Function launch_from_listener 

pub fn launch_from_listener(listener: TcpListener) -> Result<EventHub, Error>

Start listening for websocket connections with the specified TcpListener. The listener must be bound (by calling bind) before being passed to launch_from_listener.

use std::net::TcpListener;

fn main() {
    // Example of using a pre-bound listener instead of providing a port.
    let listener = TcpListener::bind("0.0.0.0:8080").unwrap();
    let event_hub = simple_websockets::launch_from_listener(listener).expect("failed to listen on port 8080");
    // ...
}