TCP Winsock: accept multiple connections/clients

Question

I tried to can multiply clients, and send it to each one. But it working only for one, after one client connected the server just useless for incoming connections.

Answer 1

After accepting socket create separate thread for client requests. Then continue wait for new accepting.

For example:

    ...
    while (1)
    {
        AcceptSocket = SOCKET_ERROR;

        while (AcceptSocket == SOCKET_ERROR )
        {
            AcceptSocket = accept( m_socket, NULL, NULL );
        }

        printf( "Client Connected.\n");

        DWORD dwThreadId;
        CreateThread (NULL, 0, ProcessClient, (LPVOID) AcceptSocket, 0, &dwThreadId);
    }
    ...

Where ProcessClient function could be like this:

DWORD WINAPI ProcessClient (LPVOID lpParameter)
{
    SOCKET AcceptSocket = (SOCKET) lpParameter;

    // Send and receive data.
    int bytesSent;
    int bytesRecv = SOCKET_ERROR;
    char sendbuf[2000]="";
    char recvbuf[2000]="";

    char timebuf[128];

    sprintf(sendbuf, "Hello, it's a test server at %s:%d (commands: 1, 2, exit)\n", ipaddr, port);
    bytesSent = send( AcceptSocket, sendbuf, strlen(sendbuf), 0);

    if (bytesSent == SOCKET_ERROR)
    {
        printf( "Error at send hello: %ld\n", WSAGetLastError());
        goto fin;
    }

    while (1)
    {
        _strtime( timebuf );
        ZeroMemory (recvbuf, sizeof(recvbuf));

        bytesRecv = recv( AcceptSocket, recvbuf, 32, 0);
        printf( "%s Client said: %s\n", timebuf, recvbuf);

        if (strcmp(recvbuf, "1") == 0)
        {
            sprintf(sendbuf, "You typed ONE\n");
            //printf("Sent '%s'\n", sendbuf);
            bytesSent = send( AcceptSocket, sendbuf, strlen(sendbuf), 0);

            if (bytesSent == SOCKET_ERROR)
            {
                printf( "Error at send: %ld\n", WSAGetLastError());
                goto fin;
            }
        }
        else if (strcmp(recvbuf, "2") == 0)
        {
            sprintf(sendbuf, "You typed TWO\n");
            //printf("Sent '%s'\n", sendbuf);
            bytesSent = send( AcceptSocket, sendbuf, strlen(sendbuf), 0);

            if (bytesSent == SOCKET_ERROR)
            {
                printf( "Error at send: %ld\n", WSAGetLastError());
                goto fin;
            }
        }
        else if (strcmp(recvbuf, "exit") == 0)
        {
            printf( "Client has logged out\n", WSAGetLastError());
            goto fin;
        }
        else
        {
            sprintf(sendbuf, "unknown command\n");
            //printf("Sent '%s'\n", sendbuf);
            bytesSent = send( AcceptSocket, sendbuf, strlen(sendbuf), 0);

            if (bytesSent == SOCKET_ERROR)
            {
                printf( "Error at send: %ld\n", WSAGetLastError());
                goto fin;
            }
        }
    }

fin:
    printf("Client processed\n");

    closesocket(AcceptSocket);
    return 0;
}

Answer 2

Of course new clients cannot be accepted because the server handles just accepted client, i.e. the server is busy.

The solution is simple: create a new thread for each accepted client and handle the client session there. Just use _beginthreadex() (#include <process.h>):

unsigned __stdcall ClientSession(void *data)
{
    SOCKET client_socket = (SOCKET)data;
    // Process the client.
}

int _tmain(int argc, _TCHAR* argv[])
{
    ...

    SOCKET client_socket;
    while ((client_socket = accept(server_socket, NULL, NULL))) {
        // Create a new thread for the accepted client (also pass the accepted client socket).
        unsigned threadID;
        HANDLE hThread = (HANDLE)_beginthreadex(NULL, 0, &ClientSession, (void*)client_socket, 0, &threadID);
    }
}

By the way, send()/recv() functions do not guarantee that all the data would be sent/received at one call. Please see the documentation for return value of these functions.