More docs and expand key_value_store example

src/service/future.rs

@@ -0,0 +1,47 @@
+//! [`Service`](tower::Service) future types.
+
+use crate::{body::BoxBody, response::IntoResponse};
+use bytes::Bytes;
+use futures_util::ready;
+use http::Response;
+use pin_project::pin_project;
+use std::{
+    convert::Infallible,
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
+use tower::BoxError;
+
+/// Response future for [`HandleError`](super::HandleError).
+#[pin_project]
+#[derive(Debug)]
+pub struct HandleErrorFuture<Fut, F> {
+    #[pin]
+    pub(super) inner: Fut,
+    pub(super) f: Option<F>,
+}
+
+impl<Fut, F, E, B, Res> Future for HandleErrorFuture<Fut, F>
+where
+    Fut: Future<Output = Result<Response<B>, E>>,
+    F: FnOnce(E) -> Res,
+    Res: IntoResponse,
+    B: http_body::Body<Data = Bytes> + Send + Sync + 'static,
+    B::Error: Into<BoxError> + Send + Sync + 'static,
+{
+    type Output = Result<Response<BoxBody>, Infallible>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.project();
+
+        match ready!(this.inner.poll(cx)) {
+            Ok(res) => Ok(res.map(BoxBody::new)).into(),
+            Err(err) => {
+                let f = this.f.take().unwrap();
+                let res = f(err).into_response();
+                Ok(res.map(BoxBody::new)).into()
+            }
+        }
+    }
+}