Re: [xmpp] [Technical Errata Reported] RFC7622 (5769)

[Florian Zeitz <[e-mail]>]

Am 02.07.19 um 09:25 schrieb Florian Schmaus:
>> c) I don't think we want A-Labels. It's just going to cause confusion -
>> is 商业.中国 the same as xn--vhqr8o.xn--fiqs8s? They always look up the
>> same in DNS, after all, by definition. I can't see why we'd think
>> allowing them wasn't going to cause problems.
> 
> I can not remember that I ever ran into problems caused by A-labels in
> domainparts. And hence I assume that the cost of explicitly disallowing
> them isn't worth the gain. If we can, we should not make the PRECIS
> operations on the domainpart to require anything besides the
> "inspection" of every code point, with as less as possible context
> around the inspected code point involved.
> 
> Note that instead of forbidding A-labels / ACE in domainparts, RFC7622
> currently states in § 5.
> 
>   XMPP applications MUST support IDNA2008 for domainparts
> 
> which I interpret as "use U-labels of your DNS name in the domainpart
> (if applicable)".
> 
> - Florian
> 

While I have not personally experienced problems there definitely were
reports of people struggling with using A-labels during an XMPP summit
in Brussels. In particular they were struggling with using U-labels in
some and A-labels in other places. Many servers do not perform any
normalization in this regard when processing JID-slots. This caused
problems when e.g. the server configuration contained A-labels, but the
client configuration was done with U-labels, or vice versa.

The intend of 7622 (in particular Section 3.2.1) as I recall it was that
A-labels would generally be valid in JIDs. However, software would be
required to process (user) input containing A-labels so that any
JID-slots would only contain U-labels on the wire.