Remove concept of a non-limited stream.

synapse/replication/tcp/streams/_base.py

@@ -17,10 +17,12 @@
 import itertools
 import logging
 from collections import namedtuple
-from typing import Any, List, Optional
+from typing import Any, List, Optional, Tuple
 
 import attr
 
+from synapse.types import JsonDict
+
 logger = logging.getLogger(__name__)
 
 
@@ -166,16 +168,18 @@ async def get_updates(self):
 
         return updates, current_token
 
-    async def get_updates_since(self, from_token):
+    async def get_updates_since(
+        self, from_token: int
+    ) -> Tuple[List[Tuple[int, JsonDict]], int]:
         """Like get_updates except allows specifying from when we should
         stream updates
 
         Returns:
-            Deferred[Tuple[List[Tuple[int, Any]], int]:
-                Resolves to a pair ``(updates, current_token)``, where ``updates`` is a
-                list of ``(token, row)`` entries. ``row`` will be json-serialised and
-                sent over the replication steam.
+            Resolves to a pair `(updates, new_last_token)`, where `updates` is
+            a list of `(token, row)` entries and `new_last_token` is the new
+            position in stream.
         """
+
         if from_token in ("NOW", "now"):
             return [], self.current_token()
 
@@ -200,6 +204,8 @@ async def get_updates_since(self, from_token):
         if len(updates) >= MAX_EVENTS_BEHIND:
             raise Exception("stream %s has fallen behind" % (self.NAME))
 
+        # Due to the assertin above we know we're up to date, so we know that
+        # our new stream position is `current_token`.
         return updates, current_token
 
     def current_token(self):