Unconditional punycode conversion

John C Klensin klensin at jck.com
Tue Mar 8 14:12:02 CET 2011


--On Tuesday, March 08, 2011 06:42 -0500 Andrew Sullivan
<ajs at shinkuro.com> wrote:

> On Tue, Mar 08, 2011 at 01:02:14AM +0100, Simon Josefsson
> wrote:
>> The next-to-last part of IDNA2008-lookup is section 5.5 of
>> RFC 5891:
>>    The string that has now been validated for lookup is
>>    converted to ACE form by applying the Punycode algorithm
>>    to the string and then adding the ACE prefix ("xn--").
>> Consider an IDNA2008-lookup input label of "foo".  The above
>> appear to say that this string should be punycode encoded,
>> which seems wrong.
> Sections 5.2 and 5.3 suggest that the label should be "in
> Unicode" and need to be a putative U-label.  It is unfortunate
> that the text doesn't explicitly here say that the algorithm
> already doesn't apply to NR-LDH labels, but I think that's
> correct.  So you shouldn't need to run "foo" through punycode
> because you didn't take that branch: you can tell before you
> get to the IDNA2008 lookup rules that it's an NR-LDH label, so
> it won't be processed.

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