fd_set listen_fds = all_fds;
if (select(max_fd + 1, &listen_fds, NULL, NULL, NULL) == -1) {
    perror("server: select");
    exit(1);
}

// Is it the original socket? Create a new connection ...
if (FD_ISSET(sock_fd, &listen_fds)) {
    int client_fd = accept_connection(sock_fd, users);
    if (client_fd > max_fd) {
        max_fd = client_fd;
    }
    FD_SET(client_fd, &all_fds);
    printf("Accepted connection\n");
}
