Re: [dnssd] A concrete example of the Punycode fallback variants for the <Domain> portion

[Andrew Sullivan <[e-mail]>]

Hi,

I'm not sure I entirely understand your message.  But. . .

On Mon, Dec 16, 2013 at 09:07:31AM -0800, Douglas Otis wrote:
> 
> 1) Hostnames should be subjected to the same canonicalization to
> establish valid UTF-8 strings prior to conversion.  Bonjour already
> supports a means to override naming conflicts often seen as a
> prefixed number value (n).  Once proper canonicalization is applied,
> users may be required to adjust the hostname if unhappy with the
> results. 

When you say "the same canonicalization", what do you mean?  The DNS
owner names that result from RFC 6763 are in Net-Unicode (RFC 5198);
this entails NFC, but not much more.  The U-label portions of any
owner name arising from IDNA2008 have more restrictions -- most
punctuation is disallowed, upper case characters are not permitted
because they're not stable under case folding and NFKC, spaces are
disallowed, and so on.  This difference is why I suggested a common
interoperable profile (see draft-sullivan-dnssd-label-miprofile-00.
Stuart had some quibbles about the recommendations in there, but in
any case the recommendations are outside our charter.  I'm supposed to
pull out the problem statement part, which I guess I could be doing
rather than writing this mail).

> 2) There are two processes normally involved.  One is discovering
> services after selecting from a list of domains, and resolving
> services after selecting from a list of hostnames.  In each case,
> both of these presentations can be done using UTF-8 (provided proper
> canonicalization is applied.  Whether the label gets converted to an
> A-Label will depend on the selection of the domain.  

If I understand the above, you're suggesting that the user will know
how to cope with the issue.  Frankly, I think that is just naïve.
Users do not have a theory of operation of IDNA vs. plain UTF-8 labels
in the DNS, and subtle inconsistencies between them are going to be at
least mystifying and at worst opportunities for bad behaviour.

Best,

A

-- 
Andrew Sullivan
[e-mail]