winsock学习笔记（三）

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#c++ #socket #winsock #网络

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本文档是关于Winsock的入门学习笔记，主要涵盖如何在Windows环境下进行网络编程，包括初始化Winsock、创建套接字、绑定、监听、接受连接、收发数据以及断开连接等基本步骤。

PS：这几篇学习笔记都是在windows dev center上学习的东西，大部分是翻译。传送门：http://msdn.microsoft.com/en-us/library/windows/desktop/ms738545(v=vs.85).aspx#winsock.advanced_winsock_samples

服务端：

Initialize Winsock.（初始化winsock）
Create a socket.（创建套接字）
Bind the socket.（绑定套接字）
Listen on the socket for a client.（监听套接字，等待客户端连接）
Accept a connection from a client.（接受客户端连接）
Receive and send data.（接受和发送数据或消息）
Disconnect.（断开连接）

1、Create a socket：

#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;

// Create a SOCKET for the server to listen for client connections

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;
}

**代码基本跟创建客户端socket的时候一样，唯一值得注意的是，hints.ai_flags设置为AI_PASSIVE，当这个位被置位时候，通常在getaddrinfo函数中的第一个参数，也即是地址名设置为NULL，这样就会返回一个通配地址。网上也有资料说系统会将主机自己的地址填充进去。像我自己这样测试之后打印出来是0.0.0.0。

**这里要拓展一下，返回的result结构中一个属性是sockaddr*结构指针类型的ai_addr。它包含了两个属性，一个是AF_Family，一个是14个字节的char数组，填充了使用网络字节顺序的地址和端口号。sockaddr的类型随着AF_Family的值而变，当其值为AF_INET使，可用sockaddr_in结构强制转换。然后可以通过两个函数inet_ntoa（（sockaddr_in*）ai_addr->sin_addr）和ntohs(（sockaddr_in*）ai_addr->sin_port)将网络字节顺序的数据转化为机器字节顺序的输出。一般来说，编程的时候我们不使用sockaddr结构，这个是给操作系统用的。做法是使用sockaddr_in对我们使用的信息进行填充，然后强制转化为sockaddr结构，当做参数传入bind，accept等函数。

2、 Bind a socket:

C++:

// Setup the TCP listening socket
    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;
    }

对于服务端socket来说，必须将地址和端口号和你的socket绑定起来，才能进行下一步的对其进行监听。由于绑定之后，由getaddrinfo所返回的result结构我们不再需要，所以可以用freeaddrinfo释放对应的资源。

3、 Listen to a socket:

C++:

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

Listen函数的第二个参数比较值得研究，它是表示还没连接的在缓冲池中的客户端数。具体的情况可以看看网上一篇博客上的分析，写的很好。传送门：http://blog.youkuaiyun.com/ordeder/article/details/21551567 有时候这个参数设置得很小但是客户端连接依旧没有问题，这是因为操作系统从缓冲池中取出然后处理的时间太短，所以很少出现同时几个客户端都在连接的情况。

4、 Accept a socket

SOCKET ClientSocket;

ClientSocket = INVALID_SOCKET;
// Accept a client socket

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

closesocket(ListenSocket);

WSACleanup();

ClientSocket = INVALID_SOCKET;

// Accept a client socket

ClientSocket = accept(ListenSocket, NULL, NULL);

if(ClientSocket == INVALID_SOCKET) {

printf("accept failed: %d\n", WSAGetLastError());

closesocket(ListenSocket);

WSACleanup();

return 1;

}

接入一个客户端socket并用CLientSocket保存，因为还要往这个客户端socket写回信息。如果在更高级点的技术或者多线程接入多个客户端的话，通常accept之后，后面处理IO之类的工作会丢给工作线程去处理而自己不再管这个客户端socket，因为server socket还要继续处理listen，accept之类的工作。可用select函数或者WSAPoll来帮忙处理实现。

5、 receive and send data

6、 disconnect

上述两步跟客户端的操作基本一样，不再敖述。下面贴出完整的服务端socket代码。

#undef UNICODE

#define WIN32_LEAN_AND_MEAN

#include <windows.h>

#include <winsock2.h>

#include <ws2tcpip.h>

#include <stdlib.h>

#include <stdio.h>

// Need to link with Ws2_32.lib

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

// #pragma comment (lib, "Mswsock.lib")

#define DEFAULT_BUFLEN 512

#define DEFAULT_PORT "27015"

int

__cdecl main(void)

    WSADATA wsaData;

    int iResult;

    SOCKET ListenSocket = INVALID_SOCKET;

    SOCKET ClientSocket = INVALID_SOCKET;

    struct addrinfo *result = NULL;

    struct addrinfo hints;

    int iSendResult;

    char recvbuf[DEFAULT_BUFLEN];

    int recvbuflen = DEFAULT_BUFLEN;

    // Initialize Winsock

    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);

    if (iResult != 0) {

        printf("WSAStartup failed with error: %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;

    // Resolve the server address and port

    iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result);

    if ( iResult != 0 ) {

        printf("getaddrinfo failed with error: %d\n", iResult);

        WSACleanup();

        return 1;

    // Create a SOCKET for connecting to server

    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;

    // Setup the TCP listening socket

    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;

    // Accept a client socket

    ClientSocket = accept(ListenSocket, NULL, NULL);

    if (ClientSocket == INVALID_SOCKET) {

        printf("accept failed with error: %d\n", WSAGetLastError());

        closesocket(ListenSocket);

        WSACleanup();

        return 1;

    // No longer need server socket

    closesocket(ListenSocket);

    // Receive until the peer shuts down the connection

    do {

        iResult = recv(ClientSocket, recvbuf, recvbuflen, 0);

        if (iResult > 0) {

            printf("Bytes received: %d\n", iResult);

        // Echo the buffer back to the sender

            iSendResult = send( ClientSocket, recvbuf, iResult, 0 );

            if (iSendResult == SOCKET_ERROR) {

                printf("send failed with error: %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 with error: %d\n", WSAGetLastError());

            closesocket(ClientSocket);

            WSACleanup();

            return 1;

    } while (iResult > 0);

    // shutdown the connection since we're done

    iResult = shutdown(ClientSocket, SD_SEND);

    if (iResult == SOCKET_ERROR) {

        printf("shutdown failed with error: %d\n", WSAGetLastError());

        closesocket(ClientSocket);

        WSACleanup();

        return 1;

    // cleanup

    closesocket(ClientSocket);

    WSACleanup();

    return 0;