Clean up logic and add comments

synapse/replication/tcp/protocol.py

@@ -487,15 +487,19 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
                 # through tokens until we find one that is not None and then
                 # process all previous updates in the batch as if they had the
                 # final token.
-                if not token or len(batch_updates) > 0:
                 if token is None:
-                        # Store this update as part of the batch
+                    # Store this update as part of a batch
                     batch_updates.append(update)
-                    elif current_token <= current_token:
-                        # This batch is older than current_token, dismiss
+                    continue
+
+                if len(batch_updates) > 0:
+                    # There is an ongoing batch and this is the end
+                    if current_token <= current_token:
+                        # This batch is older than current_token, dismiss it
                         batch_updates = []
                     else:
-                        # Append final update of this batch before sending
+                        # This is the end of the batch. Append final update of
+                        # this batch before sending
                         batch_updates.append(update)
 
                         # Send all updates that are part of this batch with the
@@ -505,7 +509,10 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
 
                         # Clear saved batch updates
                         batch_updates = []
-                else:
+                    continue
+
+                # This is an update that's not part of a batch.
+                #
                 # Only send updates newer than the current token
                 if token > current_token:
                     self.send_command(RdataCommand(stream_name, token, update))