Make shutdown_signal() Function a One Line Operation Called as a Default

[LeahWhalen]

Calling a default shutdown signal function prevents redundant code
I think putting the shutdown signal function as a default somewhere would make crates like axum look nicer when defining a shutdown signal, building servers would be easier, and developers wouldn't have to initialize it every time.

Proposal
One could easily make some sort of "shutdown signal" struct with a default new and a few customization options.
Here is the shutdown_signal function being referred to:

async fn shutdown_signal() {
    let ctrl_c = async {
        signal::ctrl_c()
            .await
            .expect("failed to install Ctrl+C handler");
    };

    #[cfg(unix)]
    let terminate = async {
        signal::unix::signal(signal::unix::SignalKind::terminate())
            .expect("failed to install signal handler")
            .recv()
            .await;
    };

    #[cfg(not(unix))]
    let terminate = std::future::pending::<()>();

    tokio::select! {
        _ = ctrl_c => {},
        _ = terminate => {},
    }
    println!("signal received, starting graceful shutdown");
}

Describe alternatives you've considered
I could possibly make my own wrapper? I tried to ask axum to do this as I use their crate, but they pointed out it was part of the hyper::server::Server struct

[seanmonstar]

Hey there! 👋 I need to understand what you mean by a shutdown function. Hyper, as of v0.14.x, has a graceful shutdown helper part of the Server builder. Do you mean more control of that? Or are you suggesting hyper should have a function that looks like what you wrote, since many might want exactly what that one does?

[kahlstrm]

Resurrecting this as I was wondering how come there is no such default available. The example snippet is from this axum example and I think it's quite widely used to achieve the wanted result. I at least have it copy-pasted in basically all axum apps.

Having this kind of helper/default for the graceful shutdown handler would reduce this boilerplate needed from downstream projects.

This could probably be introduced as a constant function GRACEFUL_SHUTDOWN_DEFAULT_SIGNAL or something along those lines.