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https://issues.apache.org/jira/browse/KAFKA-14671?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Greg Harris updated KAFKA-14671:
--------------------------------
Description:
The PredicatedTransformation
[https://github.com/apache/kafka/blob/trunk/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/PredicatedTransformation.java]
is an instance of Transformation, a plugin class.
This allows both a PredicatedTransformation and a base Transformation to exist
in the same list inside of the TransformationChain.
However, the PredicatedTransformation is not a compliant general-purpose
Transformation, and has a number of non-standard behaviors:
1. The PredicatedTransformation is hidden from the REST API plugin listings
2. PredicatedTransformation::config and ::configure throw an exception, as they
are not called under normal circumstances
3. The PredicatedTransformation has no default constructor, and would throw an
exception if loaded via the standard plugin initialization logic.
4. The TransformationChain calls `.getClass()` on the PredicatedTransformation,
which returns the PredicatedTransformation class itself, and not the wrapped
transformation class.
The current implementation is also an exceptional case and would conflict with
potential future changes:
1. If the "Versioned" interface were added to SMTs, the
PredicatedTransformation would throw exceptions during plugin scanning
2. If the `connect-plugin-path.sh` script is implement as-described in KIP-898,
the PredicatedTransformation would show up as a non-migrated plugin class
3. If https://issues.apache.org/jira/browse/KAFKA-14670 is implemented, then
there will be no common interface for wrapped transformations and
PredicatedTransformations to exist in the same data structure.
The PredicatedTransformation is a reasonable abstraction to compose a predicate
and transformation, but it can do so without subclassing Transformation, and
incurring the above pitfalls.
was:
The PredicatedTransformation
[https://github.com/apache/kafka/blob/trunk/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/PredicatedTransformation.java]
is an instance of Transformation, a plugin class.
This allows both a PredicatedTransformation and a base Transformation to exist
in the same list inside of the TransformationChain.
However, the PredicatedTransformation is not a compliant general-purpose
Transformation, and has a number of non-standard behaviors:
1. The PredicatedTransformation is hidden from the REST API plugin listings
2. PredicatedTransformation::config and ::configure throw an exception, as they
are not called under normal circumstances
3. The PredicatedTransformation has no default constructor, and would throw an
exception if loaded via the standard plugin initialization logic.
4. The TransformationChain calls `.getClass()` on the PredicatedTransformation,
which returns the PredicatedTransformation class itself, and not the wrapped
transformation class.
The PredicatedTransformation is a reasonable abstraction to compose a predicate
and transformation, but it can do so without subclassing Transformation, and
incurring the above pitfalls.
> Refactor PredicatedTransformation to not implement Transformation
> -----------------------------------------------------------------
>
> Key: KAFKA-14671
> URL: https://issues.apache.org/jira/browse/KAFKA-14671
> Project: Kafka
> Issue Type: Task
> Components: KafkaConnect
> Affects Versions: 3.5.0
> Reporter: Greg Harris
> Assignee: Greg Harris
> Priority: Minor
>
> The PredicatedTransformation
> [https://github.com/apache/kafka/blob/trunk/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/PredicatedTransformation.java]
>
> is an instance of Transformation, a plugin class.
> This allows both a PredicatedTransformation and a base Transformation to
> exist in the same list inside of the TransformationChain.
> However, the PredicatedTransformation is not a compliant general-purpose
> Transformation, and has a number of non-standard behaviors:
> 1. The PredicatedTransformation is hidden from the REST API plugin listings
> 2. PredicatedTransformation::config and ::configure throw an exception, as
> they are not called under normal circumstances
> 3. The PredicatedTransformation has no default constructor, and would throw
> an exception if loaded via the standard plugin initialization logic.
> 4. The TransformationChain calls `.getClass()` on the
> PredicatedTransformation, which returns the PredicatedTransformation class
> itself, and not the wrapped transformation class.
>
> The current implementation is also an exceptional case and would conflict
> with potential future changes:
> 1. If the "Versioned" interface were added to SMTs, the
> PredicatedTransformation would throw exceptions during plugin scanning
> 2. If the `connect-plugin-path.sh` script is implement as-described in
> KIP-898, the PredicatedTransformation would show up as a non-migrated plugin
> class
> 3. If https://issues.apache.org/jira/browse/KAFKA-14670 is implemented, then
> there will be no common interface for wrapped transformations and
> PredicatedTransformations to exist in the same data structure.
> The PredicatedTransformation is a reasonable abstraction to compose a
> predicate and transformation, but it can do so without subclassing
> Transformation, and incurring the above pitfalls.
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