[regext] Re: RDAP responses for invalid domain names

[Mario Loffredo <[e-mail]>]

Hi Pawel,

if the third character is hypen (ASCII 45), example 1 is not an IDN 
because it begins with "xn-" instead of "xn--". Therefore, the response 
should be 404 if it is not registered.

If the third character is the Unicode character "–" (U+2013), then it's 
punycode is xn--xnfdkp0gtc-pu6e.com and the response should still be 
404  if it is not registered.

Best,

Mario


Il 11/04/2026 19:26, Pawel Kowalik ha scritto:
>
> 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
>
>
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-- 
Dott. Mario Loffredo
Senior Technologist
Technological Unit “Digital Innovation”
Institute of Informatics and Telematics (IIT)
National Research Council (CNR)
Address: Via G. Moruzzi 1, I-56124 PISA, Italy
Phone: [phone]
Web:http://www.iit.cnr.it/mario.loffredo