Details
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Bug
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Status: Resolved
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Major
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Resolution: Fixed
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None
Description
The TopologyTestDriver#read(topic) methods all call #getRecordsQueue which checks
final Queue<ProducerRecord<byte[], byte[]>> outputRecords = outputRecordsByTopic.get(topicName); if (outputRecords == null) { if (!processorTopology.sinkTopics().contains(topicName)) { throw new IllegalArgumentException("Unknown topic: " + topicName); } }
The outputRecordsByTopic map keeps track of all topics that are actually produced to, but obviously doesn't capture any topics that haven't yet received output. The `processorTopology#sinkTopics` is supposed to account for that by checking to make sure the topic is actually registered in the topology, and throw an exception if not in case the user supplied the wrong topic name to read from.
Unfortunately the TopicNameExtractor allows for dynamic routing of records to any topic, so the topology isn't aware of all the possible output topics. If trying to read from one of these topics that happens to not have received any output yet, the test will throw the above misleading IllegalArgumentException.
We could just relax this check, but warning users who may actually have accidentally passed in the wrong topic to read from seems quite useful. A better solution would be to require registering all possible output topics to the TTD up front. This would obviously require a KIP, but it would be a very small one and shouldn't be too much trouble
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