pub extern "C" fn sendto(
    fn_ptr: Option<&extern "C" fn(_: c_int, _: *const c_void, _: size_t, _: c_int, _: *const sockaddr, _: socklen_t) -> ssize_t>,
    socket: c_int,
    buf: *const c_void,
    len: size_t,
    flags: c_int,
    addr: *const sockaddr,
    addrlen: socklen_t
) -> ssize_t