Fix bug where Sliding Sync could get stuck when using workers

synapse/types/__init__.py

@@ -668,6 +668,11 @@ async def parse(cls, store: "PurgeEventsStore", string: str) -> "RoomStreamToken
 
                 instance_map = {}
                 for part in parts[1:]:
+                    if not part:
+                        # Handle tokens of the form `m5~`, which were created by
+                        # a bug
+                        continue
+
                     key, value = part.split(".")
                     instance_id = int(key)
                     pos = int(value)
@@ -778,6 +783,11 @@ async def parse(cls, store: "DataStore", string: str) -> "MultiWriterStreamToken
 
                 instance_map = {}
                 for part in parts[1:]:
+                    if not part:
+                        # Handle tokens of the form `m5~`, which were created by
+                        # a bug
+                        continue
+
                     key, value = part.split(".")
                     instance_id = int(key)
                     pos = int(value)

tests/test_types.py

@@ -167,3 +167,11 @@ def test_instance_map_assertion(self) -> None:
 
         with self.assertRaises(ValueError):
             RoomStreamToken(stream=5, instance_map=immutabledict({"foo": 4}))
+
+    def test_parse_bad_token(self) -> None:
+        """Test that we can parse tokens produced by a bug in Synapse of the
+        form `m5~`"""
+        store = self.hs.get_datastores().main
+
+        parsed_token = self.get_success(RoomStreamToken.parse(store, "m5~"))
+        self.assertEqual(parsed_token, RoomStreamToken(stream=5))