Add WatchStreamExt::modify() to modify events

Add `WatchStreamExt::modify()` which returns an `EventModify` stream.
This allows for users to directly modify the inner value of an `Event`
returned by the watcher stream, thus avoiding the usage of nested maps.

Example usage:

```rust
let stream = watcher(api, watcher::Config::default()).modify(|pod| {
    pod.managed_fields_mut().clear();
    pod.annotations_mut().clear();
    pod.status = None;
});
```

Signed-off-by: Sanskar Jaiswal <[email protected]>

examples/pod_reflector.rs

@@ -28,13 +28,11 @@ async fn main() -> anyhow::Result<()> {
         }
     });
 
-    let stream = watcher(api, watcher::Config::default()).map_ok(|ev| {
-        ev.modify(|pod| {
-            // memory optimization for our store - we don't care about fields/annotations/status
-            pod.managed_fields_mut().clear();
-            pod.annotations_mut().clear();
-            pod.status = None;
-        })
+    let stream = watcher(api, watcher::Config::default()).modify(|pod| {
+        // memory optimization for our store - we don't care about managed fields/annotations/status
+        pod.managed_fields_mut().clear();
+        pod.annotations_mut().clear();
+        pod.status = None;
     });
 
     let rf = reflector(writer, stream)

kube-runtime/src/utils/event_modify.rs

@@ -0,0 +1,72 @@
+use core::{
+    pin::Pin,
+    task::{Context, Poll},
+};
+use std::task::ready;
+
+use futures::{Stream, TryStream};
+use pin_project::pin_project;
+
+use crate::watcher::{Error, Event};
+
+#[pin_project]
+/// Stream returned by the [`modify`](super::WatchStreamExt::modify) method.
+/// Modifies the [`Event`] item returned by the inner stream by calling
+/// [`modify`](Event::modify()) on it.
+pub struct EventModify<St, F> {
+    #[pin]
+    stream: St,
+    f: F,
+}
+
+impl<St, F, K> EventModify<St, F>
+where
+    St: TryStream<Ok = Event<K>>,
+    F: FnMut(&mut K),
+{
+    pub(super) fn new(stream: St, f: F) -> EventModify<St, F> {
+        Self { stream, f }
+    }
+}
+
+impl<St, F, K> Stream for EventModify<St, F>
+where
+    St: Stream<Item = Result<Event<K>, Error>>,
+    F: FnMut(&mut K),
+{
+    type Item = Result<Event<K>, Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut me = self.project();
+        Poll::Ready(match ready!(me.stream.as_mut().poll_next(cx)) {
+            Some(Ok(event)) => Some(Ok(event.modify(me.f))),
+            Some(Err(err)) => Some(Err(err)),
+            None => return Poll::Ready(None),
+        })
+    }
+}
+
+#[cfg(test)]
+pub(crate) mod test {
+    use std::task::Poll;
+
+    use super::{Error, Event, EventModify};
+    use futures::{pin_mut, poll, stream, StreamExt};
+
+    #[tokio::test]
+    async fn eventmodify_modifies_innner_value_of_event() {
+        let st = stream::iter([Ok(Event::Applied(0)), Err(Error::TooManyObjects)]);
+        let ev_modify = EventModify::new(st, |x| {
+            *x += 1;
+        });
+        pin_mut!(ev_modify);
+        assert!(matches!(
+            poll!(ev_modify.next()),
+            Poll::Ready(Some(Ok(Event::Applied(1))))
+        ));
+        assert!(matches!(
+            poll!(ev_modify.next()),
+            Poll::Ready(Some(Err(Error::TooManyObjects)))
+        ));
+    }
+}

kube-runtime/src/utils/mod.rs

@@ -3,13 +3,15 @@
 mod backoff_reset_timer;
 pub(crate) mod delayed_init;
 mod event_flatten;
+mod event_modify;
 #[cfg(feature = "unstable-runtime-predicates")] mod predicate;
 mod stream_backoff;
 #[cfg(feature = "unstable-runtime-subscribe")] pub mod stream_subscribe;
 mod watch_ext;
 
 pub use backoff_reset_timer::ResetTimerBackoff;
 pub use event_flatten::EventFlatten;
+pub use event_modify::EventModify;
 #[cfg(feature = "unstable-runtime-predicates")]
 pub use predicate::{predicates, Predicate, PredicateFilter};
 pub use stream_backoff::StreamBackoff;

kube-runtime/src/utils/watch_ext.rs

@@ -3,7 +3,7 @@ use crate::utils::predicate::{Predicate, PredicateFilter};
 #[cfg(feature = "unstable-runtime-subscribe")]
 use crate::utils::stream_subscribe::StreamSubscribe;
 use crate::{
-    utils::{event_flatten::EventFlatten, stream_backoff::StreamBackoff},
+    utils::{event_flatten::EventFlatten, event_modify::EventModify, stream_backoff::StreamBackoff},
     watcher,
 };
 #[cfg(feature = "unstable-runtime-predicates")] use kube_client::Resource;
@@ -53,6 +53,16 @@ pub trait WatchStreamExt: Stream {
         EventFlatten::new(self, true)
     }
 
+    /// Modify the [`Event`](crate::watcher::Event) returned by a [`watcher()`] stream.
+    /// by calling [`modify()`][crate::watcher::Event::modify()] on it.
+    fn modify<F, K>(self, f: F) -> EventModify<Self, F>
+    where
+        Self: Stream<Item = Result<watcher::Event<K>, watcher::Error>> + Sized,
+        F: FnMut(&mut K),
+    {
+        EventModify::new(self, f)
+    }
+
     /// Filter out a flattened stream on [`predicates`](crate::predicates).
     ///
     /// This will filter out repeat calls where the predicate returns the same result.