[Metadata Immutability] Change different indices lookup objects from array type to lists

Changed the arrays to immutable List instances, added new versions of the getters which returns List instances.

Resolves #8647

Signed-off-by: Abdul Muneer Kolarkunnu <muneer.kolarkunnu@netapp.com>

Author: akolarkunnu

server/src/main/java/org/opensearch/action/admin/cluster/health/ClusterHealthResponse.java

@@ -60,6 +60,7 @@
 import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 
 import static java.util.Collections.emptyMap;
 import static org.opensearch.core.xcontent.ConstructingObjectParser.constructorArg;
@@ -215,13 +216,13 @@ public ClusterHealthResponse(StreamInput in) throws IOException {
     }
 
     /** needed for plugins BWC */
-    public ClusterHealthResponse(String clusterName, String[] concreteIndices, ClusterState clusterState) {
+    public ClusterHealthResponse(String clusterName, Set<String> concreteIndices, ClusterState clusterState) {
         this(clusterName, concreteIndices, clusterState, -1, -1, -1, TimeValue.timeValueHours(0));
     }
 
     public ClusterHealthResponse(
         String clusterName,
-        String[] concreteIndices,
+        Set<String> concreteIndices,
         ClusterState clusterState,
         int numberOfPendingTasks,
         int numberOfInFlightFetch,
@@ -242,7 +243,7 @@ public ClusterHealthResponse(
         String clusterName,
         ClusterState clusterState,
         ClusterSettings clusterSettings,
-        String[] concreteIndices,
+        Set<String> concreteIndices,
         String awarenessAttributeName,
         int numberOfPendingTasks,
         int numberOfInFlightFetch,

server/src/main/java/org/opensearch/action/admin/cluster/health/TransportClusterHealthAction.java

@@ -59,7 +59,6 @@
 import org.opensearch.common.inject.Inject;
 import org.opensearch.common.unit.TimeValue;
 import org.opensearch.core.action.ActionListener;
-import org.opensearch.core.common.Strings;
 import org.opensearch.core.common.io.stream.StreamInput;
 import org.opensearch.core.common.util.CollectionUtils;
 import org.opensearch.discovery.ClusterManagerNotDiscoveredException;
@@ -71,6 +70,8 @@
 import org.opensearch.transport.TransportService;
 
 import java.io.IOException;
+import java.util.Collections;
+import java.util.Set;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
 
@@ -490,10 +491,10 @@ private ClusterHealthResponse clusterHealth(
             logger.trace("Calculating health based on state version [{}]", clusterState.version());
         }
 
-        String[] concreteIndices;
+        Set<String> concreteIndices;
         if (request.level().equals(ClusterHealthRequest.Level.AWARENESS_ATTRIBUTES)) {
             String awarenessAttribute = request.getAwarenessAttribute();
-            concreteIndices = clusterState.getMetadata().getConcreteAllIndices().toArray(String[]::new);
+            concreteIndices = clusterState.getMetadata().getConcreteAllIndices();
             return new ClusterHealthResponse(
                 clusterState.getClusterName().value(),
                 clusterState,
@@ -508,12 +509,12 @@ private ClusterHealthResponse clusterHealth(
         }
 
         try {
-            concreteIndices = indexNameExpressionResolver.concreteIndexNames(clusterState, request);
+            concreteIndices = Set.of(indexNameExpressionResolver.concreteIndexNames(clusterState, request));
         } catch (IndexNotFoundException e) {
             // one of the specified indices is not there - treat it as RED.
             ClusterHealthResponse response = new ClusterHealthResponse(
                 clusterState.getClusterName().value(),
-                Strings.EMPTY_ARRAY,
+                Collections.emptySet(),
                 clusterState,
                 numberOfPendingTasks,
                 numberOfInFlightFetch,

server/src/main/java/org/opensearch/action/admin/indices/datastream/GetDataStreamAction.java

@@ -336,7 +336,7 @@ protected void clusterManagerOperation(Request request, ClusterState state, Acti
                 }
                 ClusterStateHealth streamHealth = new ClusterStateHealth(
                     state,
-                    dataStream.getIndices().stream().map(Index::getName).toArray(String[]::new)
+                    dataStream.getIndices().stream().map(Index::getName).collect(Collectors.toSet())
                 );
                 dataStreamInfos.add(new Response.DataStreamInfo(dataStream, streamHealth.getStatus(), indexTemplate));
             }

server/src/main/java/org/opensearch/cluster/health/ClusterStateHealth.java

@@ -47,6 +47,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 
 /**
  * Cluster state health information
@@ -73,16 +74,16 @@ public final class ClusterStateHealth implements Iterable<ClusterIndexHealth>, W
      * @param clusterState The current cluster state. Must not be null.
      */
     public ClusterStateHealth(final ClusterState clusterState) {
-        this(clusterState, clusterState.metadata().getConcreteAllIndices().toArray(String[]::new));
+        this(clusterState, clusterState.metadata().getConcreteAllIndices());
     }
 
     /**
      * Creates a new <code>ClusterStateHealth</code> instance considering the current cluster state and the provided index names.
      *
      * @param clusterState    The current cluster state. Must not be null.
-     * @param concreteIndices An array of index names to consider. Must not be null but may be empty.
+     * @param concreteIndices A set of index names to consider. Must not be null but may be empty.
      */
-    public ClusterStateHealth(final ClusterState clusterState, final String[] concreteIndices) {
+    public ClusterStateHealth(final ClusterState clusterState, final Set<String> concreteIndices) {
         numberOfNodes = clusterState.nodes().getSize();
         numberOfDataNodes = clusterState.nodes().getDataNodes().size();
         hasDiscoveredClusterManager = clusterState.nodes().getClusterManagerNodeId() != null;

server/src/test/java/org/opensearch/action/admin/cluster/health/ClusterHealthResponsesTests.java

@@ -62,6 +62,7 @@
 import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Set;
 import java.util.function.Predicate;
 import java.util.regex.Pattern;
 
@@ -93,7 +94,7 @@ public void testClusterHealth() throws IOException {
         TimeValue pendingTaskInQueueTime = TimeValue.timeValueMillis(randomIntBetween(1000, 100000));
         ClusterHealthResponse clusterHealth = new ClusterHealthResponse(
             "bla",
-            new String[] { Metadata.ALL },
+            Set.of(Metadata.ALL),
             clusterState,
             pendingTasks,
             inFlight,
@@ -121,7 +122,7 @@ public void testClusterHealthVerifyClusterManagerNodeDiscovery() throws IOExcept
         TimeValue pendingTaskInQueueTime = TimeValue.timeValueMillis(randomIntBetween(1000, 100000));
         ClusterHealthResponse clusterHealth = new ClusterHealthResponse(
             "bla",
-            new String[] { Metadata.ALL },
+            Set.of(Metadata.ALL),
             clusterState,
             pendingTasks,
             inFlight,

server/src/test/java/org/opensearch/action/admin/cluster/health/TransportClusterHealthActionTests.java

@@ -50,14 +50,15 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Set;
 import java.util.stream.IntStream;
 
 import static org.hamcrest.core.IsEqual.equalTo;
 
 public class TransportClusterHealthActionTests extends OpenSearchTestCase {
 
     public void testWaitForInitializingShards() throws Exception {
-        final String[] indices = { "test" };
+        final Set<String> indices = Set.of("test");
         final ClusterHealthRequest request = new ClusterHealthRequest();
         request.waitForNoInitializingShards(true);
         ClusterState clusterState = randomClusterStateWithInitializingShards("test", 0);
@@ -76,7 +77,7 @@ public void testWaitForInitializingShards() throws Exception {
     }
 
     public void testWaitForAllShards() {
-        final String[] indices = { "test" };
+        final Set<String> indices = Set.of("test");
         final ClusterHealthRequest request = new ClusterHealthRequest();
         request.waitForActiveShards(ActiveShardCount.ALL);
 

server/src/test/java/org/opensearch/cluster/health/ClusterStateHealthTests.java

@@ -213,10 +213,8 @@ public void testClusterHealth() throws IOException {
             .routingTable(routingTable.build())
             .nodes(clusterService.state().nodes())
             .build();
-        String[] concreteIndices = indexNameExpressionResolver.concreteIndexNames(
-            clusterState,
-            IndicesOptions.strictExpand(),
-            (String[]) null
+        Set<String> concreteIndices = Set.of(
+            indexNameExpressionResolver.concreteIndexNames(clusterState, IndicesOptions.strictExpand(), (String[]) null)
         );
         ClusterStateHealth clusterStateHealth = new ClusterStateHealth(clusterState, concreteIndices);
         logger.info("cluster status: {}, expected {}", clusterStateHealth.getStatus(), counter.status());
@@ -230,7 +228,7 @@ public void testClusterHealth() throws IOException {
 
     public void testClusterHealthOnIndexCreation() {
         final String indexName = "test-idx";
-        final String[] indices = new String[] { indexName };
+        final Set<String> indices = Set.of(indexName);
         final List<ClusterState> clusterStates = simulateIndexCreationStates(indexName, false);
         for (int i = 0; i < clusterStates.size(); i++) {
             // make sure cluster health is always YELLOW, up until the last state where it should be GREEN
@@ -246,7 +244,7 @@ public void testClusterHealthOnIndexCreation() {
 
     public void testClusterHealthOnIndexCreationWithFailedAllocations() {
         final String indexName = "test-idx";
-        final String[] indices = new String[] { indexName };
+        final Set<String> indices = Set.of(indexName);
         final List<ClusterState> clusterStates = simulateIndexCreationStates(indexName, true);
         for (int i = 0; i < clusterStates.size(); i++) {
             // make sure cluster health is YELLOW up until the final cluster state, which contains primary shard
@@ -263,7 +261,7 @@ public void testClusterHealthOnIndexCreationWithFailedAllocations() {
 
     public void testClusterHealthOnClusterRecovery() {
         final String indexName = "test-idx";
-        final String[] indices = new String[] { indexName };
+        final Set<String> indices = Set.of(indexName);
         final List<ClusterState> clusterStates = simulateClusterRecoveryStates(indexName, false, false);
         for (int i = 0; i < clusterStates.size(); i++) {
             // make sure cluster health is YELLOW up until the final cluster state, when it turns GREEN
@@ -279,7 +277,7 @@ public void testClusterHealthOnClusterRecovery() {
 
     public void testClusterHealthOnClusterRecoveryWithFailures() {
         final String indexName = "test-idx";
-        final String[] indices = new String[] { indexName };
+        final Set<String> indices = Set.of(indexName);
         final List<ClusterState> clusterStates = simulateClusterRecoveryStates(indexName, false, true);
         for (int i = 0; i < clusterStates.size(); i++) {
             // make sure cluster health is YELLOW up until the final cluster state, which contains primary shard
@@ -296,7 +294,7 @@ public void testClusterHealthOnClusterRecoveryWithFailures() {
 
     public void testClusterHealthOnClusterRecoveryWithPreviousAllocationIds() {
         final String indexName = "test-idx";
-        final String[] indices = new String[] { indexName };
+        final Set<String> indices = Set.of(indexName);
         final List<ClusterState> clusterStates = simulateClusterRecoveryStates(indexName, true, false);
         for (int i = 0; i < clusterStates.size(); i++) {
             // because there were previous allocation ids, we should be RED until the primaries are started,
@@ -319,7 +317,7 @@ public void testClusterHealthOnClusterRecoveryWithPreviousAllocationIds() {
 
     public void testClusterHealthOnClusterRecoveryWithPreviousAllocationIdsAndAllocationFailures() {
         final String indexName = "test-idx";
-        final String[] indices = new String[] { indexName };
+        final Set<String> indices = Set.of(indexName);
         for (final ClusterState clusterState : simulateClusterRecoveryStates(indexName, true, true)) {
             final ClusterStateHealth health = new ClusterStateHealth(clusterState, indices);
             // if the inactive primaries are due solely to recovery (not failed allocation or previously being allocated)