[OASIS Issue Tracker] Commented: (MQTT-76) Should "+" be allowed at the beginning of the topic filter in a subscription?

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    [ http://tools.oasis-open.org/issues/browse/MQTT-76?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=34497#action_34497 ] 

Peter Niblett commented on MQTT-76:
-----------------------------------

If we are being picky about words, then the phrase "It MUST be the only character between two topic level separators" would seem to preclude  topics like /a/  which is clearly not the case.  How about the following?

4.5.1.3 Single level wildcard
The plus sign ('+' 0x2B) is a wildcard character that matches only one topic level.

The single-level wildcard can be used at any level in the topic filter, including first and last levels. Where it is used it MUST occupy an entire level of the filter. Therefore  +,. finance/+  and  finance/+/ibm are all valid but finance+ is not valid.  It can be used at more than one level in the topic filter, e.g. +/+/ibm and can be used in conjunction with the multilevel wildcard, e.g. +/ibm/#

> Should "+" be allowed at the beginning of the topic filter in a subscription?
> -----------------------------------------------------------------------------
>
>                 Key: MQTT-76
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-76
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>            Reporter: Andrew Banks
>
> Draft09 says 
> 4.5.1.3 Single level wildcard
> The plus sign ('+' 0x2B) is a wildcard character that matches only one topic level. 
> The single-level wildcard can be used at any level in the topic filter. It can be used in conjunction with the multilevel wildcard. 
> It MUST be the only character between two topic level separators, or the last level, or on its own. 
> The input Specification says:
> The single-level wildcard can be used at any level in the topic tree, and in
> conjunction with the multilevel wildcard. It must be used next to the topic level
> separator, except when it is specified on its own. Therefore, + and finance/+ are
> both valid, but finance+ is not valid. The single-level wildcard can be used at the
> end of the topic tree or within the topic tree. For example, finance/+ and
> finance/+/ibm are both valid.
> Apparently the intent of the input specification was to mean "either end of the topic tree" ie at the beginning or the end, 
> hence +/finance would be a valid topic filter.

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