allow for watching future values with watcher

Include StopIterSentinel

oops

nats/js/kv.py

@@ -35,6 +35,12 @@
 logger = logging.getLogger(__name__)
 
 
+class StopIterSentinel:
+    """A sentinel class used to indicate that iteration should stop."""
+
+    pass
+
+
 class KeyValue:
     """
     KeyValue uses the JetStream KeyValue functionality.
@@ -278,6 +284,9 @@ async def purge_deletes(self, olderthan: int = 30 * 60) -> bool:
         watcher = await self.watchall()
         delete_markers = []
         async for update in watcher:
+            if update is None:
+                break
+
             if update.operation == KV_DEL or update.operation == KV_PURGE:
                 delete_markers.append(update)
 
@@ -300,11 +309,11 @@ async def status(self) -> BucketStatus:
         return KeyValue.BucketStatus(stream_info=info, bucket=self._name)
 
     class KeyWatcher:
+        STOP_ITER = StopIterSentinel()
 
         def __init__(self, js):
             self._js = js
-            self._updates: asyncio.Queue[KeyValue.Entry
-                                         | None] = asyncio.Queue(maxsize=256)
+            self._updates: asyncio.Queue[KeyValue.Entry | None | StopIterSentinel] = asyncio.Queue(maxsize=256)
             self._sub = None
             self._pending: Optional[int] = None
 
@@ -317,6 +326,7 @@ async def stop(self):
             stop will stop this watcher.
             """
             await self._sub.unsubscribe()
+            await self._updates.put(KeyValue.KeyWatcher.STOP_ITER)
 
         async def updates(self, timeout=5.0):
             """
@@ -331,10 +341,10 @@ def __aiter__(self):
             return self
 
         async def __anext__(self):
-            entry = await self._updates.get()
-            if not entry:
-                raise StopAsyncIteration
-            else:
+            while True:
+                entry = await self._updates.get()
+                if isinstance(entry, StopIterSentinel):
+                    raise StopAsyncIteration
                 return entry
 
     async def watchall(self, **kwargs) -> KeyWatcher:

nats/js/object_store.py

@@ -33,7 +33,7 @@
     ObjectDeletedError,
     ObjectNotFoundError,
 )
-from nats.js.kv import MSG_ROLLUP_SUBJECT
+from nats.js.kv import MSG_ROLLUP_SUBJECT, StopIterSentinel
 
 VALID_BUCKET_RE = re.compile(r"^[a-zA-Z0-9_-]+$")
 VALID_KEY_RE = re.compile(r"^[-/_=\.a-zA-Z0-9]+$")
@@ -427,10 +427,11 @@ async def update_meta(
             await self._js.purge_stream(self._stream, subject=meta_subj)
 
     class ObjectWatcher:
+        STOP_ITER = StopIterSentinel()
 
         def __init__(self, js):
             self._js = js
-            self._updates = asyncio.Queue(maxsize=256)
+            self._updates: asyncio.Queue[Union[api.ObjectInfo, None, StopIterSentinel]] = asyncio.Queue(maxsize=256)
             self._sub = None
             self._pending: Optional[int] = None
 
@@ -457,10 +458,11 @@ def __aiter__(self):
             return self
 
         async def __anext__(self):
-            entry = await self._updates.get()
-            if not entry:
-                raise StopAsyncIteration
-            else:
+            while True:
+                entry = await self._updates.get()
+
+                if isinstance(entry, StopIterSentinel):
+                    raise StopAsyncIteration
                 return entry
 
     async def watch(