currently I am writing a C++ Application for simulating some flying objects in the real world (like GIS).
All the visualization stuff should be made in one or more browser (1 server, X clients).
To connect the Sim APP with the Browser-Clients I decided to choose WebSocket (ws) for the data exchange.

I quickly landed on Boost.beast and looked at the examples… –> /example/websocket/server/async/websocket_server_async.cpp

This example works very well, but it’s not really what I need. It only responds to requests from a client.
I want the server to be able to send messages to a client (or all) independently.
Now I don’t know exactly what I need to change in the code to achieve this.
I have a listener that waits for connections from outside.
As soon as a connection needs to be established, a session is apparently created that is assigned to a socket.
Okay, I got it.

My first approach was to save all sessions in a std::vector in the listener class –> on_accept().

void
    on_accept(beast::error_code ec, tcp::socket socket)
    {
        if(ec)
        {
            fail(ec, "accept");
        }
        else
        {
            // Create the session and run it
            std::shared_ptr<session> oneSession = std::make_shared<session>(std::move(socket));
            managedSessions.push_back(oneSession);
            oneSession->run();
        }

        // Accept another connection
        do_accept();
    }

    std::vector<std::shared_ptr<session>> managedSessions;

I adapted the on_read() function in the session class as a test to find out how I send “my own data” in the first place. That worked too:

void
    on_read(
        beast::error_code ec,
        std::size_t bytes_transferred)
    {
        boost::ignore_unused(bytes_transferred);

        // This indicates that the session was closed
        if(ec == websocket::error::closed)
            return;

        if(ec)
            return fail(ec, "read");

        // Send the message
        ws_.async_write(net::buffer(std::string("Data from the Server")), 
                beast::bind_front_handler(
                &session::on_write,
                shared_from_this()));

}

What I have is a sim loop where I calculate the movements of all entities and then of course have to report the changes to the clients.

It would be great if someone could give me a tip.

Thank you!!