bug#23068: 25.1.50; unix socket address in abstract namespace

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Magne Ingebrigtsen <larsi@gnus.org>
> Cc: Eli Zaretskii <eliz@gnu.org>,  23068@debbugs.gnu.org
> Date: Sun, 20 Mar 2016 18:11:09 +0100
> 
> Mark Oteiza <mvoteiza@udel.edu> writes:
> 
> > and I'm able to connect to it otherwise. The above elisp does:
> >
> >   socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC, 0) = 8
> >   connect(8, {sa_family=AF_LOCAL, sun_path=@""}, 110) = -1
> > ECONNREFUSED (Connection refused)
> >   close(8) 
> 
> Yeah, this code in conv_lisp_to_sockaddr doesn't look very correct:
> 
>   else if (STRINGP (address))
>     {
> #ifdef HAVE_LOCAL_SOCKETS
>       if (family == AF_LOCAL)
> 	{
> 	  struct sockaddr_un *sockun = (struct sockaddr_un *) sa;
> 	  cp = SDATA (address);
> 	  for (i = 0; i < sizeof (sockun->sun_path) && *cp; i++)
> 	    sockun->sun_path[i] = *cp++;
> 	  sa->sa_family = family;
> 	}
> #endif
>       return;
>     }

That should be trivial to fix.  Elsewhere, we specifically attempt to
support this feature:

  #ifdef HAVE_LOCAL_SOCKETS
      case AF_LOCAL:
	{
	  struct sockaddr_un *sockun = (struct sockaddr_un *) sa;
	  ptrdiff_t name_length = len - offsetof (struct sockaddr_un, sun_path);
	  /* If the first byte is NUL, the name is a Linux abstract
	     socket name, and the name can contain embedded NULs.  If
	     it's not, we have a NUL-terminated string.  Be careful not
	     to walk past the end of the object looking for the name
	     terminator, however.  */
	  if (name_length > 0 && sockun->sun_path[0] != '\0')
	    {
	      const char *terminator
		= memchr (sockun->sun_path, '\0', name_length);

	      if (terminator)
		name_length = terminator - (const char *) sockun->sun_path;
	    }

	  return make_unibyte_string (sockun->sun_path, name_length);
	}

IOW, this is not a wishlist feature request, but a routine bug report ;-)