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List:       kde-devel
Subject:    Re: DNS based service discovery
From:       Thiago Macieira <thiago.macieira () kdemail ! net>
Date:       2004-10-27 23:26:54
Message-ID: 200410272027.01150.thiago.macieira () kdemail ! net
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Jakub Stachowski wrote:
>For the last month I have been working on DNS based service discovery
>(ZeroConf, Rendezvous) for KDE. You can get it from kdenonbeta/kdnssd.

I have an additional question regarding mDNS and you may be able to answer 
it:

how does it handle IDN domains? In specific, ACE-encoded ones.

Our current resolver code uses Unicode for input and will perform the 
necessary conversions to ACE. mDNS, on the other hand, specifies (quote)

   * uses UTF-8, and only UTF-8, to encode resource record names
 
and also says that mDNS should respect normal uppercase/lowercase rules.

I ask that because our current code (in KURL nonetheless) relies on the fact 
that ACE-encoded names are equivalent to their full-blown Unicode 
counterparts.

So, what happens if:
a) an ACE-encoded hostname is queried in mDNS?
(tentative answer: it's treated as if it were different from the non-encoded 
form)

b) a hostname whose case-folding, as per Nameprep (RFC 3491), matches an 
existing record?
(tentative answer: it is considered equivalent)

Examples:
1) original: Thiago-José-Macieira.local
lowercased/case folded: thiago-josé-macieira.local
ACE-encoded: xn--thiago-jos-macieira-kzb.local

the first two match in mDNS; the third matches only in DNS.

2) original:  µprocessor.local
lowercased:  µprocessor.local
case-folded: μprocessor.local (note that's a mu, not a micro)
also equivalent: Îœprocessor.local (that's also a mu)
ACE-encoded: xn--processor-u0g.local

same thing: all but the last must match in all cases; the last one only in 
DNS.

3) original: fußball.local
lowercased: fußball.local
case-folded: fussball.local
ACE-encoded: fussball.local
(the same thing would happen for Å¿s -> ss)

here everything matches, but only because the case-folding rendered it into 
ASCII
-- 
  Thiago Macieira  -  Registered Linux user #65028
   thiago (AT) macieira (DOT) info
    ICQ UIN: 1967141   PGP/GPG: 0x6EF45358; fingerprint:
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