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;
}