Unix-domain (local) sockets do not support getsockname() or getpeername().

[Deven T. Corzine]

Hi folks...

I'll start with a very brief introduction -- I just joined this mailing 
list, so that I could report a Hurd bug I found last night.  I never 
used the Hurd before yesterday, but I would be interested in working 
with it, if I can just find the time...

Anyway, I was on #hug on IRC last night, talking to "bddebian", who was 
having trouble getting "orbit2" (GNOME's CORBA broker) to run on the 
Hurd.  I offered to help, so he gave me an account on his machine and I 
traced the problem, which turned out to be that getsockname() was 
returning a null pathname instead of the correct pathname of the 
Unix-domain socket.  Since orbit2 expects this call to work, it broke 
the software.  After I found the problem, I stripped down the code to a 
36-line test case (attached) which exhibits the bug.  Under Linux, 
getsockname() returns the same sockaddr_un structure that was sent to 
bind(), while the Hurd is returning a null path instead.

This morning, I took a quick glance at the Hurd sources, and noticed the 
following comment on S_socket_whatis_address() in hurd/pflocal/pf.c:

/* Implement socket_whatis_address as described in <hurd/socket.defs>.
  Since we cannot tell what our adress is, return an empty string as
  the file name.  This is primarily for the implementation of accept
  and recvfrom.  The functions getsockname and getpeername remain
  unsupported for the local namespace.  */

So it appears that no attempt was ever made to implement getsockname() 
or getpeername() for Unix-domain sockets.

Since this bug (unsupported feature) may break other applications 
besides orbit2, perhaps someone would like to take a stab at filling in 
the gap?

Deven

#include <stdio.h>
#include <malloc.h>
#include <sys/socket.h>
#include <sys/un.h>

#define PATH "./getsockname_bug.socket"

main()
{
        unlink(PATH);

        int saddr_len = sizeof(struct sockaddr_un);
        struct sockaddr_un *saddr = (struct sockaddr_un *) malloc(saddr_len);
        if (!saddr) exit(1);

        memset(saddr, 0, saddr_len);
        saddr->sun_family = AF_UNIX;
        strcpy(saddr->sun_path, PATH);
        int pathlen = strlen(PATH) + 1;
        saddr_len = sizeof(struct sockaddr_un) - sizeof(saddr->sun_path) + 
pathlen;

        int fd = socket(PF_UNIX, SOCK_STREAM, 0);
        if (fd < 0) exit(1);

        if (bind(fd, (struct sockaddr *) saddr, saddr_len)) exit(1);

        printf("before: path = \"%s\", saddr_len = %d\n", saddr->sun_path, 
saddr_len);

        if (getsockname(fd, (struct sockaddr *) saddr, &saddr_len)) exit(1);

        printf("after: path = \"%s\", saddr_len = %d\n", saddr->sun_path, 
saddr_len);

        close(fd);

        unlink(PATH);
}