Move methods from ServiceExt to RoutingDsl (#160)

Previously, on `main`, this wouldn't compile:

```rust
let app = route("/", get(handler))
    .layer(
        ServiceBuilder::new()
            .timeout(Duration::from_secs(10))
            .into_inner(),
    )
    .handle_error(...)
    .route(...); // <-- doesn't work
```

That is because `handle_error` would be
`axum::service::ServiceExt::handle_error` which returns `HandleError<_,
_, _, HandleErrorFromService>` which does _not_ implement `RoutingDsl`.
So you couldn't call `route`. This was caused by
https://github.com/tokio-rs/axum/pull/120.

Basically `handle_error` when called on a `RoutingDsl`, the resulting
service should also implement `RoutingDsl`, but if called on another
random service it should _not_ implement `RoutingDsl`.

I don't think thats possible by having `handle_error` on `ServiceExt`
which is implemented for any service, since all axum routers are also
services by design.

This resolves the issue by removing `ServiceExt` and moving its methods
to `RoutingDsl`. Then we have more tight control over what has a
`handle_error` method.

`service::OnMethod` now also has a `handle_error` so you can still
handle errors from random services, by doing
`service::any(svc).handle_error(...)`.

CHANGELOG.md

@@ -9,8 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Make `FromRequest` default to being generic over `body::Body` ([#146](https://github.com/tokio-rs/axum/pull/146))
 - Implement `std::error::Error` for all rejections ([#153](https://github.com/tokio-rs/axum/pull/153))
-- Fix `Uri` extractor not being the full URI if using `nest` ([#156](https://github.com/tokio-rs/axum/pull/156))
 - Add `RoutingDsl::or` for combining routes ([#108](https://github.com/tokio-rs/axum/pull/108))
+- Add `handle_error` to `service::OnMethod` ([#160](https://github.com/tokio-rs/axum/pull/160))
 
 ## Breaking changes
 
@@ -24,9 +24,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Ensure a `HandleError` service created from `ServiceExt::handle_error`
   _does not_ implement `RoutingDsl` as that could lead to confusing routing
   behavior ([#120](https://github.com/tokio-rs/axum/pull/120))
+- Fix `Uri` extractor not being the full URI if using `nest` ([#156](https://github.com/tokio-rs/axum/pull/156))
 - Implement `routing::MethodFilter` via [`bitflags`](https://crates.io/crates/bitflags)
 - Removed `extract::UrlParams` and `extract::UrlParamsMap`. Use `extract::Path` instead
 - `EmptyRouter` now requires the response body to implement `Send + Sync + 'static'` ([#108](https://github.com/tokio-rs/axum/pull/108))
+- `ServiceExt` has been removed and its methods have been moved to `RoutingDsl` ([#160](https://github.com/tokio-rs/axum/pull/160))
 - These future types have been moved
     - `extract::extractor_middleware::ExtractorMiddlewareResponseFuture` moved
       to `extract::extractor_middleware::future::ResponseFuture` ([#133](https://github.com/tokio-rs/axum/pull/133))

examples/key_value_store.rs

@@ -12,7 +12,6 @@ use axum::{
     prelude::*,
     response::IntoResponse,
     routing::BoxRoute,
-    service::ServiceExt,
 };
 use bytes::Bytes;
 use http::StatusCode;

examples/sse.rs

@@ -4,7 +4,7 @@
 //! cargo run --example sse --features=headers
 //! ```
 
-use axum::{extract::TypedHeader, prelude::*, routing::nest, service::ServiceExt, sse::Event};
+use axum::{extract::TypedHeader, prelude::*, routing::nest, sse::Event};
 use futures::stream::{self, Stream};
 use http::StatusCode;
 use std::{convert::Infallible, net::SocketAddr, time::Duration};
@@ -19,20 +19,17 @@ async fn main() {
     }
     tracing_subscriber::fmt::init();
 
-    // build our application with a route
+    let static_files_service =
-    let app = nest(
+        axum::service::get(ServeDir::new("examples/sse").append_index_html_on_directories(true))
-        "/",
-        axum::service::get(
-            ServeDir::new("examples/sse")
-                .append_index_html_on_directories(true)
             .handle_error(|error: std::io::Error| {
                 Ok::<_, std::convert::Infallible>((
                     StatusCode::INTERNAL_SERVER_ERROR,
                     format!("Unhandled internal error: {}", error),
                 ))
-                }),
+            });
-        ),
+
-    )
+    // build our application with a route
+    let app = nest("/", static_files_service)
         .route("/sse", axum::sse::sse(make_stream))
         .layer(TraceLayer::new_for_http());
 

examples/static_file_server.rs

@@ -4,7 +4,7 @@
 //! cargo run --example static_file_server
 //! ```
 
-use axum::{prelude::*, routing::nest, service::ServiceExt};
+use axum::{prelude::*, routing::nest};
 use http::StatusCode;
 use std::net::SocketAddr;
 use tower_http::{services::ServeDir, trace::TraceLayer};
@@ -19,12 +19,12 @@ async fn main() {
 
     let app = nest(
         "/static",
-        axum::service::get(ServeDir::new(".").handle_error(|error: std::io::Error| {
+        axum::service::get(ServeDir::new(".")).handle_error(|error: std::io::Error| {
             Ok::<_, std::convert::Infallible>((
                 StatusCode::INTERNAL_SERVER_ERROR,
                 format!("Unhandled internal error: {}", error),
             ))
-        })),
+        }),
     )
     .layer(TraceLayer::new_for_http());
 

examples/todos.rs

@@ -17,7 +17,6 @@ use axum::{
     extract::{Extension, Json, Path, Query},
     prelude::*,
     response::IntoResponse,
-    service::ServiceExt,
 };
 use http::StatusCode;
 use serde::{Deserialize, Serialize};

examples/websocket.rs

@@ -14,7 +14,6 @@ use axum::{
     prelude::*,
     response::IntoResponse,
     routing::nest,
-    service::ServiceExt,
 };
 use http::StatusCode;
 use std::net::SocketAddr;
@@ -35,15 +34,14 @@ async fn main() {
     let app = nest(
         "/",
         axum::service::get(
-            ServeDir::new("examples/websocket")
+            ServeDir::new("examples/websocket").append_index_html_on_directories(true),
-                .append_index_html_on_directories(true)
+        )
         .handle_error(|error: std::io::Error| {
             Ok::<_, std::convert::Infallible>((
                 StatusCode::INTERNAL_SERVER_ERROR,
                 format!("Unhandled internal error: {}", error),
             ))
         }),
-        ),
     )
     // routes are matched from bottom to top, so we have to put `nest` at the
     // top since it matches all routes

src/handler/mod.rs

@@ -366,9 +366,9 @@ impl<S, T> Layered<S, T> {
     /// This is used to convert errors to responses rather than simply
     /// terminating the connection.
     ///
-    /// It works similarly to [`routing::Layered::handle_error`]. See that for more details.
+    /// It works similarly to [`routing::RoutingDsl::handle_error`]. See that for more details.
     ///
-    /// [`routing::Layered::handle_error`]: crate::routing::Layered::handle_error
+    /// [`routing::RoutingDsl::handle_error`]: crate::routing::RoutingDsl::handle_error
     pub fn handle_error<F, ReqBody, ResBody, Res, E>(
         self,
         f: F,

src/lib.rs

@@ -493,7 +493,7 @@
 //! return `Result<T, E>` where `T` implements
 //! [`IntoResponse`](response::IntoResponse).
 //!
-//! See [`routing::Layered::handle_error`] for more details.
+//! See [`routing::RoutingDsl::handle_error`] for more details.
 //!
 //! ## Applying multiple middleware
 //!

src/routing.rs

@@ -6,7 +6,7 @@ use crate::{
     buffer::MpscBuffer,
     extract::connect_info::{Connected, IntoMakeServiceWithConnectInfo},
     response::IntoResponse,
-    service::HandleErrorFromRouter,
+    service::{HandleError, HandleErrorFromRouter},
     util::ByteStr,
 };
 use async_trait::async_trait;
@@ -348,6 +348,94 @@ pub trait RoutingDsl: crate::sealed::Sealed + Sized {
             second: other,
         }
     }
+
+    /// Handle errors services in this router might produce, by mapping them to
+    /// responses.
+    ///
+    /// Unhandled errors will close the connection without sending a response.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use axum::{http::StatusCode, prelude::*};
+    /// use tower::{BoxError, timeout::TimeoutLayer};
+    /// use std::{time::Duration, convert::Infallible};
+    ///
+    /// // This router can never fail, since handlers can never fail.
+    /// let app = route("/", get(|| async {}));
+    ///
+    /// // Now the router can fail since the `tower::timeout::Timeout`
+    /// // middleware will return an error if the timeout elapses.
+    /// let app = app.layer(TimeoutLayer::new(Duration::from_secs(10)));
+    ///
+    /// // With `handle_error` we can handle errors `Timeout` might produce.
+    /// // Our router now cannot fail, that is its error type is `Infallible`.
+    /// let app = app.handle_error(|error: BoxError| {
+    ///     if error.is::<tower::timeout::error::Elapsed>() {
+    ///         Ok::<_, Infallible>((
+    ///             StatusCode::REQUEST_TIMEOUT,
+    ///             "request took too long to handle".to_string(),
+    ///         ))
+    ///     } else {
+    ///         Ok::<_, Infallible>((
+    ///             StatusCode::INTERNAL_SERVER_ERROR,
+    ///             format!("Unhandled error: {}", error),
+    ///         ))
+    ///     }
+    /// });
+    /// # async {
+    /// # hyper::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
+    /// # };
+    /// ```
+    ///
+    /// You can return `Err(_)` from the closure if you don't wish to handle
+    /// some errors:
+    ///
+    /// ```
+    /// use axum::{http::StatusCode, prelude::*};
+    /// use tower::{BoxError, timeout::TimeoutLayer};
+    /// use std::time::Duration;
+    ///
+    /// let app = route("/", get(|| async {}))
+    ///     .layer(TimeoutLayer::new(Duration::from_secs(10)))
+    ///     .handle_error(|error: BoxError| {
+    ///         if error.is::<tower::timeout::error::Elapsed>() {
+    ///             Ok((
+    ///                 StatusCode::REQUEST_TIMEOUT,
+    ///                 "request took too long to handle".to_string(),
+    ///             ))
+    ///         } else {
+    ///             // return the error as is
+    ///             Err(error)
+    ///         }
+    ///     });
+    /// # async {
+    /// # hyper::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
+    /// # };
+    /// ```
+    fn handle_error<ReqBody, ResBody, F, Res, E>(
+        self,
+        f: F,
+    ) -> HandleError<Self, F, ReqBody, HandleErrorFromRouter>
+    where
+        Self: Service<Request<ReqBody>, Response = Response<ResBody>>,
+        F: FnOnce(Self::Error) -> Result<Res, E>,
+        Res: IntoResponse,
+        ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
+        ResBody::Error: Into<BoxError> + Send + Sync + 'static,
+    {
+        HandleError::new(self, f)
+    }
+
+    /// Check that your service cannot fail.
+    ///
+    /// That is, its error type is [`Infallible`].
+    fn check_infallible<ReqBody>(self) -> Self
+    where
+        Self: Service<Request<ReqBody>, Error = Infallible>,
+    {
+        self
+    }
 }
 
 impl<S, F> RoutingDsl for Route<S, F> {}
@@ -646,97 +734,6 @@ impl<S> RoutingDsl for Layered<S> {}
 
 impl<S> crate::sealed::Sealed for Layered<S> {}
 
-impl<S> Layered<S> {
-    /// Create a new [`Layered`] service where errors will be handled using the
-    /// given closure.
-    ///
-    /// This is used to convert errors to responses rather than simply
-    /// terminating the connection.
-    ///
-    /// That can be done using `handle_error` like so:
-    ///
-    /// ```rust
-    /// use axum::prelude::*;
-    /// use http::StatusCode;
-    /// use tower::{BoxError, timeout::TimeoutLayer};
-    /// use std::{convert::Infallible, time::Duration};
-    ///
-    /// async fn handler() { /* ... */ }
-    ///
-    /// // `Timeout` will fail with `BoxError` if the timeout elapses...
-    /// let layered_app = route("/", get(handler))
-    ///     .layer(TimeoutLayer::new(Duration::from_secs(30)));
-    ///
-    /// // ...so we should handle that error
-    /// let with_errors_handled = layered_app.handle_error(|error: BoxError| {
-    ///     if error.is::<tower::timeout::error::Elapsed>() {
-    ///         Ok::<_, Infallible>((
-    ///             StatusCode::REQUEST_TIMEOUT,
-    ///             "request took too long".to_string(),
-    ///         ))
-    ///     } else {
-    ///         Ok::<_, Infallible>((
-    ///             StatusCode::INTERNAL_SERVER_ERROR,
-    ///             format!("Unhandled internal error: {}", error),
-    ///         ))
-    ///     }
-    /// });
-    /// # async {
-    /// # axum::Server::bind(&"".parse().unwrap())
-    /// #     .serve(with_errors_handled.into_make_service())
-    /// #     .await
-    /// #     .unwrap();
-    /// # };
-    /// ```
-    ///
-    /// The closure must return `Result<T, E>` where `T` implements [`IntoResponse`].
-    ///
-    /// You can also return `Err(_)` if you don't wish to handle the error:
-    ///
-    /// ```rust
-    /// use axum::prelude::*;
-    /// use http::StatusCode;
-    /// use tower::{BoxError, timeout::TimeoutLayer};
-    /// use std::time::Duration;
-    ///
-    /// async fn handler() { /* ... */ }
-    ///
-    /// let layered_app = route("/", get(handler))
-    ///     .layer(TimeoutLayer::new(Duration::from_secs(30)));
-    ///
-    /// let with_errors_handled = layered_app.handle_error(|error: BoxError| {
-    ///     if error.is::<tower::timeout::error::Elapsed>() {
-    ///         Ok((
-    ///             StatusCode::REQUEST_TIMEOUT,
-    ///             "request took too long".to_string(),
-    ///         ))
-    ///     } else {
-    ///         // keep the error as is
-    ///         Err(error)
-    ///     }
-    /// });
-    /// # async {
-    /// # axum::Server::bind(&"".parse().unwrap())
-    /// #     .serve(with_errors_handled.into_make_service())
-    /// #     .await
-    /// #     .unwrap();
-    /// # };
-    /// ```
-    pub fn handle_error<F, ReqBody, ResBody, Res, E>(
-        self,
-        f: F,
-    ) -> crate::service::HandleError<S, F, ReqBody, HandleErrorFromRouter>
-    where
-        S: Service<Request<ReqBody>, Response = Response<ResBody>> + Clone,
-        F: FnOnce(S::Error) -> Result<Res, E>,
-        Res: IntoResponse,
-        ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
-        ResBody::Error: Into<BoxError> + Send + Sync + 'static,
-    {
-        crate::service::HandleError::new(self.inner, f)
-    }
-}
-
 impl<S, R> Service<R> for Layered<S>
 where
     S: Service<R>,
@@ -809,7 +806,7 @@ where
 ///
 /// ```
 /// use axum::{
-///     routing::nest, service::{get, ServiceExt}, prelude::*,
+///     routing::nest, service::get, prelude::*,
 /// };
 /// use tower_http::services::ServeDir;
 ///

src/service/mod.rs

@@ -94,7 +94,6 @@ use crate::{
 use bytes::Bytes;
 use http::{Request, Response};
 use std::{
-    convert::Infallible,
     fmt,
     marker::PhantomData,
     task::{Context, Poll},
@@ -428,6 +427,26 @@ impl<S, F> OnMethod<S, F> {
             fallback: self,
         }
     }
+
+    /// Handle errors this service might produce, by mapping them to responses.
+    ///
+    /// Unhandled errors will close the connection without sending a response.
+    ///
+    /// Works similarly to [`RoutingDsl::handle_error`]. See that for more
+    /// details.
+    ///
+    /// [`RoutingDsl::handle_error`]: crate::routing::RoutingDsl::handle_error
+    pub fn handle_error<ReqBody, H, Res, E>(
+        self,
+        f: H,
+    ) -> HandleError<Self, H, ReqBody, HandleErrorFromService>
+    where
+        Self: Service<Request<ReqBody>, Response = Response<BoxBody>>,
+        H: FnOnce(<Self as Service<Request<ReqBody>>>::Error) -> Result<Res, E>,
+        Res: IntoResponse,
+    {
+        HandleError::new(self, f)
+    }
 }
 
 // this is identical to `routing::OnMethod`'s implementation. Would be nice to find a way to clean
@@ -462,7 +481,7 @@ where
 ///
 /// Created with
 /// [`handler::Layered::handle_error`](crate::handler::Layered::handle_error) or
-/// [`routing::Layered::handle_error`](crate::routing::Layered::handle_error).
+/// [`routing::RoutingDsl::handle_error`](crate::routing::RoutingDsl::handle_error).
 /// See those methods for more details.
 pub struct HandleError<S, F, B, T> {
     inner: S,
@@ -542,75 +561,6 @@ where
     }
 }
 
-/// Extension trait that adds additional methods to [`Service`].
-pub trait ServiceExt<ReqBody, ResBody>:
-    Service<Request<ReqBody>, Response = Response<ResBody>>
-{
-    /// Handle errors from a service.
-    ///
-    /// `handle_error` takes a closure that will map errors from the service
-    /// into responses. The closure's return type must be `Result<T, E>` where
-    /// `T` implements [`IntoResponse`](crate::response::IntoResponse).
-    ///
-    /// # Example
-    ///
-    /// ```rust,no_run
-    /// use axum::{service::{self, ServiceExt}, prelude::*};
-    /// use http::{Response, StatusCode};
-    /// use tower::{service_fn, BoxError};
-    /// use std::convert::Infallible;
-    ///
-    /// // A service that might fail with `std::io::Error`
-    /// let service = service_fn(|_: Request<Body>| async {
-    ///     let res = Response::new(Body::empty());
-    ///     Ok::<_, std::io::Error>(res)
-    /// });
-    ///
-    /// let app = route(
-    ///     "/",
-    ///     service.handle_error(|error: std::io::Error| {
-    ///         Ok::<_, Infallible>((
-    ///             StatusCode::INTERNAL_SERVER_ERROR,
-    ///             error.to_string(),
-    ///         ))
-    ///     }),
-    /// );
-    /// #
-    /// # async {
-    /// # axum::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
-    /// # };
-    /// ```
-    ///
-    /// It works similarly to [`routing::Layered::handle_error`]. See that for more details.
-    ///
-    /// [`routing::Layered::handle_error`]: crate::routing::Layered::handle_error
-    fn handle_error<F, Res, E>(self, f: F) -> HandleError<Self, F, ReqBody, HandleErrorFromService>
-    where
-        Self: Sized,
-        F: FnOnce(Self::Error) -> Result<Res, E>,
-        Res: IntoResponse,
-        ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
-        ResBody::Error: Into<BoxError> + Send + Sync + 'static,
-    {
-        HandleError::new(self, f)
-    }
-
-    /// Check that your service cannot fail.
-    ///
-    /// That is, its error type is [`Infallible`].
-    fn check_infallible(self) -> Self
-    where
-        Self: Service<Request<ReqBody>, Response = Response<ResBody>, Error = Infallible> + Sized,
-    {
-        self
-    }
-}
-
-impl<S, ReqBody, ResBody> ServiceExt<ReqBody, ResBody> for S where
-    S: Service<Request<ReqBody>, Response = Response<ResBody>>
-{
-}
-
 /// A [`Service`] that boxes response bodies.
 pub struct BoxResponseBody<S, B> {
     inner: S,

src/tests.rs

@@ -16,9 +16,9 @@ use std::{
     task::{Context, Poll},
     time::Duration,
 };
-use tower::{make::Shared, service_fn, BoxError, Service, ServiceBuilder};
+use tower::{make::Shared, service_fn, BoxError, Service};
-use tower_http::{compression::CompressionLayer, trace::TraceLayer};
 
+mod handle_error;
 mod nest;
 mod or;
 
@@ -326,53 +326,6 @@ async fn boxing() {
     assert_eq!(res.text().await.unwrap(), "hi from POST");
 }
 
-#[tokio::test]
-async fn service_handlers() {
-    use crate::service::ServiceExt as _;
-    use tower_http::services::ServeFile;
-
-    let app = route(
-        "/echo",
-        service::post(
-            service_fn(|req: Request<Body>| async move {
-                Ok::<_, BoxError>(Response::new(req.into_body()))
-            })
-            .handle_error(|_error: BoxError| Ok(StatusCode::INTERNAL_SERVER_ERROR)),
-        ),
-    )
-    .route(
-        "/static/Cargo.toml",
-        service::on(
-            MethodFilter::GET,
-            ServeFile::new("Cargo.toml").handle_error(|error: std::io::Error| {
-                Ok::<_, Infallible>((StatusCode::INTERNAL_SERVER_ERROR, error.to_string()))
-            }),
-        ),
-    );
-
-    let addr = run_in_background(app).await;
-
-    let client = reqwest::Client::new();
-
-    let res = client
-        .post(format!("http://{}/echo", addr))
-        .body("foobar")
-        .send()
-        .await
-        .unwrap();
-    assert_eq!(res.status(), StatusCode::OK);
-    assert_eq!(res.text().await.unwrap(), "foobar");
-
-    let res = client
-        .get(format!("http://{}/static/Cargo.toml", addr))
-        .body("foobar")
-        .send()
-        .await
-        .unwrap();
-    assert_eq!(res.status(), StatusCode::OK);
-    assert!(res.text().await.unwrap().contains("edition ="));
-}
-
 #[tokio::test]
 async fn routing_between_services() {
     use std::convert::Infallible;
@@ -466,55 +419,6 @@ async fn middleware_on_single_route() {
     assert_eq!(body, "Hello, World!");
 }
 
-#[tokio::test]
-async fn handling_errors_from_layered_single_routes() {
-    async fn handle(_req: Request<Body>) -> &'static str {
-        tokio::time::sleep(Duration::from_secs(10)).await;
-        ""
-    }
-
-    let app = route(
-        "/",
-        get(handle
-            .layer(
-                ServiceBuilder::new()
-                    .timeout(Duration::from_millis(100))
-                    .layer(TraceLayer::new_for_http())
-                    .into_inner(),
-            )
-            .handle_error(|_error: BoxError| {
-                Ok::<_, Infallible>(StatusCode::INTERNAL_SERVER_ERROR)
-            })),
-    );
-
-    let addr = run_in_background(app).await;
-
-    let res = reqwest::get(format!("http://{}", addr)).await.unwrap();
-    assert_eq!(res.status(), StatusCode::INTERNAL_SERVER_ERROR);
-}
-
-#[tokio::test]
-async fn layer_on_whole_router() {
-    async fn handle(_req: Request<Body>) -> &'static str {
-        tokio::time::sleep(Duration::from_secs(10)).await;
-        ""
-    }
-
-    let app = route("/", get(handle))
-        .layer(
-            ServiceBuilder::new()
-                .layer(CompressionLayer::new())
-                .timeout(Duration::from_millis(100))
-                .into_inner(),
-        )
-        .handle_error(|_err: BoxError| Ok::<_, Infallible>(StatusCode::INTERNAL_SERVER_ERROR));
-
-    let addr = run_in_background(app).await;
-
-    let res = reqwest::get(format!("http://{}", addr)).await.unwrap();
-    assert_eq!(res.status(), StatusCode::INTERNAL_SERVER_ERROR);
-}
-
 #[tokio::test]
 #[cfg(feature = "header")]
 async fn typed_header() {

src/tests/handle_error.rs

@@ -0,0 +1,203 @@
+use super::*;
+use futures_util::future::{pending, ready};
+use tower::{timeout::TimeoutLayer, MakeService};
+
+async fn unit() {}
+
+async fn forever() {
+    pending().await
+}
+
+fn timeout() -> TimeoutLayer {
+    TimeoutLayer::new(Duration::from_millis(10))
+}
+
+#[derive(Clone)]
+struct Svc;
+
+impl<R> Service<R> for Svc {
+    type Response = Response<Body>;
+    type Error = hyper::Error;
+    type Future = Ready<Result<Self::Response, Self::Error>>;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, _req: R) -> Self::Future {
+        ready(Ok(Response::new(Body::empty())))
+    }
+}
+
+fn check_make_svc<M, R, T, E>(_make_svc: M)
+where
+    M: MakeService<(), R, Response = T, Error = E>,
+{
+}
+
+fn handle_error<E>(_: E) -> Result<StatusCode, Infallible> {
+    Ok(StatusCode::INTERNAL_SERVER_ERROR)
+}
+
+#[tokio::test]
+async fn handler() {
+    let app = route(
+        "/",
+        get(forever
+            .layer(timeout())
+            .handle_error(|_: BoxError| Ok::<_, Infallible>(StatusCode::REQUEST_TIMEOUT))),
+    );
+
+    let addr = run_in_background(app).await;
+
+    let client = reqwest::Client::new();
+
+    let res = client
+        .get(format!("http://{}/", addr))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(res.status(), StatusCode::REQUEST_TIMEOUT);
+}
+
+#[tokio::test]
+async fn handler_multiple_methods_first() {
+    let app = route(
+        "/",
+        get(forever
+            .layer(timeout())
+            .handle_error(|_: BoxError| Ok::<_, Infallible>(StatusCode::REQUEST_TIMEOUT)))
+        .post(unit),
+    );
+
+    let addr = run_in_background(app).await;
+
+    let client = reqwest::Client::new();
+
+    let res = client
+        .get(format!("http://{}/", addr))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(res.status(), StatusCode::REQUEST_TIMEOUT);
+}
+
+#[tokio::test]
+async fn handler_multiple_methods_middle() {
+    let app = route(
+        "/",
+        delete(unit)
+            .get(
+                forever
+                    .layer(timeout())
+                    .handle_error(|_: BoxError| Ok::<_, Infallible>(StatusCode::REQUEST_TIMEOUT)),
+            )
+            .post(unit),
+    );
+
+    let addr = run_in_background(app).await;
+
+    let client = reqwest::Client::new();
+
+    let res = client
+        .get(format!("http://{}/", addr))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(res.status(), StatusCode::REQUEST_TIMEOUT);
+}
+
+#[tokio::test]
+async fn handler_multiple_methods_last() {
+    let app = route(
+        "/",
+        delete(unit).get(
+            forever
+                .layer(timeout())
+                .handle_error(|_: BoxError| Ok::<_, Infallible>(StatusCode::REQUEST_TIMEOUT)),
+        ),
+    );
+
+    let addr = run_in_background(app).await;
+
+    let client = reqwest::Client::new();
+
+    let res = client
+        .get(format!("http://{}/", addr))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(res.status(), StatusCode::REQUEST_TIMEOUT);
+}
+
+#[test]
+fn service_propagates_errors() {
+    let app = route::<_, Body>("/echo", service::post(Svc));
+
+    check_make_svc::<_, _, _, hyper::Error>(app.into_make_service());
+}
+
+#[test]
+fn service_nested_propagates_errors() {
+    let app = route::<_, Body>("/echo", nest("/foo", service::post(Svc)));
+
+    check_make_svc::<_, _, _, hyper::Error>(app.into_make_service());
+}
+
+#[test]
+fn service_handle_on_method() {
+    let app = route::<_, Body>(
+        "/echo",
+        service::get(Svc).handle_error(handle_error::<hyper::Error>),
+    );
+
+    check_make_svc::<_, _, _, Infallible>(app.into_make_service());
+}
+
+#[test]
+fn service_handle_on_method_multiple() {
+    let app = route::<_, Body>(
+        "/echo",
+        service::get(Svc)
+            .post(Svc)
+            .handle_error(handle_error::<hyper::Error>),
+    );
+
+    check_make_svc::<_, _, _, Infallible>(app.into_make_service());
+}
+
+#[test]
+fn service_handle_on_router() {
+    let app =
+        route::<_, Body>("/echo", service::get(Svc)).handle_error(handle_error::<hyper::Error>);
+
+    check_make_svc::<_, _, _, Infallible>(app.into_make_service());
+}
+
+#[test]
+fn service_handle_on_router_still_impls_routing_dsl() {
+    let app = route::<_, Body>("/echo", service::get(Svc))
+        .handle_error(handle_error::<hyper::Error>)
+        .route("/", get(unit));
+
+    check_make_svc::<_, _, _, Infallible>(app.into_make_service());
+}
+
+#[test]
+fn layered() {
+    let app = route::<_, Body>("/echo", get(unit))
+        .layer(timeout())
+        .handle_error(handle_error::<BoxError>);
+
+    check_make_svc::<_, _, _, Infallible>(app.into_make_service());
+}
+
+#[tokio::test] // async because of `.boxed()`
+async fn layered_boxed() {
+    let app = route::<_, Body>("/echo", get(unit))
+        .layer(timeout())
+        .boxed()
+        .handle_error(handle_error::<BoxError>);
+
+    check_make_svc::<_, _, _, Infallible>(app.into_make_service());
+}