Zero Buffer Implementation and Tests (#5416)

* Zero Buffer Implementation and Tests

Signed-off-by: Mohammed Aghil Puthiyottil <57040494+MohammedAghil@users.noreply.github.com>

* Moved ZeroBuffer Implementation into data-prepper-core and addressed comments

Signed-off-by: Mohammed Aghil Puthiyottil <57040494+MohammedAghil@users.noreply.github.com>

* Modified ZeroBufferTests to use MockitoExtension and addressed comments

Signed-off-by: Mohammed Aghil Puthiyottil <57040494+MohammedAghil@users.noreply.github.com>

---------

Signed-off-by: Mohammed Aghil Puthiyottil <57040494+MohammedAghil@users.noreply.github.com>

data-prepper-core/src/main/java/org/opensearch/dataprepper/core/pipeline/PipelineRunner.java

@@ -0,0 +1,5 @@
+package org.opensearch.dataprepper.core.pipeline;
+
+public interface PipelineRunner {
+    void runAllProcessorsAndPublishToSinks();
+}

data-prepper-core/src/main/java/org/opensearch/dataprepper/core/pipeline/SupportsPipelineRunner.java

@@ -0,0 +1,7 @@
+package org.opensearch.dataprepper.core.pipeline;
+
+public interface SupportsPipelineRunner {
+    PipelineRunner getPipelineRunner();
+
+    void setPipelineRunner(PipelineRunner pipelineRunner);
+}

data-prepper-core/src/main/java/org/opensearch/dataprepper/core/pipeline/buffer/ZeroBuffer.java

@@ -0,0 +1,110 @@
+package org.opensearch.dataprepper.core.pipeline.buffer;
+
+import com.google.common.annotations.VisibleForTesting;
+import org.opensearch.dataprepper.core.pipeline.PipelineRunner;
+import org.opensearch.dataprepper.core.pipeline.SupportsPipelineRunner;
+import org.opensearch.dataprepper.metrics.MetricNames;
+import org.opensearch.dataprepper.metrics.PluginMetrics;
+import org.opensearch.dataprepper.model.annotations.DataPrepperPlugin;
+import org.opensearch.dataprepper.model.annotations.DataPrepperPluginConstructor;
+import org.opensearch.dataprepper.model.buffer.Buffer;
+import org.opensearch.dataprepper.model.CheckpointState;
+import org.opensearch.dataprepper.model.configuration.PipelineDescription;
+import org.opensearch.dataprepper.model.record.Record;
+import io.micrometer.core.instrument.Counter;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Map;
+import java.util.concurrent.TimeoutException;
+
+@DataPrepperPlugin(name = "zero", pluginType = Buffer.class)
+public class ZeroBuffer<T extends Record<?>> implements Buffer<T>, SupportsPipelineRunner {
+    private static final Logger LOG = LoggerFactory.getLogger(ZeroBuffer.class);
+    private static final String PLUGIN_COMPONENT_ID = "ZeroBuffer";
+    private final PluginMetrics pluginMetrics;
+    private final ThreadLocal<Collection<T>> threadLocalStore;
+    private PipelineRunner pipelineRunner;
+    @VisibleForTesting
+    final String pipelineName;
+    private final Counter writeRecordsCounter;
+    private final Counter readRecordsCounter;
+
+    @DataPrepperPluginConstructor
+    public ZeroBuffer(PipelineDescription pipelineDescription) {
+        this.pluginMetrics = PluginMetrics.fromNames(PLUGIN_COMPONENT_ID, pipelineDescription.getPipelineName());
+        this.pipelineName = pipelineDescription.getPipelineName();
+        this.threadLocalStore = new ThreadLocal<>();
+        this.writeRecordsCounter = pluginMetrics.counter(MetricNames.RECORDS_WRITTEN);
+        this.readRecordsCounter = pluginMetrics.counter(MetricNames.RECORDS_READ);
+    }
+
+    @Override
+    public void write(T record, int timeoutInMillis) throws TimeoutException {
+        if (record == null) {
+            throw new NullPointerException("The write record cannot be null");
+        }
+
+        if (threadLocalStore.get() == null) {
+            threadLocalStore.set(new ArrayList<>());
+        }
+
+        threadLocalStore.get().add(record);
+        writeRecordsCounter.increment();
+
+        getPipelineRunner().runAllProcessorsAndPublishToSinks();
+    }
+
+    @Override
+    public void writeAll(Collection<T> records, int timeoutInMillis) throws Exception {
+        if (records == null) {
+            throw new NullPointerException("The write records cannot be null");
+        }
+
+        if (threadLocalStore.get() == null) {
+            threadLocalStore.set(new ArrayList<>(records));
+        } else {
+            // Add the new records to the existing records
+            threadLocalStore.get().addAll(records);
+        }
+
+        writeRecordsCounter.increment((double) records.size());
+        getPipelineRunner().runAllProcessorsAndPublishToSinks();
+    }
+
+    @Override
+    public Map.Entry<Collection<T>, CheckpointState> read(int timeoutInMillis) {
+        if (threadLocalStore.get() == null) {
+            threadLocalStore.set(new ArrayList<>());
+        }
+
+        Collection<T> storedRecords = threadLocalStore.get();
+        CheckpointState checkpointState = new CheckpointState(0);
+        if (storedRecords!= null && !storedRecords.isEmpty()) {
+            checkpointState = new CheckpointState(storedRecords.size());
+            threadLocalStore.remove();
+            readRecordsCounter.increment((double) storedRecords.size());
+        }
+
+        return Map.entry(storedRecords, checkpointState);
+    }
+
+    @Override
+    public void checkpoint(CheckpointState checkpointState) {}
+
+    @Override
+    public boolean isEmpty() {
+        return (this.threadLocalStore.get() == null || this.threadLocalStore.get().isEmpty());
+    }
+
+    @Override
+    public PipelineRunner getPipelineRunner() {
+        return pipelineRunner;
+    }
+
+    @Override
+    public void setPipelineRunner(PipelineRunner pipelineRunner) {
+        this.pipelineRunner = pipelineRunner;
+    }
+}