homepage

socket.setsockopt() sets an optlen of '4' in the setsockopt system call
for options IP_MULTICAST_TTL and IP_MULTICAST_LOOP. On OpenBSD, this
causes the kernel to hit an error condition and set errno 22 when these
options are set:
socket.error: (22, 'Invalid argument')
Yielded by e.g. socket.setsockopt(socket.IPPROTO_IP,
socket.IP_MULTICAST_TTL, 1)
According to both FreeBSD and OpenBSD manual pages (see e.g.
http://www.freebsd.org/cgi/man.cgi?query=ip&apropos=0&sektion=0&manpath=FreeBSD+7.0-RELEASE&format=html),
these fields are in fact both 8 bit unsigned, and the manuals suggest
the following:
u_char ttl; /* range: 0 to 255, default = 1 */ 
 
setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
While '4' (sizeof int) is correct for many options, special casing is
needed in Modules/socketmodule.c. The following diff fixes the issue
for me on OpenBSD:
 @@ -1716,12 +1719,8 @@ sock_setsockopt(PySocketSockObject *s, PyObject
*args)
 
 if (PyArg_ParseTuple(args, "iii:setsockopt",
 &level, &optname, &flag)) {
- buflen = sizeof flag;
- /* Multi cast options take shorter arguments */
- if (optname == IP_MULTICAST_TTL
- || optname == IP_MULTICAST_LOOP)
- buflen = sizeof(u_char);
 buf = (char *) &flag;
+ buflen = sizeof flag;
 }
 else {
 PyErr_Clear();