Re: getaddrinfo error for existing host without requested address family

Mike,
	Just commenting to clarify what seems to be unclear
about some RFC's.
Rod

> 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.

RFC2553bis-02 is an old version of a draft that went to -09, this draft
existed from May 2000 to March 2003, when it was changed to RFC3493 and
published.  When looking at RFC versions and history please use the
IETF datatracker to help one find history and latest versions:

https://datatracker.ietf.org/doc/rfc3493/
https://datatracker.ietf.org/doc/rfc2553/ Says obsolete by rfc3493
https://datatracker.ietf.org/doc/rfc2553bis/ redirects to rfc3493

Sadly goggle often sends one to a html version of a rfc/draft
when one searches there for it.  The html version does have
a link in the banner to the proper datatracker page though.

Use of and reference to IETF drafts in comments of the FreeBSD
code and implementing them is full of the perils that there is
rarely anyone tracking the work and keeping things up to date
as the draft evolves and we end up with stale comments, and
even stale implementations.

rfc3493 still does not define EAI_ADDRFAMILY, one would have
to search the mailing list archives to find what the rational
for its removal was.  Sadly that this is not summarized in
section 9 of rfc3493, it should of been.

> 
> 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.
> 
> 		Mike
> 
> 

-- 
Rod Grimes                                                 rgrimes@freebsd.org