/// Receives multile messages on a socket
///
/// Returns number of messages received.
///
/// # Examples
/// ```
/// use std::ffi::c_void;
/// use std::ptr;
/// use std::thread;
///
/// const READ_SIDE: usize = 0;
/// const WRITE_SIDE: usize = 1;
///
/// fn main() {
///     let mut fds = [-1_i32; 2];
///
///     let ret = unsafe { nc::socketpair(nc::AF_UNIX, nc::SOCK_STREAM, 0, &mut fds) };
///     assert!(ret.is_ok());
///     println!("socket pairs: {}, {}", fds[0], fds[1]);
///
///     // Start worker thread
///     thread::spawn(move || {
///         println!("worker thread started");
///         let msg = "Hello, Rust";
///         println!("[worker] Will send msg: {msg}");
///         let mut iov = [nc::iovec_t {
///             iov_base: msg.as_ptr() as *const c_void,
///             iov_len: msg.len(),
///         }];
///         let msg_hdr = nc::msghdr_t {
///             msg_name: ptr::null(),
///             msg_namelen: 0,
///             msg_iov: iov.as_mut_ptr(),
///             msg_iovlen: iov.len(),
///             msg_control: ptr::null(),
///             msg_controllen: 0,
///             msg_flags: 0,
///         };
///         let mmsg_hdr = [nc::mmsghdr_t {
///             msg_hdr,
///             msg_len: 0,
///         }];
///         let ret = unsafe { nc::sendmmsg(fds[WRITE_SIDE], &mmsg_hdr, 0) };
///         assert!(ret.is_ok());
///         //assert_eq!(ret, Ok(msg.len() as nc::ssize_t));
///     });
///
///     let mut buf = [[0_u8; 64]; 4];
///     let mut iov = Vec::with_capacity(buf.len());
///     for ref mut item in (&mut buf).iter() {
///         iov.push(nc::iovec_t {
///             iov_base: item.as_ptr() as *const c_void,
///             iov_len: item.len(),
///         });
///     }
///     let msg_hdr = nc::msghdr_t {
///         msg_name: ptr::null(),
///         msg_namelen: 0,
///         msg_iov: iov.as_mut_ptr(),
///         msg_iovlen: iov.len(),
///         msg_control: ptr::null(),
///         msg_controllen: 0,
///         msg_flags: 0,
///     };
///     let mut mmsg_hdr = [nc::mmsghdr_t {
///         msg_hdr,
///         msg_len: 0,
///     }];
///     let ret = unsafe { nc::recvmmsg(fds[READ_SIDE], &mut mmsg_hdr, 0, None) };
///     assert!(ret.is_ok());
///     let msgs_read = ret.unwrap();
///     assert_eq!(msgs_read, 1);
///     // We only read the first buffer block.
///     for i in 0..msgs_read {
///         let nread = mmsg_hdr[i].msg_len;
///         let msg = std::str::from_utf8(&buf[0][..nread as usize]).unwrap();
///         println!("[main] recv msg: {msg}");
///     }
///
///     unsafe {
///         let _ = nc::close(fds[0]);
///         let _ = nc::close(fds[1]);
///     }
/// }
/// ```
pub unsafe fn recvmmsg(
    sockfd: i32,
    msgvec: &mut [mmsghdr_t],
    flags: i32,
    timeout: Option<&mut timespec_t>,
) -> Result<size_t, Errno> {
    let sockfd = sockfd as usize;
    let msgvec_ptr = msgvec.as_mut_ptr() as usize;
    let vlen = msgvec.len();
    let flags = flags as usize;
    let timeout_ptr = timeout.map_or(core::ptr::null_mut::<timespec_t>() as usize, |timeout| {
        core::ptr::from_mut(timeout) as usize
    });
    unsafe { syscall5(SYS_RECVMMSG, sockfd, msgvec_ptr, vlen, flags, timeout_ptr) }
}
