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 = ;
     int                  Ret;
     char                 DataBuffer[];

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

     // 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 -;
     }

     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 -;
     }

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

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

     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 -;
     }

     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...**\n";

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

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

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

     closesocket(NewConnection);
     WSACleanup();

     return ;
 }

Server Code

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 = ;
     int                  Ret;

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

     // Initialize Winsock version 2.2

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

     // 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 -;
     }

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

     // 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) << "...\n";

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

     cout << "Our connection succeeded.\n";

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

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

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

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

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

     closesocket(s);

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

     WSACleanup();
     return ;
 }

Client Code

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。。？？