expose default settings on /_cluster/settings?defaults=true

core/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java

@@ -109,6 +109,20 @@ public final class ClusterSettings {
         return defaults;
     }
 
+    /**
+     * Returns a settings object that contains all clustersettings that are not
+     * already set in the given source.
+     */
+    public Settings diff(Settings source) {
+        Settings.Builder builder = Settings.builder();
+        for (Setting<?> setting : keySettings.values()) {
+            if (setting.exists(source) == false) {
+                builder.put(setting.getKey(), setting.getRaw(source));
+            }
+        }
+        return builder.build();
+    }
+
     public static Set<Setting<?>> BUILT_IN_CLUSTER_SETTINGS = Collections.unmodifiableSet(new HashSet<>(Arrays.asList(AwarenessAllocationDecider.CLUSTER_ROUTING_ALLOCATION_AWARENESS_ATTRIBUTE_SETTING,
     AwarenessAllocationDecider.CLUSTER_ROUTING_ALLOCATION_AWARENESS_FORCE_GROUP_SETTING,
     BalancedShardsAllocator.INDEX_BALANCE_FACTOR_SETTING,
@@ -167,4 +181,5 @@ public final class ClusterSettings {
     TransportService.TRACE_LOG_INCLUDE_SETTING,
     TransportCloseIndexAction.CLUSTER_INDICES_CLOSE_ENABLE_SETTING,
     ShardsLimitAllocationDecider.CLUSTER_TOTAL_SHARDS_PER_NODE_SETTING)));
+
 }

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

@@ -23,19 +23,27 @@ import org.elasticsearch.action.admin.cluster.state.ClusterStateRequest;
 import org.elasticsearch.action.admin.cluster.state.ClusterStateResponse;
 import org.elasticsearch.client.Client;
 import org.elasticsearch.client.Requests;
+import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.common.inject.Inject;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.rest.*;
 import org.elasticsearch.rest.action.support.RestBuilderListener;
 
+import java.io.IOException;
+
 /**
  */
 public class RestClusterGetSettingsAction extends BaseRestHandler {
 
+    private final ClusterSettings clusterSettings;
+
     @Inject
-    public RestClusterGetSettingsAction(Settings settings, RestController controller, Client client) {
+    public RestClusterGetSettingsAction(Settings settings, RestController controller, Client client, ClusterSettings clusterSettings) {
         super(settings, controller, client);
+        this.clusterSettings = clusterSettings;
         controller.registerHandler(RestRequest.Method.GET, "/_cluster/settings", this);
     }
 
@@ -44,24 +52,34 @@ public class RestClusterGetSettingsAction extends BaseRestHandler {
         ClusterStateRequest clusterStateRequest = Requests.clusterStateRequest()
                 .routingTable(false)
                 .nodes(false);
+        final boolean renderDefaults = request.paramAsBoolean("defaults", false);
         clusterStateRequest.local(request.paramAsBoolean("local", clusterStateRequest.local()));
         client.admin().cluster().state(clusterStateRequest, new RestBuilderListener<ClusterStateResponse>(channel) {
             @Override
             public RestResponse buildResponse(ClusterStateResponse response, XContentBuilder builder) throws Exception {
-                builder.startObject();
+                return new BytesRestResponse(RestStatus.OK, renderResponse(clusterSettings, response.getState(), renderDefaults, builder, request));
-
-                builder.startObject("persistent");
-                response.getState().metaData().persistentSettings().toXContent(builder, request);
-                builder.endObject();
-
-                builder.startObject("transient");
-                response.getState().metaData().transientSettings().toXContent(builder, request);
-                builder.endObject();
-
-                builder.endObject();
-
-                return new BytesRestResponse(RestStatus.OK, builder);
             }
         });
     }
+
+    private static XContentBuilder renderResponse(ClusterSettings settings, ClusterState state, boolean renderDefaults, XContentBuilder builder, ToXContent.Params params) throws IOException {
+        builder.startObject();
+
+        builder.startObject("persistent");
+        state.metaData().persistentSettings().toXContent(builder, params);
+        builder.endObject();
+
+        builder.startObject("transient");
+        state.metaData().transientSettings().toXContent(builder, params);
+        builder.endObject();
+
+        if (renderDefaults) {
+            builder.startObject("defaults");
+            settings.diff(state.metaData().settings()).toXContent(builder, params);
+            builder.endObject();
+        }
+
+        builder.endObject();
+        return builder;
+    }
 }

core/src/test/java/org/elasticsearch/common/settings/ClusterSettingsTests.java

@@ -0,0 +1,57 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.elasticsearch.common.settings;
+
+import org.elasticsearch.cluster.routing.allocation.decider.FilterAllocationDecider;
+import org.elasticsearch.cluster.routing.allocation.decider.ShardsLimitAllocationDecider;
+import org.elasticsearch.test.ESTestCase;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.HashSet;
+
+/**
+ */
+public class ClusterSettingsTests extends ESTestCase {
+
+    public void testGet() {
+        ClusterSettings settings = new ClusterSettings();
+        Setting setting = settings.get("cluster.routing.allocation.require.value");
+        assertEquals(setting, FilterAllocationDecider.CLUSTER_ROUTING_REQUIRE_GROUP_SETTING);
+
+        setting = settings.get("cluster.routing.allocation.total_shards_per_node");
+        assertEquals(setting, ShardsLimitAllocationDecider.CLUSTER_TOTAL_SHARDS_PER_NODE_SETTING);
+    }
+
+    public void testIsDynamic(){
+        ClusterSettings settings = new ClusterSettings(new HashSet<>(Arrays.asList(Setting.intSetting("foo.bar", 1, true, Setting.Scope.Cluster), Setting.intSetting("foo.bar.baz", 1, false, Setting.Scope.Cluster))));
+        assertFalse(settings.hasDynamicSetting("foo.bar.baz"));
+        assertTrue(settings.hasDynamicSetting("foo.bar"));
+        assertNotNull(settings.get("foo.bar.baz"));
+    }
+
+    public void testDiff() throws IOException {
+        Setting<Integer> foobarbaz = Setting.intSetting("foo.bar.baz", 1, false, Setting.Scope.Cluster);
+        Setting<Integer> foobar = Setting.intSetting("foo.bar", 1, true, Setting.Scope.Cluster);
+        ClusterSettings settings = new ClusterSettings(new HashSet<>(Arrays.asList(foobar, foobarbaz)));
+        Settings diff = settings.diff(Settings.builder().put("foo.bar", 5).build());
+        assertEquals(diff.getAsMap().size(), 1);
+        assertEquals(diff.getAsInt("foo.bar.baz", null), Integer.valueOf(1));
+    }
+}