Add unique future types for all services (#157)

So we can more easily change them in the future.

src/service/future.rs

@@ -6,14 +6,14 @@ use crate::{
 };
 use bytes::Bytes;
 use futures_util::ready;
-use http::Response;
+use http::{Request, Response};
 use pin_project_lite::pin_project;
 use std::{
     future::Future,
     pin::Pin,
     task::{Context, Poll},
 };
-use tower::BoxError;
+use tower::{BoxError, Service};
 
 pin_project! {
     /// Response future for [`HandleError`](super::HandleError).
@@ -74,3 +74,28 @@ where
         Poll::Ready(Ok(res))
     }
 }
+
+pin_project! {
+    /// The response future for [`OnMethod`](super::OnMethod).
+    #[derive(Debug)]
+    pub struct OnMethodFuture<S, F, B>
+    where
+        S: Service<Request<B>>,
+        F: Service<Request<B>>
+    {
+        #[pin]
+        pub(super) inner: crate::routing::future::RouteFuture<S, F, B>,
+    }
+}
+
+impl<S, F, B> Future for OnMethodFuture<S, F, B>
+where
+    S: Service<Request<B>, Response = Response<BoxBody>>,
+    F: Service<Request<B>, Response = Response<BoxBody>, Error = S::Error>,
+{
+    type Output = Result<Response<BoxBody>, S::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.project().inner.poll(cx)
+    }
+}