Re: [idn] length restrictions on IDN label

[Paul Hoffman / IMC <phoffman@imc.org>]

At 3:56 PM +0900 10/13/02, Soobok Lee wrote:
> [ When i read IDNA draft today, I still can't find
>   the answer from it for the following question about IDN label length.
>  If the following issue is already addressed in the draft, please 
> correct me. ]
It is indeed covered in the draft. The input to IDNA is code points, 
not encoded characters. As you point out, different encodings give 
different lengths for the same string. The only lengths that matter 
are those that are already in STD 13.

>  Many internet applications impose/assumes  the 63-octets-limit of 
> label lengths.
>  IF this assumption is violated, the label will be regarded as invalid
>  labels, and produce unpredictable errors by some implementations.
Which Internet applications are you speaking of? Which encodings are 
they using? As you pointed out, different encodings give different 
lengths. Thus, no sensible application could assume a 63-octet length 
if it deals with different encodings.

>  From implementators' point of view, more precise specificiation is needed
>  about whether IDN label/FQDN has *NEW* length restrictions in 
> various char encodings,
>  if IDNA tries to extend the character repertoires of allowable characters.
It seems likely that most implementers can understand that they must 
continue to follow the same rules that they always have for the 
length of domain names and labels.

--Paul Hoffman, Director
--Internet Mail Consortium