gistfile1.c

#ifndef UNICODE
#define UNICODE
#endif

#define WIN32_LEAN_AND_MEAN

#include <winsock2.h>
#include <Ws2tcpip.h>
#include <stdio.h>

int __cdecl main()
{
    WSADATA wsaData;
    WSABUF DataBuf;
    WSAOVERLAPPED Overlapped;

    SOCKET RecvSocket = INVALID_SOCKET;
    struct sockaddr_in RecvAddr;
    struct sockaddr_in SenderAddr;

    int SenderAddrSize = sizeof (SenderAddr);
    u_short Port = 27015;

    char RecvBuf[65507];
    int BufLen = 65507;
    DWORD BytesRecv = 0;
    DWORD Flags = 0;

    int err = 0;
    int rc;
    int retval = 0;
    DWORD bytes;
    ULONG_PTR key;
    OVERLAPPED* o;
    
    //-----------------------------------------------
    // Initialize Winsock
    rc = WSAStartup(MAKEWORD(2, 2), &wsaData);

    SecureZeroMemory((PVOID) &Overlapped, sizeof(WSAOVERLAPPED) );

    HANDLE iocp = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 1);

    // Create a receiver socket to receive datagrams
    RecvSocket = WSASocket(AF_INET,
                           SOCK_DGRAM,
                           IPPROTO_UDP, NULL, 0, WSA_FLAG_OVERLAPPED);

    RecvAddr.sin_family = AF_INET;
    RecvAddr.sin_port = htons(Port);
    RecvAddr.sin_addr.s_addr = inet_addr("0.0.0.0");

    CreateIoCompletionPort((HANDLE)RecvSocket, iocp, (ULONG_PTR)RecvSocket, 0);

    rc = bind(RecvSocket, (SOCKADDR *) & RecvAddr, sizeof (RecvAddr));

    DataBuf.len = 0;
    DataBuf.buf = 0;
    Flags = MSG_PEEK;
    rc = WSARecv(RecvSocket,
                      &DataBuf,
                      1,
                      &BytesRecv,
                      &Flags,
                      &Overlapped, NULL);

    closesocket(RecvSocket);
    GetQueuedCompletionStatus(iocp, &bytes, &key, &o, INFINITE);
}