Clean up request/response for get-cluster-settings (#86347)

Today there are request and response objects for the
get-cluster-settings action but the request is unused and the response
is only used in the REST layer. This commit removes the unused request
and renames the response to reflect that it's not a transport-layer
response. It also tidies a few things up in this area, removing the
unused `ActionResponse` superclass, making its fields final, and
replacing the overly-general `RestBuilderListener` with a regular
`RestToXContentListener` in the REST action.

Relates #82342 because to resolve that issue we will want to introduce
transport-layer request/response classes, and the classes involved in
this commit are in the way of that change.

qa/full-cluster-restart/src/test/java/org/elasticsearch/upgrades/FullClusterRestartIT.java

@@ -10,7 +10,7 @@ package org.elasticsearch.upgrades;
 
 import org.apache.http.util.EntityUtils;
 import org.elasticsearch.Version;
-import org.elasticsearch.action.admin.cluster.settings.ClusterGetSettingsResponse;
+import org.elasticsearch.action.admin.cluster.settings.RestClusterGetSettingsResponse;
 import org.elasticsearch.client.Request;
 import org.elasticsearch.client.Response;
 import org.elasticsearch.client.ResponseException;
@@ -1849,8 +1849,7 @@ public class FullClusterRestartIT extends AbstractFullClusterRestartTestCase {
             final Request getSettingsRequest = new Request("GET", "/_cluster/settings");
             final Response getSettingsResponse = client().performRequest(getSettingsRequest);
             try (XContentParser parser = createParser(JsonXContent.jsonXContent, getSettingsResponse.getEntity().getContent())) {
-                final ClusterGetSettingsResponse clusterGetSettingsResponse = ClusterGetSettingsResponse.fromXContent(parser);
+                final Settings settings = RestClusterGetSettingsResponse.fromXContent(parser).getPersistentSettings();
-                final Settings settings = clusterGetSettingsResponse.getPersistentSettings();
                 assertThat(REMOTE_CLUSTER_COMPRESS.getConcreteSettingForNamespace("foo").get(settings), equalTo(Compression.Enabled.TRUE));
             }
         }

server/src/main/java/org/elasticsearch/action/admin/cluster/settings/ClusterGetSettingsRequest.java

@@ -1,37 +0,0 @@
-/*
- * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
- * or more contributor license agreements. Licensed under the Elastic License
- * 2.0 and the Server Side Public License, v 1; you may not use this file except
- * in compliance with, at your election, the Elastic License 2.0 or the Server
- * Side Public License, v 1.
- */
-
-package org.elasticsearch.action.admin.cluster.settings;
-
-import org.elasticsearch.action.ActionRequestValidationException;
-import org.elasticsearch.action.support.master.MasterNodeReadRequest;
-
-/**
- * This request is specific to the REST client. {@link org.elasticsearch.action.admin.cluster.state.ClusterStateRequest}
- * is used on the transport layer.
- */
-public class ClusterGetSettingsRequest extends MasterNodeReadRequest<ClusterGetSettingsRequest> {
-    private boolean includeDefaults = false;
-
-    @Override
-    public ActionRequestValidationException validate() {
-        return null;
-    }
-
-    /**
-     * When include_defaults is set, return default settings which are normally suppressed.
-     */
-    public ClusterGetSettingsRequest includeDefaults(boolean includeDefaults) {
-        this.includeDefaults = includeDefaults;
-        return this;
-    }
-
-    public boolean includeDefaults() {
-        return includeDefaults;
-    }
-}

server/src/main/java/org/elasticsearch/action/admin/cluster/settings/RestClusterGetSettingsResponse.java

@@ -8,9 +8,7 @@
 
 package org.elasticsearch.action.admin.cluster.settings;
 
-import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.common.Strings;
-import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.xcontent.ConstructingObjectParser;
 import org.elasticsearch.xcontent.ParseField;
@@ -28,22 +26,22 @@ import static org.elasticsearch.xcontent.ConstructingObjectParser.optionalConstr
  * This response is specific to the REST client. {@link org.elasticsearch.action.admin.cluster.state.ClusterStateResponse}
  * is used on the transport layer.
  */
-public class ClusterGetSettingsResponse extends ActionResponse implements ToXContentObject {
+public class RestClusterGetSettingsResponse implements ToXContentObject {
 
-    private Settings persistentSettings = Settings.EMPTY;
+    private final Settings persistentSettings;
-    private Settings transientSettings = Settings.EMPTY;
+    private final Settings transientSettings;
-    private Settings defaultSettings = Settings.EMPTY;
+    private final Settings defaultSettings;
 
     static final String PERSISTENT_FIELD = "persistent";
     static final String TRANSIENT_FIELD = "transient";
     static final String DEFAULTS_FIELD = "defaults";
 
-    private static final ConstructingObjectParser<ClusterGetSettingsResponse, Void> PARSER = new ConstructingObjectParser<>(
+    private static final ConstructingObjectParser<RestClusterGetSettingsResponse, Void> PARSER = new ConstructingObjectParser<>(
         "cluster_get_settings_response",
         true,
         a -> {
             Settings defaultSettings = a[2] == null ? Settings.EMPTY : (Settings) a[2];
-            return new ClusterGetSettingsResponse((Settings) a[0], (Settings) a[1], defaultSettings);
+            return new RestClusterGetSettingsResponse((Settings) a[0], (Settings) a[1], defaultSettings);
         }
     );
     static {
@@ -52,16 +50,10 @@ public class ClusterGetSettingsResponse extends ActionResponse implements ToXCon
         PARSER.declareObject(optionalConstructorArg(), (p, c) -> Settings.fromXContent(p), new ParseField(DEFAULTS_FIELD));
     }
 
-    public ClusterGetSettingsResponse(Settings persistentSettings, Settings transientSettings, Settings defaultSettings) {
+    public RestClusterGetSettingsResponse(Settings persistentSettings, Settings transientSettings, Settings defaultSettings) {
-        if (persistentSettings != null) {
+        this.persistentSettings = Objects.requireNonNullElse(persistentSettings, Settings.EMPTY);
-            this.persistentSettings = persistentSettings;
+        this.transientSettings = Objects.requireNonNullElse(transientSettings, Settings.EMPTY);
-        }
+        this.defaultSettings = Objects.requireNonNullElse(defaultSettings, Settings.EMPTY);
-        if (transientSettings != null) {
-            this.transientSettings = transientSettings;
-        }
-        if (defaultSettings != null) {
-            this.defaultSettings = defaultSettings;
-        }
     }
 
     /**
@@ -127,7 +119,7 @@ public class ClusterGetSettingsResponse extends ActionResponse implements ToXCon
         return builder;
     }
 
-    public static ClusterGetSettingsResponse fromXContent(XContentParser parser) {
+    public static RestClusterGetSettingsResponse fromXContent(XContentParser parser) {
         return PARSER.apply(parser, null);
     }
 
@@ -135,7 +127,7 @@ public class ClusterGetSettingsResponse extends ActionResponse implements ToXCon
     public boolean equals(Object o) {
         if (this == o) return true;
         if (o == null || getClass() != o.getClass()) return false;
-        ClusterGetSettingsResponse that = (ClusterGetSettingsResponse) o;
+        RestClusterGetSettingsResponse that = (RestClusterGetSettingsResponse) o;
         return Objects.equals(transientSettings, that.transientSettings)
             && Objects.equals(persistentSettings, that.persistentSettings)
             && Objects.equals(defaultSettings, that.defaultSettings);
@@ -150,7 +142,4 @@ public class ClusterGetSettingsResponse extends ActionResponse implements ToXCon
     public String toString() {
         return Strings.toString(this);
     }
-
-    @Override
-    public void writeTo(StreamOutput out) throws IOException {}
 }

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterGetSettingsAction.java

@@ -8,9 +8,8 @@
 
 package org.elasticsearch.rest.action.admin.cluster;
 
-import org.elasticsearch.action.admin.cluster.settings.ClusterGetSettingsResponse;
+import org.elasticsearch.action.admin.cluster.settings.RestClusterGetSettingsResponse;
 import org.elasticsearch.action.admin.cluster.state.ClusterStateRequest;
-import org.elasticsearch.action.admin.cluster.state.ClusterStateResponse;
 import org.elasticsearch.client.internal.Requests;
 import org.elasticsearch.client.internal.node.NodeClient;
 import org.elasticsearch.cluster.ClusterState;
@@ -18,13 +17,8 @@ import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.settings.SettingsFilter;
 import org.elasticsearch.rest.BaseRestHandler;
-import org.elasticsearch.rest.BytesRestResponse;
 import org.elasticsearch.rest.RestRequest;
-import org.elasticsearch.rest.RestResponse;
+import org.elasticsearch.rest.action.RestToXContentListener;
-import org.elasticsearch.rest.RestStatus;
-import org.elasticsearch.rest.action.RestBuilderListener;
-import org.elasticsearch.xcontent.ToXContent;
-import org.elasticsearch.xcontent.XContentBuilder;
 
 import java.io.IOException;
 import java.util.List;
@@ -60,12 +54,14 @@ public class RestClusterGetSettingsAction extends BaseRestHandler {
         final boolean renderDefaults = request.paramAsBoolean("include_defaults", false);
         clusterStateRequest.local(request.paramAsBoolean("local", clusterStateRequest.local()));
         clusterStateRequest.masterNodeTimeout(request.paramAsTime("master_timeout", clusterStateRequest.masterNodeTimeout()));
-        return channel -> client.admin().cluster().state(clusterStateRequest, new RestBuilderListener<ClusterStateResponse>(channel) {
+        return channel -> client.admin()
-            @Override
+            .cluster()
-            public RestResponse buildResponse(ClusterStateResponse response, XContentBuilder builder) throws Exception {
+            .state(
-                return new BytesRestResponse(RestStatus.OK, renderResponse(response.getState(), renderDefaults, builder, request));
+                clusterStateRequest,
-            }
+                new RestToXContentListener<RestClusterGetSettingsResponse>(channel).map(
-        });
+                    response -> response(response.getState(), renderDefaults, settingsFilter, clusterSettings, settings)
+                )
+            );
     }
 
     @Override
@@ -78,19 +74,14 @@ public class RestClusterGetSettingsAction extends BaseRestHandler {
         return false;
     }
 
-    private XContentBuilder renderResponse(ClusterState state, boolean renderDefaults, XContentBuilder builder, ToXContent.Params params)
+    static RestClusterGetSettingsResponse response(
-        throws IOException {
-        return response(state, renderDefaults, settingsFilter, clusterSettings, settings).toXContent(builder, params);
-    }
-
-    static ClusterGetSettingsResponse response(
         final ClusterState state,
         final boolean renderDefaults,
         final SettingsFilter settingsFilter,
         final ClusterSettings clusterSettings,
         final Settings settings
     ) {
-        return new ClusterGetSettingsResponse(
+        return new RestClusterGetSettingsResponse(
             settingsFilter.filter(state.metadata().persistentSettings()),
             settingsFilter.filter(state.metadata().transientSettings()),
             renderDefaults ? settingsFilter.filter(clusterSettings.diff(state.metadata().settings(), settings)) : Settings.EMPTY

server/src/test/java/org/elasticsearch/action/admin/cluster/settings/RestClusterGetSettingsResponseTests.java

@@ -15,11 +15,11 @@ import org.elasticsearch.xcontent.XContentParser;
 import java.io.IOException;
 import java.util.function.Predicate;
 
-public class ClusterGetSettingsResponseTests extends AbstractXContentTestCase<ClusterGetSettingsResponse> {
+public class RestClusterGetSettingsResponseTests extends AbstractXContentTestCase<RestClusterGetSettingsResponse> {
 
     @Override
-    protected ClusterGetSettingsResponse doParseInstance(XContentParser parser) throws IOException {
+    protected RestClusterGetSettingsResponse doParseInstance(XContentParser parser) throws IOException {
-        return ClusterGetSettingsResponse.fromXContent(parser);
+        return RestClusterGetSettingsResponse.fromXContent(parser);
     }
 
     @Override
@@ -28,17 +28,17 @@ public class ClusterGetSettingsResponseTests extends AbstractXContentTestCase<Cl
     }
 
     @Override
-    protected ClusterGetSettingsResponse createTestInstance() {
+    protected RestClusterGetSettingsResponse createTestInstance() {
         Settings persistentSettings = ClusterUpdateSettingsResponseTests.randomClusterSettings(0, 2);
         Settings transientSettings = ClusterUpdateSettingsResponseTests.randomClusterSettings(0, 2);
         Settings defaultSettings = randomBoolean() ? ClusterUpdateSettingsResponseTests.randomClusterSettings(0, 2) : Settings.EMPTY;
-        return new ClusterGetSettingsResponse(persistentSettings, transientSettings, defaultSettings);
+        return new RestClusterGetSettingsResponse(persistentSettings, transientSettings, defaultSettings);
     }
 
     @Override
     protected Predicate<String> getRandomFieldsExcludeFilter() {
-        return p -> p.startsWith(ClusterGetSettingsResponse.TRANSIENT_FIELD)
+        return p -> p.startsWith(RestClusterGetSettingsResponse.TRANSIENT_FIELD)
-            || p.startsWith(ClusterGetSettingsResponse.PERSISTENT_FIELD)
+            || p.startsWith(RestClusterGetSettingsResponse.PERSISTENT_FIELD)
-            || p.startsWith(ClusterGetSettingsResponse.DEFAULTS_FIELD);
+            || p.startsWith(RestClusterGetSettingsResponse.DEFAULTS_FIELD);
     }
 }

server/src/test/java/org/elasticsearch/rest/action/admin/cluster/RestClusterGetSettingsActionTests.java

@@ -8,7 +8,7 @@
 
 package org.elasticsearch.rest.action.admin.cluster;
 
-import org.elasticsearch.action.admin.cluster.settings.ClusterGetSettingsResponse;
+import org.elasticsearch.action.admin.cluster.settings.RestClusterGetSettingsResponse;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.Metadata;
 import org.elasticsearch.common.settings.ClusterSettings;
@@ -27,16 +27,16 @@ import java.util.stream.Stream;
 public class RestClusterGetSettingsActionTests extends ESTestCase {
 
     public void testFilterPersistentSettings() {
-        runTestFilterSettingsTest(Metadata.Builder::persistentSettings, ClusterGetSettingsResponse::getPersistentSettings);
+        runTestFilterSettingsTest(Metadata.Builder::persistentSettings, RestClusterGetSettingsResponse::getPersistentSettings);
     }
 
     public void testFilterTransientSettings() {
-        runTestFilterSettingsTest(Metadata.Builder::transientSettings, ClusterGetSettingsResponse::getTransientSettings);
+        runTestFilterSettingsTest(Metadata.Builder::transientSettings, RestClusterGetSettingsResponse::getTransientSettings);
     }
 
     private void runTestFilterSettingsTest(
         final BiConsumer<Metadata.Builder, Settings> md,
-        final Function<ClusterGetSettingsResponse, Settings> s
+        final Function<RestClusterGetSettingsResponse, Settings> s
     ) {
         final Metadata.Builder mdBuilder = new Metadata.Builder();
         final Settings settings = Settings.builder().put("foo.filtered", "bar").put("foo.non_filtered", "baz").build();
@@ -52,7 +52,7 @@ public class RestClusterGetSettingsActionTests extends ESTestCase {
             )
         ).collect(Collectors.toSet());
         final ClusterSettings clusterSettings = new ClusterSettings(Settings.EMPTY, settingsSet);
-        final ClusterGetSettingsResponse response = RestClusterGetSettingsAction.response(
+        final RestClusterGetSettingsResponse response = RestClusterGetSettingsAction.response(
             builder.build(),
             randomBoolean(),
             filter,