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Date: Mon, 24 Aug 2020 12:16:47 -0400
From: Rich Felker <>
Subject: Re: Incompatible behaviour of res_query(3) w.r.t. NXDOMAIN

On Sun, Aug 23, 2020 at 11:31:32PM +0200, Daniel Neri wrote:
>   Hello,
> Musl’s res_query(3) returns success for a query that results in an
> NXDOMAIN response, which disagrees with other common
> implementations.
> Simple test case:
> On Debian Linux, OpenBSD and FreeBSD this program prints:
>   error: Unknown host
> but on Alpine Linux edge (musl v1.2.1):
>   success (size 91)

I think there's a good argument that this should be changed, but that
would require making res_* set h_errno, which would require making
h_errno thread-local -- which it probably should have been all along,
but the standard interfaces that used it, gethostby* etc., were
non-thread-safe anyway and thus it seemed unnecessary.

FWIW I think the musl behavior is *better* here (more informative to
the application), but usually it's preferable not to break the
existing (even if informal) contracts of the interfaces being
implemented than to be "better".


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