[regext] Re: RDAP responses for invalid domain names

[Pawel Kowalik <[e-mail]>]

Hi,

On 10.04.26 20:13, Jasdip Singh wrote:
>
> *From: *Andy Newton <[e-mail]>
> *Date: *Friday, April 10, 2026 at 1:57 PM
> *To: *Thomas Corte (TANGO support) <[e-mail]>, 
> [e-mail] <[e-mail]>
> *Subject: *[regext] Re: RDAP responses for invalid domain names
>
>
> On 4/10/26 12:47 PM, Thomas Corte (TANGO support) wrote:
> …
>
> > But as a *registrar*, I wouldn't know where to begin here – do you 
> expect each registrar to
> > determine and encode the IDN policies for each gTLD registry they're 
> working with into their RDAP
> > servers, so they can decide correctly, on a per-TLD basis, whether a 
> query for a specific IDN domain
> > name should yield 400 (= impossible to register) or 404 (= possible, 
> but we don't sponsor it)?
>
> That does seem onerous for a registrar and unlikely something a most 
> registrars can do. So 404 is the best effort. Good point.
>
> [JS] Agreed.
>
I agree as well taking registrar use-cases into account.

I don't agree however that RDAP shall carry logic "impossible to 
register" as it is not RDAP's responsibility to claim that.

For generally invalid domain names, objectively no matter what server 
policy is - like examples 1 and 3, 400 looks like appropriate response 
to me as well.

For other cases, where a name may be invalid in the server context 
(because of idn language not supported, or maybe because single-digit 
registration is not allowed per policy etc.) both responses 404 or 400 
look appropriate.

404 is just telling the domain does not exist (which is true), 400 is 
telling that that such domain name does not make sense to the server.

Kind Regards,
Pawel