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Subject: [OASIS Issue Tracker] Commented: (MQTT-11) Length of client Identifier

    [ http://tools.oasis-open.org/issues/browse/MQTT-11?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=33475#action_33475 ] 

Nick O'Leary commented on MQTT-11:

Looking at the two parts of the proposal:

"There should be no restriction on the clientId other than it MUST comprise only Unicode characters, and the length of the UTF-8 encoding MUST be less than or equal 65535."

 - this seems sensible. The 23 byte limit was, iirc, a by-product of an existing limitation of one of the early brokers to add support for MQTT. A lower limit than 65535 could be identified, which I'm ambivalent about. The encoding scheme allows up to 65535, anything lower would be an arbitrary restriction.

"The clientId MAY contain zero characters."
 - The clientId is used to identify the client to the broker. If cleansession=0 the clientId MUST NOT contain zero characters otherwise the broker cannot identify the client.
 - For cleansession=1 clients, the clientId is only useful for serviceability reasons - although that usefulness should not be underestimated.

It is a breaking change - albeit to a small subset of existing clients and brokers. It is a simple fix to remove the single "if" statement each of those existing implementations inevitable has.

> Length of client Identifier
> ---------------------------
>                 Key: MQTT-11
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-11
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>            Reporter: Andrew Banks
> The current specification says that the client Identifier must be 1 - 23 characters in length.
> Should this mean 
> 1-23 bytes when transformed to UTF-8
> 1-23 Unicode characters, counting surrogate pairs as single characters
> 1-23 Unicode characters, counting surrogate pairs as two characters 

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