socketFunc        func(int, int, int) (int, error)  = syscall.Socket
	connectFunc       func(int, syscall.Sockaddr) error = syscall.Connect
	listenFunc        func(int, int) error              = syscall.Listen
	getsockoptIntFunc func(int, int, int) (int, error)  = syscall.GetsockoptInt

		// details.
		if err := fd.pfd.WaitWrite(); err != nil {
			select {
			case <-ctxDone:
				return nil, mapErr(ctx.Err())
			default:
			}
			return nil, err
		}
		nerr, err := getsockoptIntFunc(fd.pfd.Sysfd, syscall.SOL_SOCKET, syscall.SO_ERROR)
		if err != nil {
			return nil, os.NewSyscallError("getsockopt", err)
		}
		switch err := syscall.Errno(nerr); err {