Jonas Grabber created BEAM-13924:
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Summary: Coder information lost in Kafka Read
Key: BEAM-13924
URL: https://issues.apache.org/jira/browse/BEAM-13924
Project: Beam
Issue Type: Bug
Components: io-java-kafka
Affects Versions: 2.36.0
Reporter: Jonas Grabber
When upgrading from 2.29.0 to 2.36.0 our Kafka Read transform broke.
While debugging, I saw that information of the key and value coders is lost
after [this statement in
KafkaIO|https://github.com/apache/beam/blob/v2.36.0/sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaIO.java#L1459]:
{code:java}
return output.apply(readTransform).setCoder(KafkaRecordCoder.of(keyCoder,
valueCoder));
{code}
The issue seems to be that output.apply already checks for the presence of key
and value coders and ends up trying to infer them with the help of
[LocalDeserializerProvider|https://github.com/apache/beam/blob/v2.36.0/sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/LocalDeserializerProvider.java],
so the process never arrives at setCoder.
In our case this inference fails since we implement the Deserializer interface
in a super class of the instance passed as the Deserializer.
This was not yet broken on 2.29.0, so all versions after that could be affected.
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