Winsock网络编程笔记（2）----基于TCP的server和client

今天抽空看了一些简单的东西，主要是对服务器server和客户端client的简单实现。

面向连接的server和client，其工作流程如下图所示：

服务器和客户端将按照这个流程就行开发。。（个人觉得：通过这个流程图，Server应该要先于Client启动，不然Client的connect函数的执行就会出错啦，不知道我的个人感觉对不对，后面试试就知道了。。O(∩_∩)O~）

注意：上图的Server和Client的工作流程是基于面向有连接通信的工作流程，如果是无连接的通信，则不必调用listen和accept。 在无连接的通信中，Server调用recvfrom函数来接收消息    

在编写服务器和客户端之前，需要对TCP状态有所了解。。在server和client通信之间，二者都是通过发送/接收不同的信号来改变自己的状态，其tcp状态转换图如下：

了解了二者的开发流程，就可以通过接口来具体实现。

简单的server代码实现：

#include"winsock2.h"
#include<iostream>
using namespace std;
//This line is very important

#pragma comment(lib,"ws2_32.lib")
int main()
{
    WSADATA              wsaData;
    SOCKET               ListeningSocket;
    SOCKET               NewConnection;
    SOCKADDR_IN          ServerAddr;
    SOCKADDR_IN          ClientAddr;
    int                  ClientAddrLen;
    int                  Port = 5150;
    int                  Ret;
    char                 DataBuffer[1024];

    if ((Ret = WSAStartup(MAKEWORD(2,2), &wsaData)) != 0)
    {
        cout<<"WSAStartup failed with error "<<Ret<<endl;
        //here no WSACleanup，because we do not create anything;
        return -1;
    }

    // Create a new socket to listening for client connections.
    ListeningSocket = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
    if ( INVALID_SOCKET == ListeningSocket)
    {
        cout<<"Socket failed with error "<<WSAGetLastError()<<endl;
        WSACleanup();
        return -1;
    }

    ServerAddr.sin_family = AF_INET;
    ServerAddr.sin_addr.s_addr = htonl(INADDR_ANY);
    ServerAddr.sin_port = htons(Port);

    //to bind
    if (bind(ListeningSocket, (SOCKADDR *)&ServerAddr, sizeof(ServerAddr)) == SOCKET_ERROR)
    {
        cout<<"Binding failed with error "<<WSAGetLastError()<<endl;
        closesocket(ListeningSocket);
        WSACleanup();
        return -1;
    }

    // Listen for client connections. We used a backlog of 5 which is
    // normal for many applications.

    if (listen(ListeningSocket,5) == SOCKET_ERROR)
    {
        cout<<"Listen failed with error "<<WSAGetLastError()<<endl;
        closesocket(ListeningSocket);
        WSACleanup();
        return -1;
    }

    cout<<"** We are waiting for a connection on port "<<Port<<"**"<<endl;

    //accep a connection when one arrives

    NewConnection = accept(ListeningSocket,(SOCKADDR*)&ClientAddr,&ClientAddrLen);
    if (INVALID_SOCKET == NewConnection)
    {
        cout<<"Accept failed with error "<<WSAGetLastError()<<endl;
        closesocket(ListeningSocket);
        WSACleanup();
        return -1;
    }

    cout<<"** We successfully got a connection from "<<inet_ntoa(ClientAddr.sin_addr)
        <<":port "<<ntohs(ClientAddr.sin_port)<<"!!**"<<endl;

    closesocket(ListeningSocket);
    cout<<"** We are waiting for data...**
";

    Ret = recv(NewConnection,DataBuffer,sizeof(DataBuffer),0);
    if (SOCKET_ERROR == Ret)
    {
        cout<<"Recv failed with error "<<WSAGetLastError()<<endl;
        closesocket(NewConnection);
        WSACleanup();
        return -1;
    }

    cout<<"**We have successfully recieve "<<Ret<<" Byte(s) data!**
";

    cout<<"**We are going to close the client connection...**
";

    closesocket(NewConnection);
    WSACleanup();

    return 0;
}

客户端的实现：

#include"winsock2.h"
#include<iostream>
using namespace std;
//This line is very important

#pragma comment(lib,"ws2_32.lib")
int main(int argc, char **argv)
{
    WSADATA              wsaData;
    SOCKET               s;
    SOCKADDR_IN          ServerAddr;
    int                  Port = 5150;
    int                  Ret;

    if (argc <= 1)
    {
        cout<<"USAGE: tcpclient <Server IP address>.
";
        return -1;
    }

    // Initialize Winsock version 2.2

    if ((Ret = WSAStartup(MAKEWORD(2,2), &wsaData)) != 0)
    {
        cout<<"WSAStartup failed with error "<<Ret<<endl;
        return -1;
    }

    // Create a new socket to make a client connection.

    s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (INVALID_SOCKET == s)
    {
        cout << "socket failed with error " << WSAGetLastError()<<endl;
        WSACleanup();
        return -1;
    }

    ServerAddr.sin_family = AF_INET;
    ServerAddr.sin_port = htons(Port);    
    ServerAddr.sin_addr.s_addr = inet_addr(argv[1]);

    // Make a connection to the server with socket s.

    cout<< "We are trying to connect to " << inet_ntoa(ServerAddr.sin_addr)
        << ":" << htons(ServerAddr.sin_port) << "...
";

    if (connect(s, (SOCKADDR *) &ServerAddr, sizeof(ServerAddr)) 
        == SOCKET_ERROR)
    {
        cout << "connect failed with error " << WSAGetLastError() << endl;
        closesocket(s);
        WSACleanup();
        return -1;
    } 

    cout << "Our connection succeeded.
";


    cout << "We will now try to send a hello message.
";

    if ((Ret = send(s, "Hello", 5, 0)) == SOCKET_ERROR)
    {
        cout << "send failed with error " << WSAGetLastError()<<endl;
        closesocket(s);
        WSACleanup();
        return -1;
    }

    cout << "We successfully sent " << Ret << " byte(s).
";

    // When you are finished sending and receiving data on socket s,
    // you should close the socket.

    cout << "We are closing the connection.
";

    closesocket(s);

    // When your application is finished handling the connection, call
    // WSACleanup.

    WSACleanup();
    return 0;
}

咦，奇了怪了，按照书上的代码，执行起来居然报错。。这是咋回事啊。。

运行Server时，出现这样的错误：

通过报错信息可以知道是accept函数出错了。

那就对症下药，哪儿错儿改哪儿。。

上网查找资料，找到accept函数定义：

SOCKET accept(
__in SOCKET s,
__out struct sockaddr *addr,
__inout int *addrlen
);

       第一个参数就是套接字描述符，第二个参数是，接受客户端基本信息的结构体，第三参数很重要，是准备接受结构体的大小，上面的程序 int ClientAddrLen；传进去的时候只是把未知的ClientAddrLen的地址传进去，要传进去的应该是接收这些信息的基本大小啊，所以 得加ClientAddrLen = sizeof(SOCKADDR);。这样程序就执行accept。

注意：客户端需要在服务器运行的时候才能执行，不然会出错的。。

运行Server和Client（需要ip作为main函数的参数，不会的自己百度怎样在VS2008中给main传递参数），二者可以连接了。。执行还没有实现二者的通信。。。呜呜~~~~(>_<)~~~~ 

拓展：

观察Server中的recv函数和Client中send函数，我想是否可以利用无限循环的方式在Client端输入字符串，在Server端打印该字符串？----就像聊天一样，你输入一句，我这边就显示这一句。。。只是这样只能是单工方式的传输，不能从Server发送到Client端。。那是否可以考虑多线程呢，一个线程运行Server，一个线程运行Client。。？？