Have access to request in fallback

[GuillaumeGomez]

Summary

Hi,

I'm in the middle of a rewrite of a server and for now, all requests are handled in one function and I'd like to keep it this way for now. However, using fallback, I can't pass Request or basically anything to my method and I can't get my head around it. I was someone suggesting to use axum::middleware::from_fn with layer to be able to access Request but again, impossible to make it work:

The code looks like this:

    let app = Router::new()
        .layer(axum::middleware::from_fn(|request: Request<_>, next: axum::middleware::Next| async move {
            let req_id = request.headers().get("x-request-id").cloned();
            let span = tracing::span!(tracing::Level::INFO, "request", ?req_id);
            let log_info_response = matches!(request.uri().path(), "/github-hook" | "/zulip-hook");
            let ctx = ctx.clone();
            let agenda = agenda.clone();
            serve_req(request, ctx.clone(), agenda.clone())
                .map(move |mut resp: Result<_, _>| {
                    if log_info_response {
                        log::info!("response = {resp:?}");
                    } else {
                        log::debug!("response = {resp:?}");
                    }
                    resp
                })
                .instrument(span)
                .await
        }));

serve_req (which is the central function) is defined like this:

async fn serve_req(
    req: Request<BoxBody<Bytes, hyper::Error>>,
    ctx: Arc<Context>,
    mut agenda: impl Service<String, Response = String, Error = tower::BoxError>,
) -> Result<Response<BoxBody<Bytes, std::convert::Infallible>>, hyper::Error> {

Everytime I'm stuck with errors similar to:

error[E0277]: the trait bound `FromFn<{closure@...}, (), ..., _>: Service<...>` is not satisfied
   --> src/main.rs:365:16
    |
365 |   ...   .layer(axum::middleware::from_fn(|request: Request<_>, next: axum::middleware::Next| as...
    |  ________-----_^
    | |        |
    | |        required by a bound introduced by this call
366 | | ...       let req_id = request.headers().get("x-request-id").cloned();
367 | | ...       let span = tracing::span!(tracing::Level::INFO, "request", ?req_id);
368 | | ...       let log_info_response = matches!(request.uri().path(), "/github-hook" | "/zulip-hoo...
...   |
381 | | ...           .await
382 | | ...   }));
    | |________^ unsatisfied trait bound
    |
    = help: the trait `tower::Service<hyper::Request<axum::body::Body>>` is not implemented for `FromFn<{[email protected]:365:42}, (), Route, _>`
    = help: the following other types implement trait `tower::Service<Request>`:
              axum::middleware::FromFn<F, S, I, (T1, T2)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5, T6)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5, T6, T7)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5, T6, T7, T8)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5, T6, T7, T8, T9)>

So some traits are not implemented for async closures but that's not really helpful.

Anyway, if anyone has an idea, I'd love to hear it!

axum version

0.8.4

[jplatte]

You can definitely use axum::extract::Request (type alias for http::Request<_>), or any other extractors, in a fallback handler. Try debug_handler to figure out what's wrong with your handler function.

[GuillaumeGomez]

debug_handler seems really, but unless I missed something, it can only be used on functions, right? In my case I have a closure because of some variables that I need to capture before sending to serve_req.

[jplatte]

In that case, try copy-pasting the closure body to an async fn, adding the closure-captured thing as a parameter (use a dummy FromRequestParts impl for its type if you need to silence unrelated errors from #[debug_handler]).

[GuillaumeGomez]

I feel very stupid not thinking about that... Thanks a lot!

[jplatte]

No worries! I don't think it's that obvious.

Did you find the issue with your handler?