Make a GracefulShutdown helper in hyper-util

[seanmonstar]

With the removal of hyper::Server, the graceful shutdown stuff would disappear. We want to continue to provide a helper to do that, in hyper-util, but make it also able to be used with timeouts. Perhaps something like this:

let listener = TcpListener::bind("0.0.0.0:0").await?;

let server = Server::new();

let graceful = GracefulShutdown::new();
let ctrl_c = tokio::signal::ctrl_c();

loop {
    tokio::select! {
        conn = listener.accept() => {
            let server = server.clone();
            let graceful = graceful.clone();
            task::spawn(async move {
                // maybe TLS accept here...

                let conn = server.serve_connection(conn);
                let conn = graceful.watch(conn);

                if let Err(e) = conn.await {
                    eprintln!("http server conn error: {}", e);
                }
            });
        },

        _ = ctrl_c => {
            eprintln!("Ctrl-C received, starting shutdown");
                break;
        }
    }
}

tokio::select! {
    _ = graceful.shutdown() => {
        eprintln!("Gracefully shutdown!");
    },
    _ = tokio::time::sleep(10.seconds()) => {
        eprintln!("Waited 10 seconds for graceful shutdown, aborting...");
    }
}

[jacob-pro]

Hi @seanmonstar

I previously had a go at writing an implementation of this here:
https://github.com/jacob-pro/hyper-graceful/blob/master/examples/example.rs

One issue I struggled with doing this in a seperate crate is that I need to call UpgradeableConnection::graceful_shutdown when UpgradeableConnection is private - I wonder if graceful_shutdown needs to be a public trait instead?

For now I worked around it by using a closure so the user has to call graceful_shutdown directly themselves.

My other suggestion / question was about building a more general purpose "Connection Manager" which could have features similar to http://nginx.org/en/docs/http/ngx_http_limit_conn_module.html ?

[jfreedman0212]

Hey! Not sure if this is still an outstanding issue, but I can take a stab at it. I've implemented something like this with tokio's JoinSet before (docs). Would that be interesting?

I can whip up a little code example later, not at my computer right now.

[seanmonstar]

It is still outstanding :)

I admit I'm less familiar with JoinSet, what would it bring to the table? It would probably be nice if this util didn't need to be tied to Tokio. I think the usage pattern shown in the issue description is probably still a good thing to aim for, which allows people to spawn the tasks in whatever thing they want, after wrapping the connection in some watcher. I'd imagine the watcher itself is just an impl Future.