A simple application using I/O Completion Ports and WinSock

#include "stdafx.h"

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#include <winsock2.h>

#define ACK_MESG_RECV "Message received successfully"

//global functions
void AcceptConnections(SOCKET ListenSocket);
DWORD WINAPI AcceptHandler(void* Socket);

int main(int argc, char *argv[])
{
     //Validate the input
     if (argc < 2) 
     {
          printf("\nUsage: %s port.", argv[0]);
          goto error;
     }
     
     // Initialize Winsock
     WSADATA wsaData;
     
     int nResult;
     
     nResult = WSAStartup(MAKEWORD(2,2), &wsaData);
     
     if (NO_ERROR != nResult)
     {
          printf("\nError occurred while executing WSAStartup().");
          return 1; //error
     }
     else
     {
          printf("\nWSAStartup() successful.");
     }
     
     SOCKET ListenSocket; 
     int    nPortNo;
     
     struct sockaddr_in ServerAddress;
     
     //Create a socket
     ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
     
     if (INVALID_SOCKET == ListenSocket) 
     {
          printf("\nError occurred while opening socket: %ld.", WSAGetLastError());
          goto error;
     }
     else
     {
          printf("\nsocket() successful.");
     }
     
     //Cleanup and Init with 0 the ServerAddress
     ZeroMemory((char *)&ServerAddress, sizeof(ServerAddress));
     
     //Port number will be supplied as a commandline argument
     nPortNo = atoi(argv[1]);
     
     
     //Fill up the address structure
     ServerAddress.sin_family = AF_INET;
     ServerAddress.sin_addr.s_addr = INADDR_ANY; //WinSock will supply address
     ServerAddress.sin_port = htons(nPortNo);    //comes from commandline
     
     //Assign local address and port number
     if (SOCKET_ERROR == bind(ListenSocket, (struct sockaddr *) &ServerAddress, sizeof(ServerAddress))) 
     {
          closesocket(ListenSocket);
          
          printf("\nError occurred while binding.");
          goto error;
     }
     else
     {
          printf("\nbind() successful.");
     }
     
     //Make the socket a listening socket
     if (SOCKET_ERROR == listen(ListenSocket,SOMAXCONN))
     {
          closesocket(ListenSocket);
          
          printf("\nError occurred while listening.");
          goto error;
     }
     else
     {
          printf("\nlisten() successful.");
     }
     
     //This function will take are of multiple clients using threads
     AcceptConnections(ListenSocket);
     
     //Close open sockets
     closesocket(ListenSocket);
     
     //Cleanup Winsock
     WSACleanup();
     return 0; //success
     
error:
     // Cleanup Winsock
     WSACleanup();
     return 1; //error
}

//This function will loop on while creating a new thread for each client connection
void AcceptConnections(SOCKET ListenSocket)
{
     sockaddr_in ClientAddress;
     int nClientLength = sizeof(ClientAddress);
     
     //Infinite, no graceful shutdown of server implemented, 
     //preferably server should be implemented as a service
     //Events can also be used for graceful shutdown
     while (1)
     {
          //Accept remote connection attempt from the client
          SOCKET Socket = accept(ListenSocket, (sockaddr*)&ClientAddress, &nClientLength);
          
          if (INVALID_SOCKET == Socket)
          {
               printf("\nError occurred while accepting socket: %ld.", WSAGetLastError());
          }
          
          //Display Client's IP
          printf("\nClient connected from: %s", inet_ntoa(ClientAddress.sin_addr)); 
          
          DWORD nThreadID;
          
          //Spawn one thread for each client connection, not a wise idea.
          //One should limit the number of threads or use I/O completion port
          CreateThread(0, 0, AcceptHandler, (void*)Socket, 0, &nThreadID);
     }
     
}

//Thread procedure one thread will be created for each client.
DWORD WINAPI AcceptHandler(void* Socket) 
{
     SOCKET RemoteSocket = (SOCKET)Socket;
     
     char szBuffer[256];
     
     //Cleanup and Init with 0 the szBuffer
     ZeroMemory(szBuffer,256);
     
     int nBytesSent;
     int nBytesRecv;
     
     //Receive data from a connected or bound socket
     nBytesRecv = recv(RemoteSocket, szBuffer, 255, 0 );
     
     if (SOCKET_ERROR == nBytesRecv)
     {
          closesocket(RemoteSocket);
          printf("\nError occurred while receiving from socket.");
          return 1; //error
     }
     else
     {
          printf("\nrecv() successful.");
     }
     
     //Display the message received on console
     printf("\nThe following message was received: %s", szBuffer);
     
     //Send data on a connected socket to the client
     nBytesSent = send(RemoteSocket, ACK_MESG_RECV , strlen(ACK_MESG_RECV), 0);
     
     if (SOCKET_ERROR == nBytesSent) 
     {
          closesocket(RemoteSocket);
          printf("\nError occurred while writing to socket.");
          return 1; //error
     }
     else
     {
          printf("\nsend() successful.");
     }
     
     return 0; //success
}