schema-reader: Log the erroring kafka message key

- we add the kafka message key to the log in the case of an error,
this makes it easier to debug issues
- we also add a check for kafka messages without a key

karapace/schema_reader.py

@@ -364,7 +364,13 @@ def consume_messages(self, msgs: list[Message], watch_offsets: bool) -> None:
                 assert message_key is not None
                 key = json_decode(message_key)
             except JSONDecodeError as exc:
-                LOG.warning("Invalid JSON in msg.key() at offset %s", msg.offset())
+                non_bytes_key = msg.key().decode()  # type: ignore[union-attr]
+                LOG.warning("Invalid JSON in msg.key(): %s at offset %s", non_bytes_key, msg.offset())
+                self.offset = msg.offset()  # Invalid entry shall also move the offset so Karapace makes progress.
+                self.kafka_error_handler.handle_error(location=KafkaErrorLocation.SCHEMA_READER, error=exc)
+                continue  # [non-strict mode]
+            except AssertionError as exc:
+                LOG.warning("Empty msg.key() at offset %s", msg.offset())
                 self.offset = msg.offset()  # Invalid entry shall also move the offset so Karapace makes progress.
                 self.kafka_error_handler.handle_error(location=KafkaErrorLocation.SCHEMA_READER, error=exc)
                 continue  # [non-strict mode]

tests/unit/test_schema_reader.py

@@ -213,7 +213,7 @@ def test_schema_reader_can_end_to_ready_state_if_last_message_is_invalid_in_sche
     ok1_message.value.return_value = schema_str
     ok1_message.offset.return_value = 1
     invalid_key_message = Mock(spec=Message)
-    invalid_key_message.key.return_value = "invalid-key"
+    invalid_key_message.key.return_value = b"invalid-key"
     invalid_key_message.error.return_value = None
     invalid_key_message.value.return_value = schema_str
     invalid_key_message.offset.return_value = 2
@@ -388,7 +388,16 @@ def factory(key: bytes, value: bytes, offset: int = 1) -> Message:
             schema_type=None,
             message_type=MessageType.schema,
             expected_error=CorruptKafkaRecordException,
-            expected_log_message="Invalid JSON in msg.key() at offset 1",
+            expected_log_message='Invalid JSON in msg.key(): {subject1::::"test""version":1"magic":1} at offset 1',
+        ),
+        KafkaMessageHandlingErrorTestCase(
+            test_name="Message key is empty, i.e. `null/None`",
+            key=None,
+            value=b'{"value": "value does not matter at this stage, just correct JSON"}',
+            schema_type=None,
+            message_type=MessageType.schema,
+            expected_error=CorruptKafkaRecordException,
+            expected_log_message="Empty msg.key() at offset 1",
         ),
         KafkaMessageHandlingErrorTestCase(
             test_name="Keytype is missing from message key",