[SOLVED] How asyncio UDP connection receives whole datagrams?

How asyncio UDP connection receives whole datagrams?

There is an interface asyncio.DatagramProtocol from Python library. It gives possibility to implement receiving datagrams by using method datagram_received(self, data, addr):

class MyDatagramProtocol(asyncio.DatagramProtocol):
    def datagram_received(self, data: bytes, addr: tuple[str, int]):
        # Here I can use data as whole datagram. 
        # If there are more pending datagrams, it will called more than once
        pass

The asyncio eventloop receives whole datagrams. But when I use BSD socket, I should use all or part of received data. Total data can be greater than one datagram. And I don't know the bounds of this data. I just can parse it by using of my own algorithms (read heading, count of bytes in body, etc).

if (ioctlsocket(Socket, FIONREAD, (u_long*)(&PendingDataSize)) == 0)
{
    BytesRead = recv(Socket, (char*)Data, PendingDataSize, Flags); 
    // Now I can use Data and parse it here. 
    // But Data can be two or more datagrams if remote machine sent two or more packets?
}

How can I repeat the behavior of asyncio but with just BSD sockets?

Solution

With a datagram socket, recv always receives only one datagram at a time.

See man page udp(7):

All receive operations return only one packet.