Router::fallback does not get called for routes that are not added for different methods

[emirhantasdeviren]

Bug Report

Version

axum v0.5.4

Platform

Arch Linux
5.17.5-arch1-1

Description

Sorry for that complex title. Here is my code,

const HOST: [u8; 4] = [127, 0, 0, 1];
const PORT: u16 = 8080;

#[tokio::main]
async fn main() {
    let app = Router::new()
        .route(
            "/api/validateSession",
            get(controllers::api::validate_session),
        )
        .route("/login", post(controllers::user::sign_in))
        .fallback(
            get_service(ServeDir::new("public").fallback(ServeFile::new("public/index.html")))
                .handle_error(|_e: std::io::Error| async move {
                    (
                        axum::http::StatusCode::INTERNAL_SERVER_ERROR,
                        "You know what happened.",
                    )
                }),
        );

    let addr = SocketAddr::from((HOST, PORT));
    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap();
}

So my goal is to handle specific routes and leave other routes to be served by public folder. If the file does not exist in public, public/index.html will be served. Here the issue is I added /login router with only POST method.

My expectation is that GET /login route will call fallback since I only added POST /login.

Instead, I get 405 Method Not Allowed. If I delete the line route("/login", post(controllers::user::sign_in)), GET /login renders public/index.html.

[jplatte]

There is some magic that makes the method router work a little bit as if it was part of the path router, but they are really separate things. This really seems like it's working as intended to me. I think this would be the best solution:

let static_files =
    get_service(ServeDir::new("public").fallback(ServeFile::new("public/index.html")))
        .handle_error(|_e: std::io::Error| async move {
            (
                axum::http::StatusCode::INTERNAL_SERVER_ERROR,
                "You know what happened.",
            )
        });

let app = Router::new()
    .route(
        "/api/validateSession",
        get(controllers::api::validate_session),
    )
    .route("/login", post(controllers::user::sign_in).merge(static_files.clone()))
    .fallback(static_files);

[davidpdrsn]

That's intentional. The design we chose for axum means that a route for /login exists it just doesn't support POST, thus 405 is appropriate.

It's a trade off and making that go to the fallback has other downsides (see issues for rocket never returning 405)

If you want to handle 405 in a custom way you have to write a middleware to catch 405s and return a different response. Using axum::middleware::from_fn is the easiest way to do that.