Dry up Empty ActionResponse Implementations (#65035)

No need to have multiple empty action response implementations.
=> Use a single class and singleton for all of them like we do for
empty flat transport responses.

Author: original-brownbear

server/src/main/java/org/elasticsearch/action/ActionResponse.java

@@ -20,6 +20,9 @@
 package org.elasticsearch.action;
 
 import org.elasticsearch.common.io.stream.StreamInput;
+import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.xcontent.ToXContentObject;
+import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.transport.TransportResponse;
 
 import java.io.IOException;
@@ -35,4 +38,21 @@ public ActionResponse() {
     public ActionResponse(StreamInput in) throws IOException {
         super(in);
     }
+
+    public static final class Empty extends ActionResponse implements ToXContentObject {
+        public static final ActionResponse.Empty INSTANCE = new ActionResponse.Empty();
+
+        @Override
+        public String toString() {
+            return "EmptyActionResponse{}";
+        }
+
+        @Override
+        public void writeTo(StreamOutput out) {}
+
+        @Override
+        public XContentBuilder toXContent(final XContentBuilder builder, final Params params) {
+            return builder;
+        }
+    }
 }

server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/AddVotingConfigExclusionsAction.java

@@ -18,13 +18,14 @@
  */
 package org.elasticsearch.action.admin.cluster.configuration;
 
+import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.action.ActionType;
 
-public class AddVotingConfigExclusionsAction extends ActionType<AddVotingConfigExclusionsResponse> {
+public class AddVotingConfigExclusionsAction extends ActionType<ActionResponse.Empty> {
     public static final AddVotingConfigExclusionsAction INSTANCE = new AddVotingConfigExclusionsAction();
     public static final String NAME = "cluster:admin/voting_config/add_exclusions";
 
     private AddVotingConfigExclusionsAction() {
-        super(NAME, AddVotingConfigExclusionsResponse::new);
+        super(NAME, in -> ActionResponse.Empty.INSTANCE);
     }
 }

server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/AddVotingConfigExclusionsResponse.java

@@ -18,13 +18,14 @@
  */
 package org.elasticsearch.action.admin.cluster.configuration;
 
+import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.action.ActionType;
 
-public class ClearVotingConfigExclusionsAction extends ActionType<ClearVotingConfigExclusionsResponse> {
+public class ClearVotingConfigExclusionsAction extends ActionType<ActionResponse.Empty> {
     public static final ClearVotingConfigExclusionsAction INSTANCE = new ClearVotingConfigExclusionsAction();
     public static final String NAME = "cluster:admin/voting_config/clear_exclusions";
 
     private ClearVotingConfigExclusionsAction() {
-        super(NAME, ClearVotingConfigExclusionsResponse::new);
+        super(NAME, in -> ActionResponse.Empty.INSTANCE);
     }
 }

server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/ClearVotingConfigExclusionsAction.java

@@ -23,6 +23,7 @@
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.ElasticsearchTimeoutException;
 import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.action.support.ActionFilters;
 import org.elasticsearch.action.support.master.TransportMasterNodeAction;
 import org.elasticsearch.cluster.ClusterState;
@@ -52,7 +53,7 @@
 import java.util.stream.Collectors;
 
 public class TransportAddVotingConfigExclusionsAction extends TransportMasterNodeAction<AddVotingConfigExclusionsRequest,
-    AddVotingConfigExclusionsResponse> {
+        ActionResponse.Empty> {
 
     private static final Logger logger = LogManager.getLogger(TransportAddVotingConfigExclusionsAction.class);
 
@@ -66,7 +67,7 @@ public TransportAddVotingConfigExclusionsAction(Settings settings, ClusterSettin
                                                     ClusterService clusterService, ThreadPool threadPool, ActionFilters actionFilters,
                                                     IndexNameExpressionResolver indexNameExpressionResolver) {
         super(AddVotingConfigExclusionsAction.NAME, transportService, clusterService, threadPool, actionFilters,
-            AddVotingConfigExclusionsRequest::new, indexNameExpressionResolver, AddVotingConfigExclusionsResponse::new,
+            AddVotingConfigExclusionsRequest::new, indexNameExpressionResolver, in -> ActionResponse.Empty.INSTANCE,
                 ThreadPool.Names.SAME);
 
         maxVotingConfigExclusions = MAXIMUM_VOTING_CONFIG_EXCLUSIONS_SETTING.get(settings);
@@ -79,7 +80,7 @@ private void setMaxVotingConfigExclusions(int maxVotingConfigExclusions) {
 
     @Override
     protected void masterOperation(Task task, AddVotingConfigExclusionsRequest request, ClusterState state,
-                                   ActionListener<AddVotingConfigExclusionsResponse> listener) throws Exception {
+                                   ActionListener<ActionResponse.Empty> listener) throws Exception {
 
         resolveVotingConfigExclusionsAndCheckMaximum(request, state, maxVotingConfigExclusions);
         // throws IAE if no nodes matched or maximum exceeded
@@ -124,7 +125,7 @@ public void clusterStateProcessed(String source, ClusterState oldState, ClusterS
                 final Listener clusterStateListener = new Listener() {
                     @Override
                     public void onNewClusterState(ClusterState state) {
-                        listener.onResponse(new AddVotingConfigExclusionsResponse());
+                        listener.onResponse(ActionResponse.Empty.INSTANCE);
                     }
 
                     @Override

server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/ClearVotingConfigExclusionsResponse.java

@@ -23,6 +23,7 @@
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.ElasticsearchTimeoutException;
 import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.action.support.ActionFilters;
 import org.elasticsearch.action.support.master.TransportMasterNodeAction;
 import org.elasticsearch.cluster.ClusterState;
@@ -46,7 +47,7 @@
 import java.util.function.Predicate;
 
 public class TransportClearVotingConfigExclusionsAction
-    extends TransportMasterNodeAction<ClearVotingConfigExclusionsRequest, ClearVotingConfigExclusionsResponse> {
+    extends TransportMasterNodeAction<ClearVotingConfigExclusionsRequest, ActionResponse.Empty> {
 
     private static final Logger logger = LogManager.getLogger(TransportClearVotingConfigExclusionsAction.class);
 
@@ -55,13 +56,13 @@ public TransportClearVotingConfigExclusionsAction(TransportService transportServ
                                                       ThreadPool threadPool, ActionFilters actionFilters,
                                                       IndexNameExpressionResolver indexNameExpressionResolver) {
         super(ClearVotingConfigExclusionsAction.NAME, transportService, clusterService, threadPool, actionFilters,
-            ClearVotingConfigExclusionsRequest::new, indexNameExpressionResolver, ClearVotingConfigExclusionsResponse::new,
+            ClearVotingConfigExclusionsRequest::new, indexNameExpressionResolver, in -> ActionResponse.Empty.INSTANCE,
                 ThreadPool.Names.SAME);
     }
 
     @Override
     protected void masterOperation(Task task, ClearVotingConfigExclusionsRequest request, ClusterState initialState,
-                                   ActionListener<ClearVotingConfigExclusionsResponse> listener) throws Exception {
+                                   ActionListener<ActionResponse.Empty> listener) throws Exception {
 
         final long startTimeMillis = threadPool.relativeTimeInMillis();
 
@@ -104,7 +105,7 @@ public void onTimeout(TimeValue timeout) {
     }
 
     private void submitClearVotingConfigExclusionsTask(ClearVotingConfigExclusionsRequest request, long startTimeMillis,
-                                                       ActionListener<ClearVotingConfigExclusionsResponse> listener) {
+                                                       ActionListener<ActionResponse.Empty> listener) {
         clusterService.submitStateUpdateTask("clear-voting-config-exclusions", new ClusterStateUpdateTask(Priority.URGENT,
                 TimeValue.timeValueMillis(
                         Math.max(0, request.getTimeout().millis() + startTimeMillis - threadPool.relativeTimeInMillis()))) {
@@ -124,7 +125,7 @@ public void onFailure(String source, Exception e) {
 
             @Override
             public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
-                listener.onResponse(new ClearVotingConfigExclusionsResponse());
+                listener.onResponse(ActionResponse.Empty.INSTANCE);
             }
         });
     }