Trait bound error when attaching middleware with `from_fn_with_state` #2664

avsaase · 2024-03-20T10:15:20Z

avsaase
Mar 20, 2024

Summary

I'm trying to create a middleware that needs access to my app state. Following the documentation, the signature of my middleware is

pub async fn required_role(
    State(state): State<AppState>,
    headers: HeaderMap,
    request: Request,
    next: Next,
) -> Response

I'm adding it to my router like this

let axum_response = axum::Router::new()
    .route("/v0/test", get(|| async { "Hello from axum router" }))
    .route_layer(axum::middleware::from_fn_with_state(
        app_state.clone(),
        middleware::required_role,
    ))
    .with_state(app_state)
    .call(axum_request) // tower_service::Service
    .await?;

This is the error I get:

error[E0277]: the trait bound `axum::middleware::FromFn<fn(axum::extract::State<AppState>, axum::http::HeaderMap, axum::http::Request<axum::body::Body>, axum::middleware::Next) -> impl futures::Future<Output = axum::http::Response<axum::body::Body>> {required_role}, AppState, Route, _>: Service<axum::http::Request<axum::body::Body>>` is not satisfied
   --> src/lib.rs:927:22
    |
927 |           .route_layer(axum::middleware::from_fn_with_state(
    |  __________-----------_^
    | |          |
    | |          required by a bound introduced by this call
928 | |             app_state.clone(),
929 | |             middleware::required_role,
930 | |         ))
    | |_________^ the trait `Service<axum::http::Request<axum::body::Body>>` is not implemented for `FromFn<fn(State<AppState>, HeaderMap, Request<Body>, Next) -> ... {required_role}, ..., ..., ...>`
    |
    = help: the following other types implement trait `Service<Request>`:
              axum::middleware::FromFn<F, S, I, (T1,)>
              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)>
            and 8 others
note: required by a bound in `axum::Router::<S>::route_layer`
   --> /home/alexander/.cargo/registry/src/index.crates.io-6f17d22bba15001f/axum-0.7.4/src/routing/mod.rs:296:21
    |
293 |     pub fn route_layer<L>(self, layer: L) -> Self
    |            ----------- required by a bound in this associated function
...
296 |         L::Service: Service<Request> + Clone + Send + 'static,
    |                     ^^^^^^^^^^^^^^^^ required by this bound in `Router::<S>::route_layer`

The issue seems to be related to the HeaderMap extractor because when I remove it (and all the code in the middleware that uses the headers) the error goes away. Is this a known limitation? If so, how do I work around this? I tried removing the HeaderMap parameter and extracting the headers at the top of my middleware using request.headers() but then I get the same error as before.

Any help would appreciated.

axum version

0.7.4

Answered by avsaase

Mar 21, 2024

The problem is that inside my middleware I'm holding as !Send type across an await point. I figured this out by using the #[axum_macros::debug_handler] macro.

View full answer

avsaase · 2024-03-21T21:58:46Z

avsaase
Mar 21, 2024
Author

The problem is that inside my middleware I'm holding as !Send type across an await point. I figured this out by using the #[axum_macros::debug_handler] macro.

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Trait bound error when attaching middleware with from_fn_with_state #2664

avsaase Mar 20, 2024

Summary

axum version

Replies: 1 comment

avsaase Mar 21, 2024 Author

Trait bound error when attaching middleware with `from_fn_with_state` #2664

avsaase
Mar 20, 2024

avsaase
Mar 21, 2024
Author