Question

I am trying to add SSL functionality to my existing TCP echo client-server application.

Earlier in my simple server, I was spawning a new child for every incoming client connection. To this child, I was passing the conn-fd (char*) as a command-line argument. (shown below)

execl("./simple_server_instance", conn_fd, NULL);

Now, for my secure server, I need to pass a CYASSL object (a structure in effect) instead of the conn_fd. (shown below)

ssl = CyaSSL_new(ctx);
CyaSSL_set_fd(ssl, connfd);

Here ‘ssl’ is the object that needs to be passed to the child process. I tried the following ways to achieve it, but unsuccessful. Is there a simple alternative, or should i go the serialization way?

1. Typecasting the ssl object to char*

2. Creating a buffer and doing a memcpy of the entire structure. (shown below)

unsigned char sslobjbuf[sizeof(ssl)];
memcpy(&sslobjbuf, ssl, sizeof(ssl));
execl("./secure_server_instance", "hello", "25", sslobjbuf, NULL );

sdsd

Answer 1

When you execl() a process, you completely replace the running process with the exec’ed process. The exec family of functions expect a sequence of null terminated strings which will become available as arvg[] in the spawned application. You can’t just pass arbitrary objects via this interface.

When you probably want to use instead is the fork system call which gives you a new child process which shares its code/data with the parent. The code for ./simple_server_instance would be merged with the main server code. You can do your ssl = CyaSSL_new(ctx); call in the parent process to obtain the object you require, then fork. The parent can then continue to serve new requests while the child runs the the ssl object.

Something like this flow of control may work:

while (1) {
    wait_connection();
    pid_t child_pid = -1;
    ssl = CyaSSL_new(ctx);
    child_pid = fork();
    if (child_pid == 0) {
        /* We're now running the child process which also has access to ssl.
         * Run simple_server_instance handler code
         */
    }
    else {
        /* Code running in parent.  Do housekeeping, save child_pid if necessary.
         * clean up ssl, object, get ready for next connection, handle finished
         * child processes.
         */
    }
}