[dns-operations] check if a domain has been registered via DNS

[Stephane Bortzmeyer]

On Thu, Apr 27, 2017 at 04:13:36PM +0800,
 Peng Yonghua <pyh at vodafonemail.de> wrote 
 a message of 21 lines which said:

> if rcode is NXDOMAIN then domain not taken.

No. Some registries (like .fr) allow registration without
delegation. Some have a "on hold" system where the domain is
temporarily not published in the DNS. And I do not even mention
redemption periods and domains not registered but not registreable
(such as the seven dirty words in .us).

Bad idea, sorry. The DNS does not replace a proper DAS.