Skip control batches (dpkp#2361)

kafka/consumer/fetcher.py

@@ -464,6 +464,13 @@ def _unpack_message_set(self, tp, records):
                 except AttributeError:
                     pass
 
+                # Control messages are used to enable transactions in Kafka and are generated by the
+                # broker. Clients should not return control batches (ie. those with this bit set) to
+                # applications. (since 0.11.0.0)
+                if getattr(batch, "is_control_batch", False):
+                    batch = records.next_batch()
+                    continue
+
                 for record in batch:
                     key_size = len(record.key) if record.key is not None else -1
                     value_size = len(record.value) if record.value is not None else -1