CODEWITHSUNDEEP
c++socketstcpnetwork-programming
Lightgod131
Lightgod131

Reputation: 31

Why does connecting to server with 2nd socket while using select() "break" first connection?

I'm following the tutorial (big code block near the bottom of that section) here:http://beej.us/guide/bgnet/output/html/multipage/advanced.html#select And the main server code code is like so:

while (true)
{   
    read_fds = master;
    if (select(fd_max + 1, &read_fds, NULL, NULL, NULL) == -1)
    {   
        cerr << "ERROR. Select failed" << endl;
        return -1;
    }

    for (int i = 0; i <= fd_max; i++)
    {   
        if (FD_ISSET(i, &read_fds))
        {   
            if (i == welcome_socket)
            {   
                cout << "NEW CONNECTION" << endl;
                client_len = sizeof(struct sockaddr_in);
                client_sock = accept(welcome_socket, (struct sockaddr *) &client_addr, &client_len);
                if (client_sock != -1)
                {   
                    FD_SET(client_sock, &master);
                    if (client_sock > fd_max)
                    {   
                        fd_max = client_sock;
                    }
                }
            }
            else
            {   
                int length, total_read = 0;

                // CONNECTION CLOSED BY CLIENT
                if (safe_recv(client_sock, &length, sizeof(int)) <= 0)
                {   
                    cout << "CONNECTION CLOSED" << endl;
                    close(i);
                    FD_CLR(i, &master);
                }
                else
                {   
                    char *message = (char *)memset((char *)malloc(length + 1), 0, length);
                    // while ((total_read += safe_recv(client_sock, message + total_read, length - total_read)) < length) {}
                    safe_recv(client_sock, message, length);

                    // RESPOND WITH MESSAGE
                    cout << "MESSAGE: " << message << endl;

                    write(client_sock, process(message), length);
                    free(message);
                }
            }
        }
    }
}

What I'm doing is first sending (from the client) the length of the string, then the string itself. Then the server sends back process(message). When I only have 1 connection, I'm seeing correct behaviour. However if 1 is connected already and I connect a new client, what I'm seeing is:

I've tried to keep this very similar to the tutorial code. I've run the tutorial server, and that works as intended with several clients. I'm new to network programming, so I apologise if this is a beginner problem or just something dumb I overlooked.

Upvotes: 0

Views: 62

Answers (1)

user4581301
user4581301

Reputation: 33931

The code reads from and writes to only client_sock, and client_sock is replaced with the new socket in the accept handling portion of the code.

Most likely you want to interact with i rather than client_sock.

Upvotes: 1

Related Questions