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Status

Current state:  [One of "Under Discussion", "Accepted", "Rejected"]

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: here [Change the link from KAFKA-1 to your own ticket]

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Describe the problems you are trying to solve.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

Proposed Changes

...

accepted

Vote thread: https://lists.apache.org/thread/jsy1ld5f6b6k8qcjzpy5k08ropqd4dd1

Discussion thread: https://lists.apache.org/thread/n3k6vb4vddl1s5nopcyglnddtvzp4j63

JIRA: KAFKA-16796

Motivation

We are going to move all tools-related code from core module (scala) to tools module (java) in 4.0. kafka.serializer.Decoder is a public APIs and it is in core module. Hence we need to introduce replacement to deprecate it in 3.8.0

Public Interfaces

The new java interface org.apache.kafka.tools.api.Decoder is shown below. It is located at tools-api module, since it must be accessible by core module.

@FunctionalInterface
public interface Decoder<T> {
    T fromBytes(byte[] bytes);
}

The old scala trait will extend the new java interface with deprecated  annotation

@deprecated(since = "3.8.0")
trait Decoder[T] {
  def fromBytes(bytes: Array[Byte]): T
}

Proposed Changes

1. Introduce a new java interface org.apache.kafka.tools.api.Decoder to replace scala trait kafka.serializer.Decoder
   
2. deprecate all "class names" of kafka.serializer.Decoder implementations. That includes kafka.serializer.DefaultDecoder, kafka.serializer.StringDecoder, kafka.serializer.LongDecoder, and kafka.serializer.IntegerDecoder 
3. remove the VerifiableProperties from constructor. We "always" pass empty VerifiableProperties before (known issue:

   Jira
   server ASF JIRA serverId 5aa69414-a9e9-3523-82ec-879b028fb15b key KAFKA-12311

   ), and hence using the VerifiableProperties to create new decoder does not make sense. If users require configurable decoder, we can make decoder extend Configurable in the future.

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Test Plan

Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Rejected Alternatives

• before 4.0, users can keep using the deprecated kafka.serializer.Decoder
• after 4.0, all users need to update superclass from kafka.serializer.Decoder to org.apache.kafka.tools.api.Decoder. They have same method, but the new constructor does not accept VerifiableProperties. Hence, users' custom decoders have to offer default constructor
  
• before 4.0, users can access both interfaces by depending on core module.
• after 4.0, users can import tools-api module instead of core module.
  

Test Plan

The new unit test used to verify the "warning messages" about deprecated kafka.serializer.Decoder will be added. The messages are used to encourage users to adopt the new interface

Rejected Alternatives

N/AIf there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.