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FLIP-27 sources are non-trivial to implement. At the same time, it is frequently required to generate arbitrary events with a "mock" source. Such requirement arises both for Flink users, in the scope of demo/PoC projects, and for Flink developers when writing tests. The go-to solution for these purposes so far was using pre-FLIP-27 APIs and implementing data generators as SourceFunctions. 
While the new FLIP-27 Source interface introduces important additional functionality, it comes with significant complexity that presents a hurdle for Flink users for implementing drop-in replacements of the SourceFunction-based data generators.  Meanwhile, SourceFunction is effectively superseded by the Source interface and needs to be eventually deprecated. To fill this gap, this FLIP proposes the introduction of a generic data generator source based on FLIP-27 API.

Public Interfaces

The following 

package org.apache.flink.api.connector.source.lib;

/**
 * A data source that produces generators N events of an arbitrary type in parallel. This source is useful for
 * testing and for cases that just need a stream of N events of any kind.
 *
 * <p>The source splits the sequence into as many parallel sub-sequences as there are parallel
 * source readers. Each sub-sequence will be produced in order. Consequently, if the parallelism is
 * limited to one, this will produce one sequence in order.
 *
 * <p>This source is always bounded. For very long sequences user may want to consider executing 
 * the application in a streaming manner, because, despite the fact that the produced stream is bounded, 
 * the end bound is pretty far away.
 */

@Public
public class DataGeneratorSource<T>DataGeneratorSource<OUT>
        implements Source<TSource<OUT, GeneratorSequenceSplit<T>GeneratorSequenceSplit<OUT>, Collection<GeneratorSequenceSplit<T>>>Collection<GeneratorSequenceSplit<OUT>>>,
                ResultTypeQueryable<T>ResultTypeQueryable<OUT> {


    /**
     * Creates a new {@code DataGeneratorSource} that produces {@code count} records in
     * parallel.
     *
     * @param generatorFunction theThe generator function that receives index numbers and translates them into events of the output type.
     * @param count The countnumber of events to be produced.
     * @param typeInfo The type info of the returned events.
     */
    public DataGeneratorSource(
            MapFunction<Long, T>OUT> generatorFunction, long count, TypeInformation<T>TypeInformation<OUT> typeInfo) {
     ...
	}

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:

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Binary log format

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The network protocol and api behavior

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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)

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Monitoring

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Command line tools and arguments

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Proposed Changes

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

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