https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=291145
Bug ID: 291145
Summary: UDP connected sockets cannot be disconnected
Product: Base System
Version: 14.3-RELEASE
Hardware: amd64
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: [email protected]
Reporter: [email protected]
Hello,
I've been trying to use the libc connect syscall to change the association of a
UDP datagram socket in a Rust application, but I have had trouble with
successfully invoking connect on the same socket fd multiple times. I read the
connect(2) man page says this:
Generally, stream sockets may successfully connect() only once; data-
gram sockets may use connect() multiple times to change their associa-
tion. Datagram sockets may dissolve the association by connecting to
an invalid address, such as a null address.
However, I have not been successful in disconnecting and dissolving the socket
association when I end a connection from a UDP client. The following code works
as expected on macOS Tahoe 26.1 and removes the association with a single
address:
{
// sockaddr WITH sa_len on these platforms
let addr = libc::sockaddr {
sa_len: std::mem::size_of::<libc::sockaddr>() as u8,
sa_family: libc::AF_UNSPEC as libc::sa_family_t,
sa_data: [0; 14],
};
let rc = unsafe {
libc::connect(
fd,
&addr as *const libc::sockaddr,
addr.sa_len as libc::socklen_t,
)
};
if ok_or_eafnosupport(rc).is_ok() {
return Ok(());
}
// Fallback: connect(fd, NULL, 0)
let rc2 = unsafe { libc::connect(fd, std::ptr::null(), 0) };
return ok_or_eafnosupport(rc2);
}
macOS will return EAFNOSUPPORT from the AF_UNSPEC call and stop filtering to a
single address, but FreeBSD 14.3 returns EAFNOSUPPORT from AF_UNSPEC and does
not change the socket behavior. The call with the NULL address also returns
EINVAL on FreeBSD and does not dissolve the association like the man page would
imply. Can you please advise if this is the expected behavior?
Thank you
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