Date: Mon, 17 Oct 2022 10:37:22 -0500 From: Mike Karels <mike@karels.net> To: freebsd-net@freebsd.org Cc: Konstantin Belousov <kostikbel@gmail.com> Subject: Re: getaddrinfo error for existing host without requested address family Message-ID: <202210171537.29HFbMJd075006@mail.karels.net> In-Reply-To: Your message of Wed, 28 Sep 2022 00:09:57 %2B0300. <YzNmpXpwZPuDk6di@kib.kiev.ua>
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On Wed, 28 Sep 2022, Konstantin Belousov wrote: > 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. I participated in a short discussion on that list. The TL;DR: - Linux/glibc (Ubuntu at least) uses EAI_NODATA ("No address associated with hostname") when a name is valid but does not have the requested address family. This is better than FreeBSD currently, as it is distinguished from EAI_NONAME ("Name or service not known"). But it implies that there is no address in any family. (I showed an example from ping6 above, but it turns out to be atypical.) - The author of the musl C library for Linux plans to use EAI_NODATA as well, but with a different error message. - Linux also uses EAI_ADDRFAMILY, but only when a numeric address is in the wrong family, e.g. telnet -6 127.0.0.1. - POSIX, like the latest RFC, does not define EAI_NODATA or EAI_ADDRFAMILY. - There were no other opinions expressed. I see two choices for FreeBSD when there is no address in the requested family. One is to use EAI_NODATA, probably using a modified error message. The has the main disadvantage that we have several NLS translations. Also, it is different than Linux. The other choice is to use EAI_ADDRFAMILY ("Address family for hostname not supported") as originally proposed. The existing error message seems reasonable for this case. Any comments or votes? I am inclined to use EAI_ADDRFAMILY as originally proposed. Mike
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