Final Sigma (was: RE: Esszett, Final Sigma, ZWJ and ZWNJ)

[John C Klensin]

--On Thursday, February 26, 2009 22:03 -0800 Erik van der Poel
<erikv at google.com> wrote:

> Just an afterthought, but if it really is impossible to add a
> new field to DNS, one might imagine a new HTTP response header
> that contains the hint. Of course, one would have to come up
> with other ideas for protocols other than HTTP, but I hope you
> get the gist.

I should let one of the DNS experts who follow the list respond
to this, but...

Nothing is impossible, but this comes close.

It is far more complex than this because of rules about caching,
additional information, and RR set integrity, but looking data
up separately for two separate RRs (if that is what you mean by
"field" causes the DNS overhead for IDNs to double (probably not
acceptable) and introduces race conditions and vulnerabilities
to attack (certainly not acceptable if we care anything about
conditions).

And making a special rule for HTTP and coming up with different
ideas for other protocols would, in essence, limit IDN
applicability to a small list of protocols (probably two) and
make implementation a nightmare.   On the other hand, if we
wanted to change this protocol into IDNHAN (IDNs for HTTP and
HTML), I can think of far easier ways to provide support for
that than to mess with the complexity of IDNA (either version). 

> Or perhaps even a small file that contains the hint, and that
> can be cached, similar to favicon.ico. I.e. instead of:
> 
> http://xo--qxan.gr/favicon.ico
> 
> we might have:
> 
> http://xo--qxan.gr/idndisplay.txt

See comment about solutions limited to HTTP above and note that
we've already got language-associated headers that could easily
be expanded.

best, 
    john