This discussion is about
http://hurd.gnufans.org/bin/view/Distrib/PortingIssues#Uncompliant_use_of_sockaddr_un_t
We need an agreement about what should be in this page.
Robert Millan wrote:
On Sat, Apr 05, 2003 at 06:01:16PM +0300, Ognyan Kulev wrote:
sub.sun_path[sizeof(sun.sun_path) - 1] = '\0';
I've changed my mind about this, so I've added it again.
I understand that my changes are somewhat intrusive to what Robert Millan wrote, but I wouldn't do it if I didn't beleive they are right. Please say your mind about the current text.
Uncompliant use of sockaddr_un
The following declaration:
sockaddr_un sun = { AF_UNIX, "/path/to/socket" };won't work on GNU/Hurd. The Glibc API requires that the second parameter of a sockaddr_un struct is array of chars, but NOT pointer to array of chars. So we have to copy them directly into the sun_path address. Glibc wants string of chars there that doesn't need to end in nul character _and_ correct size of sockaddr_un passed to socket functions. When calling socket functions one should always use SUN_LEN (su) for the sockaddr length argument. An example:
sockaddr_un su; /* AF_LOCAL is the canonical flag in Glibc. Use AF_UNIX if you want compatibility. */ su.sun_family = AF_LOCAL; /* Copy the string into sun_path. It must be no longer than approximately 100 characters. */ strcpy (su.sun_path, "/path/to/socket");
SUN_LEN macro is not defined in The Single UNIX Specification Version 3 (see sys/un.h manpage). You can use the following definition to handle this case (definition taken from NetBSD):
#ifndef SUN_LEN #define SUN_LEN(su) \ (sizeof(*(su)) - sizeof((su)->sun_path) + \ strlen((su)->sun_path)) #endif
If you have pointer to array of characters as file name, you'd better use the following code to set sun_path:
strncpy (su.sun_path, filename, sizeof (su.sun_path)); su.sun_path[sizeof (su.sun_path) - 1] = '\0';
If you expect file name longer than approximately 100 characters, use the following code. This is the recommended code for GNU systems. You can include it whenever __GLIBC__ is defined.
/* `offsetof', `alloca' and `AF_LOCAL' may not
be available everywhere. */
socklen_t su_len = offsetof (struct sockaddr_un, sun_path)
+ strlen (filename) + 1;
struct sockaddr_un *su = alloca (su_len);
su->sun_family = AF_LOCAL;
strcpy (su->sun_path, filename);NOTE: the current API is subject to change, see the notes in Glibc's docs ("info libc" and search for sockaddr_un) and Debian bug #187391.
Regards -- Ognyan Kulev <[EMAIL PROTECTED]>, "\"Programmer\""
