서버

/*
## 소켓 서버 : 1 v n - overlapped callback
1. socket()			: 소켓생성
2. bind()			: 소켓설정
3. listen()			: 수신대기열생성
4. accept()			: 연결대기
5. read()&write()
	WIN recv()&send	: 데이터 읽고쓰기
6. close()
	WIN closesocket	: 소켓종료
*/

#include "stdafx.h"
#include <winsock2.h>

#pragma comment(lib, "Ws2_32.lib")

#define MAX_BUFFER		1024
#define SERVER_PORT		3500

struct SOCKETINFO
{
	WSAOVERLAPPED overlapped;
	WSABUF dataBuffer;
	SOCKET socket;
	char messageBuffer[MAX_BUFFER];
	int receiveBytes;
	int sendBytes;
};

void CALLBACK callback(DWORD Error, DWORD dataBytes, LPWSAOVERLAPPED overlapped, DWORD lnFlags);

int _tmain(int argc, _TCHAR* argv[])
{
	// Winsock Start - windock.dll 로드
	WSADATA WSAData;
	if (WSAStartup(MAKEWORD(2, 2), &WSAData) != 0)
	{
		printf("Error - Can not load 'winsock.dll' file\n");
		return 1;
	}

	// 1. 소켓생성  
	SOCKET listenSocket = WSASocket(AF_INET, SOCK_STREAM, 0, NULL, 0, WSA_FLAG_OVERLAPPED);
	if (listenSocket == INVALID_SOCKET)
	{
		printf("Error - Invalid socket\n");
		return 1;
	}

	// 서버정보 객체설정
	SOCKADDR_IN serverAddr;
	memset(&serverAddr, 0, sizeof(SOCKADDR_IN));
	serverAddr.sin_family = PF_INET;
	serverAddr.sin_port = htons(SERVER_PORT);
	serverAddr.sin_addr.S_un.S_addr = htonl(INADDR_ANY);

	// 2. 소켓설정
	if (bind(listenSocket, (struct sockaddr*)&serverAddr, sizeof(SOCKADDR_IN)) == SOCKET_ERROR)
	{
		printf("Error - Fail bind\n");
		// 6. 소켓종료
		closesocket(listenSocket);
		// Winsock End
		WSACleanup();
		return 1;
	}

	// 3. 수신대기열생성
	if (listen(listenSocket, 5) == SOCKET_ERROR)
	{
		printf("Error - Fail listen\n");
		// 6. 소켓종료
		closesocket(listenSocket);
		// Winsock End
		WSACleanup();
		return 1;
	}

	SOCKADDR_IN clientAddr;
	int addrLen = sizeof(SOCKADDR_IN);
	memset(&clientAddr, 0, addrLen);
	SOCKET clientSocket;
	SOCKETINFO *socketInfo;
	DWORD receiveBytes;
	DWORD flags;
	
	while (1)
	{
		clientSocket = accept(listenSocket, (struct sockaddr *)&clientAddr, &addrLen);
		if (clientSocket == INVALID_SOCKET)
		{
			printf("Error - Accept Failure\n");
			return 1;
		}

		socketInfo = (struct SOCKETINFO *)malloc(sizeof(struct SOCKETINFO));
		memset((void *)socketInfo, 0x00, sizeof(struct SOCKETINFO));
		socketInfo->socket = clientSocket;
		socketInfo->dataBuffer.len = MAX_BUFFER;
		socketInfo->dataBuffer.buf = socketInfo->messageBuffer;
		flags = 0;

		// 중첩 소캣을 지정하고 완료시 실행될 함수를 넘겨준다.
		if (WSARecv(socketInfo->socket, &socketInfo->dataBuffer, 1, &receiveBytes, &flags, &(socketInfo->overlapped), callback))
		{
			if (WSAGetLastError() != WSA_IO_PENDING)
			{
				printf("Error - IO pending Failure\n");
				return 1;
			}
		}
	}

	// 6-2. 리슨 소켓종료
	closesocket(listenSocket);

	// Winsock End
	WSACleanup();
	
	return 0;
}

void CALLBACK callback(DWORD Error, DWORD dataBytes, LPWSAOVERLAPPED overlapped, DWORD lnFlags)
{
	struct SOCKETINFO *socketInfo;
	DWORD sendBytes = 0;
	DWORD receiveBytes = 0;
	DWORD flags = 0;

	socketInfo = (struct SOCKETINFO *)overlapped;
	memset(&(socketInfo->overlapped), 0x00, sizeof(WSAOVERLAPPED));

	if (dataBytes == 0)
	{
		closesocket(socketInfo->socket);
		free(socketInfo);
		return;
	}

	if (socketInfo->receiveBytes == 0)
	{
		// WSARecv(최초 대기에 대한)의 콜백일 경우
		socketInfo->receiveBytes = dataBytes;
		socketInfo->sendBytes = 0;		
		socketInfo->dataBuffer.buf = socketInfo->messageBuffer;
		socketInfo->dataBuffer.len = socketInfo->receiveBytes;

		printf("TRACE - Receive message : %s (%d bytes)\n", socketInfo->messageBuffer, dataBytes);

		if (WSASend(socketInfo->socket, &(socketInfo->dataBuffer), 1, &sendBytes, 0, &(socketInfo->overlapped), callback) == SOCKET_ERROR)
		{
			if (WSAGetLastError() != WSA_IO_PENDING)
			{
				printf("Error - Fail WSASend(error_code : %d)\n", WSAGetLastError());
			}			
		}
	}
	else
	{
		// WSASend(응답에 대한)의 콜백일 경우
		socketInfo->sendBytes += dataBytes;
		socketInfo->receiveBytes = 0;		
		socketInfo->dataBuffer.len = MAX_BUFFER;
		socketInfo->dataBuffer.buf = socketInfo->messageBuffer;

		printf("TRACE - Send message : %s (%d bytes)\n", socketInfo->messageBuffer, dataBytes);

		if (WSARecv(socketInfo->socket, &socketInfo->dataBuffer, 1, &receiveBytes, &flags, &(socketInfo->overlapped), callback) == SOCKET_ERROR)
		{
			if (WSAGetLastError() != WSA_IO_PENDING)
			{
				printf("Error - Fail WSARecv(error_code : %d)\n", WSAGetLastError());
			}			
		}
	}
}

---

클라이언트

/*
## 소켓 서버 : 1 v n - overlapped callback
1. socket()			: 소켓생성
2. connect()		: 연결요청
3. read()&write()
	WIN recv()&send	: 데이터 읽고쓰기
4. close()
	WIN closesocket	: 소켓종료
*/

#include "stdafx.h"
#include <winsock2.h>

#pragma comment(lib, "Ws2_32.lib")

#define MAX_BUFFER		1024
#define SERVER_IP		"127.0.0.1"
#define SERVER_PORT		3500

struct SOCKETINFO
{	
	WSAOVERLAPPED overlapped;
	WSABUF dataBuffer;	
	int receiveBytes;
	int sendBytes;
};

int _tmain(int argc, _TCHAR* argv[])
{	
	// Winsock Start - winsock.dll 로드
	WSADATA WSAData;
	if (WSAStartup(MAKEWORD(2, 0), &WSAData) != 0)
	{
		printf("Error - Can not load 'winsock.dll' file\n");
		return 1;
	}

	// 1. 소켓생성
	SOCKET listenSocket = WSASocket(AF_INET, SOCK_STREAM, 0, NULL, 0, WSA_FLAG_OVERLAPPED);
	if (listenSocket == INVALID_SOCKET)
	{
		printf("Error - Invalid socket\n");
		return 1;
	}

	// 서버정보 객체설정
	SOCKADDR_IN serverAddr;
	memset(&serverAddr, 0, sizeof(SOCKADDR_IN));
	serverAddr.sin_family = AF_INET;
	serverAddr.sin_port = htons(SERVER_PORT);
	serverAddr.sin_addr.S_un.S_addr = inet_addr(SERVER_IP);

	// 2. 연결요청
	if (connect(listenSocket, (struct sockaddr *)&serverAddr, sizeof(serverAddr)) == SOCKET_ERROR)
	{
		printf("Error - Fail to connect\n");
		// 4. 소켓종료
		closesocket(listenSocket);
		// Winsock End
		WSACleanup();
		return 1;
	}
	else
	{
		printf("Server Connected\n* Enter Message\n->");
	}
	
	SOCKETINFO *socketInfo;
	DWORD sendBytes;
	DWORD receiveBytes;
	DWORD flags;

	while (1)
	{		
		// 메시지 입력
		char messageBuffer[MAX_BUFFER];
		int i, bufferLen;
		for (i = 0; 1; i++)
		{
			messageBuffer[i] = getchar();
			if (messageBuffer[i] == '\n')
			{
				messageBuffer[i++] = '\0';
				break;
			}
		}
		bufferLen = i;
		
		socketInfo = (struct SOCKETINFO *)malloc(sizeof(struct SOCKETINFO));
		memset((void *)socketInfo, 0x00, sizeof(struct SOCKETINFO));		
		socketInfo->dataBuffer.len = bufferLen;
		socketInfo->dataBuffer.buf = messageBuffer;

		// 3-1. 데이터 쓰기
		int sendBytes = send(listenSocket, messageBuffer, bufferLen, 0);
		if (sendBytes > 0)
		{
			printf("TRACE - Send message : %s (%d bytes)\n", messageBuffer, sendBytes);
			// 3-2. 데이터 읽기
			int receiveBytes = recv(listenSocket, messageBuffer, MAX_BUFFER, 0);
			if (receiveBytes > 0)
			{
				printf("TRACE - Receive message : %s (%d bytes)\n* Enter Message\n->", messageBuffer, receiveBytes);
			}			
		}
		
	}		

	// 4. 소켓종료
	closesocket(listenSocket);

	// Winsock End
	WSACleanup();
	
	return 0;
}