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

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

    [ http://tools.oasis-open.org/issues/browse/MQTT-11?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=33473#action_33473 ] 

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

How would an increase to 255 bytes / codepoints suit? That would allow interaction with systems that want to put a FQDN in the field (DNS labels are 63 bytes, so you could get at least 3 in and most likely many, many more, and accommodate punycode), and with systems that want to interact with, say, AMQP's container-id or TLS's SNI extension. It also works well if using textual forms of things like XA transaction identifiers. It would allow for 63 codepoint long non-BMP names.

255 bytes isn't onerous for even the smallest clients to support - things like internal offset values and field sizes fit in 1 byte.

How much of a breaking change is this? It certainly makes things much more useful, and allows folks to experiment with all sorts of interesting schemes for identification (including nested identifications, eg so one could map SASL PLAIN or EXTERNAL onto the protocol).


> 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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