Add axum-handle-error-extract crate

[davidpdrsn]

For a project I'm working on with axum I have a "application renderer" extractor thing that takes HTML templates and renders those with a standard application layout around it. It needs to be an extractor because it grabs data from the session to show in the layout like whether the user is logged in or not.

However I couldn't easily use this same setup for handling errors from middleware since HandleErrorLayer doesn't support running extractors. I think that is something that makes sense to support. If you don't need to run any extractors you just don't specify any and things work like they did before.

I also think it makes sense to support async functions for handling errors in case users wanna do some async logging or whatnot while handling the error.

So this PR introduces a new crate called axum-handle-error-extract which has its own HandleErrorLayer that supports extractors and async functions.

For axum 0.4 I'm thinking we should replace the current HandleErrorLayer with this new more powerful version. Thats of course a breaking change but figured we could at least release it as a standalone crate so users can try it. Pretty neat that axum is flexible enough to support something like this 😊

Example usage

use axum::{
    Router,
    BoxError,
    response::IntoResponse,
    http::{StatusCode, Method, Uri},
    routing::get,
};
use tower::{ServiceBuilder, timeout::error::Elapsed};
use std::time::Duration;
use axum_handle_error_extract::HandleErrorLayer;

let app = Router::new()
    .route("/", get(|| async {}))
    .layer(
        ServiceBuilder::new()
            // timeouts produces errors, so we handle those with `handle_error`
            .layer(HandleErrorLayer::new(handle_error))
            .timeout(Duration::from_secs(10))
    );

// our handler take can 0 to 16 extractors and the final argument must
// always be the error produced by the middleware
async fn handle_error(
    method: Method,
    uri: Uri,
    error: BoxError,
) -> impl IntoResponse {
    if error.is::<Elapsed>() {
        (
            StatusCode::REQUEST_TIMEOUT,
            format!("{} {} took too long", method, uri),
        )
    } else {
        (
            StatusCode::INTERNAL_SERVER_ERROR,
            format!("{} {} failed: {}", method, uri, error),
        )
    }
}

[jplatte]

Wouldn't &type_name(), w/o the format_args!, work too?

[davidpdrsn]

Yeah I think thats right! No idea why we wrote it like this in tower. Seems to do the same.

[jplatte]

I think I know now actually 😅

W/o format_args it will add quotes, right?

[davidpdrsn]

Oh yeah thats true. I'll revert to keep the format_args.

[davidpdrsn]

I think I'll go ahead and merge this now. We can always improve things later as we add more crates and use this in practice.