produce errors you have to tell axum how to
convert those errors into responses.

```rust
use axum::{
    Router,
    body::Body,
    http::{Request, Response, StatusCode},
    error_handling::HandleError,
};

async fn thing_that_might_fail() -> Result<(), anyhow::Error> {
    # Ok(())
    // ...
}

// this service might fail with `anyhow::Error`
let some_fallible_service = tower::service_fn(|_req| async {
    thing_that_might_fail().await?;
    Ok::<_, anyhow::Error>(Response::new(Body::empty()))
});

let app = Router::new().route_service(
    "/",
    // we cannot route to `some_fallible_service` directly since it might fail.
    // we have to use `handle_error` which converts its errors into responses
    // and changes its error type from `anyhow::Error` to `Infallible`.
    HandleError::new(some_fallible_service, handle_anyhow_error),
);

// handle errors by converting them into something that implements
// `IntoResponse`
async fn handle_anyhow_error(err: anyhow::Error) -> (StatusCode, String) {
    (
        StatusCode::INTERNAL_SERVER_ERROR,
        format!("Something went wrong: {err}"),
    )
}
# let _: Router = app;
```

# Applying fallible middleware

Similarly axum requires you to handle errors from middleware. That is done with
[`HandleErrorLayer`]:

```rust
use axum::{
    Router,
    BoxError,
    routing::get,
    http::StatusCode,
    error_handling::HandleErrorLayer,
};
use std::time::Duration;
use tower::ServiceBuilder;

let app = Router::new()
    .route("/", get(|| async {}))
    .layer(
        ServiceBuilder::new()
            // `timeout` will produce an error if the handler takes
            // too long so we must handle those
            .layer(HandleErrorLayer::new(handle_timeout_error))
            .timeout(Duration::from_secs(30))
    );

async fn handle_timeout_error(err: BoxError) -> (StatusCode, String) {
    if err.is::<tower::timeout::error::Elapsed>() {
        (
            StatusCode::REQUEST_TIMEOUT,
            "Request took too long".to_string(),
        )
    } else {
        (
            StatusCode::INTERNAL_SERVER_ERROR,
            format!("Unhandled internal error: {err}"),
        )
    }
}
# let _: Router = app;
```

# Running extractors for error handling

`HandleErrorLayer` also supports running extractors:

```rust
use axum::{
    Router,
    BoxError,
    routing::get,
    http::{StatusCode, Method, Uri},
    error_handling::HandleErrorLayer,
};
use std::time::Duration;
use tower::ServiceBuilder;

let app = Router::new()
    .route("/", get(|| async {}))
    .layer(
        ServiceBuilder::new()
            // `timeout` will produce an error if the handler takes
            // too long so we must handle those
            .layer(HandleErrorLayer::new(handle_timeout_error))
            .timeout(Duration::from_secs(30))
    );

async fn handle_timeout_error(
    // `Method` and `Uri` are extractors so they can be used here
    method: Method,
    uri: Uri,
    // the last argument must be the error itself
    err: BoxError,
) -> (StatusCode, String) {
    (
        StatusCode::INTERNAL_SERVER_ERROR,
        format!("`{method} {uri}` failed with {err}"),
    )
}
# let _: Router = app;
```

[`tower::Service`]: `tower::Service`
[`Infallible`]: std::convert::Infallible
[`Response`]: crate::response::Response
[`IntoResponse`]: crate::response::IntoResponse