Add Index UUID to /_stats Response (#31871)

* Add "uuid" field to each index's section in the `/_stats` response
* closes #31791

Author: original-brownbear

rest-api-spec/src/main/resources/rest-api-spec/test/indices.stats/10_index.yml

@@ -47,7 +47,9 @@ setup:
   - match: { _shards.total: 18 }
   - is_true: _all
   - is_true: indices.test1
+  - is_true: indices.test1.uuid
   - is_true: indices.test2
+  - is_true: indices.test2.uuid
 
 
 ---

server/src/main/java/org/elasticsearch/action/admin/indices/stats/IndexStats.java

@@ -29,17 +29,24 @@ public class IndexStats implements Iterable<IndexShardStats> {
 
     private final String index;
 
+    private final String uuid;
+
     private final ShardStats shards[];
 
-    public IndexStats(String index, ShardStats[] shards) {
+    public IndexStats(String index, String uuid, ShardStats[] shards) {
         this.index = index;
+        this.uuid = uuid;
         this.shards = shards;
     }
 
     public String getIndex() {
         return this.index;
     }
 
+    public String getUuid() {
+        return uuid;
+    }
+
     public ShardStats[] getShards() {
         return this.shards;
     }

server/src/main/java/org/elasticsearch/action/admin/indices/stats/IndicesStatsResponse.java

@@ -26,6 +26,7 @@
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.index.Index;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -84,19 +85,22 @@ public Map<String, IndexStats> getIndices() {
         }
         Map<String, IndexStats> indicesStats = new HashMap<>();
 
-        Set<String> indices = new HashSet<>();
+        Set<Index> indices = new HashSet<>();
         for (ShardStats shard : shards) {
-            indices.add(shard.getShardRouting().getIndexName());
+            indices.add(shard.getShardRouting().index());
         }
 
-        for (String indexName : indices) {
+        for (Index index : indices) {
             List<ShardStats> shards = new ArrayList<>();
+            String indexName = index.getName();
             for (ShardStats shard : this.shards) {
                 if (shard.getShardRouting().getIndexName().equals(indexName)) {
                     shards.add(shard);
                 }
             }
-            indicesStats.put(indexName, new IndexStats(indexName, shards.toArray(new ShardStats[shards.size()])));
+            indicesStats.put(
+                indexName, new IndexStats(indexName, index.getUUID(), shards.toArray(new ShardStats[shards.size()]))
+            );
         }
         this.indicesStats = indicesStats;
         return indicesStats;
@@ -169,7 +173,7 @@ protected void addCustomXContentFields(XContentBuilder builder, Params params) t
             builder.startObject(Fields.INDICES);
             for (IndexStats indexStats : getIndices().values()) {
                 builder.startObject(indexStats.getIndex());
-
+                builder.field("uuid", indexStats.getUuid());
                 builder.startObject("primaries");
                 indexStats.getPrimaries().toXContent(builder, params);
                 builder.endObject();

server/src/test/java/org/elasticsearch/action/admin/indices/stats/IndicesStatsTests.java

@@ -153,12 +153,18 @@ public void testRefreshListeners() throws Exception {
         assertEquals(0, common.refresh.getListeners());
     }
 
+    @SuppressWarnings("unchecked")
+    public void testUuidOnRootStatsIndices() {
+        String uuid = createIndex("test").indexUUID();
+        IndicesStatsResponse rsp = client().admin().indices().prepareStats().get();
+        assertEquals(uuid, rsp.getIndex("test").getUuid());
+    }
+
     /**
      * Gives access to package private IndicesStatsResponse constructor for test purpose.
      **/
     public static IndicesStatsResponse newIndicesStatsResponse(ShardStats[] shards, int totalShards, int successfulShards,
                                                                int failedShards, List<DefaultShardOperationFailedException> shardFailures) {
         return new IndicesStatsResponse(shards, totalShards, successfulShards, failedShards, shardFailures);
     }
-
 }

x-pack/plugin/monitoring/src/test/java/org/elasticsearch/xpack/monitoring/collector/indices/IndicesStatsMonitoringDocTests.java

@@ -45,7 +45,7 @@ public class IndicesStatsMonitoringDocTests extends BaseFilteredMonitoringDocTes
     @Before
     public void setUp() throws Exception {
         super.setUp();
-        indicesStats = Collections.singletonList(new IndexStats("index-0", new ShardStats[] {
+        indicesStats = Collections.singletonList(new IndexStats("index-0", "dcvO5uZATE-EhIKc3tk9Bg", new ShardStats[] {
                 // Primaries
                 new ShardStats(mockShardRouting(true), mockShardPath(), mockCommonStats(), null, null),
                 new ShardStats(mockShardRouting(true), mockShardPath(), mockCommonStats(), null, null),