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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=33671#action_33671 ] 

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

The existing implementations within RSMB/Mosquitto has an additional behaviour that must be considered: a client that subscribes to # does NOT get subscribed to the $SYS part of the topic space. A client must explicitly subscribe to $SYS/# to access that part of the topic space.

We should consider, as part of this issue or otherwise create a new one, whether a client that subscribes to '#' will receive messages published to a reserved topic.

My proposal, consistent with the existing behaviour (in some of the implementations), is that they should NOT.



> 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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