> -----------------------
>
>                 Key: MQTT-16
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-16
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 3.1.1
>            Reporter: David Locke
>             Fix For: 3.1.1
>
>
> Many MQTT implementations today use $SYS as the head of a topic string for use in administration  (configuration, operations, monitoring).   
> Can the $SYS or a similar topic name be reserved for future use ?   As $SYS is already used by a number of servers using a different top level topic would avoid conflicts. 
> Would be good to collect ideas for a $SYS topic space.  These ideas could initially go into a non-normative document but with potential for inclusion in a future spec.  The intent being servers can implement  some aspects of administration and monitoring in a consistent way
> Some examples:
> - Admin action like "unretain" a retained topic   e.g. $SYS/topic/unretain    (payload is the topic to unretain)
> - Client wishes to query what subscriptions it has made    e.g. $SYS/client/getsubs  (topic is clientid)
> - Client wishes to query how many messages are queued up awaiting delivery e.g. $SYS/client/getNoQueuedMessages  
> - Query the  state of the MQTT server e.g. $SYS/server/getStatus 
> These examples should not be taken literally they are purely to show the type of things a $SYS topic space could be used for.

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