Implementing pagination for _cat/indices API

server/src/main/java/org/opensearch/action/ActionModule.java

@@ -456,6 +456,9 @@
 import org.opensearch.rest.action.ingest.RestGetPipelineAction;
 import org.opensearch.rest.action.ingest.RestPutPipelineAction;
 import org.opensearch.rest.action.ingest.RestSimulatePipelineAction;
+import org.opensearch.rest.action.list.AbstractListAction;
+import org.opensearch.rest.action.list.RestIndicesListAction;
+import org.opensearch.rest.action.list.RestListAction;
 import org.opensearch.rest.action.search.RestClearScrollAction;
 import org.opensearch.rest.action.search.RestCountAction;
 import org.opensearch.rest.action.search.RestCreatePitAction;
@@ -793,9 +796,12 @@ private ActionFilters setupActionFilters(List<ActionPlugin> actionPlugins) {
 
     public void initRestHandlers(Supplier<DiscoveryNodes> nodesInCluster) {
         List<AbstractCatAction> catActions = new ArrayList<>();
+        List<AbstractListAction> listActions = new ArrayList<>();
         Consumer<RestHandler> registerHandler = handler -> {
             if (handler instanceof AbstractCatAction) {
                 catActions.add((AbstractCatAction) handler);
+            } else if (handler instanceof AbstractListAction) {
+                listActions.add((AbstractListAction) handler);
             }
             restController.registerHandler(handler);
         };
@@ -968,6 +974,9 @@ public void initRestHandlers(Supplier<DiscoveryNodes> nodesInCluster) {
         registerHandler.accept(new RestSnapshotAction());
         registerHandler.accept(new RestTemplatesAction());
 
+        // LIST API
+        registerHandler.accept(new RestIndicesListAction());
+
         // Point in time API
         registerHandler.accept(new RestCreatePitAction());
         registerHandler.accept(new RestDeletePitAction());
@@ -999,6 +1008,7 @@ public void initRestHandlers(Supplier<DiscoveryNodes> nodesInCluster) {
             }
         }
         registerHandler.accept(new RestCatAction(catActions));
+        registerHandler.accept(new RestListAction(listActions));
         registerHandler.accept(new RestDecommissionAction());
         registerHandler.accept(new RestGetDecommissionStateAction());
         registerHandler.accept(new RestRemoteStoreStatsAction());

server/src/main/java/org/opensearch/common/Table.java

@@ -43,6 +43,8 @@
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
+import reactor.util.annotation.NonNull;
+
 import static java.util.Collections.emptyMap;
 
 /**
@@ -59,9 +61,18 @@ public class Table {
     private List<Cell> currentCells;
     private boolean inHeaders = false;
     private boolean withTime = false;
+    private PaginationMetadata paginationMetadata = new PaginationMetadata(false, null, null);
     public static final String EPOCH = "epoch";
     public static final String TIMESTAMP = "timestamp";
 
+    public Table() {}
+
+    public Table(@Nullable PaginationMetadata paginationMetadata) {
+        if (paginationMetadata != null) {
+            this.paginationMetadata = paginationMetadata;
+        }
+    }
+
     public Table startHeaders() {
         inHeaders = true;
         currentCells = new ArrayList<>();
@@ -230,6 +241,18 @@ public Map<String, String> getAliasMap() {
         return headerAliasMap;
     }
 
+    public boolean isPaginated() {
+        return paginationMetadata.isResponsePaginated;
+    }
+
+    public String getPaginatedElement() {
+        return paginationMetadata.paginatedElement;
+    }
+
+    public String getNextToken() {
+        return paginationMetadata.nextToken;
+    }
+
     /**
      * Cell in a table
      *
@@ -254,4 +277,34 @@ public Cell(Object value, Map<String, String> attr) {
             this.attr = attr;
         }
     }
+
+    /**
+     * Pagination metadata for a table.
+     *
+     * @opensearch.internal
+     */
+    public static class PaginationMetadata {
+
+        /**
+         * boolean denoting whether the table is paginated or not.
+         */
+        public final boolean isResponsePaginated;
+
+        /**
+         * String denoting the element which is being paginated (for e.g. shards, indices..).
+         */
+        public final String paginatedElement;
+
+        /**
+         * String denoting the next_token of paginated response, which will be used to fetch next page (if any).
+         */
+        public final String nextToken;
+
+        public PaginationMetadata(@NonNull boolean isResponsePaginated, @Nullable String paginatedElement, @Nullable String nextToken) {
+            this.isResponsePaginated = isResponsePaginated;
+            assert !isResponsePaginated || paginatedElement != null : "paginatedElement must be specified for a table which is paginated";
+            this.paginatedElement = paginatedElement;
+            this.nextToken = nextToken;
+        }
+    }
 }