Ensure watch_object handles objects removed before init (#1577)

* Stream produced by `watch_object` will include an item when the object isn't in any initial list

fixes #1576

Signed-off-by: Mark Ingram <[email protected]>

* Stream produced by `watch_object` will include an item when the object isn't in any initial list

- added a comment
- resolved a nightly clippy
- use a match guard instead of an nested if

Signed-off-by: Mark Ingram <[email protected]>

---------

Signed-off-by: Mark Ingram <[email protected]>

Author: markdingram

kube-runtime/src/watcher.rs

@@ -14,7 +14,7 @@ use kube_client::{
     Api, Error as ClientErr,
 };
 use serde::de::DeserializeOwned;
-use std::{clone::Clone, collections::VecDeque, fmt::Debug, time::Duration};
+use std::{clone::Clone, collections::VecDeque, fmt::Debug, future, time::Duration};
 use thiserror::Error;
 use tracing::{debug, error, warn};
 
@@ -844,18 +844,36 @@ pub fn watch_object<K: Resource + Clone + DeserializeOwned + Debug + Send + 'sta
     // filtering by object name in given scope, so there's at most one matching object
     // footgun: Api::all may generate events from namespaced objects with the same name in different namespaces
     let fields = format!("metadata.name={name}");
-    watcher(api, Config::default().fields(&fields)).filter_map(|event| async {
-        match event {
-            // Pass up `Some` for Found / Updated
-            Ok(Event::Apply(obj) | Event::InitApply(obj)) => Some(Ok(Some(obj))),
-            // Pass up `None` for Deleted
-            Ok(Event::Delete(_)) => Some(Ok(None)),
-            // Ignore marker events
-            Ok(Event::Init | Event::InitDone) => None,
-            // Bubble up errors
-            Err(err) => Some(Err(err)),
-        }
-    })
+    watcher(api, Config::default().fields(&fields))
+        // The `obj_seen` state is used to track whether the object exists in each Init / InitApply / InitDone
+        // sequence of events. If the object wasn't seen in any particular sequence it is treated as deleted and
+        // `None` is emitted when the InitDone event is received.
+        //
+        // The first check ensures `None` is emitted if the object was already gone (or not found), subsequent
+        // checks ensure `None` is emitted even if for some reason the Delete event wasn't received, which
+        // could happen given K8S events aren't guaranteed delivery.
+        .scan(false, |obj_seen, event| {
+            if matches!(event, Ok(Event::Init)) {
+                *obj_seen = false;
+            } else if matches!(event, Ok(Event::InitApply(_))) {
+                *obj_seen = true;
+            }
+            future::ready(Some((*obj_seen, event)))
+        })
+        .filter_map(|(obj_seen, event)| async move {
+            match event {
+                // Pass up `Some` for Found / Updated
+                Ok(Event::Apply(obj) | Event::InitApply(obj)) => Some(Ok(Some(obj))),
+                // Pass up `None` for Deleted
+                Ok(Event::Delete(_)) => Some(Ok(None)),
+                // Pass up `None` if the object wasn't seen in the initial list
+                Ok(Event::InitDone) if !obj_seen => Some(Ok(None)),
+                // Ignore marker events
+                Ok(Event::Init | Event::InitDone) => None,
+                // Bubble up errors
+                Err(err) => Some(Err(err)),
+            }
+        })
 }
 
 /// Default watcher backoff inspired by Kubernetes' client-go.