WinSock网络编程基础（3）server

上一篇讲的是简单的发送数据的客户端的实现。接下来讲的是如何实现收发数据服务器。
这里说的服务器其实就是一个进程，它需要等待任意数量的客户端与之建立起连接，以便响应它们的请求。

服务器必须在已知的名称上监听连接（在TCP/IP中是ip地址和端口号，不同协议的寻址方案和命名方法也不同）

创建服务器程序的第一步和客户端一样，要先初始化并且创建SOCKET（LISTENSOCKET用于监听客户端连接）

#define DEFAULT_PORT "27015"

struct addrinfo *result = NULL, *ptr = NULL, hints;

ZeroMemory(&hints, sizeof (hints));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
hints.ai_flags = AI_PASSIVE;

// Resolve the local address and port to be used by the server
iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result);
if (iResult != 0) {
    printf("getaddrinfo failed: %d\n", iResult);
    WSACleanup();
    return 1;
}
SOCKET ListenSocket = INVALID_SOCKET;
ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
if (ListenSocket == INVALID_SOCKET) {
    printf("Error at socket(): %ld\n", WSAGetLastError());
    freeaddrinfo(result);
    WSACleanup();
    return 1;
}

　　

这里的套接字设置的监听地址为AF_INET，也就是IPv4的地址。如果想监听IPv6的地址就可以设置为AF_INET6，如果想同时监听的话就需要创建两个监听套接字，（vista系统之后提供了一个特殊的套接字能够同时监听IPv4和IPv6。详情： Dual-Stack Sockets）

接下来需要将套接字绑定到它已知的地址（IP和端口）

iResult = bind( ListenSocket, result->ai_addr, (int)result->ai_addrlen);
if (iResult == SOCKET_ERROR) {
        printf("bind failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
}
freeaddrinfo(result);

　　

bind函数：

int bind(
  _In_ SOCKET s, //等待客户端连接的套接字
  _In_ const struct sockaddr *name, // 指向进行绑定的地址结构 
  _In_ int namelen //表示要传递的，由协议决定的地址结构的长度
);

一旦绑定出错，bind回返回SOCKET_ERROR。对bind而言，最常见的错误是WSAEADDRINUSE（表示另一进程已经同本地ip及端口号绑定，或者该ip和端口号处于TIME——WAIT状态）和WSAEFAULT（调用的套接字已经被绑定）

bind函数被调用之后，getaddrinfo函数返回的地址信息就基本没有什么作用了，可以使用freeaddrinfo释放地址信息。

接下来要做的是将套接字设置为监听模式：

if ( listen( ListenSocket, SOMAXCONN ) == SOCKET_ERROR ) {
    printf( "Listen failed with error: %ld\n", WSAGetLastError() );
    closesocket(ListenSocket);
    WSACleanup();
    return 1;
}

　　

listen函数：

int listen(
  _In_ SOCKET s, // 被绑定的套接字
  _In_ int backlog // 监听队列中允许保持的尚未处理的最大连接数量
);

backlog这个参数很重要，它指定了被搁置的连接的最大队列长度（比如backlog参数为3，但是有4台客户端同时发出请求，那么前3个会被放在挂起队列之中，而第四个会连接请求失败返回WSAECONNREFUSED错误）

现在可以接受客服端的连接了：

SOCKET ClientSocket;

ClientSocket = INVALID_SOCKET;

ClientSocket = accept(ListenSocket, NULL, NULL);
if (ClientSocket == INVALID_SOCKET) {
    printf("accept failed: %d\n", WSAGetLastError());
    closesocket(ListenSocket);
    WSACleanup();
    return 1;
}

　　

accept函数会返回一个新的套接字描述符，它对应已经接受了客户端的连接，该客户端的后续操作都用这个新的套接字，而原来LinstenSocket仍然处于监听模式：

SOCKET accept(
  _In_ SOCKET s, //一个出于监听模式的套接字
  _Out_ struct sockaddr *addr, //一个指向sockaddr_in结构的指针，用于取得对方的地址信息
  _Inout_ int *addrlen //addr结构的长度
);

接受客户端的连接之后，就使用RECV和SEND函数接收发送数据了

#define DEFAULT_BUFLEN 512

char recvbuf[DEFAULT_BUFLEN];
int iResult, iSendResult;
int recvbuflen = DEFAULT_BUFLEN;

do {
    iResult = recv(ClientSocket, recvbuf, recvbuflen, 0);
    if (iResult > 0) {
        printf("Bytes received: %d\n", iResult);
        iSendResult = send(ClientSocket, recvbuf, iResult, 0);
        if (iSendResult == SOCKET_ERROR) {
            printf("send failed: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }
        printf("Bytes sent: %d\n", iSendResult);
    } else if (iResult == 0)
        printf("Connection closing...\n");
    else {
        printf("recv failed: %d\n", WSAGetLastError());
        closesocket(ClientSocket);
        WSACleanup();
        return 1;
    }

} while (iResult > 0);

　　

通信完毕，断开连接：

iResult = shutdown(ClientSocket, SD_SEND);
if (iResult == SOCKET_ERROR) {
    printf("shutdown failed: %d\n", WSAGetLastError());
    closesocket(ClientSocket);
    WSACleanup();
    return 1;
}
closesocket(ClientSocket);
WSACleanup();

　　

完整的server源代码：

#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif
#include <windows.h>
#include <WinSock2.h>
#include <WS2tcpip.h>
#include <IPHlpApi.h>
#include <stdio.h>

#pragma comment(lib, "Ws2_32.lib")
//#pragma comment(lib, "Mssock.lib")
//#pragma comment(lib, "Advapi32.lib")

#define DEFAULT_PORT "27015"
#define DeFAULT_BUFLEN 512
int main()
{
	WSADATA wsaData;
	int iResult;
	int iSendResult;
	struct addrinfo *result = NULL;
	struct addrinfo	hints;
	char recvbuf[DeFAULT_BUFLEN];
	int recvbuflen = DeFAULT_BUFLEN;
	SOCKET ListenSocket = INVALID_SOCKET;
	SOCKET ClientSocket = INVALID_SOCKET;

	iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
	if (iResult != 0)
	{
		printf("WSAStartup failed: %d\n", iResult);
		return 1;
	}

	ZeroMemory(&hints, sizeof(hints));
	hints.ai_family = AF_INET;
	hints.ai_socktype = SOCK_STREAM;
	hints.ai_protocol = IPPROTO_TCP;
	hints.ai_flags = AI_PASSIVE;

	// 为服务器确定本地地址和端口
	iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result);
	if (iResult != 0)
	{
		printf("getaddrinfo failed: %d\n", iResult);
		WSACleanup();
		return 1;
	}

	ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
	if (ListenSocket == INVALID_SOCKET)
	{
		printf("socket failed with error: %ld\n", WSAGetLastError());
		freeaddrinfo(result);
		WSACleanup();
		return 1;
	}

	iResult = bind(ListenSocket, result->ai_addr, (int)result->ai_addrlen);
	if (iResult == SOCKET_ERROR)
	{
		printf("bind failed with error: %d\n", WSAGetLastError());
		freeaddrinfo(result);
		closesocket(ListenSocket);
		WSACleanup();
		return 1;
	}
	freeaddrinfo(result);

	iResult = listen(ListenSocket, SOMAXCONN);
	if (iResult == SOCKET_ERROR)
	{
		printf("Listen failed with error: %d\n", WSAGetLastError());
		closesocket(ListenSocket);
		WSACleanup();
		return 1;
	}

	ClientSocket = accept(ListenSocket, NULL, NULL);
	if (ClientSocket == INVALID_SOCKET)
	{
		printf("accept failed: %d\n", WSAGetLastError());
		closesocket(ClientSocket);
		WSACleanup();
		return 1;
	}
	closesocket(ListenSocket);

	do
	{
		iResult = recv(ClientSocket, recvbuf, recvbuflen, 0);
		if (iResult > 0)
		{
			printf("Bytes received: %d\n", iResult);
			iSendResult = send(ClientSocket, recvbuf, iResult, 0);
			if (iSendResult == SOCKET_ERROR)
			{
				printf("send failed: %d\n", WSAGetLastError());
				closesocket(ClientSocket);
				WSACleanup();
				return 1;
			}
			printf("Bytes sent: %d\n", iSendResult);
		}
		else if (iResult == 0)
		{
			printf("Connection closing...\n");
		}
		else
		{
			printf("recv failed: %d\n", WSAGetLastError());
			closesocket(ClientSocket);
			WSACleanup();
			return 1;
		}
	} while (iResult > 0);

	// 断开连接
	iResult = shutdown(ClientSocket, SD_SEND);
	if (iResult == SOCKET_ERROR)
	{
		printf("shutdown failed: %d\n", WSAGetLastError());
		closesocket(ClientSocket);
		WSACleanup();
		return 1;
	}
	// 清理连接
	printf("recv message: %s", recvbuf);
	closesocket(ClientSocket);
	WSACleanup();

	return 0;
}

　　

原文链接: http://www.bugcoding.com/entry/11