Require `Sync` for services (#2473)

Co-authored-by: Jonas Platte <jplatte+git@posteo.de>

14 files changed, 137 insertions, 47 deletions

diff --git a/axum-extra/src/handler/mod.rs b/axum-extra/src/handler/mod.rs
index 915852a1..c3bf7024 100644
--- a/axum-extra/src/handler/mod.rs
+++ b/axum-extra/src/handler/mod.rs
@@ -165,7 +165,7 @@ pub struct IntoHandler<H, T, S> {
 
 impl<H, T, S> Handler<T, S> for IntoHandler<H, T, S>
 where
-    H: HandlerCallWithExtractors<T, S> + Clone + Send + 'static,
+    H: HandlerCallWithExtractors<T, S> + Clone + Send + Sync + 'static,
     T: FromRequest<S> + Send + 'static,
     T::Rejection: Send,
     S: Send + Sync + 'static,
diff --git a/axum-extra/src/handler/or.rs b/axum-extra/src/handler/or.rs
index 0a468db7..faa68516 100644
--- a/axum-extra/src/handler/or.rs
+++ b/axum-extra/src/handler/or.rs
@@ -54,8 +54,8 @@ where
 
 impl<S, L, R, Lt, Rt, M> Handler<(M, Lt, Rt), S> for Or<L, R, Lt, Rt, S>
 where
-    L: HandlerCallWithExtractors<Lt, S> + Clone + Send + 'static,
-    R: HandlerCallWithExtractors<Rt, S> + Clone + Send + 'static,
+    L: HandlerCallWithExtractors<Lt, S> + Clone + Send + Sync + 'static,
+    R: HandlerCallWithExtractors<Rt, S> + Clone + Send + Sync + 'static,
     Lt: FromRequestParts<S> + Send + 'static,
     Rt: FromRequest<S, M> + Send + 'static,
     Lt::Rejection: Send,
diff --git a/axum-extra/src/routing/mod.rs b/axum-extra/src/routing/mod.rs
index a294c547..bf99bbcf 100644
--- a/axum-extra/src/routing/mod.rs
+++ b/axum-extra/src/routing/mod.rs
@@ -165,7 +165,7 @@ pub trait RouterExt<S>: sealed::Sealed {
     /// This works like [`RouterExt::route_with_tsr`] but accepts any [`Service`].
     fn route_service_with_tsr<T>(self, path: &str, service: T) -> Self
     where
-        T: Service<Request, Error = Infallible> + Clone + Send + 'static,
+        T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse,
         T::Future: Send + 'static,
         Self: Sized;
@@ -268,7 +268,7 @@ where
     #[track_caller]
     fn route_service_with_tsr<T>(mut self, path: &str, service: T) -> Self
     where
-        T: Service<Request, Error = Infallible> + Clone + Send + 'static,
+        T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse,
         T::Future: Send + 'static,
         Self: Sized,
diff --git a/axum/CHANGELOG.md b/axum/CHANGELOG.md
index b897e757..47b69e2c 100644
--- a/axum/CHANGELOG.md
+++ b/axum/CHANGELOG.md
@@ -7,9 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
+- **breaking:** Require `Sync` for all handlers and services added to `Router`
+  and `MethodRouter` ([#2473])
 - **breaking:** The tuple and tuple_struct `Path` extractor deserializers now check that the number of parameters matches the tuple length exactly ([#2931])
 - **change:** Update minimum rust version to 1.75 ([#2943])
 
+[#2473]: https://github.com/tokio-rs/axum/pull/2473
 [#2931]: https://github.com/tokio-rs/axum/pull/2931
 [#2943]: https://github.com/tokio-rs/axum/pull/2943
 
@@ -55,7 +58,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 [#2201]: https://github.com/tokio-rs/axum/pull/2201
 [#2483]: https://github.com/tokio-rs/axum/pull/2483
-[#2201]: https://github.com/tokio-rs/axum/pull/2201
 [#2484]: https://github.com/tokio-rs/axum/pull/2484
 
 # 0.7.3 (29. December, 2023)
diff --git a/axum/src/box_clone_service.rs b/axum/src/box_clone_service.rs
new file mode 100644
index 00000000..25c0b205
--- /dev/null
+++ b/axum/src/box_clone_service.rs
@@ -0,0 +1,80 @@
+use futures_util::future::BoxFuture;
+use std::{
+    fmt,
+    task::{Context, Poll},
+};
+use tower::ServiceExt;
+use tower_service::Service;
+
+/// Like `tower::BoxCloneService` but `Sync`
+pub(crate) struct BoxCloneService<T, U, E>(
+    Box<
+        dyn CloneService<T, Response = U, Error = E, Future = BoxFuture<'static, Result<U, E>>>
+            + Send
+            + Sync,
+    >,
+);
+
+impl<T, U, E> BoxCloneService<T, U, E> {
+    pub(crate) fn new<S>(inner: S) -> Self
+    where
+        S: Service<T, Response = U, Error = E> + Clone + Send + Sync + 'static,
+        S::Future: Send + 'static,
+    {
+        let inner = inner.map_future(|f| Box::pin(f) as _);
+        BoxCloneService(Box::new(inner))
+    }
+}
+
+impl<T, U, E> Service<T> for BoxCloneService<T, U, E> {
+    type Response = U;
+    type Error = E;
+    type Future = BoxFuture<'static, Result<U, E>>;
+
+    #[inline]
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), E>> {
+        self.0.poll_ready(cx)
+    }
+
+    #[inline]
+    fn call(&mut self, request: T) -> Self::Future {
+        self.0.call(request)
+    }
+}
+
+impl<T, U, E> Clone for BoxCloneService<T, U, E> {
+    fn clone(&self) -> Self {
+        Self(self.0.clone_box())
+    }
+}
+
+trait CloneService<R>: Service<R> {
+    fn clone_box(
+        &self,
+    ) -> Box<
+        dyn CloneService<R, Response = Self::Response, Error = Self::Error, Future = Self::Future>
+            + Send
+            + Sync,
+    >;
+}
+
+impl<R, T> CloneService<R> for T
+where
+    T: Service<R> + Send + Sync + Clone + 'static,
+{
+    fn clone_box(
+        &self,
+    ) -> Box<
+        dyn CloneService<R, Response = T::Response, Error = T::Error, Future = T::Future>
+            + Send
+            + Sync,
+    > {
+        Box::new(self.clone())
+    }
+}
+
+impl<T, U, E> fmt::Debug for BoxCloneService<T, U, E> {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt.debug_struct("BoxCloneService").finish()
+    }
+}
diff --git a/axum/src/boxed.rs b/axum/src/boxed.rs
index 32808f51..6347de58 100644
--- a/axum/src/boxed.rs
+++ b/axum/src/boxed.rs
@@ -33,7 +33,7 @@ impl<S, E> BoxedIntoRoute<S, E> {
     where
         S: 'static,
         E: 'static,
-        F: FnOnce(Route<E>) -> Route<E2> + Clone + Send + 'static,
+        F: FnOnce(Route<E>) -> Route<E2> + Clone + Send + Sync + 'static,
         E2: 'static,
     {
         BoxedIntoRoute(AxumMutex::new(Box::new(Map {
@@ -59,7 +59,7 @@ impl<S, E> fmt::Debug for BoxedIntoRoute<S, E> {
     }
 }
 
-pub(crate) trait ErasedIntoRoute<S, E>: Send {
+pub(crate) trait ErasedIntoRoute<S, E>: Send + Sync {
     fn clone_box(&self) -> Box<dyn ErasedIntoRoute<S, E>>;
 
     fn into_route(self: Box<Self>, state: S) -> Route<E>;
@@ -75,7 +75,7 @@ pub(crate) struct MakeErasedHandler<H, S> {
 
 impl<H, S> ErasedIntoRoute<S, Infallible> for MakeErasedHandler<H, S>
 where
-    H: Clone + Send + 'static,
+    H: Clone + Send + Sync + 'static,
     S: 'static,
 {
     fn clone_box(&self) -> Box<dyn ErasedIntoRoute<S, Infallible>> {
@@ -165,13 +165,13 @@ where
     }
 }
 
-pub(crate) trait LayerFn<E, E2>: FnOnce(Route<E>) -> Route<E2> + Send {
+pub(crate) trait LayerFn<E, E2>: FnOnce(Route<E>) -> Route<E2> + Send + Sync {
     fn clone_box(&self) -> Box<dyn LayerFn<E, E2>>;
 }
 
 impl<F, E, E2> LayerFn<E, E2> for F
 where
-    F: FnOnce(Route<E>) -> Route<E2> + Clone + Send + 'static,
+    F: FnOnce(Route<E>) -> Route<E2> + Clone + Send + Sync + 'static,
 {
     fn clone_box(&self) -> Box<dyn LayerFn<E, E2>> {
         Box::new(self.clone())
diff --git a/axum/src/handler/mod.rs b/axum/src/handler/mod.rs
index 04c66c4a..8485390b 100644
--- a/axum/src/handler/mod.rs
+++ b/axum/src/handler/mod.rs
@@ -131,7 +131,7 @@ pub use self::service::HandlerService;
         note = "Consider using `#[axum::debug_handler]` to improve the error message"
     )
 )]
-pub trait Handler<T, S>: Clone + Send + Sized + 'static {
+pub trait Handler<T, S>: Clone + Send + Sync + Sized + 'static {
     /// The type of future calling this handler returns.
     type Future: Future<Output = Response> + Send + 'static;
 
@@ -192,7 +192,7 @@ pub trait Handler<T, S>: Clone + Send + Sized + 'static {
 
 impl<F, Fut, Res, S> Handler<((),), S> for F
 where
-    F: FnOnce() -> Fut + Clone + Send + 'static,
+    F: FnOnce() -> Fut + Clone + Send + Sync + 'static,
     Fut: Future<Output = Res> + Send,
     Res: IntoResponse,
 {
@@ -210,7 +210,7 @@ macro_rules! impl_handler {
         #[allow(non_snake_case, unused_mut)]
         impl<F, Fut, S, Res, M, $($ty,)* $last> Handler<(M, $($ty,)* $last,), S> for F
         where
-            F: FnOnce($($ty,)* $last,) -> Fut + Clone + Send + 'static,
+            F: FnOnce($($ty,)* $last,) -> Fut + Clone + Send + Sync + 'static,
             Fut: Future<Output = Res> + Send,
             S: Send + Sync + 'static,
             Res: IntoResponse,
@@ -257,7 +257,7 @@ mod private {
 
 impl<T, S> Handler<private::IntoResponseHandler, S> for T
 where
-    T: IntoResponse + Clone + Send + 'static,
+    T: IntoResponse + Clone + Send + Sync + 'static,
 {
     type Future = std::future::Ready<Response>;
 
@@ -302,7 +302,7 @@ where
 
 impl<H, S, T, L> Handler<T, S> for Layered<L, H, T, S>
 where
-    L: Layer<HandlerService<H, T, S>> + Clone + Send + 'static,
+    L: Layer<HandlerService<H, T, S>> + Clone + Send + Sync + 'static,
     H: Handler<T, S>,
     L::Service: Service<Request, Error = Infallible> + Clone + Send + 'static,
     <L::Service as Service<Request>>::Response: IntoResponse,
diff --git a/axum/src/lib.rs b/axum/src/lib.rs
index 64d4a6a2..27b87e90 100644
--- a/axum/src/lib.rs
+++ b/axum/src/lib.rs
@@ -463,6 +463,7 @@
 #[macro_use]
 pub(crate) mod macros;
 
+mod box_clone_service;
 mod boxed;
 mod extension;
 #[cfg(feature = "form")]
diff --git a/axum/src/middleware/from_fn.rs b/axum/src/middleware/from_fn.rs
index f0f47611..e34fd058 100644
--- a/axum/src/middleware/from_fn.rs
+++ b/axum/src/middleware/from_fn.rs
@@ -1,3 +1,4 @@
+use crate::box_clone_service::BoxCloneService;
 use crate::response::{IntoResponse, Response};
 use axum_core::extract::{FromRequest, FromRequestParts, Request};
 use futures_util::future::BoxFuture;
@@ -10,7 +11,7 @@ use std::{
     pin::Pin,
     task::{Context, Poll},
 };
-use tower::{util::BoxCloneService, ServiceBuilder};
+use tower::ServiceBuilder;
 use tower_layer::Layer;
 use tower_service::Service;
 
@@ -260,6 +261,7 @@ macro_rules! impl_service {
             I: Service<Request, Error = Infallible>
                 + Clone
                 + Send
+                + Sync
                 + 'static,
             I::Response: IntoResponse,
             I::Future: Send + 'static,
@@ -298,7 +300,7 @@ macro_rules! impl_service {
                     };
 
                     let inner = ServiceBuilder::new()
-                        .boxed_clone()
+                        .layer_fn(BoxCloneService::new)
                         .map_response(IntoResponse::into_response)
                         .service(ready_inner);
                     let next = Next { inner };
diff --git a/axum/src/routing/method_routing.rs b/axum/src/routing/method_routing.rs
index 1eb6075b..8c50eccf 100644
--- a/axum/src/routing/method_routing.rs
+++ b/axum/src/routing/method_routing.rs
@@ -78,7 +78,7 @@ macro_rules! top_level_service_fn {
         $(#[$m])+
         pub fn $name<T, S>(svc: T) -> MethodRouter<S, T::Error>
         where
-            T: Service<Request> + Clone + Send + 'static,
+            T: Service<Request> + Clone + Send + Sync + 'static,
             T::Response: IntoResponse + 'static,
             T::Future: Send + 'static,
             S: Clone,
@@ -210,6 +210,7 @@ macro_rules! chained_service_fn {
             T: Service<Request, Error = E>
                 + Clone
                 + Send
+                + Sync
                 + 'static,
             T::Response: IntoResponse + 'static,
             T::Future: Send + 'static,
@@ -312,7 +313,7 @@ top_level_service_fn!(trace_service, TRACE);
 /// ```
 pub fn on_service<T, S>(filter: MethodFilter, svc: T) -> MethodRouter<S, T::Error>
 where
-    T: Service<Request> + Clone + Send + 'static,
+    T: Service<Request> + Clone + Send + Sync + 'static,
     T::Response: IntoResponse + 'static,
     T::Future: Send + 'static,
     S: Clone,
@@ -371,7 +372,7 @@ where
 /// ```
 pub fn any_service<T, S>(svc: T) -> MethodRouter<S, T::Error>
 where
-    T: Service<Request> + Clone + Send + 'static,
+    T: Service<Request> + Clone + Send + Sync + 'static,
     T::Response: IntoResponse + 'static,
     T::Future: Send + 'static,
     S: Clone,
@@ -736,7 +737,7 @@ where
     #[track_caller]
     pub fn on_service<T>(self, filter: MethodFilter, svc: T) -> Self
     where
-        T: Service<Request, Error = E> + Clone + Send + 'static,
+        T: Service<Request, Error = E> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse + 'static,
         T::Future: Send + 'static,
     {
@@ -868,7 +869,7 @@ where
     #[doc = include_str!("../docs/method_routing/fallback.md")]
     pub fn fallback_service<T>(mut self, svc: T) -> Self
     where
-        T: Service<Request, Error = E> + Clone + Send + 'static,
+        T: Service<Request, Error = E> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse + 'static,
         T::Future: Send + 'static,
     {
@@ -879,8 +880,8 @@ where
     #[doc = include_str!("../docs/method_routing/layer.md")]
     pub fn layer<L, NewError>(self, layer: L) -> MethodRouter<S, NewError>
     where
-        L: Layer<Route<E>> + Clone + Send + 'static,
-        L::Service: Service<Request> + Clone + Send + 'static,
+        L: Layer<Route<E>> + Clone + Send + Sync + 'static,
+        L::Service: Service<Request> + Clone + Send + Sync + 'static,
         <L::Service as Service<Request>>::Response: IntoResponse + 'static,
         <L::Service as Service<Request>>::Error: Into<NewError> + 'static,
         <L::Service as Service<Request>>::Future: Send + 'static,
@@ -908,8 +909,8 @@ where
     #[track_caller]
     pub fn route_layer<L>(mut self, layer: L) -> MethodRouter<S, E>
     where
-        L: Layer<Route<E>> + Clone + Send + 'static,
-        L::Service: Service<Request, Error = E> + Clone + Send + 'static,
+        L: Layer<Route<E>> + Clone + Send + Sync + 'static,
+        L::Service: Service<Request, Error = E> + Clone + Send + Sync + 'static,
         <L::Service as Service<Request>>::Response: IntoResponse + 'static,
         <L::Service as Service<Request>>::Future: Send + 'static,
         E: 'static,
@@ -1151,7 +1152,7 @@ where
     where
         S: 'static,
         E: 'static,
-        F: FnOnce(Route<E>) -> Route<E2> + Clone + Send + 'static,
+        F: FnOnce(Route<E>) -> Route<E2> + Clone + Send + Sync + 'static,
         E2: 'static,
     {
         match self {
diff --git a/axum/src/routing/mod.rs b/axum/src/routing/mod.rs
index dc6ca815..4bd8b28b 100644
--- a/axum/src/routing/mod.rs
+++ b/axum/src/routing/mod.rs
@@ -165,7 +165,7 @@ where
     #[doc = include_str!("../docs/routing/route_service.md")]
     pub fn route_service<T>(self, path: &str, service: T) -> Self
     where
-        T: Service<Request, Error = Infallible> + Clone + Send + 'static,
+        T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse,
         T::Future: Send + 'static,
     {
@@ -211,7 +211,7 @@ where
     #[track_caller]
     pub fn nest_service<T>(self, path: &str, service: T) -> Self
     where
-        T: Service<Request, Error = Infallible> + Clone + Send + 'static,
+        T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse,
         T::Future: Send + 'static,
     {
@@ -275,8 +275,8 @@ where
     #[doc = include_str!("../docs/routing/layer.md")]
     pub fn layer<L>(self, layer: L) -> Router<S>
     where
-        L: Layer<Route> + Clone + Send + 'static,
-        L::Service: Service<Request> + Clone + Send + 'static,
+        L: Layer<Route> + Clone + Send + Sync + 'static,
+        L::Service: Service<Request> + Clone + Send + Sync + 'static,
         <L::Service as Service<Request>>::Response: IntoResponse + 'static,
         <L::Service as Service<Request>>::Error: Into<Infallible> + 'static,
         <L::Service as Service<Request>>::Future: Send + 'static,
@@ -293,8 +293,8 @@ where
     #[track_caller]
     pub fn route_layer<L>(self, layer: L) -> Self
     where
-        L: Layer<Route> + Clone + Send + 'static,
-        L::Service: Service<Request> + Clone + Send + 'static,
+        L: Layer<Route> + Clone + Send + Sync + 'static,
+        L::Service: Service<Request> + Clone + Send + Sync + 'static,
         <L::Service as Service<Request>>::Response: IntoResponse + 'static,
         <L::Service as Service<Request>>::Error: Into<Infallible> + 'static,
         <L::Service as Service<Request>>::Future: Send + 'static,
@@ -331,7 +331,7 @@ where
     /// See [`Router::fallback`] for more details.
     pub fn fallback_service<T>(self, service: T) -> Self
     where
-        T: Service<Request, Error = Infallible> + Clone + Send + 'static,
+        T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse,
         T::Future: Send + 'static,
     {
@@ -638,7 +638,7 @@ where
     where
         S: 'static,
         E: 'static,
-        F: FnOnce(Route<E>) -> Route<E2> + Clone + Send + 'static,
+        F: FnOnce(Route<E>) -> Route<E2> + Clone + Send + Sync + 'static,
         E2: 'static,
     {
         match self {
@@ -701,8 +701,8 @@ where
 {
     fn layer<L>(self, layer: L) -> Endpoint<S>
     where
-        L: Layer<Route> + Clone + Send + 'static,
-        L::Service: Service<Request> + Clone + Send + 'static,
+        L: Layer<Route> + Clone + Send + Sync + 'static,
+        L::Service: Service<Request> + Clone + Send + Sync + 'static,
         <L::Service as Service<Request>>::Response: IntoResponse + 'static,
         <L::Service as Service<Request>>::Error: Into<Infallible> + 'static,
         <L::Service as Service<Request>>::Future: Send + 'static,
diff --git a/axum/src/routing/path_router.rs b/axum/src/routing/path_router.rs
index e132f1dc..6a7d3cee 100644
--- a/axum/src/routing/path_router.rs
+++ b/axum/src/routing/path_router.rs
@@ -85,7 +85,7 @@ where
         service: T,
     ) -> Result<(), Cow<'static, str>>
     where
-        T: Service<Request, Error = Infallible> + Clone + Send + 'static,
+        T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse,
         T::Future: Send + 'static,
     {
@@ -201,7 +201,7 @@ where
         svc: T,
     ) -> Result<(), Cow<'static, str>>
     where
-        T: Service<Request, Error = Infallible> + Clone + Send + 'static,
+        T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse,
         T::Future: Send + 'static,
     {
@@ -236,8 +236,8 @@ where
 
     pub(super) fn layer<L>(self, layer: L) -> PathRouter<S, IS_FALLBACK>
     where
-        L: Layer<Route> + Clone + Send + 'static,
-        L::Service: Service<Request> + Clone + Send + 'static,
+        L: Layer<Route> + Clone + Send + Sync + 'static,
+        L::Service: Service<Request> + Clone + Send + Sync + 'static,
         <L::Service as Service<Request>>::Response: IntoResponse + 'static,
         <L::Service as Service<Request>>::Error: Into<Infallible> + 'static,
         <L::Service as Service<Request>>::Future: Send + 'static,
@@ -261,8 +261,8 @@ where
     #[track_caller]
     pub(super) fn route_layer<L>(self, layer: L) -> Self
     where
-        L: Layer<Route> + Clone + Send + 'static,
-        L::Service: Service<Request> + Clone + Send + 'static,
+        L: Layer<Route> + Clone + Send + Sync + 'static,
+        L::Service: Service<Request> + Clone + Send + Sync + 'static,
         <L::Service as Service<Request>>::Response: IntoResponse + 'static,
         <L::Service as Service<Request>>::Error: Into<Infallible> + 'static,
         <L::Service as Service<Request>>::Future: Send + 'static,
diff --git a/axum/src/routing/route.rs b/axum/src/routing/route.rs
index 242e25f3..71349ba6 100644
--- a/axum/src/routing/route.rs
+++ b/axum/src/routing/route.rs
@@ -1,5 +1,6 @@
 use crate::{
     body::{Body, HttpBody},
+    box_clone_service::BoxCloneService,
     response::Response,
     util::AxumMutex,
 };
@@ -18,7 +19,7 @@ use std::{
     task::{Context, Poll},
 };
 use tower::{
-    util::{BoxCloneService, MapErrLayer, MapRequestLayer, MapResponseLayer, Oneshot},
+    util::{MapErrLayer, MapRequestLayer, MapResponseLayer, Oneshot},
     ServiceExt,
 };
 use tower_layer::Layer;
@@ -33,7 +34,7 @@ pub struct Route<E = Infallible>(AxumMutex<BoxCloneService<Request, Response, E>
 impl<E> Route<E> {
     pub(crate) fn new<T>(svc: T) -> Self
     where
-        T: Service<Request, Error = E> + Clone + Send + 'static,
+        T: Service<Request, Error = E> + Clone + Send + Sync + 'static,
         T::Response: IntoResponse + 'static,
         T::Future: Send + 'static,
     {
@@ -52,7 +53,7 @@ impl<E> Route<E> {
     pub(crate) fn layer<L, NewError>(self, layer: L) -> Route<NewError>
     where
         L: Layer<Route<E>> + Clone + Send + 'static,
-        L::Service: Service<Request> + Clone + Send + 'static,
+        L::Service: Service<Request> + Clone + Send + Sync + 'static,
         <L::Service as Service<Request>>::Response: IntoResponse + 'static,
         <L::Service as Service<Request>>::Error: Into<NewError> + 'static,
         <L::Service as Service<Request>>::Future: Send + 'static,
diff --git a/clippy.toml b/clippy.toml
new file mode 100644
index 00000000..62530998
--- /dev/null
+++ b/clippy.toml
@@ -0,0 +1,3 @@
+disallowed-types = [
+    { path = "tower::util::BoxCloneService", reason = "Use our internal BoxCloneService which is Sync" },
+]