C ++ Winsock - 服务器只与单个客户端通信，而它应该与每个客户端通信

c++ winsock - server communicates only with single client while it should communicate with every client

本文关键字：通信客户端服务器 Winsock 单个更新时间：2023-10-16

我正在编写一个带有GUI的聊天程序。我想编写一个可以接受许多客户端的服务器。每个客户端都可以成功连接。但是发送和接收数据存在一个奇怪的问题。我使用 select(( 和一个线程同时处理许多套接字。如果客户端向服务器发送一些数据，它将接收它并将其发送回该客户端(特别是客户端在没有"预测"的情况下编写(。但是服务器不会将其进一步发送到另一个客户端(就像每个客户端都与服务器进行自己的私人对话一样(。这是我的代码：

// this is rewritten from the Beej's tutorial with a little and insignificant changes
/* in the thread */
fd_set mainfd;
fd_set readfd;
// sin-size, newfd, maxfd - int
while(TRUE)
{
    readfd = mainfd;
    if(select(maxfd+1, &readfd, NULL, NULL, NULL) == -1)
    {
        MessageBoxA(NULL, "Error while trying to accept incoming connections (select)", "Error", 16);
        itoa(GetLastError(), buf, 10);
        MessageBoxA(NULL, buf, buf, 0);
        break;
    }
    for(int i = 0; i <= maxfd; i++)
    {
        char* psr;
        char srMsg[256];
        if(FD_ISSET(i, &readfd))
        {
            if(i == mainSocket)
            {
                sin_size = sizeof(their_addr);
                newfd = accept(mainSocket, (struct sockaddr*)&their_addr, &sin_size);
                if(newfd == SOCKET_ERROR)
                {
                    AddTextToEdit(hStaticChat, "* Error: couldn't accept incoming connection.", TRUE);
                }
                else
                {
                    FD_SET(newfd, &mainfd);
                    if(newfd > maxfd)
                    {
                        maxfd = newfd;
                    }
                }
            }
            else
            {
                len = recv(i, srMsg, 256, 0);
                if(len == 0 || len == SOCKET_ERROR)
                {
                    AddTextToEdit(hStaticChat, "* Client has disconnected", TRUE);
                    close(i);
                    FD_CLR(i, &mainfd);
                }
                else
                {
                        AddTextToEdit(hStaticChat, srMsg, TRUE);
                        for(int j = 0; j <= maxfd; j++)
                        {
                          if(FD_ISSET(j, &readfd))
                          {
                                  send(j, srMsg, len, 0);
                          }
                        }
                }
             }
        }
     }
}

您只将数据发送到 fd 处于readfd中的客户端，也就是说，仅发送到刚刚与您通信的客户端。尝试改为测试FD_ISSET(j, mainfd)。

此代码在 WinSock 下无效。 Windows 不像其他平台那样使用整数文件描述符处理套接字。套接字改为使用实际的内核对象表示，因此不能将循环计数器用作套接字句柄等。还有 API 差异(closesocket()而不是 close()，maxfd被 select() 忽略，FD_XXX()期望SOCKET句柄而不是int，等等(。

在Windows上，你需要使用更像这样的东西：

fd_set mainfd;
SOCKET newfd;
int sin_size;
...
while(TRUE)
{
    fd_set readfd = mainfd;
    if (select(0, &readfd, NULL, NULL, NULL) == SOCKET_ERROR)
    {
        itoa(WSAGetLastError(), buf, 10);
        MessageBoxA(NULL, "Error while trying to accept incoming connections (select)", "Error", 16);
        MessageBoxA(NULL, buf, buf, 0);
        break;
    }
    for(int i = 0; i < readfd.fd_count; i++)
    {
        if (readfd.fd_array[i] == mainSocket)
        {
            sin_size = sizeof(their_addr);
            newfd = accept(mainSocket, (struct sockaddr*)&their_addr, &sin_size);
            if (newfd == INVALID_SOCKET)
            {
                AddTextToEdit(hStaticChat, "* Error: couldn't accept incoming connection.", TRUE);
            }
            else
            {
                // Note that fd_set can only hold FD_SETSIZE (64) sockets as a time!
                FD_SET(newfd, &mainfd);
            }
        }
        else
        {
            char srMsg[257];
            len = recv(readfd.fd_array[i], srMsg, 256, 0);
            if (len < 1)
            {
                if (len == 0)
                    AddTextToEdit(hStaticChat, "* Client has disconnected", TRUE);
                else
                    AddTextToEdit(hStaticChat, "* Error: couldn't read from a client connection.", TRUE);
                closesocket(readfd.fd_array[i]);
                FD_CLR(readfd.fd_array[i], &mainfd);
            }
            else
            {
                srMsg[len] = 0;
                AddTextToEdit(hStaticChat, srMsg, TRUE);
                for (int j = 0; j < mainfd.fd_count; j++)
                {
                    if (mainfd.fd_array[i] != mainSocket)
                        send(mainfd.fd_array[j], srMsg, len, 0);
                }
            }
        }
     }
}