Re: [idn] Where to do form-folding?

[James Seng <James@Seng.cc>]

Before anyone goes too far down this track, I would like to remind
everyone that IETF only concern on the data on the wire (see the big box
in the requirement I-D) and not the implementation detail.

Having said this, let me think about this and will comment something
later :)

-James Seng

Dan Oscarsson wrote:
> 
> Hi
> 
> Even if it is summer, some of you are hopefully still active. At
> least some of you going to the IETF meeting.
> 
> Here is one thing we could discuss and that could be discussed
> at the meeting.
> 
> The question is: Where should form-folding be done?
> 
> Background: With ASCII names names are compared case-insensitively.
> One way to do the comapring is to first case-fold and then binary compare.
> When we have IDNs, case-insenstivity is not enough. Instead I will call
> it form-insensitivity, which includes case-insensitivity and insensitivity
> to many other forms used in non-latin alphabets. To compare to IDNs
> you can first form-fold them and then binary compare the names.
> Form-folding is another name for all the normalisation, lower casing,
> canonisation and simplifying described in for example the NAMEPREP draft.
> Does anybody have a better name?
> 
> Places to do form-folding:
> Below I give what I think are the two most important places and the most
> important good and negative points for them. There are more points.
> 
> 1) Form-folding is done only in the DNS servers.
>    + Only authorative servers need to implement it.
>    + Only the folding for the authorative subset of UCS need to
>      be implemented.
>    + Less places where form-folding need to be implemented.
>    - Higher CPU demand on servers.
> 
> 2) Form-folding is done in resolver (and servers when zone loading).
>    + Less CPU demand on servers.
>    - More places where form-folding need to be implemented.
> 
> 
> In my draft I use 1), others have 2) instead.
> I have thought that the good points of 1) makes it the best choice. Also
> some drafts saying 2) would not fullfill any requirements good enough.
> But a few days ago I thought about one more aspect that might make
> 2) the best choice:
> 
> There are many applications that compare hosts or domain names.
> For example: sendmail and many browsers.
> These applications should also compare IDNs as equal in the same way
> that DNS does. This means that they also need to implement form-folding.
> If the resolver libraries include the standard implementation
> of form-folding (and name comparing), and had the API public, all
> applications could use it instead of implementing their own.
> 
> So by choosing 2) we can get the additional benefit of supplying
> a standard place for applications to the routines to do
> form-folding and IDN comparing. And thus reducing the risk of many
> implementations, some that will do it wrongly.
> 
> Thats it. What do you think? Am I missing some important aspects to
> make the best choice? Maybe it is something that could be
> discussed at the meeting.
> 
> Regards,
> 
>   Dan