How to do dynamic port binding and get the port

[phughk]

I am writing an app, and I am considering using Rocket for the admin API (for it's convenience).
I need the port and binding to be dynamic (0.0.0.0:0) and need to know the port after it is bound.

This is slightly different to #688 , where the user wants a specific non-default port which is known.

The code I have is as follows

    pub async fn run_forever(self) {
        let config = Config {
            port: self.port,
            address: self.host,
            ..Config::default()
        };
        let rocket = rocket::custom(config).manage(crate::api::Config {
            secret: "1234".to_string(),
        }).mount("/", routes![crate::api::authenticate]);
        let rocket = rocket.launch().await.unwrap();
        let port = rocket.config().port;
        info!("Admin API on http://{}:{}", self.host, port);
    }

With ignite before launch, the port is 0. With launch (the above code), the call is obviously blocking.

Is there a way to get the port from rocket somehow? This goes beyond trace logs as I need it in my management console.

[phughk]

FYI one option is to bind myself, and pass in a TCP Listener. Tbh that is preferable, as then it is somewhat sans-io.