Re: getaddrinfo error for existing host without requested address family

On Tue, Sep 27, 2022 at 03:53:12PM -0500, Mike Karels wrote:
> I recently noticed the following behavior:
> 
> % ping6 redrock
> ping6: Name does not resolve
> % host redrock
> redrock.karels.net has address 10.0.2.2
> redrock.karels.net mail is handled by 10 mail.karels.net.
> % ping6 nonexistenthost
> ping6: Name does not resolve
> 
> The first error message is misleading, because the name *does* resolve,
> but has no AAAA record, and it is the same error message as for a name
> that truly does not exist.  The problem comes from the set of error
> codes that getaddrinfo() returns in these two cases.  The problem did
> not exist with gethostbyname(), which has separate error codes for the
> two (although gethostbyname did not have provision for IPv6, it handled
> cases like domain names and mail domains without IPv4 addresses).
> 
> getaddrinfo() uses a richer set of error codes than gethostbyname(), but
> still misses this case.  However, looking at <netdb.h>, I see
> 
> #if 0
> /* Obsoleted on RFC 2553bis-02 */
> #define	EAI_ADDRFAMILY	 1	/* address family for hostname not supported */
> #endif
> ...
> #if 0
> /* Obsoleted on RFC 2553bis-02 */
> #define	EAI_NODATA	 7	/* no address associated with hostname */
> #endif
> 
> I don't know why these two were omitted from the update to RFC 2553, but
> the first seems to me to be the correct error for an existing name without
> an address for the requested address family.  Also, that is the error
> message produced by Linux (Ubuntu 22.04.1).
> 
> NetBSD and OpenBSD produce the second of these two errors for a host
> without the requested address.  But they also produce the same error
> when a name does not exist.
> 
> RFC 2553bis-02 has timed out, and is replaced by RFC 3493, which is also
> missing EAI_ADDRFAMILY.  These are informational RFCs, not specifying an
> Internet standard.
> 
> I propose re-enabling EAI_ADDRFAMILY and using it for the situation
> where a name exists but does not have an address in the requested family.
> This would make the error in the example less misleading, and would behave
> the same as Linux in this regard.  The change to netdb.h is trivial, but
> getaddrinfo() needs a little more work because it uses the NS_* errors
> from <nsswitch.h> internally and then translates.  But it will benefit
> from greater accuracy in other cases as well (e.g.  "out of memory"
> rather than "Name does not resolve").
> 
> Comments?  I have a change in progress, but wanted to float the idea
> before I finish it and put it into review.

Perhaps look there
https://www.openwall.com/lists/libc-coord/2022/09/27/1

You might want to participate in the thread, instead of me.