static int tcp_wait_fd(int fd, int write)
{
    int ev = write ? POLLOUT : POLLIN;
    struct pollfd p = { .fd = fd, .events = ev, .revents = 0 };
    int ret;

    ret = poll(&p, 1, 100);
    return ret < 0 ? ff_neterrno() : p.revents & ev ? 0 : AVERROR(EAGAIN);
}