Add IndexShard#getLatestReplicationCheckpoint behind segrep enable fe…

…ature flag (opensearch-project#4163)

* Add IndexShard#getLatestReplicationCheckpoint behind segrep enable feature flag

Signed-off-by: Suraj Singh <surajrider@gmail.com>

* Address review comment. Move tests to SegmentReplicationIndexShardTests

Signed-off-by: Suraj Singh <surajrider@gmail.com>

* Add segrep enbaled index settings in TargetServiceTests, SourceHandlerTests

Signed-off-by: Suraj Singh <surajrider@gmail.com>

server/src/main/java/org/opensearch/index/shard/IndexShard.java

@@ -1382,10 +1382,13 @@ public GatedCloseable<IndexCommit> acquireSafeIndexCommit() throws EngineExcepti
     }
 
     /**
-     * Returns the lastest Replication Checkpoint that shard received. Shards will return an EMPTY checkpoint before
-     * the engine is opened.
+     * Returns the latest ReplicationCheckpoint that shard received.
+     * @return EMPTY checkpoint before the engine is opened and null for non-segrep enabled indices
      */
     public ReplicationCheckpoint getLatestReplicationCheckpoint() {
+        if (indexSettings.isSegRepEnabled() == false) {
+            return null;
+        }
         if (getEngineOrNull() == null) {
             return ReplicationCheckpoint.empty(shardId);
         }

server/src/test/java/org/opensearch/index/shard/SegmentReplicationIndexShardTests.java

@@ -14,14 +14,38 @@
 import org.opensearch.index.IndexSettings;
 import org.opensearch.index.engine.NRTReplicationEngineFactory;
 import org.opensearch.index.replication.OpenSearchIndexLevelReplicationTestCase;
+import org.opensearch.indices.replication.checkpoint.ReplicationCheckpoint;
 import org.opensearch.indices.replication.common.ReplicationType;
 
+import java.io.IOException;
+
 public class SegmentReplicationIndexShardTests extends OpenSearchIndexLevelReplicationTestCase {
 
     private static final Settings settings = Settings.builder()
         .put(IndexMetadata.SETTING_REPLICATION_TYPE, ReplicationType.SEGMENT)
         .build();
 
+    /**
+     *  Test that latestReplicationCheckpoint returns null only for docrep enabled indices
+     */
+    public void testReplicationCheckpointNullForDocRep() throws IOException {
+        Settings indexSettings = Settings.builder().put(IndexMetadata.SETTING_REPLICATION_TYPE, "DOCUMENT").put(Settings.EMPTY).build();
+        final IndexShard indexShard = newStartedShard(false, indexSettings);
+        assertNull(indexShard.getLatestReplicationCheckpoint());
+        closeShards(indexShard);
+    }
+
+    /**
+     *  Test that latestReplicationCheckpoint returns ReplicationCheckpoint for segrep enabled indices
+     */
+    public void testReplicationCheckpointNotNullForSegReb() throws IOException {
+        Settings indexSettings = Settings.builder().put(IndexMetadata.SETTING_REPLICATION_TYPE, "SEGMENT").put(Settings.EMPTY).build();
+        final IndexShard indexShard = newStartedShard(indexSettings);
+        final ReplicationCheckpoint replicationCheckpoint = indexShard.getLatestReplicationCheckpoint();
+        assertNotNull(replicationCheckpoint);
+        closeShards(indexShard);
+    }
+
     public void testIgnoreShardIdle() throws Exception {
         try (ReplicationGroup shards = createGroup(1, settings, new NRTReplicationEngineFactory())) {
             shards.startAll();

server/src/test/java/org/opensearch/indices/replication/SegmentReplicationSourceHandlerTests.java

@@ -15,7 +15,9 @@
 import org.opensearch.OpenSearchException;
 import org.opensearch.Version;
 import org.opensearch.action.ActionListener;
+import org.opensearch.cluster.metadata.IndexMetadata;
 import org.opensearch.cluster.node.DiscoveryNode;
+import org.opensearch.common.settings.Settings;
 import org.opensearch.index.shard.IndexShard;
 import org.opensearch.index.shard.IndexShardTestCase;
 import org.opensearch.index.store.StoreFileMetadata;
@@ -41,7 +43,8 @@ public class SegmentReplicationSourceHandlerTests extends IndexShardTestCase {
     @Override
     public void setUp() throws Exception {
         super.setUp();
-        primary = newStartedShard(true);
+        final Settings settings = Settings.builder().put(IndexMetadata.SETTING_REPLICATION_TYPE, "SEGMENT").put(Settings.EMPTY).build();
+        primary = newStartedShard(true, settings);
         replica = newShard(primary.shardId(), false);
         recoverReplica(replica, primary, true);
         replicaDiscoveryNode = replica.recoveryState().getTargetNode();

server/src/test/java/org/opensearch/indices/replication/SegmentReplicationTargetServiceTests.java

@@ -13,6 +13,7 @@
 import org.mockito.Mockito;
 import org.opensearch.OpenSearchException;
 import org.opensearch.action.ActionListener;
+import org.opensearch.cluster.metadata.IndexMetadata;
 import org.opensearch.common.settings.ClusterSettings;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.index.shard.IndexShard;
@@ -50,7 +51,10 @@ public class SegmentReplicationTargetServiceTests extends IndexShardTestCase {
     @Override
     public void setUp() throws Exception {
         super.setUp();
-        final Settings settings = Settings.builder().put("node.name", SegmentReplicationTargetServiceTests.class.getSimpleName()).build();
+        final Settings settings = Settings.builder()
+            .put(IndexMetadata.SETTING_REPLICATION_TYPE, "SEGMENT")
+            .put("node.name", SegmentReplicationTargetServiceTests.class.getSimpleName())
+            .build();
         final ClusterSettings clusterSettings = new ClusterSettings(settings, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS);
         final RecoverySettings recoverySettings = new RecoverySettings(settings, clusterSettings);
         final TransportService transportService = mock(TransportService.class);