Re: [PATCH] man/man3/getnameinfo.3: Mention behavior for AF_UNIX

[Alejandro Colomar <alx@kernel.org>]

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Hi Jan,

> Date: 2026-10-20 18:01:02+0200
> From: Jan Engelhardt <ej@inai.de>
>
> 
> On Tuesday 2026-10-20 16:27, Alejandro Colomar wrote:
> >
> >I'd rewrite a little bit:
> >
> >	.SH VERSIONS
> >	POSIX only specifies the behavior for sockets of the
> >	.B AF_INET
> >	and
> >	.B AF_INET6
> >	address families.
> >	Other address families are non-portable;
> >	for example, for
> >	.BR AF_UNIX ,
> >	many libc implementations fail,
> >	some succeed but provide zero-length strings in
> >	.I host
> >	and
> >	.IR serv ,
> >	and some fill these buffers with pseudo-values.
> >
> >BTW, out of curiosity, what do those pseudo-values look like?
> 
> (Something must have gone wrong seeing zero-length output.
> So I redid the test program and runs.)

Thanks!  It'd be very useful to have this test program in the commit
message.  Would you mind sending v2 and incorporating it?  Please indent
the program with one tab, so the #include lines are not removed by
git(1).


Have a lovely night!
Alex

> 
> getnameinfo:
> 
> * FreeBSD 15: fills host="/path", serv="", returns success(0).
> 
> * glibc 2.44: fills host=<utsname> (flags=0) or host="localhost"
>   (flags=NI_NUMERICHOST), and serv="/path", returns success(0).
> 
> * OpenBSD 7.9: signals EAI_FAMILY. Upon seeing NI_NUMERICHOST,
>   signals EAI_SYSTEM instead (odd).
> 
> * OmniOS r151046 (Solaris): signals EAI_FAMILY.
> 
> * musl-libc 1.2.6 (Alpine Linux): signals EAI_FAMILY.
> 
> * cygwin 3.6.11: signals EAI_FAMILY.
> 
> getaddrinfo:
> 
> * FreeBSD: getaddrinfo("/the/socket/path", nullptr,
>   hints_with_AF_UNIX, ...) succeeds.
> 
> * the rest: signals EAI_FAMILY.
> 
> 
> ---
> #include <sys/un.h>
> #include <netdb.h>
> #include <sys/socket.h>
> #include <cstdio>
> #include <cstring>
> 
> int main()
> {
> 	struct sockaddr_un u{};
> 	u.sun_family = AF_UNIX;
> 	strcpy(u.sun_path, "/pa");
> 	char host[320] = "!", serv[320] = "!";
> 
> 	auto ret = getnameinfo(reinterpret_cast<struct sockaddr *>(&u),
> 	           sizeof(u), host, sizeof(host), serv, sizeof(serv), 0);
> 	printf("GNI %d %s\n", ret, gai_strerror(ret));
> 	if (ret == 0)
> 		printf("GNI <%s> <%s>\n", host, serv);
> 
> 	ret = getnameinfo(reinterpret_cast<struct sockaddr *>(&u),
> 	      sizeof(u), host, sizeof(host), serv, sizeof(serv), NI_NUMERICHOST | NI_NUMERICSERV);
> 	printf("GNI %d %s\n", ret, gai_strerror(ret));
> 	if (ret == 0)
> 		printf("GNI <%s> <%s>\n", host, serv);
> 
> 	struct addrinfo hints{};
> 	hints.ai_family = AF_UNIX;
> 	hints.ai_socktype = 0;
> 	struct addrinfo *res = nullptr;
> 	ret = getaddrinfo(host, serv, &hints, &res);
> 	printf("GAI %d %s\n", ret, gai_strerror(ret));
> 	if (ret == 0)
> 		for (; res != nullptr; res = res->ai_next)
> 			printf("GAI fam %u %u %u\n", res->ai_family,
> 				res->ai_socktype, res->ai_protocol);
> 	return 0;
> }

-- 
<https://www.alejandro-colomar.es>

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