Following pspautotests net/inet/errors, states and reuse:
- bind decides itself whether a port is in use, as 4.4BSD's in_pcbbind()
does with SO_REUSEADDR and SO_REUSEPORT. The host can't, since its
sockets have both on for running several instances, so any number of
sockets could bind the same port. A socket that's bound already is
EINVAL.
- Shutting down the sending side of an unconnected TCP socket, or a
failed connect, throws away its TCP state as in 4.4BSD's tcp_usrreq(),
after which bind, listen, connect, accept and shutdown fail with
EINVAL, and its port is free again. shutdown otherwise only fails for
a bad how, and still reaches the host, so a thread waiting in accept
wakes up.
- listen on an unbound TCP socket binds one, which Winsock didn't, and on
a connected one succeeds.
- connect on a listening socket is EOPNOTSUPP. Winsock's WSAEINVAL for
it looked like a connect in progress, and a blocking socket waited
forever. A second connect on a loopback connection the host hasn't
noticed finishing is EISCONN once it has.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
