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


     [ http://tools.oasis-open.org/issues/browse/MQTT-16?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Richard Coppen updated MQTT-16:
-------------------------------

    Proposal: 
Reserve $ in the spec and point to an external OASIS MQTT TC owned reference to provide guidance on the topic space. The referenced normative document will reserve $SYS for private use. 

This has an impact for subscribe operations. There are at least two options:
(1) If a topic starts with a $, then it's effectively a different topic tree and subscriptions to # do not include $. 
(2) Add non-normative content to subscribe suggesting that a suitable authorization policy may apply to the $ component of the topic tree

  was:
1. Applications MUST not define any topic names that start with a leading $ character
2. MQTT server implementations MAY define topic names that start with the the string "$SYS/" 
3. MQTT server implementations MUST NOT define any other topics whose names start with a leading $ character.

non-normative
Examples: 
1. A client that publishes or subscribes to $foo  would be non-compliant
2. A server that defined and accepted subscriptions to $SYS/monitor/clients would be compliant
3. A server that defined and accepted publications to $SYS/control/setMaxClients would be compliant
4. A server that accepted subscriptions or publications on $foo would be non-compliant.
5. A topic name of stock/$price is compliant


Original Proposal (updated on scrub call 22.08.2013)

1. Applications MUST not define any topic names that start with a leading $ character
2. MQTT server implementations MAY define topic names that start with the the string "$SYS/" 
3. MQTT server implementations MUST NOT define any other topics whose names start with a leading $ character.

non-normative
Examples: 
1. A client that publishes or subscribes to $foo  would be non-compliant
2. A server that defined and accepted subscriptions to $SYS/monitor/clients would be compliant
3. A server that defined and accepted publications to $SYS/control/setMaxClients would be compliant
4. A server that accepted subscriptions or publications on $foo would be non-compliant.
5. A topic name of stock/$price is compliant

> 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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