note that socket_last_error() cache the last error from the last socket syscall, it does not actually query the OS for the last error on the socket, so if an async socket have an error after the last async operation started successfully, socket_last_error() doesn't know about it, but socket_get_option($sock, SOL_SOCKET, SO_ERROR) actually query the OS, or so it seems... observed on PHP 7.1.16 on Cygwin on win7 x64 SP1 with non-blocking sockets, socket_last_error() never caught on to the fact that the current error had changed from EINPROGRESS (non-blocking connect) to 0 (connection successful)
