Making tower-http's ServeDir fall back to axum::Router #3206

utkarshkukreti · 2025-02-01T10:20:25Z

utkarshkukreti
Feb 1, 2025

Summary

I'm trying to combine tower-http's ServeDir and axum's Router in such a way that if a static file exists, it should be served, otherwise the request should be passed to the axum Router. Here's what I have so far:

use axum::ServiceExt;

#[tokio::main]
async fn main() {
    let app = axum::Router::new().route(
        "/{*wildcard}",
        axum::routing::get(|| async { "Hello, World!" }),
    );

    let app = tower_http::services::ServeDir::new("src").fallback(app);

    let listener = tokio::net::TcpListener::bind("0.0.0.0:4000").await.unwrap();

    axum::serve(listener, app.into_make_service())
        .await
        .unwrap();
}

With this, I expect to get the contents of src/main.rs if I do GET /main.rs and get Hello, World! if I do GET /something-else.rs.

This fails to compile:

error[E0271]: type mismatch resolving `<ServeDir<Router> as Service<Request<Body>>>::Response == Response<Body>`
  --> src/main.rs:14:5
   |
14 |     axum::serve(listener, app.into_make_service())
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `Response<Body>`, found `Response<ServeFileSystemResponseBody>`
   |
   = note: expected struct `Response<Body>`
              found struct `Response<ServeFileSystemResponseBody>`

I have tried many variations of this but could not get any to compile. Doing it the other way, where axum's Router falls back to ServeDir works fine, but I want the static files to be served first.

[dependencies]
axum = "0.8.1"
tokio = { version = "1.43.0", features = ["full"] }
tower-http = { version = "0.6.2", features = ["fs"] }

Any pointers?

axum version

0.8.1

mladedav · 2025-02-01T23:08:23Z

mladedav
Feb 1, 2025
Collaborator

You can try looking at #3202, or more specifically just calling map_response_body(axum::body::Body::new) might work for you to get the correct response body type.

1 reply

utkarshkukreti Feb 2, 2025
Author

Thanks for the reply. Do I have to use tower::ServiceBuilder for that?

I think I'm doing something very wrong.

use tower_http::ServiceBuilderExt;

#[tokio::main]
async fn main() {
    let app = axum::Router::new().route(
        "/{*wildcard}",
        axum::routing::get(|| async { "Hello, World!" }),
    );

    let app = tower::ServiceBuilder::new()
        .map_response_body(axum::body::Body::new)
        .service(tower_http::services::ServeDir::new("src").fallback(app));

    let listener = tokio::net::TcpListener::bind("0.0.0.0:4000").await.unwrap();

    axum::serve(listener, app).await.unwrap();
}

error[E0277]: the trait bound `for<'a> MapResponseBody<ServeDir<Router<_>>, fn(_) -> Body {Body::new::<_>}>: Service<IncomingStream<'a, tokio::net::TcpListener>>` is not satisfied
  --> src/main.rs:16:27
   |
16 |     axum::serve(listener, app).await.unwrap();
   |     -----------           ^^^ unsatisfied trait bound
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `Service<IncomingStream<'a, tokio::net::TcpListener>>` is not implemented for `MapResponseBody<ServeDir<Router<_>>, fn(ServeFileSystemResponseBody) -> Body {Body::new::<_>}>`
           but trait `Service<axum::http::Request<_>>` is implemented for `MapResponseBody<ServeDir<Router<()>>, fn(ServeFileSystemResponseBody) -> Body {Body::new::<ServeFileSystemResponseBody>}>`
   = help: for that trait implementation, expected `axum::http::Request<_>`, found `IncomingStream<'a, tokio::net::TcpListener>`
note: required by a bound in `serve`

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Making tower-http's ServeDir fall back to axum::Router #3206

utkarshkukreti Feb 1, 2025

Summary

axum version

Replies: 1 comment · 1 reply

mladedav Feb 1, 2025 Collaborator

utkarshkukreti Feb 2, 2025 Author

utkarshkukreti
Feb 1, 2025

Replies: 1 comment 1 reply

mladedav
Feb 1, 2025
Collaborator

utkarshkukreti Feb 2, 2025
Author