Major Description
In SetSchemaMetadataTest we verify that the name and version of the schema in the record have been replaced:
However, in the case of Structs, the schema will be attached to both the record and the Struct itself. So we correctly rebuild the Record:
https://github.com/apache/kafka/blob/trunk/connect/transforms/src/main/java/org/apache/kafka/connect/transforms/SetSchemaMetadata.java#L77
https://github.com/apache/kafka/blob/trunk/connect/transforms/src/main/java/org/apache/kafka/connect/transforms/SetSchemaMetadata.java#L104
https://github.com/apache/kafka/blob/trunk/connect/transforms/src/main/java/org/apache/kafka/connect/transforms/SetSchemaMetadata.java#L119
But if the key or value are a struct, they will still contain the old schema embedded in the struct.
Ultimately this can lead to validations in other code failing (even for very simple changes like adjusting the name of a schema):
(org.apache.kafka.connect.runtime.WorkerTask:141)
org.apache.kafka.connect.errors.DataException: Mismatching struct schema
at io.confluent.connect.avro.AvroData.fromConnectData(AvroData.java:471)
at io.confluent.connect.avro.AvroData.fromConnectData(AvroData.java:295)
at io.confluent.connect.avro.AvroConverter.fromConnectData(AvroConverter.java:73)
at org.apache.kafka.connect.runtime.WorkerSourceTask.sendRecords(WorkerSourceTask.java:196)
at org.apache.kafka.connect.runtime.WorkerSourceTask.execute(WorkerSourceTask.java:167)
at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:139)
at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:182)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
The solution to this is probably to check whether we're dealing with a Struct when we use a new schema and potentially copy/reallocate it.
This particular issue would only appear if we don't modify the data, so I think SetSchemaMetadata is currently the only transformation that would have the issue.
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