Docs improvements (#37)

src/service/future.rs

@@ -9,7 +9,6 @@ use futures_util::ready;
 use http::Response;
 use pin_project::pin_project;
 use std::{
-    convert::Infallible,
     future::Future,
     pin::Pin,
     task::{Context, Poll},
@@ -25,15 +24,15 @@ pub struct HandleErrorFuture<Fut, F> {
     pub(super) f: Option<F>,
 }
 
-impl<Fut, F, E, B, Res> Future for HandleErrorFuture<Fut, F>
+impl<Fut, F, E, E2, B, Res> Future for HandleErrorFuture<Fut, F>
 where
     Fut: Future<Output = Result<Response<B>, E>>,
-    F: FnOnce(E) -> Res,
+    F: FnOnce(E) -> Result<Res, E2>,
     Res: IntoResponse,
     B: http_body::Body<Data = Bytes> + Send + Sync + 'static,
     B::Error: Into<BoxError> + Send + Sync + 'static,
 {
-    type Output = Result<Response<BoxBody>, Infallible>;
+    type Output = Result<Response<BoxBody>, E2>;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         let this = self.project();
@@ -42,8 +41,10 @@ where
             Ok(res) => Ok(res.map(box_body)).into(),
             Err(err) => {
                 let f = this.f.take().unwrap();
-                let res = f(err).into_response();
-                Ok(res.map(box_body)).into()
+                match f(err) {
+                    Ok(res) => Ok(res.into_response().map(box_body)).into(),
+                    Err(err) => Err(err).into(),
+                }
             }
         }
     }