Re: [precis] RFC 8264 / 8265 Order of rules

Peter Saint-Andre <stpeter@mozilla.com> Wed, 06 December 2017 22:07 UTC

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To: William Fisher <william.w.fisher@gmail.com>, Christian Schudt <christian.schudt@gmx.de>
Cc: precis@ietf.org
References: <0207F020-32D2-4181-A020-3143BD8E88FE@gmx.de> <CAHVjMKFYO=9twJeJkM7YCv1tT6Fv=4Psw482EPS43sedMyeiSQ@mail.gmail.com>
From: Peter Saint-Andre <stpeter@mozilla.com>
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Date: Wed, 6 Dec 2017 15:07:39 -0700
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Subject: Re: [precis] RFC 8264 / 8265 Order of rules
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On 12/4/17 8:58 PM, William Fisher wrote:
> On Mon, Dec 4, 2017 at 4:06 PM, Christian Schudt
> <christian.schudt@gmx.de> wrote:
>> If a user wishes to create a username with U+212B (Angstrom sign), should an application reject it (because it’s disallowed) or allow it, because enforcement converts the character to a valid code point first?
> 
> I implemented enforcement based on the rules in RFC 8264 section 7.
> The behavioral rules (IdentifierClass) are applied last.
> 
>>>> from precis_i18n import get_profile
>>>> ic = get_profile('IdentifierClass')
>>>> ic.enforce('\u212b')
> Traceback (most recent call last):
>  ...
> UnicodeEncodeError: 'IdentifierClass' codec can't encode character
> '\u212b' in position 0: DISALLOWED/has_compat
>>>> un = get_profile('UsernameCasePreserved')
>>>> un.enforce('\u212b')
> 'Å'
> 
> See also:
>   https://www.ietf.org/mail-archive/web/precis/current/msg01225.html
> 
> You're right that the references to preparation in RFC 8265 (sections
> 3.3.2, 3.4.2) are at odds with RFC 8264 and the mailing list.

Sigh.

I'm sorry that we failed to make things clear and consistent.

I agree with Bill that implementations should follow the order of rules
in Section 7 of RFC 8264.

Let me think about how we can clarify things. That might involve filing
an erratum against RFC 8265.

Peter