Creating server-socket connection without waiting for user input

Question

My goal is to create a user-server connection. Most importantly I'm not willing to use threads. For now, I want it to work as a simple chat. I believe The issue is that It goes from one user to another in a loop waiting for their getline input, so technically only one user can send a message at a time. What I wish is that my code could handle multiple messages from one user continuously, not having to wait for all other users to send a message That's the running loop inside the server:

while (running)
{
    fd_set copy = master;

    // See who's talking to us
    int socketCount = select(0, &copy, nullptr, nullptr, nullptr);

    // Loop through all the current connections / potential connect
    for (int i = 0; i < socketCount; i++)
    {
        // Makes things easy for us doing this assignment
        SOCKET sock = copy.fd_array[i];

        // Is it an inbound communication?
        if (sock == listening)
        {
            // Accept a new connection
            sockaddr_in client;
            int clientSize = sizeof(client);
            SOCKET clientsocket = accept(listening, (sockaddr*)&client, &clientSize);

            // Add the new connection to the list of connected clients
            FD_SET(clientsocket, &master);

            // Send a welcome message to the connected client
            string welcomeMsg = "Welcome to the Awesome Chat Server!\r\n";
            send(clientsocket, welcomeMsg.c_str(), welcomeMsg.size() + 1, 0);
        }
        else // It's an inbound message
        {
            char buf[4096];
            ZeroMemory(buf, 4096);

            // Receive message
            int bytesIn = recv(sock, buf, 4096, 0);
            if (bytesIn <= 0)
            {
                // Drop the client
                closesocket(sock);
                FD_CLR(sock, &master);
            }
            else
            {
                
                // Send message to other clients, and definiately NOT the listening socket

                for (int i = 0; i < master.fd_count; i++)
                {
                    SOCKET outSock = master.fd_array[i];
                    if (outSock != listening && outSock != sock)
                    {
                        ostringstream ss;
                        ss << "SOCKET #" << sock << ": " << buf << "\r\n";
                        string strOut = ss.str();

                        send(outSock, strOut.c_str(), strOut.size() + 1, 0);
                    }
                }
            }
        }
    }
}

I belive this code should work, the issue is in my client code:

    char buf[4096];
     string userInput;

    do
    {
        // Prompt the user for some text
        cout << "> ";
        getline(cin, userInput); //THATS THE ISSUE, IT WAITS FOR GETLINE
        if (userInput.size() > 0)       // Make sure the user has typed in something
        {
            // Send the text
            int sendResult = send(sock, userInput.c_str(), userInput.size() + 1, 0);
            if (sendResult != SOCKET_ERROR)
            {
                // Wait for response
                ZeroMemory(buf, 4096);
                int bytesReceived = recv(sock, buf, 4096, 0);
                if (bytesReceived > 0)
                {
                    // Echo response to console
                    cout << "SERVER> " << string(buf, 0, bytesReceived) << endl;
                }
            }
        }

    } while (userInput.size() > 0);

My question is if its really caused by getline and if so, how can it be fixed?

Does your client program need to run under Windows? (I ask because afaict Windows does not support non-blocking reads from stdin; the best you can do is fake it with a dedicated thread that does blocking reads from stdin and forwards the data to a non-blocking pipe or socket for the rest of the program to read) — Jeremy Friesner, Apr 24 '22 at 19:43

score 1 · Accepted Answer · answered Apr 24 '22 at 15:42

1

The answer to your question is "yes," but with a big proviso: a properly designed server shouldn't care what the client is doing. You might want to look into select() or, if you anticipate a large user community, poll(). You don't want a multi-user server to depend on/wait for a single client.

answered Apr 24 '22 at 15:42

mzimmers

857
7
17

I used select() indeed, however it does not solve the problem of waiting for user input. Because my main thread will wait for user input from getline and I was wondering if there is a way to avoid this issue. – Michał Turek Apr 25 '22 at 15:20
I guess I don't fully understand the problem. The getline() call is in the client; this shouldn't affect your server. But, maybe this will help: https://stackoverflow.com/questions/15524122/how-to-implement-timeout-for-getline – mzimmers Apr 25 '22 at 16:58

Creating server-socket connection without waiting for user input

1 Answers1