[Simple] Re: [Geopriv] Domain identifier in common policy

[Henning Schulzrinne <hgs at cs.columbia.edu>]

I'm probably well beyond my I18N/IDN depth here, so I agree that 
external advice is called for.

My understanding of RFC 3987, Section 5, is that these steps are 
performed in sequence, starting with the low-cost step in 5.3.1 and 
progressing to steps requiring more work if there's no match.

First, I think we can restrict ourselves to discussing URIs appearing in 
specific protocols, such as part of a SIP From URI or an XMPP URI.

There are probably two cases: Protocols that are clearly specified as 
using IRIs already (XMPP, say) and those that require discussion (SIP, 
say). [Discussion is required for SIP since SIP itself allows UTF-8 and 
RFC 3987 Section 6.3 alludes to the fact that most schemes do not have 
to be upgraded to support IRIs.]

I'll stick to the IRI case. If the IRI shows up in the protocol request, 
the steps in 5.3.1 would be executed until either a match occurred or 
the process falls off the ladder mentioned in the spec. Clearly, some of 
the comparison steps do not apply since they concern the port number or 
path components of the comparison.

From my reading of 3987, the punycode version would be compared as well 
during the ladder, presumably by converting the IDN to punycode. (I 
suspect that the conversion from UTF-8 to punycode is unique, while I 
suspect that this is not true in the other direction. In other words, 
multiple UTF-8 strings could generate the same punycode.)

This is all a bit messier than ASCII comparison, but I don't think we 
want users to edit punycode into their XML rule files.

Henning



> At the very least, common-policy ought to point out which comparison  is 
> being done.  I would assume that since these are being used as  
> identifiers, that section 5.3.1 is the section that is relevant here.
>
> And it might be that I'm just not smart enough to understand  something 
> as trivial as internationalized character comparison, but  what happens 
> with punycode encoded domain names?  As the example from  that RFC: if I 
> receive it as domain="xn--99zt52a", do I convert it to  
> domain="納豆" for the comparison?  As the RFC states:
>
>    Implementations with scheme-specific knowledge MAY convert
>    punycode-encoded domain name labels to the corresponding characters
>    by using the ToUnicode procedure.
>
> Again, I'm not an expert, but shouldn't something specify what is to  
> happen here for doing this identity comparison?
>
> -andy

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