c - C 网络编程(数据未使用 send() 从客户端发送到服务器)

Question

我有两个文件，一个客户端和一个服务器，我想将变量(选择)的值从客户端发送到服务器，但该值没有被发送，我不知道问题是什么

这是我的客户端代码

    #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    #include<sys/types.h>
    #include<netinet/in.h>
    #include<sys/socket.h>
    #include<netdb.h>
    #include<arpa/inet.h>
    #include<fcntl.h>

    int main(int argc , char *argv[])
    {

        char buf;
        int clientSocket, cnnt,fileDiscriptor,sizeInByte=0 , size=0 , serverSocket,choice=2 ;
        struct sockaddr_in serverInfo;

        if(argc != 3)
        {
            printf("Few arguments\nUsage : ./client <ip> <port>\n");
            exit(1);    
        }

        memset(&serverInfo,0,sizeof(serverInfo));   

        serverInfo.sin_family = AF_INET;
        inet_aton(argv[1],&serverInfo.sin_addr.s_addr);
        serverInfo.sin_port = htons(atoi(argv[2]));
        clientSocket = socket(AF_INET,SOCK_STREAM,0);
        if(clientSocket < 0)
        {
            printf("Could not create client socket\n");
            exit(1);
        }

        cnnt = connect(clientSocket,(struct sockaddr *)&serverInfo,sizeof(serverInfo));
        if(cnnt < 0)
        {   
            printf("Could not create connection to the server\n");   
            exit(1);    
        }
        recv(clientSocket , &serverSocket , sizeof(int) , 0);
        send(serverSocket , &choice , sizeof(int),0);
        close(clientSocket);
        return 0;

    }

这是我的服务器代码

    #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    #include<sys/types.h>
    #include<netinet/in.h>
    #include<sys/socket.h>
    #include<netdb.h>
    #include<arpa/inet.h>
    #include<sys/stat.h>
    #include<fcntl.h>
    #include <sys/wait.h>


    int main(int argc , char *argv[])
    {   
        int choice;
        int serverSocket, bnd, lstn , clientSize, connectionFd;
        struct sockaddr_in serverInfo, clientInfo  ;

        if(argc != 2)
        {   
            printf("Few arguments\nUsage : ./server <port>\n");
            exit(1);    
        }   

        memset(&serverInfo , 0 , sizeof(serverInfo));
        memset(&clientInfo , 0 , sizeof(clientInfo));   

        serverInfo.sin_family = AF_INET;
        serverInfo.sin_port = htons(atoi(argv[1]));
        serverInfo.sin_addr.s_addr = INADDR_ANY;
        serverSocket = socket(AF_INET,SOCK_STREAM,0);
        if(serverSocket < 0)
        {
            printf("Could not create server socket\n");
            exit(1);    
        }

        bnd = bind(serverSocket , (struct sockaddr *)&serverInfo , sizeof(serverInfo));
        if(bnd < 0)
        {
            printf("Could not bind\n");
            exit(1);    
        }

        lstn = listen(serverSocket , 1);
        if(lstn < 0)
        {
            printf("Could not listen on server socket\n");
            exit(1);    
        }
        clientSize = sizeof(clientInfo);
        while(1)
        {
            connectionFd =  accept(serverSocket , (struct sockaddr *)&clientInfo , &clientSize);
            if(connectionFd < 0)
                continue;
                    send(connectionFd , &serverSocket , sizeof(int) , 0);
            recv(serverSocket , &choice , sizeof(int),0);
            close(connectionFd);
            break;
        }
        printf("CHOICE IS :%d\n",choice);
        return 0;
    }

Answer 1

服务器代码中执行以下操作的行:

 send(connectionFd , &serverSocket , sizeof(int) , 0);

不需要，因此将其删除。没有理由将服务器套接字的值发送到客户端，客户端无论如何都无法使用它，文件描述符是连接到进程的资源，并且您不能通过写入该资源的值来将该资源传输到另一个进程到客户端的 TCP 连接。

在客户端，您需要在刚刚打开的连接上发送选择变量，因此你需要更改这两行:

recv(clientSocket , &serverSocket , sizeof(int) , 0);
send(serverSocket , &choice , sizeof(int),0);

对此:

 send(clientSocket , &choice , sizeof(int),0);

除此之外，您应该养成检查所有调用是否有错误的习惯，以便您知道是否出现故障，例如

int rc;

rc = send(clientSocket , &choice , sizeof(int),0);
if (rc == -1) {
    perror("send()");
    //handle error, e.g. exit the app
}