Notes/notes-service/vendor/axum/src/docs/routing/fallback.md

Add a fallback [Handler] to the router.

This service will be called if no routes matches the incoming request.

use axum::{
    Router,
    routing::get,
    handler::Handler,
    response::IntoResponse,
    http::{StatusCode, Uri},
};

let app = Router::new()
    .route("/foo", get(|| async { /* ... */ }))
    .fallback(fallback);

async fn fallback(uri: Uri) -> (StatusCode, String) {
    (StatusCode::NOT_FOUND, format!("No route for {uri}"))
}
# let _: Router = app;

Fallbacks only apply to routes that aren't matched by anything in the router. If a handler is matched by a request but returns 404 the fallback is not called. Note that this applies to [MethodRouter]s too: if the request hits a valid path but the [MethodRouter] does not have an appropriate method handler installed, the fallback is not called (use [MethodRouter::fallback] for this purpose instead).

Handling all requests without other routes

Using Router::new().fallback(...) to accept all request regardless of path or method, if you don't have other routes, isn't optimal:

use axum::Router;

async fn handler() {}

let app = Router::new().fallback(handler);

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, app).await.unwrap();
# };

Running the handler directly is faster since it avoids the overhead of routing:

use axum::handler::HandlerWithoutStateExt;

async fn handler() {}

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, handler.into_make_service()).await.unwrap();
# };