NXDOMAIN response flag for empty answer

[fogs]

When you deliberately send an empty result using res.end(); the default convenience behavior would set the DNS return code 0 ("NOERROR"). Instead, the return code 3 ("NXDOMAIN") would be more appropriate. While technically, NOERROR is fine even if the response contains no answer, this patch will avoid the "Zero answer bug" which is already mentioned in RFC 1536.

[shark0der]

@jhs, any plans to merge this? Is this project still maintained?

[ansuz]

I've merged into my fork, which also supports serving over ipv6 addresses.