[jira] [Created] (KAFKA-12296) MockProducer behaves contrary to documentation of Callback

["Olaf (Jira)" <ji...@apache.org>]

Olaf created KAFKA-12296:
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             Summary: MockProducer behaves contrary to documentation of Callback
                 Key: KAFKA-12296
                 URL: https://issues.apache.org/jira/browse/KAFKA-12296
             Project: Kafka
          Issue Type: Bug
          Components: producer , unit tests
    Affects Versions: 2.7.0
            Reporter: Olaf


In Unit tests, a MockProducer is used to imitate a real producer.

Using the errorNext(RuntimeException e) method, it is possible to indicate failures.

BUT: the asynchronous send method with a callback has a clear documentation of that callback interface, stating that Metadata will always be set, and never null.

{{The metadata for the record that was sent (i.e. the partition and offset). An empty metadata with -1 value for all fields except for topicPartition will be returned if an error occurred.}}

 

The bug is, that in MockProducer's Completion implementation the following happens:

{{if (e == null)}}
{{    callback.onCompletion(metadata, null);}}
{{else}}
{{    callback.onCompletion(null, e);}}

 

Behaving against the own documentation lead to a very subtle bug: tests that implement the error condition checking metadata != null will be fine, but in real life fail horribly.

 

A MockProducer should at all times behave exactly like the real thing and adhere to the documentation of the Callback!



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