Remove buffer from BoxRoute (#270)

Boxing a service normally means using `tower::util::BoxService`. That
doesn't implement `Clone` however so normally I had been combining it
with `Buffer` to get that.

But recently I discovered https://github.com/dtolnay/dyn-clone which
makes it possible to clone trait objects. So this adds a new internal
utility called `CloneBoxService` which replaces the previous
`BoxService` + `Buffer` combo in `BoxRoute`.

I'll investigate upstreaming that to tower. I think it makes sense there
since box + clone is quite a common need.

src/routing/mod.rs

@@ -3,13 +3,12 @@
 use self::future::{BoxRouteFuture, EmptyRouterFuture, NestedFuture, RouteFuture};
 use crate::{
     body::{box_body, BoxBody},
-    buffer::MpscBuffer,
     extract::{
         connect_info::{Connected, IntoMakeServiceWithConnectInfo},
         OriginalUri,
     },
     service::HandleError,
-    util::ByteStr,
+    util::{ByteStr, CloneBoxService},
     BoxError,
 };
 use bytes::Bytes;
@@ -24,10 +23,7 @@ use std::{
     sync::Arc,
     task::{Context, Poll},
 };
-use tower::{
-    util::{BoxService, ServiceExt},
-    ServiceBuilder,
-};
+use tower::{util::ServiceExt, ServiceBuilder};
 use tower_http::map_response_body::MapResponseBodyLayer;
 use tower_layer::Layer;
 use tower_service::Service;
@@ -256,7 +252,7 @@ impl<S> Router<S> {
     /// routes.
     pub fn boxed<ReqBody, ResBody>(self) -> Router<BoxRoute<ReqBody, S::Error>>
     where
-        S: Service<Request<ReqBody>, Response = Response<ResBody>> + Send + 'static,
+        S: Service<Request<ReqBody>, Response = Response<ResBody>> + Clone + Send + 'static,
         S::Error: Into<BoxError> + Send,
         S::Future: Send,
         ReqBody: Send + 'static,
@@ -265,9 +261,8 @@ impl<S> Router<S> {
     {
         self.map(|svc| {
             ServiceBuilder::new()
-                .layer_fn(BoxRoute)
-                .layer_fn(MpscBuffer::new)
-                .layer(BoxService::layer())
+                .layer_fn(|inner| BoxRoute { inner })
+                .layer_fn(CloneBoxService::new)
                 .layer(MapResponseBodyLayer::new(box_body))
                 .service(svc)
         })
@@ -833,13 +828,15 @@ type Captures = Vec<(String, String)>;
 /// A boxed route trait object.
 ///
 /// See [`Router::boxed`] for more details.
-pub struct BoxRoute<B = crate::body::Body, E = Infallible>(
-    MpscBuffer<BoxService<Request<B>, Response<BoxBody>, E>, Request<B>>,
-);
+pub struct BoxRoute<B = crate::body::Body, E = Infallible> {
+    inner: CloneBoxService<Request<B>, Response<BoxBody>, E>,
+}
 
 impl<B, E> Clone for BoxRoute<B, E> {
     fn clone(&self) -> Self {
-        Self(self.0.clone())
+        BoxRoute {
+            inner: self.inner.clone(),
+        }
     }
 }
 
@@ -865,7 +862,7 @@ where
     #[inline]
     fn call(&mut self, req: Request<B>) -> Self::Future {
         BoxRouteFuture {
-            inner: self.0.clone().oneshot(req),
+            inner: self.inner.clone().oneshot(req),
         }
     }
 }