Provide example on predicate usage for shared streams (#1552)

Signed-off-by: Danil-Grigorev <danil.grigorev@suse.com>

examples/shared_stream_controllers.rs

@@ -1,9 +1,14 @@
-use std::{sync::Arc, time::Duration};
+use std::{ops::Deref, sync::Arc, time::Duration};
 
-use futures::StreamExt;
+use futures::{future, StreamExt};
 use k8s_openapi::api::{apps::v1::Deployment, core::v1::Pod};
 use kube::{
-    runtime::{controller::Action, reflector, watcher, Config, Controller, WatchStreamExt},
+    runtime::{
+        controller::Action,
+        predicates,
+        reflector::{self, ReflectHandle},
+        watcher, Config, Controller, WatchStreamExt,
+    },
     Api, Client, ResourceExt,
 };
 use tracing::{debug, error, info, warn};
@@ -49,10 +54,17 @@ async fn main() -> anyhow::Result<()> {
     let (reader, writer) = reflector::store_shared(SUBSCRIBE_BUFFER_SIZE);
     // Before threading an object watch through the store, create a subscriber.
     // Any number of subscribers can be created from one writer.
-    let subscriber = writer
+    let subscriber: ReflectHandle<Pod> = writer
         .subscribe()
         .expect("subscribers can only be created from shared stores");
 
+    // Subscriber events can be filtered in advance with predicates
+    let filtered = subscriber
+        .clone()
+        .map(|r| Ok(r.deref().clone()))
+        .predicate_filter(predicates::resource_version)
+        .filter_map(|r| future::ready(r.ok().map(Arc::new)));
+
     // Reflect a stream of pod watch events into the store and apply a backoff. For subscribers to
     // be able to consume updates, the reflector must be shared.
     let pod_watch = watcher(pods.clone(), Default::default())
@@ -68,7 +80,7 @@ async fn main() -> anyhow::Result<()> {
     // Create the first controller; the controller will log whenever it
     // reconciles a pod. The reconcile is a no-op.
     // Controllers accept subscribers through a dedicated interface.
-    let pod_controller = Controller::for_shared_stream(subscriber.clone(), reader)
+    let pod_controller = Controller::for_shared_stream(filtered, reader)
         .with_config(config.clone())
         .shutdown_on_signal()
         .run(reconcile, error_policy, Arc::new(()))