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Date: Mon, 24 Aug 2020 17:36:18 -0400
From: Rich Felker <>
Subject: Re: Incompatible behaviour of res_query(3) w.r.t. NXDOMAIN

On Mon, Aug 24, 2020 at 10:39:30PM +0200, Daniel Neri wrote:
> On 24 Aug 2020, at 18:43, Rich Felker <> wrote:
> > 
> > Hmm, I think in this case the "better" might be sufficient that we
> > want to keep it and pressure other implementations to change too. A
> > program performing a lookup where the result is NxDomain may very well
> > want to know whether that's an authenticated (by DNSSEC) NxDomain or
> > one in an insecure zone. Returning an error to the caller with no
> > packet contents discards this critical data.
> In that case, it’d be better to add a new resolver API, or implement
> an already existing one that supports this usecase. The other
> implementations I mentioned also support option flags (in global
> state) that can change the behaviour.
> res_query(3) is almost as old as DNS itself — it doesn’t seem likely
> that everyone else, both libraries and applications, are going to
> make incompatible changes at this point.

If it were really incompatible behavior I would agree, but the
behaviors aren't incompatible. Either is compatible with the same
underspecified documentation, and a reasonable caller will easily deal
with both -- the nxdomain reply looks very similar to nodata, which it
also needs to be able to handle, except for the different error code
(3 vs 0). A caller can't assume just because res_query succeeded that


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