Function std::sock_would_block

int sock_would_block()

True if the most recent non-blocking socket call (accept/recv/send/ connect/...) failed only because it would have blocked — i.e. "not ready yet, try again after await_fd()", not a real error. Checking this is genuinely platform-specific in a way none of the other functions here are: BSD/Linux report it through errno (EAGAIN/EWOULDBLOCK, and std/errno.h's ERRNO_EAGAIN()/ERRNO_EWOULDBLOCK() only recently started giving the right numbers per platform there — see that header), Windows sockets never touch errno at all and report it through a separate per-thread slot, WSAGetLastError() == WSAEWOULDBLOCK (10035). Call this immediately after the failing call, before anything else that might itself set errno/WSAGetLastError() and clobber it.