[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=33398#action_33398 ] 

Raphael Cohen commented on MQTT-11:
-----------------------------------

As MQTT is a wire protocol, it's nice to let people know what maximum size buffers they need to allocate to decode things. So I'd go for 1-23 bytes. If using UTF-8 to encode this field, then that's quite a small number if it consists only of non-BMP code points - exactly 5 code points. But non-BMP is as rare as hen's teeth. It's a pity we can't make this field bigger, because there are all sorts of useful things that could be used (eg GUIDs and FQDN of the connecting client + an instance on that client as an identifier, that sort of thing).

There's also an argument to be made that this isn't a UTF-8 field but simply bytes (thereby allowing unsigned longs, timestamps since 1970 and the GUIDs above) but that would be a breaking change.

> 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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