[译文]Winsock API实现了一个Tcp服务器 - for 初学者_c# tcp通讯 winsock

[译文] Winsock API实现了一个Tcp服务器 - for 初学者
来源：http://www.codeproject.com/internet/winsockintro01.asp

（一）介绍：
本文主要采用Winsock API实现了一个Tcp服务器。对初学者而言，相当实用。

（二）准备工作：
1 使用vc6向导建立控制台工程（console application），并选择支持MFC。
2 在stdafx.h中加入头文件conio.h和winsock2.h。
3 在头文件中加入：#pragma comment(lib, "ws2_32.lib")。

（三）主程序：主要是启动服务器线程并等待用户退出的命令。
int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{
    int nRetCode = 0;   
   
    cout << "Press ESCAPE to terminate program/r/n";
    AfxBeginThread(ServerThread,0); //启动一条线程
    while(_getch()!=27); //用户按ESC键则退出
   
    return nRetCode;
}

（四）线程代码：一个简单的tcp服务器，返回客户的ip地址。
UINT  ServerThread(LPVOID pParam)
{   
    cout << "Starting up TCP server/r/n";
   
    //A SOCKET is simply a typedef for an unsigned int.
    //In Unix, socket handles were just about same as file
    //handles which were again unsigned ints.
    //Since this cannot be entirely true under Windows
    //a new data type called SOCKET was defined.
   
    //定义一个socket句柄作为服务器
    SOCKET server;
   
    //WSADATA is a struct that is filled up by the call
    //to WSAStartup

    //这是一个结构体，用于调用函数WSAStartup时作为参数
    WSADATA wsaData;
   
    //The sockaddr_in specifies the address of the socket
    //for TCP/IP sockets. Other protocols use similar structures.

    //存放ip地址的结构体
    sockaddr_in local;
   
    //WSAStartup initializes the program for calling WinSock.
    //The first parameter specifies the highest version of the
    //WinSock specification, the program is allowed to use.

    //初始化winsock，每次必须最先调用
    int wsaret=WSAStartup(0x101,&wsaData);
   
    //WSAStartup returns zero on success.
    //If it fails we exit.

    //测试初始化是否成功
    if(wsaret!=0)
    {
        return 0;
    }
   
    //Now we populate the sockaddr_in structure

    //填充服务器的ip地址和端口号
    local.sin_family=AF_INET; //Address family
    local.sin_addr.s_addr=INADDR_ANY; //Wild card IP address
    local.sin_port=htons((u_short)8888); //port to use
   
    //the socket function creates our SOCKET

    //建立一个tcp socket
    server=socket(AF_INET,SOCK_STREAM,0);
   
    //If the socket() function fails we exit
    if(server==INVALID_SOCKET)
    {
        return 0;
    }
   
    //bind links the socket we just created with the sockaddr_in
    //structure. Basically it connects the socket with
    //the local address and a specified port.
    //If it returns non-zero quit, as this indicates error

    //绑定服务器的ip地址和端口号
    if(bind(server,(sockaddr*)&local,sizeof(local))!=0)
    {
        return 0;
    }
   
    //listen instructs the socket to listen for incoming
    //connections from clients. The second arg is the backlog
   
    //监听客户端请求，最大同时连接数10
    if(listen(server,10)!=0)
    {
        return 0;
    }
   
    //we will need variables to hold the client socket.
    //thus we declare them here.

    //接受请求后，实际同客户端socket进行交互的SOCKET client
    SOCKET client;
    sockaddr_in from;
    int fromlen=sizeof(from);
   
    while(true)//we are looping endlessly
    {
        char temp[512];
       
        //accept() will accept an incoming
        //client connection

    //接受一个连接请求，并返回一个同客户端交互的socket给变量client
        client=accept(server,
            (struct sockaddr*)&from,&fromlen);
       
    //得到客户端的ip地址，并写入缓冲区
        sprintf(temp,"Your IP is %s/r/n",inet_ntoa(from.sin_addr));
       
        //we simply send this string to the client

    // 发送回缓冲中的内容（即：客户端的ip地址）
        send(client,temp,strlen(temp),0);
        cout << "Connection from " << inet_ntoa(from.sin_addr) <<"/r/n";
       
        //close the client socket
    //关闭连接
        closesocket(client);
       
    }
   
    //closesocket() closes the socket and releases the socket descriptor
    //释放socket资源
    closesocket(server);
   
    //originally this function probably had some use
    //currently this is just for backward compatibility
    //but it is safer to call it as I still believe some
    //implementations use this to terminate use of WS2_32.DLL
    //必须作的最后的事
    WSACleanup();
   
    return 0;
}

（五）运行：
服务器端：
E:/work/Server/Debug>server
Press ESCAPE to terminate program
Starting up TCP server
Connection from 203.200.100.122
Connection from 127.0.0.1
E:/work/Server/Debug>

客户端：
E:/work/Server/Debug>telnet 202.89.211.88 8888
Trying 202.89.211.88...
Connected to 202.89.211.88.
Escape character is '^]'.
Your IP is 203.200.100.122
Connection closed by foreign host.

（六）说明：
这只是一个极为简单的tcp server程序，目的是帮助初学者学习winsock编程。因此，程序本着简单的原则，对于很多方面考虑都较少。比如，退出时候可能有socket句柄未释放的危险；只有一条线程，客户端很多时不够实用等等。这些都需要进一步的考虑。