Delegate toXContent logic from ClusterState to its member classes (#54192)

Backport of #52743

Co-authored-by: Yannick Welsch <yannick@welsch.lu>

server/src/main/java/org/elasticsearch/cluster/ClusterState.java

@@ -19,7 +19,6 @@
 
 package org.elasticsearch.cluster;
 
-import com.carrotsearch.hppc.cursors.IntObjectCursor;
 import com.carrotsearch.hppc.cursors.ObjectCursor;
 import com.carrotsearch.hppc.cursors.ObjectObjectCursor;
 
@@ -31,8 +30,6 @@ import org.elasticsearch.cluster.coordination.CoordinationMetaData;
 import org.elasticsearch.cluster.coordination.CoordinationMetaData.VotingConfiguration;
 import org.elasticsearch.cluster.coordination.CoordinationMetaData.VotingConfigExclusion;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
-import org.elasticsearch.cluster.metadata.IndexTemplateMetaData;
-import org.elasticsearch.cluster.metadata.MappingMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
@@ -45,10 +42,8 @@ import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.UUIDs;
-import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.collect.ImmutableOpenMap;
-import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.io.stream.NamedWriteableAwareStreamInput;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
@@ -58,13 +53,11 @@ import org.elasticsearch.common.io.stream.VersionedNamedWriteable;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.ToXContentFragment;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.discovery.Discovery;
 
 import java.io.IOException;
 import java.util.EnumSet;
 import java.util.HashMap;
-import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
@@ -492,101 +485,7 @@ public class ClusterState implements ToXContentFragment, Diffable<ClusterState>
 
         // meta data
         if (metrics.contains(Metric.METADATA)) {
-            builder.startObject("metadata");
+            metaData.toXContent(builder, params);
-            builder.field("cluster_uuid", metaData().clusterUUID());
-
-            builder.startObject("cluster_coordination");
-            coordinationMetaData().toXContent(builder, params);
-            builder.endObject();
-
-            builder.startObject("templates");
-            for (ObjectCursor<IndexTemplateMetaData> cursor : metaData().templates().values()) {
-                IndexTemplateMetaData templateMetaData = cursor.value;
-                builder.startObject(templateMetaData.name());
-
-                builder.field("index_patterns", templateMetaData.patterns());
-                builder.field("order", templateMetaData.order());
-
-                builder.startObject("settings");
-                Settings settings = templateMetaData.settings();
-                settings.toXContent(builder, params);
-                builder.endObject();
-
-                builder.startObject("mappings");
-                for (ObjectObjectCursor<String, CompressedXContent> cursor1 : templateMetaData.mappings()) {
-                    Map<String, Object> mapping = XContentHelper.convertToMap(new BytesArray(cursor1.value.uncompressed()), false).v2();
-                    if (mapping.size() == 1 && mapping.containsKey(cursor1.key)) {
-                        // the type name is the root value, reduce it
-                        mapping = (Map<String, Object>) mapping.get(cursor1.key);
-                    }
-                    builder.field(cursor1.key);
-                    builder.map(mapping);
-                }
-                builder.endObject();
-
-
-                builder.endObject();
-            }
-            builder.endObject();
-
-            builder.startObject("indices");
-            for (IndexMetaData indexMetaData : metaData()) {
-                builder.startObject(indexMetaData.getIndex().getName());
-
-                builder.field("state", indexMetaData.getState().toString().toLowerCase(Locale.ENGLISH));
-
-                builder.startObject("settings");
-                Settings settings = indexMetaData.getSettings();
-                settings.toXContent(builder, params);
-                builder.endObject();
-
-                builder.startObject("mappings");
-                for (ObjectObjectCursor<String, MappingMetaData> cursor : indexMetaData.getMappings()) {
-                    Map<String, Object> mapping = XContentHelper
-                            .convertToMap(new BytesArray(cursor.value.source().uncompressed()), false).v2();
-                    if (mapping.size() == 1 && mapping.containsKey(cursor.key)) {
-                        // the type name is the root value, reduce it
-                        mapping = (Map<String, Object>) mapping.get(cursor.key);
-                    }
-                    builder.field(cursor.key);
-                    builder.map(mapping);
-                }
-                builder.endObject();
-
-                builder.startArray("aliases");
-                for (ObjectCursor<String> cursor : indexMetaData.getAliases().keys()) {
-                    builder.value(cursor.value);
-                }
-                builder.endArray();
-
-                builder.startObject(IndexMetaData.KEY_PRIMARY_TERMS);
-                for (int shard = 0; shard < indexMetaData.getNumberOfShards(); shard++) {
-                    builder.field(Integer.toString(shard), indexMetaData.primaryTerm(shard));
-                }
-                builder.endObject();
-
-                builder.startObject(IndexMetaData.KEY_IN_SYNC_ALLOCATIONS);
-                for (IntObjectCursor<Set<String>> cursor : indexMetaData.getInSyncAllocationIds()) {
-                    builder.startArray(String.valueOf(cursor.key));
-                    for (String allocationId : cursor.value) {
-                        builder.value(allocationId);
-                    }
-                    builder.endArray();
-                }
-                builder.endObject();
-
-                // index metadata
-                builder.endObject();
-            }
-            builder.endObject();
-
-            for (ObjectObjectCursor<String, MetaData.Custom> cursor : metaData.customs()) {
-                builder.startObject(cursor.key);
-                cursor.value.toXContent(builder, params);
-                builder.endObject();
-            }
-
-            builder.endObject();
         }
 
         // routing table

server/src/main/java/org/elasticsearch/cluster/metadata/AliasMetaData.java

@@ -394,6 +394,8 @@ public class AliasMetaData extends AbstractDiffable<AliasMetaData> implements To
                         builder.indexRouting(parser.text());
                     } else if ("search_routing".equals(currentFieldName) || "searchRouting".equals(currentFieldName)) {
                         builder.searchRouting(parser.text());
+                    } else if ("filter".equals(currentFieldName)) {
+                        builder.filter(new CompressedXContent(parser.binaryValue()));
                     }
                 } else if (token == XContentParser.Token.START_ARRAY) {
                     parser.skipChildren();

server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetaData.java

@@ -65,6 +65,7 @@ import java.time.ZonedDateTime;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.EnumSet;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
@@ -73,6 +74,7 @@ import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
 
+import static org.elasticsearch.cluster.metadata.MetaData.CONTEXT_MODE_PARAM;
 import static org.elasticsearch.cluster.node.DiscoveryNodeFilters.IP_VALIDATOR;
 import static org.elasticsearch.cluster.node.DiscoveryNodeFilters.OpType.AND;
 import static org.elasticsearch.cluster.node.DiscoveryNodeFilters.OpType.OR;
@@ -1280,6 +1282,9 @@ public class IndexMetaData implements Diffable<IndexMetaData>, ToXContentFragmen
         }
 
         public static void toXContent(IndexMetaData indexMetaData, XContentBuilder builder, ToXContent.Params params) throws IOException {
+            MetaData.XContentContext context = MetaData.XContentContext.valueOf(
+                params.param(CONTEXT_MODE_PARAM, MetaData.CONTEXT_MODE_API));
+
             builder.startObject(indexMetaData.getIndex().getName());
 
             builder.field(KEY_VERSION, indexMetaData.getVersion());
@@ -1287,14 +1292,20 @@ public class IndexMetaData implements Diffable<IndexMetaData>, ToXContentFragmen
             builder.field(KEY_SETTINGS_VERSION, indexMetaData.getSettingsVersion());
             builder.field(KEY_ALIASES_VERSION, indexMetaData.getAliasesVersion());
             builder.field(KEY_ROUTING_NUM_SHARDS, indexMetaData.getRoutingNumShards());
+
             builder.field(KEY_STATE, indexMetaData.getState().toString().toLowerCase(Locale.ENGLISH));
 
             boolean binary = params.paramAsBoolean("binary", false);
 
             builder.startObject(KEY_SETTINGS);
+            if (context != MetaData.XContentContext.API) {
                 indexMetaData.getSettings().toXContent(builder, new MapParams(Collections.singletonMap("flat_settings", "true")));
+            } else {
+                indexMetaData.getSettings().toXContent(builder, params);
+            }
             builder.endObject();
 
+            if (context != MetaData.XContentContext.API) {
                 builder.startArray(KEY_MAPPINGS);
                 for (ObjectObjectCursor<String, MappingMetaData> cursor : indexMetaData.getMappings()) {
                     if (binary) {
@@ -1304,12 +1315,27 @@ public class IndexMetaData implements Diffable<IndexMetaData>, ToXContentFragmen
                     }
                 }
                 builder.endArray();
+            } else {
+                builder.startObject(KEY_MAPPINGS);
+                for (ObjectObjectCursor<String, MappingMetaData> cursor : indexMetaData.getMappings()) {
+                    Map<String, Object> mapping = XContentHelper
+                        .convertToMap(new BytesArray(cursor.value.source().uncompressed()), false).v2();
+                    if (mapping.size() == 1 && mapping.containsKey(cursor.key)) {
+                        // the type name is the root value, reduce it
+                        mapping = (Map<String, Object>) mapping.get(cursor.key);
+                    }
+                    builder.field(cursor.key);
+                    builder.map(mapping);
+                }
+                builder.endObject();
+            }
 
             for (ObjectObjectCursor<String, DiffableStringMap> cursor : indexMetaData.customData) {
                 builder.field(cursor.key);
                 builder.map(cursor.value);
             }
 
+            if (context != MetaData.XContentContext.API) {
                 builder.startObject(KEY_ALIASES);
                 for (ObjectCursor<AliasMetaData> cursor : indexMetaData.getAliases().values()) {
                     AliasMetaData.Builder.toXContent(cursor.value, builder, params);
@@ -1321,6 +1347,20 @@ public class IndexMetaData implements Diffable<IndexMetaData>, ToXContentFragmen
                     builder.value(indexMetaData.primaryTerm(i));
                 }
                 builder.endArray();
+            } else {
+                builder.startArray(KEY_ALIASES);
+                for (ObjectCursor<String> cursor : indexMetaData.getAliases().keys()) {
+                    builder.value(cursor.value);
+                }
+                builder.endArray();
+
+                builder.startObject(IndexMetaData.KEY_PRIMARY_TERMS);
+                for (int shard = 0; shard < indexMetaData.getNumberOfShards(); shard++) {
+                    builder.field(Integer.toString(shard), indexMetaData.primaryTerm(shard));
+                }
+                builder.endObject();
+            }
+
 
             builder.startObject(KEY_IN_SYNC_ALLOCATIONS);
             for (IntObjectCursor<Set<String>> cursor : indexMetaData.inSyncAllocationIds) {
@@ -1506,7 +1546,13 @@ public class IndexMetaData implements Diffable<IndexMetaData>, ToXContentFragmen
         return builder.build();
     }
 
-    private static final ToXContent.Params FORMAT_PARAMS = new MapParams(Collections.singletonMap("binary", "true"));
+    private static final ToXContent.Params FORMAT_PARAMS;
+    static {
+        Map<String, String> params = new HashMap<>(2);
+        params.put("binary", "true");
+        params.put(MetaData.CONTEXT_MODE_PARAM, MetaData.CONTEXT_MODE_GATEWAY);
+        FORMAT_PARAMS = new MapParams(params);
+    }
 
     /**
      * State format for {@link IndexMetaData} to write to and load from disk

server/src/main/java/org/elasticsearch/cluster/metadata/IndexTemplateMetaData.java

@@ -51,6 +51,8 @@ import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
 
+import static org.elasticsearch.cluster.metadata.MetaData.CONTEXT_MODE_PARAM;
+
 public class IndexTemplateMetaData extends AbstractDiffable<IndexTemplateMetaData> {
 
     private static final DeprecationLogger deprecationLogger = new DeprecationLogger(LogManager.getLogger(IndexTemplateMetaData.class));
@@ -390,6 +392,8 @@ public class IndexTemplateMetaData extends AbstractDiffable<IndexTemplateMetaDat
                                             XContentBuilder builder,
                                             ToXContent.Params params,
                                             boolean includeTypeName) throws IOException {
+            MetaData.XContentContext context = params.param(CONTEXT_MODE_PARAM) != null ? MetaData.XContentContext.valueOf(
+                params.param(CONTEXT_MODE_PARAM)) : null;
 
             builder.field("order", indexTemplateMetaData.order());
             if (indexTemplateMetaData.version() != null) {
@@ -401,7 +405,19 @@ public class IndexTemplateMetaData extends AbstractDiffable<IndexTemplateMetaDat
             indexTemplateMetaData.settings().toXContent(builder, params);
             builder.endObject();
 
-            if (params.paramAsBoolean("reduce_mappings", false)) {
+            if (context == MetaData.XContentContext.API) {
+                builder.startObject("mappings");
+                for (ObjectObjectCursor<String, CompressedXContent> cursor1 : indexTemplateMetaData.mappings()) {
+                    Map<String, Object> mapping = XContentHelper.convertToMap(new BytesArray(cursor1.value.uncompressed()), false).v2();
+                    if (mapping.size() == 1 && mapping.containsKey(cursor1.key)) {
+                        // the type name is the root value, reduce it
+                        mapping = (Map<String, Object>) mapping.get(cursor1.key);
+                    }
+                    builder.field(cursor1.key);
+                    builder.map(mapping);
+                }
+                builder.endObject();
+            } else if (params.paramAsBoolean("reduce_mappings", false)) {
                 // The parameter include_type_name is only ever used in the REST API, where reduce_mappings is
                 // always set to true. We therefore only check for include_type_name in this branch.
                 if (includeTypeName == false) {

server/src/main/java/org/elasticsearch/cluster/metadata/MetaData.java

@@ -53,10 +53,8 @@ import org.elasticsearch.common.xcontent.NamedObjectNotFoundException;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.ToXContentFragment;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.common.xcontent.XContentParser;
-import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.gateway.MetaDataStateFormat;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.IndexNotFoundException;
@@ -158,6 +156,8 @@ public class MetaData implements Iterable<IndexMetaData>, Diffable<MetaData>, To
 
     public static final String CONTEXT_MODE_GATEWAY = XContentContext.GATEWAY.toString();
 
+    public static final String CONTEXT_MODE_API = XContentContext.API.toString();
+
     public static final String GLOBAL_STATE_FILE_PREFIX = "global-";
 
     private static final NamedDiffableValueSerializer<Custom> CUSTOM_VALUE_SERIALIZER = new NamedDiffableValueSerializer<>(Custom.class);
@@ -1447,20 +1447,16 @@ public class MetaData implements Iterable<IndexMetaData>, Diffable<MetaData>, To
             return aliasAndIndexLookup;
         }
 
-        public static String toXContent(MetaData metaData) throws IOException {
+        public static void toXContent(MetaData metaData, XContentBuilder builder, ToXContent.Params params) throws IOException {
-            XContentBuilder builder = XContentFactory.contentBuilder(XContentType.JSON);
+            XContentContext context = XContentContext.valueOf(params.param(CONTEXT_MODE_PARAM, CONTEXT_MODE_API));
-            builder.startObject();
+
-            toXContent(metaData, builder, ToXContent.EMPTY_PARAMS);
+            if (context == XContentContext.API) {
-            builder.endObject();
+                builder.startObject("metadata");
-            return Strings.toString(builder);
+            } else {
+                builder.startObject("meta-data");
+                builder.field("version", metaData.version());
             }
 
-        public static void toXContent(MetaData metaData, XContentBuilder builder, ToXContent.Params params) throws IOException {
-            XContentContext context = XContentContext.valueOf(params.param(CONTEXT_MODE_PARAM, "API"));
-
-            builder.startObject("meta-data");
-
-            builder.field("version", metaData.version());
             builder.field("cluster_uuid", metaData.clusterUUID);
             builder.field("cluster_uuid_committed", metaData.clusterUUIDCommitted);
 
@@ -1468,25 +1464,19 @@ public class MetaData implements Iterable<IndexMetaData>, Diffable<MetaData>, To
             metaData.coordinationMetaData().toXContent(builder, params);
             builder.endObject();
 
-            if (!metaData.persistentSettings().isEmpty()) {
+            if (context != XContentContext.API && !metaData.persistentSettings().isEmpty()) {
                 builder.startObject("settings");
                 metaData.persistentSettings().toXContent(builder, new MapParams(Collections.singletonMap("flat_settings", "true")));
                 builder.endObject();
             }
 
-            if (context == XContentContext.API && !metaData.transientSettings().isEmpty()) {
-                builder.startObject("transient_settings");
-                metaData.transientSettings().toXContent(builder, new MapParams(Collections.singletonMap("flat_settings", "true")));
-                builder.endObject();
-            }
-
             builder.startObject("templates");
             for (ObjectCursor<IndexTemplateMetaData> cursor : metaData.templates().values()) {
                 IndexTemplateMetaData.Builder.toXContentWithTypes(cursor.value, builder, params);
             }
             builder.endObject();
 
-            if (context == XContentContext.API && !metaData.indices().isEmpty()) {
+            if (context == XContentContext.API) {
                 builder.startObject("indices");
                 for (IndexMetaData indexMetaData : metaData) {
                     IndexMetaData.Builder.toXContent(indexMetaData, builder, params);

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

@@ -25,9 +25,11 @@ import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.client.Requests;
 import org.elasticsearch.client.node.NodeClient;
 import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.settings.SettingsFilter;
+import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.rest.BaseRestHandler;
 import org.elasticsearch.rest.BytesRestResponse;
@@ -44,6 +46,7 @@ import java.util.List;
 import java.util.Set;
 
 import static java.util.Arrays.asList;
+import static java.util.Collections.singletonMap;
 import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
@@ -109,7 +112,9 @@ public class RestClusterStateAction extends BaseRestHandler {
                     builder.field(Fields.WAIT_FOR_TIMED_OUT, response.isWaitForTimedOut());
                 }
                 builder.field(Fields.CLUSTER_NAME, response.getClusterName().value());
-                response.getState().toXContent(builder, request);
+                ToXContent.Params params = new ToXContent.DelegatingMapParams(
+                    singletonMap(MetaData.CONTEXT_MODE_PARAM, MetaData.CONTEXT_MODE_API), request);
+                response.getState().toXContent(builder, params);
                 builder.endObject();
                 return new BytesRestResponse(RestStatus.OK, builder);
             }

server/src/test/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponseTests.java

@@ -84,6 +84,7 @@ public class ClusterRerouteResponseTests extends ESTestCase {
                     "    },\n" +
                     "    \"metadata\" : {\n" +
                     "      \"cluster_uuid\" : \"_na_\",\n" +
+                    "      \"cluster_uuid_committed\" : false,\n" +
                     "      \"cluster_coordination\" : {\n" +
                     "        \"term\" : 0,\n" +
                     "        \"last_committed_config\" : [ ],\n" +
@@ -93,6 +94,11 @@ public class ClusterRerouteResponseTests extends ESTestCase {
                     "      \"templates\" : { },\n" +
                     "      \"indices\" : {\n" +
                     "        \"index\" : {\n" +
+                    "          \"version\" : 1,\n" +
+                    "          \"mapping_version\" : 1,\n" +
+                    "          \"settings_version\" : 1,\n" +
+                    "          \"aliases_version\" : 1,\n" +
+                    "          \"routing_num_shards\" : 1,\n" +
                     "          \"state\" : \"open\",\n" +
                     "          \"settings\" : {\n" +
                     "            \"index\" : {\n" +
@@ -114,7 +120,8 @@ public class ClusterRerouteResponseTests extends ESTestCase {
                     "          },\n" +
                     "          \"in_sync_allocations\" : {\n" +
                     "            \"0\" : [ ]\n" +
-                    "          }\n" +
+                    "          },\n" +
+                    "          \"rollover_info\" : { }\n" +
                     "        }\n" +
                     "      },\n" +
                     "      \"index-graveyard\" : {\n" +
@@ -179,6 +186,7 @@ public class ClusterRerouteResponseTests extends ESTestCase {
                     "    \"cluster_uuid\" : \"_na_\",\n" +
                     "    \"metadata\" : {\n" +
                     "      \"cluster_uuid\" : \"_na_\",\n" +
+                    "      \"cluster_uuid_committed\" : false,\n" +
                     "      \"cluster_coordination\" : {\n" +
                     "        \"term\" : 0,\n" +
                     "        \"last_committed_config\" : [ ],\n" +
@@ -188,6 +196,11 @@ public class ClusterRerouteResponseTests extends ESTestCase {
                     "      \"templates\" : { },\n" +
                     "      \"indices\" : {\n" +
                     "        \"index\" : {\n" +
+                    "          \"version\" : 1,\n" +
+                    "          \"mapping_version\" : 1,\n" +
+                    "          \"settings_version\" : 1,\n" +
+                    "          \"aliases_version\" : 1,\n" +
+                    "          \"routing_num_shards\" : 1,\n" +
                     "          \"state\" : \"open\",\n" +
                     "          \"settings\" : {\n" +
                     "            \"index\" : {\n" +
@@ -204,7 +217,8 @@ public class ClusterRerouteResponseTests extends ESTestCase {
                     "          },\n" +
                     "          \"in_sync_allocations\" : {\n" +
                     "            \"0\" : [ ]\n" +
-                    "          }\n" +
+                    "          },\n" +
+                    "          \"rollover_info\" : { }\n" +
                     "        }\n" +
                     "      },\n" +
                     "      \"index-graveyard\" : {\n" +

server/src/test/java/org/elasticsearch/cluster/ClusterStateTests.java

@@ -19,14 +19,49 @@
 package org.elasticsearch.cluster;
 
 import org.elasticsearch.Version;
+import org.elasticsearch.action.admin.indices.rollover.RolloverInfo;
+import org.elasticsearch.cluster.block.ClusterBlock;
+import org.elasticsearch.cluster.block.ClusterBlockLevel;
+import org.elasticsearch.cluster.block.ClusterBlocks;
+import org.elasticsearch.cluster.coordination.CoordinationMetaData;
+import org.elasticsearch.cluster.metadata.AliasMetaData;
+import org.elasticsearch.cluster.metadata.IndexMetaData;
+import org.elasticsearch.cluster.metadata.IndexTemplateMetaData;
+import org.elasticsearch.cluster.metadata.MappingMetaData;
+import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.cluster.routing.IndexRoutingTable;
+import org.elasticsearch.cluster.routing.IndexShardRoutingTable;
+import org.elasticsearch.cluster.routing.RoutingTable;
+import org.elasticsearch.cluster.routing.ShardRoutingState;
+import org.elasticsearch.cluster.routing.TestShardRouting;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.collect.ImmutableOpenMap;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.transport.TransportAddress;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.json.JsonXContent;
+import org.elasticsearch.index.Index;
+import org.elasticsearch.index.shard.ShardId;
+import org.elasticsearch.rest.RestStatus;
 import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.TestCustomMetaData;
+
+import java.io.IOException;
+import java.net.InetAddress;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
 
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.emptySet;
+import static java.util.Collections.singletonMap;
+import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_VERSION_CREATED;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 
@@ -73,4 +108,751 @@ public class ClusterStateTests extends ESTestCase {
         final ImmutableOpenMap<String, ClusterState.Custom> map = mapBuilder.build();
         assertThat(expectThrows(NullPointerException.class, () -> builder.customs(map)).getMessage(), containsString(key));
     }
+
+    public void testToXContent() throws IOException {
+        final ClusterState clusterState = buildClusterState();
+
+        IndexRoutingTable index = clusterState.getRoutingTable().getIndicesRouting().get("index");
+
+        String ephemeralId = clusterState.getNodes().get("nodeId1").getEphemeralId();
+        String allocationId = index.getShards().get(1).getAllAllocationIds().iterator().next();
+
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        builder.startObject();
+        clusterState.toXContent(builder, new ToXContent.MapParams(singletonMap(MetaData.CONTEXT_MODE_PARAM, MetaData.CONTEXT_MODE_API)));
+        builder.endObject();
+
+        assertEquals("{\n" +
+            "  \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "  \"version\" : 0,\n" +
+            "  \"state_uuid\" : \"stateUUID\",\n" +
+            "  \"master_node\" : \"masterNodeId\",\n" +
+            "  \"blocks\" : {\n" +
+            "    \"global\" : {\n" +
+            "      \"1\" : {\n" +
+            "        \"description\" : \"description\",\n" +
+            "        \"retryable\" : true,\n" +
+            "        \"disable_state_persistence\" : true,\n" +
+            "        \"levels\" : [\n" +
+            "          \"read\",\n" +
+            "          \"write\",\n" +
+            "          \"metadata_read\",\n" +
+            "          \"metadata_write\"\n" +
+            "        ]\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"2\" : {\n" +
+            "          \"description\" : \"description2\",\n" +
+            "          \"retryable\" : false,\n" +
+            "          \"levels\" : [\n" +
+            "            \"read\",\n" +
+            "            \"write\",\n" +
+            "            \"metadata_read\",\n" +
+            "            \"metadata_write\"\n" +
+            "          ]\n" +
+            "        }\n" +
+            "      }\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"nodes\" : {\n" +
+            "    \"nodeId1\" : {\n" +
+            "      \"name\" : \"\",\n" +
+            "      \"ephemeral_id\" : \"" + ephemeralId + "\",\n" +
+            "      \"transport_address\" : \"127.0.0.1:111\",\n" +
+            "      \"attributes\" : { }\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"metadata\" : {\n" +
+            "    \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "    \"cluster_uuid_committed\" : false,\n" +
+            "    \"cluster_coordination\" : {\n" +
+            "      \"term\" : 1,\n" +
+            "      \"last_committed_config\" : [\n" +
+            "        \"commitedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"last_accepted_config\" : [\n" +
+            "        \"acceptedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"voting_config_exclusions\" : [\n" +
+            "        {\n" +
+            "          \"node_id\" : \"exlucdedNodeId\",\n" +
+            "          \"node_name\" : \"excludedNodeName\"\n" +
+            "        }\n" +
+            "      ]\n" +
+            "    },\n" +
+            "    \"templates\" : {\n" +
+            "      \"template\" : {\n" +
+            "        \"order\" : 0,\n" +
+            "        \"index_patterns\" : [\n" +
+            "          \"pattern1\",\n" +
+            "          \"pattern2\"\n" +
+            "        ],\n" +
+            "        \"settings\" : {\n" +
+            "          \"index\" : {\n" +
+            "            \"version\" : {\n" +
+            "              \"created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"key1\" : { }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : { }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"version\" : 1,\n" +
+            "        \"mapping_version\" : 1,\n" +
+            "        \"settings_version\" : 1,\n" +
+            "        \"aliases_version\" : 1,\n" +
+            "        \"routing_num_shards\" : 1,\n" +
+            "        \"state\" : \"open\",\n" +
+            "        \"settings\" : {\n" +
+            "          \"index\" : {\n" +
+            "            \"number_of_shards\" : \"1\",\n" +
+            "            \"number_of_replicas\" : \"2\",\n" +
+            "            \"version\" : {\n" +
+            "              \"created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"type1\" : {\n" +
+            "              \"key\" : \"value\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : [\n" +
+            "          \"alias\"\n" +
+            "        ],\n" +
+            "        \"primary_terms\" : {\n" +
+            "          \"0\" : 1\n" +
+            "        },\n" +
+            "        \"in_sync_allocations\" : {\n" +
+            "          \"0\" : [\n" +
+            "            \"allocationId\"\n" +
+            "          ]\n" +
+            "        },\n" +
+            "        \"rollover_info\" : {\n" +
+            "          \"rolloveAlias\" : {\n" +
+            "            \"met_conditions\" : { },\n" +
+            "            \"time\" : 1\n" +
+            "          }\n" +
+            "        }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"index-graveyard\" : {\n" +
+            "      \"tombstones\" : [ ]\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"routing_table\" : {\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"shards\" : {\n" +
+            "          \"1\" : [\n" +
+            "            {\n" +
+            "              \"state\" : \"STARTED\",\n" +
+            "              \"primary\" : true,\n" +
+            "              \"node\" : \"nodeId2\",\n" +
+            "              \"relocating_node\" : null,\n" +
+            "              \"shard\" : 1,\n" +
+            "              \"index\" : \"index\",\n" +
+            "              \"allocation_id\" : {\n" +
+            "                \"id\" : \"" + allocationId + "\"\n" +
+            "              }\n" +
+            "            }\n" +
+            "          ]\n" +
+            "        }\n" +
+            "      }\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"routing_nodes\" : {\n" +
+            "    \"unassigned\" : [ ],\n" +
+            "    \"nodes\" : {\n" +
+            "      \"nodeId2\" : [\n" +
+            "        {\n" +
+            "          \"state\" : \"STARTED\",\n" +
+            "          \"primary\" : true,\n" +
+            "          \"node\" : \"nodeId2\",\n" +
+            "          \"relocating_node\" : null,\n" +
+            "          \"shard\" : 1,\n" +
+            "          \"index\" : \"index\",\n" +
+            "          \"allocation_id\" : {\n" +
+            "            \"id\" : \"" + allocationId + "\"\n" +
+            "          }\n" +
+            "        }\n" +
+            "      ],\n" +
+            "      \"nodeId1\" : [ ]\n" +
+            "    }\n" +
+            "  }\n" +
+            "}", Strings.toString(builder));
+
+    }
+
+    public void testToXContent_FlatSettingTrue_ReduceMappingFalse() throws IOException {
+        Map<String, String> mapParams = new HashMap<String,String>(){{
+            put("flat_settings", "true");
+            put("reduce_mappings", "false");
+            put(MetaData.CONTEXT_MODE_PARAM, MetaData.CONTEXT_MODE_API);
+        }};
+
+        final ClusterState clusterState = buildClusterState();
+        IndexRoutingTable index = clusterState.getRoutingTable().getIndicesRouting().get("index");
+
+        String ephemeralId = clusterState.getNodes().get("nodeId1").getEphemeralId();
+        String allocationId = index.getShards().get(1).getAllAllocationIds().iterator().next();
+
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        builder.startObject();
+        clusterState.toXContent(builder, new ToXContent.MapParams(mapParams));
+        builder.endObject();
+
+        assertEquals("{\n" +
+            "  \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "  \"version\" : 0,\n" +
+            "  \"state_uuid\" : \"stateUUID\",\n" +
+            "  \"master_node\" : \"masterNodeId\",\n" +
+            "  \"blocks\" : {\n" +
+            "    \"global\" : {\n" +
+            "      \"1\" : {\n" +
+            "        \"description\" : \"description\",\n" +
+            "        \"retryable\" : true,\n" +
+            "        \"disable_state_persistence\" : true,\n" +
+            "        \"levels\" : [\n" +
+            "          \"read\",\n" +
+            "          \"write\",\n" +
+            "          \"metadata_read\",\n" +
+            "          \"metadata_write\"\n" +
+            "        ]\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"2\" : {\n" +
+            "          \"description\" : \"description2\",\n" +
+            "          \"retryable\" : false,\n" +
+            "          \"levels\" : [\n" +
+            "            \"read\",\n" +
+            "            \"write\",\n" +
+            "            \"metadata_read\",\n" +
+            "            \"metadata_write\"\n" +
+            "          ]\n" +
+            "        }\n" +
+            "      }\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"nodes\" : {\n" +
+            "    \"nodeId1\" : {\n" +
+            "      \"name\" : \"\",\n" +
+            "      \"ephemeral_id\" : \"" + ephemeralId + "\",\n" +
+            "      \"transport_address\" : \"127.0.0.1:111\",\n" +
+            "      \"attributes\" : { }\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"metadata\" : {\n" +
+            "    \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "    \"cluster_uuid_committed\" : false,\n" +
+            "    \"cluster_coordination\" : {\n" +
+            "      \"term\" : 1,\n" +
+            "      \"last_committed_config\" : [\n" +
+            "        \"commitedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"last_accepted_config\" : [\n" +
+            "        \"acceptedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"voting_config_exclusions\" : [\n" +
+            "        {\n" +
+            "          \"node_id\" : \"exlucdedNodeId\",\n" +
+            "          \"node_name\" : \"excludedNodeName\"\n" +
+            "        }\n" +
+            "      ]\n" +
+            "    },\n" +
+            "    \"templates\" : {\n" +
+            "      \"template\" : {\n" +
+            "        \"order\" : 0,\n" +
+            "        \"index_patterns\" : [\n" +
+            "          \"pattern1\",\n" +
+            "          \"pattern2\"\n" +
+            "        ],\n" +
+            "        \"settings\" : {\n" +
+            "          \"index.version.created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"key1\" : { }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : { }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"version\" : 1,\n" +
+            "        \"mapping_version\" : 1,\n" +
+            "        \"settings_version\" : 1,\n" +
+            "        \"aliases_version\" : 1,\n" +
+            "        \"routing_num_shards\" : 1,\n" +
+            "        \"state\" : \"open\",\n" +
+            "        \"settings\" : {\n" +
+            "          \"index.number_of_replicas\" : \"2\",\n" +
+            "          \"index.number_of_shards\" : \"1\",\n" +
+            "          \"index.version.created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"type1\" : {\n" +
+            "              \"key\" : \"value\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : [\n" +
+            "          \"alias\"\n" +
+            "        ],\n" +
+            "        \"primary_terms\" : {\n" +
+            "          \"0\" : 1\n" +
+            "        },\n" +
+            "        \"in_sync_allocations\" : {\n" +
+            "          \"0\" : [\n" +
+            "            \"allocationId\"\n" +
+            "          ]\n" +
+            "        },\n" +
+            "        \"rollover_info\" : {\n" +
+            "          \"rolloveAlias\" : {\n" +
+            "            \"met_conditions\" : { },\n" +
+            "            \"time\" : 1\n" +
+            "          }\n" +
+            "        }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"index-graveyard\" : {\n" +
+            "      \"tombstones\" : [ ]\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"routing_table\" : {\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"shards\" : {\n" +
+            "          \"1\" : [\n" +
+            "            {\n" +
+            "              \"state\" : \"STARTED\",\n" +
+            "              \"primary\" : true,\n" +
+            "              \"node\" : \"nodeId2\",\n" +
+            "              \"relocating_node\" : null,\n" +
+            "              \"shard\" : 1,\n" +
+            "              \"index\" : \"index\",\n" +
+            "              \"allocation_id\" : {\n" +
+            "                \"id\" : \"" + allocationId + "\"\n" +
+            "              }\n" +
+            "            }\n" +
+            "          ]\n" +
+            "        }\n" +
+            "      }\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"routing_nodes\" : {\n" +
+            "    \"unassigned\" : [ ],\n" +
+            "    \"nodes\" : {\n" +
+            "      \"nodeId2\" : [\n" +
+            "        {\n" +
+            "          \"state\" : \"STARTED\",\n" +
+            "          \"primary\" : true,\n" +
+            "          \"node\" : \"nodeId2\",\n" +
+            "          \"relocating_node\" : null,\n" +
+            "          \"shard\" : 1,\n" +
+            "          \"index\" : \"index\",\n" +
+            "          \"allocation_id\" : {\n" +
+            "            \"id\" : \"" + allocationId + "\"\n" +
+            "          }\n" +
+            "        }\n" +
+            "      ],\n" +
+            "      \"nodeId1\" : [ ]\n" +
+            "    }\n" +
+            "  }\n" +
+            "}", Strings.toString(builder));
+
+    }
+
+    public void testToXContent_FlatSettingFalse_ReduceMappingTrue() throws IOException {
+        Map<String, String> mapParams = new HashMap<String,String>(){{
+            put("flat_settings", "false");
+            put("reduce_mappings", "true");
+            put(MetaData.CONTEXT_MODE_PARAM, MetaData.CONTEXT_MODE_API);
+        }};
+
+        final ClusterState clusterState = buildClusterState();
+
+        IndexRoutingTable index = clusterState.getRoutingTable().getIndicesRouting().get("index");
+
+        String ephemeralId = clusterState.getNodes().get("nodeId1").getEphemeralId();
+        String allocationId = index.getShards().get(1).getAllAllocationIds().iterator().next();
+
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        builder.startObject();
+        clusterState.toXContent(builder, new ToXContent.MapParams(mapParams));
+        builder.endObject();
+
+        assertEquals("{\n" +
+            "  \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "  \"version\" : 0,\n" +
+            "  \"state_uuid\" : \"stateUUID\",\n" +
+            "  \"master_node\" : \"masterNodeId\",\n" +
+            "  \"blocks\" : {\n" +
+            "    \"global\" : {\n" +
+            "      \"1\" : {\n" +
+            "        \"description\" : \"description\",\n" +
+            "        \"retryable\" : true,\n" +
+            "        \"disable_state_persistence\" : true,\n" +
+            "        \"levels\" : [\n" +
+            "          \"read\",\n" +
+            "          \"write\",\n" +
+            "          \"metadata_read\",\n" +
+            "          \"metadata_write\"\n" +
+            "        ]\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"2\" : {\n" +
+            "          \"description\" : \"description2\",\n" +
+            "          \"retryable\" : false,\n" +
+            "          \"levels\" : [\n" +
+            "            \"read\",\n" +
+            "            \"write\",\n" +
+            "            \"metadata_read\",\n" +
+            "            \"metadata_write\"\n" +
+            "          ]\n" +
+            "        }\n" +
+            "      }\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"nodes\" : {\n" +
+            "    \"nodeId1\" : {\n" +
+            "      \"name\" : \"\",\n" +
+            "      \"ephemeral_id\" : \"" + ephemeralId + "\",\n" +
+            "      \"transport_address\" : \"127.0.0.1:111\",\n" +
+            "      \"attributes\" : { }\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"metadata\" : {\n" +
+            "    \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "    \"cluster_uuid_committed\" : false,\n" +
+            "    \"cluster_coordination\" : {\n" +
+            "      \"term\" : 1,\n" +
+            "      \"last_committed_config\" : [\n" +
+            "        \"commitedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"last_accepted_config\" : [\n" +
+            "        \"acceptedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"voting_config_exclusions\" : [\n" +
+            "        {\n" +
+            "          \"node_id\" : \"exlucdedNodeId\",\n" +
+            "          \"node_name\" : \"excludedNodeName\"\n" +
+            "        }\n" +
+            "      ]\n" +
+            "    },\n" +
+            "    \"templates\" : {\n" +
+            "      \"template\" : {\n" +
+            "        \"order\" : 0,\n" +
+            "        \"index_patterns\" : [\n" +
+            "          \"pattern1\",\n" +
+            "          \"pattern2\"\n" +
+            "        ],\n" +
+            "        \"settings\" : {\n" +
+            "          \"index\" : {\n" +
+            "            \"version\" : {\n" +
+            "              \"created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"key1\" : { }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : { }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"version\" : 1,\n" +
+            "        \"mapping_version\" : 1,\n" +
+            "        \"settings_version\" : 1,\n" +
+            "        \"aliases_version\" : 1,\n" +
+            "        \"routing_num_shards\" : 1,\n" +
+            "        \"state\" : \"open\",\n" +
+            "        \"settings\" : {\n" +
+            "          \"index\" : {\n" +
+            "            \"number_of_shards\" : \"1\",\n" +
+            "            \"number_of_replicas\" : \"2\",\n" +
+            "            \"version\" : {\n" +
+            "              \"created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"type1\" : {\n" +
+            "              \"key\" : \"value\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : [\n" +
+            "          \"alias\"\n" +
+            "        ],\n" +
+            "        \"primary_terms\" : {\n" +
+            "          \"0\" : 1\n" +
+            "        },\n" +
+            "        \"in_sync_allocations\" : {\n" +
+            "          \"0\" : [\n" +
+            "            \"allocationId\"\n" +
+            "          ]\n" +
+            "        },\n" +
+            "        \"rollover_info\" : {\n" +
+            "          \"rolloveAlias\" : {\n" +
+            "            \"met_conditions\" : { },\n" +
+            "            \"time\" : 1\n" +
+            "          }\n" +
+            "        }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"index-graveyard\" : {\n" +
+            "      \"tombstones\" : [ ]\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"routing_table\" : {\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"shards\" : {\n" +
+            "          \"1\" : [\n" +
+            "            {\n" +
+            "              \"state\" : \"STARTED\",\n" +
+            "              \"primary\" : true,\n" +
+            "              \"node\" : \"nodeId2\",\n" +
+            "              \"relocating_node\" : null,\n" +
+            "              \"shard\" : 1,\n" +
+            "              \"index\" : \"index\",\n" +
+            "              \"allocation_id\" : {\n" +
+            "                \"id\" : \"" + allocationId + "\"\n" +
+            "              }\n" +
+            "            }\n" +
+            "          ]\n" +
+            "        }\n" +
+            "      }\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"routing_nodes\" : {\n" +
+            "    \"unassigned\" : [ ],\n" +
+            "    \"nodes\" : {\n" +
+            "      \"nodeId2\" : [\n" +
+            "        {\n" +
+            "          \"state\" : \"STARTED\",\n" +
+            "          \"primary\" : true,\n" +
+            "          \"node\" : \"nodeId2\",\n" +
+            "          \"relocating_node\" : null,\n" +
+            "          \"shard\" : 1,\n" +
+            "          \"index\" : \"index\",\n" +
+            "          \"allocation_id\" : {\n" +
+            "            \"id\" : \"" + allocationId + "\"\n" +
+            "          }\n" +
+            "        }\n" +
+            "      ],\n" +
+            "      \"nodeId1\" : [ ]\n" +
+            "    }\n" +
+            "  }\n" +
+            "}", Strings.toString(builder));
+
+    }
+
+    public void testToXContentSameTypeName() throws IOException {
+        final ClusterState clusterState = ClusterState.builder(ClusterName.DEFAULT)
+                                                    .stateUUID("stateUUID")
+                                                    .metaData(MetaData.builder()
+                                                        .clusterUUID("clusterUUID")
+                                                        .coordinationMetaData(CoordinationMetaData.builder()
+                                                            .build())
+                                                        .put(IndexMetaData.builder("index")
+                                                            .state(IndexMetaData.State.OPEN)
+                                                            .settings(Settings.builder()
+                                                                .put(SETTING_VERSION_CREATED, Version.CURRENT.id))
+                                                            .putMapping(new MappingMetaData("type",
+                                                                // the type name is the root value,
+                                                                // the original logic in ClusterState.toXContent will reduce
+                                                                new HashMap<String,Object>(){{
+                                                                    put("type", new HashMap<String, Object>(){{
+                                                                        put("key", "value");
+                                                                    }});
+                                                                }}))
+                                                            .numberOfShards(1)
+                                                            .primaryTerm(0, 1L)
+                                                            .numberOfReplicas(2)))
+                                                    .build();
+
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        builder.startObject();
+        clusterState.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        builder.endObject();
+
+        assertEquals("{\n" +
+            "  \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "  \"version\" : 0,\n" +
+            "  \"state_uuid\" : \"stateUUID\",\n" +
+            "  \"master_node\" : null,\n" +
+            "  \"blocks\" : { },\n" +
+            "  \"nodes\" : { },\n" +
+            "  \"metadata\" : {\n" +
+            "    \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "    \"cluster_uuid_committed\" : false,\n" +
+            "    \"cluster_coordination\" : {\n" +
+            "      \"term\" : 0,\n" +
+            "      \"last_committed_config\" : [ ],\n" +
+            "      \"last_accepted_config\" : [ ],\n" +
+            "      \"voting_config_exclusions\" : [ ]\n" +
+            "    },\n" +
+            "    \"templates\" : { },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"version\" : 2,\n" +
+            "        \"mapping_version\" : 1,\n" +
+            "        \"settings_version\" : 1,\n" +
+            "        \"aliases_version\" : 1,\n" +
+            "        \"routing_num_shards\" : 1,\n" +
+            "        \"state\" : \"open\",\n" +
+            "        \"settings\" : {\n" +
+            "          \"index\" : {\n" +
+            "            \"number_of_shards\" : \"1\",\n" +
+            "            \"number_of_replicas\" : \"2\",\n" +
+            "            \"version\" : {\n" +
+            "              \"created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"key\" : \"value\"\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : [ ],\n" +
+            "        \"primary_terms\" : {\n" +
+            "          \"0\" : 1\n" +
+            "        },\n" +
+            "        \"in_sync_allocations\" : {\n" +
+            "          \"0\" : [ ]\n" +
+            "        },\n" +
+            "        \"rollover_info\" : { }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"index-graveyard\" : {\n" +
+            "      \"tombstones\" : [ ]\n" +
+            "    }\n" +
+            "  },\n" +
+            "  \"routing_table\" : {\n" +
+            "    \"indices\" : { }\n" +
+            "  },\n" +
+            "  \"routing_nodes\" : {\n" +
+            "    \"unassigned\" : [ ],\n" +
+            "    \"nodes\" : { }\n" +
+            "  }\n" +
+            "}", Strings.toString(builder));
+    }
+
+    private ClusterState buildClusterState() throws IOException {
+        IndexMetaData indexMetaData = IndexMetaData.builder("index")
+            .state(IndexMetaData.State.OPEN)
+            .settings(Settings.builder()
+                .put(SETTING_VERSION_CREATED, Version.CURRENT.id))
+            .putMapping(new MappingMetaData("type",
+                new HashMap<String,Object>() {{
+                    put("type1", new HashMap<String, Object>(){{
+                        put("key", "value");
+                    }});
+                }}))
+            .putAlias(AliasMetaData.builder("alias")
+                .indexRouting("indexRouting")
+                .build())
+            .numberOfShards(1)
+            .primaryTerm(0, 1L)
+            .putInSyncAllocationIds(0, new HashSet<String>() {{
+                add("allocationId");
+            }})
+            .numberOfReplicas(2)
+            .putRolloverInfo(new RolloverInfo("rolloveAlias", new ArrayList<>(), 1L))
+            .build();
+
+        return ClusterState.builder(ClusterName.DEFAULT)
+            .stateUUID("stateUUID")
+            .nodes(DiscoveryNodes.builder()
+                .masterNodeId("masterNodeId")
+                .add(new DiscoveryNode("nodeId1", new TransportAddress(InetAddress.getByName("127.0.0.1"), 111),
+                                                                Version.CURRENT))
+                .build())
+            .blocks(ClusterBlocks.builder()
+                .addGlobalBlock(
+                    new ClusterBlock(1, "description", true, true, true, RestStatus.ACCEPTED, EnumSet.allOf((ClusterBlockLevel.class))))
+                .addBlocks(indexMetaData)
+                .addIndexBlock("index",
+                    new ClusterBlock(2, "description2", false, false, false, RestStatus.ACCEPTED, EnumSet.allOf((ClusterBlockLevel.class))))
+                .build())
+            .metaData(MetaData.builder()
+                .clusterUUID("clusterUUID")
+                .coordinationMetaData(CoordinationMetaData.builder()
+                    .term(1)
+                    .lastCommittedConfiguration(new CoordinationMetaData.VotingConfiguration(new HashSet<String>(){{
+                        add("commitedConfigurationNodeId");
+                    }}))
+                    .lastAcceptedConfiguration(new CoordinationMetaData.VotingConfiguration(new HashSet<String>(){{
+                        add("acceptedConfigurationNodeId");
+                    }}))
+                    .addVotingConfigExclusion(new CoordinationMetaData.VotingConfigExclusion("exlucdedNodeId", "excludedNodeName"))
+                    .build())
+                .persistentSettings(Settings.builder()
+                    .put(SETTING_VERSION_CREATED, Version.CURRENT.id).build())
+                .transientSettings(Settings.builder()
+                    .put(SETTING_VERSION_CREATED, Version.CURRENT.id).build())
+                .put(indexMetaData, false)
+                .put(IndexTemplateMetaData.builder("template")
+                    .patterns(Arrays.asList("pattern1", "pattern2"))
+                    .order(0)
+                    .settings(Settings.builder().put(SETTING_VERSION_CREATED, Version.CURRENT.id))
+                    .putMapping("type", "{ \"key1\": {} }")
+                    .build()))
+            .routingTable(RoutingTable.builder()
+                .add(IndexRoutingTable.builder(new Index("index", "indexUUID"))
+                    .addIndexShard(new IndexShardRoutingTable.Builder(new ShardId("index", "_na_", 1))
+                        .addShard(TestShardRouting.newShardRouting(
+                            new ShardId("index", "_na_", 1), "nodeId2", true, ShardRoutingState.STARTED))
+                        .build())
+                    .build())
+                .build())
+            .build();
+    }
+
+    public static class CustomMetaData extends TestCustomMetaData {
+        public static final String TYPE = "custom_md";
+
+        CustomMetaData(String data) {
+            super(data);
+        }
+
+        @Override
+        public String getWriteableName() {
+            return TYPE;
+        }
+
+        @Override
+        public Version getMinimalSupportedVersion() {
+            return Version.CURRENT;
+        }
+
+        @Override
+        public EnumSet<MetaData.XContentContext> context() {
+            return EnumSet.of(MetaData.XContentContext.GATEWAY, MetaData.XContentContext.SNAPSHOT);
+        }
+    }
 }

server/src/test/java/org/elasticsearch/cluster/coordination/ElasticsearchNodeCommandTests.java

@@ -19,22 +19,12 @@
 
 package org.elasticsearch.cluster.coordination;
 
-import org.elasticsearch.Version;
-import org.elasticsearch.action.admin.indices.rollover.MaxAgeCondition;
-import org.elasticsearch.action.admin.indices.rollover.MaxDocsCondition;
-import org.elasticsearch.action.admin.indices.rollover.MaxSizeCondition;
-import org.elasticsearch.action.admin.indices.rollover.RolloverInfo;
 import org.elasticsearch.cluster.ClusterModule;
 import org.elasticsearch.cluster.metadata.IndexGraveyard;
-import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.bytes.BytesReference;
-import org.elasticsearch.common.collect.ImmutableOpenMap;
-import org.elasticsearch.common.unit.ByteSizeValue;
-import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
-import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
@@ -44,7 +34,6 @@ import org.elasticsearch.test.ESTestCase;
 
 import java.io.IOException;
 import java.nio.file.Path;
-import java.util.Arrays;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -52,7 +41,6 @@ import java.util.stream.Stream;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.not;
-import static org.hamcrest.Matchers.notNullValue;
 
 public class ElasticsearchNodeCommandTests extends ESTestCase {
 
@@ -76,7 +64,7 @@ public class ElasticsearchNodeCommandTests extends ESTestCase {
         final MetaData latestMetaData = randomMeta();
         final XContentBuilder builder = JsonXContent.contentBuilder();
         builder.startObject();
-        latestMetaData.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        MetaData.FORMAT.toXContent(builder, latestMetaData);
         builder.endObject();
 
         MetaData loadedMetaData;
@@ -86,17 +74,6 @@ public class ElasticsearchNodeCommandTests extends ESTestCase {
         }
         assertThat(loadedMetaData.clusterUUID(), not(equalTo("_na_")));
         assertThat(loadedMetaData.clusterUUID(), equalTo(latestMetaData.clusterUUID()));
-        ImmutableOpenMap<String, IndexMetaData> indices = loadedMetaData.indices();
-        assertThat(indices.size(), equalTo(latestMetaData.indices().size()));
-        for (IndexMetaData original : latestMetaData) {
-            IndexMetaData deserialized = indices.get(original.getIndex().getName());
-            assertThat(deserialized, notNullValue());
-            assertThat(deserialized.getVersion(), equalTo(original.getVersion()));
-            assertThat(deserialized.getMappingVersion(), equalTo(original.getMappingVersion()));
-            assertThat(deserialized.getSettingsVersion(), equalTo(original.getSettingsVersion()));
-            assertThat(deserialized.getNumberOfReplicas(), equalTo(original.getNumberOfReplicas()));
-            assertThat(deserialized.getNumberOfShards(), equalTo(original.getNumberOfShards()));
-        }
 
         // make sure the index tombstones are the same too
         if (hasMissingCustoms) {
@@ -116,12 +93,8 @@ public class ElasticsearchNodeCommandTests extends ESTestCase {
     }
 
     private MetaData randomMeta() {
-        int numIndices = randomIntBetween(1, 10);
         MetaData.Builder mdBuilder = MetaData.builder();
         mdBuilder.generateClusterUuidIfNeeded();
-        for (int i = 0; i < numIndices; i++) {
-            mdBuilder.put(indexBuilder(randomAlphaOfLength(10) + "idx-"+i));
-        }
         int numDelIndices = randomIntBetween(0, 5);
         final IndexGraveyard.Builder graveyard = IndexGraveyard.builder();
         for (int i = 0; i < numDelIndices; i++) {
@@ -131,17 +104,6 @@ public class ElasticsearchNodeCommandTests extends ESTestCase {
         return mdBuilder.build();
     }
 
-    private IndexMetaData.Builder indexBuilder(String index) {
-        return IndexMetaData.builder(index)
-            .settings(settings(Version.CURRENT).put(IndexMetaData.SETTING_NUMBER_OF_SHARDS, randomIntBetween(1, 10))
-                .put(IndexMetaData.SETTING_NUMBER_OF_REPLICAS, randomIntBetween(0, 5)))
-            .putRolloverInfo(new RolloverInfo("test", randomSubsetOf(Arrays.asList(
-                new MaxAgeCondition(TimeValue.timeValueSeconds(100)),
-                new MaxDocsCondition(100L),
-                new MaxSizeCondition(new ByteSizeValue(100))
-            )), 0));
-    }
-
     @Override
     protected NamedXContentRegistry xContentRegistry() {
         return new NamedXContentRegistry(Stream.of(ClusterModule.getNamedXWriteables().stream(), IndicesModule.getNamedXContents().stream())

server/src/test/java/org/elasticsearch/cluster/coordination/Zen1IT.java

@@ -86,6 +86,11 @@ public class Zen1IT extends ESIntegTestCase {
         return Collections.singletonList(MockTransportService.TestPlugin.class);
     }
 
+    @Override
+    protected void ensureClusterStateConsistency() {
+        // Zen1 does not properly handle the cluster_uuid_committed field
+    }
+
     public void testZen2NodesJoiningZen1Cluster() {
         internalCluster().startNodes(randomIntBetween(1, 3), ZEN1_SETTINGS);
         internalCluster().startNodes(randomIntBetween(1, 3), ZEN2_SETTINGS);

server/src/test/java/org/elasticsearch/cluster/metadata/IndexMetaDataTests.java

@@ -36,7 +36,6 @@ import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.set.Sets;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
-import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
@@ -99,7 +98,7 @@ public class IndexMetaDataTests extends ESTestCase {
 
         final XContentBuilder builder = JsonXContent.contentBuilder();
         builder.startObject();
-        metaData.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        IndexMetaData.FORMAT.toXContent(builder, metaData);
         builder.endObject();
         XContentParser parser = createParser(JsonXContent.jsonXContent, BytesReference.bytes(builder));
         final IndexMetaData fromXContentMeta = IndexMetaData.fromXContent(parser);

server/src/test/java/org/elasticsearch/cluster/metadata/MetaDataTests.java

@@ -34,7 +34,6 @@ import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.set.Sets;
-import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.common.xcontent.XContentParser;
@@ -438,7 +437,7 @@ public class MetaDataTests extends ESTestCase {
         final MetaData originalMeta = MetaData.builder().indexGraveyard(graveyard).build();
         final XContentBuilder builder = JsonXContent.contentBuilder();
         builder.startObject();
-        originalMeta.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        MetaData.FORMAT.toXContent(builder, originalMeta);
         builder.endObject();
         try (XContentParser parser = createParser(JsonXContent.jsonXContent, BytesReference.bytes(builder))) {
             final MetaData fromXContentMeta = MetaData.fromXContent(parser);
@@ -451,7 +450,7 @@ public class MetaDataTests extends ESTestCase {
             .clusterUUIDCommitted(randomBoolean()).build();
         final XContentBuilder builder = JsonXContent.contentBuilder();
         builder.startObject();
-        originalMeta.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        MetaData.FORMAT.toXContent(builder, originalMeta);
         builder.endObject();
         try (XContentParser parser = createParser(JsonXContent.jsonXContent, BytesReference.bytes(builder))) {
             final MetaData fromXContentMeta = MetaData.fromXContent(parser);
@@ -504,7 +503,7 @@ public class MetaDataTests extends ESTestCase {
 
         final XContentBuilder builder = JsonXContent.contentBuilder();
         builder.startObject();
-        metaData.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        MetaData.FORMAT.toXContent(builder, metaData);
         builder.endObject();
 
         try (XContentParser parser = createParser(JsonXContent.jsonXContent, BytesReference.bytes(builder))) {

server/src/test/java/org/elasticsearch/cluster/metadata/ToAndFromJsonMetaDataTests.java

@@ -20,101 +20,37 @@
 package org.elasticsearch.cluster.metadata;
 
 import org.elasticsearch.Version;
+import org.elasticsearch.action.admin.indices.rollover.RolloverInfo;
+import org.elasticsearch.cluster.coordination.CoordinationMetaData;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
 import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.TestCustomMetaData;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
 
 import static org.elasticsearch.cluster.metadata.AliasMetaData.newAliasMetaDataBuilder;
+import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_VERSION_CREATED;
+import static org.elasticsearch.cluster.metadata.MetaData.CONTEXT_MODE_API;
+import static org.elasticsearch.cluster.metadata.MetaData.CONTEXT_MODE_GATEWAY;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.is;
-import static org.hamcrest.Matchers.nullValue;
 
 public class ToAndFromJsonMetaDataTests extends ESTestCase {
 
     public void testSimpleJsonFromAndTo() throws IOException {
         MetaData metaData = MetaData.builder()
-                .put(IndexMetaData.builder("test1")
-                        .settings(settings(Version.CURRENT))
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .primaryTerm(0, 1))
-                .put(IndexMetaData.builder("test2")
-                        .settings(settings(Version.CURRENT).put("setting1", "value1").put("setting2", "value2"))
-                        .numberOfShards(2)
-                        .numberOfReplicas(3)
-                        .primaryTerm(0, 2)
-                        .primaryTerm(1, 2))
-                .put(IndexMetaData.builder("test3")
-                        .settings(settings(Version.CURRENT))
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .putMapping("mapping1", MAPPING_SOURCE1))
-                .put(IndexMetaData.builder("test4")
-                        .settings(settings(Version.CURRENT))
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .creationDate(2L))
-                .put(IndexMetaData.builder("test5")
-                        .settings(settings(Version.CURRENT).put("setting1", "value1").put("setting2", "value2"))
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .putMapping("mapping1", MAPPING_SOURCE1)
-                        .putMapping("mapping2", MAPPING_SOURCE2))
-                .put(IndexMetaData.builder("test6")
-                        .settings(settings(Version.CURRENT).put("setting1", "value1").put("setting2", "value2"))
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .creationDate(2L))
-                .put(IndexMetaData.builder("test7")
-                        .settings(settings(Version.CURRENT))
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .creationDate(2L)
-                        .putMapping("mapping1", MAPPING_SOURCE1)
-                        .putMapping("mapping2", MAPPING_SOURCE2))
-                .put(IndexMetaData.builder("test8")
-                        .settings(settings(Version.CURRENT).put("setting1", "value1").put("setting2", "value2"))
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .putMapping("mapping1", MAPPING_SOURCE1)
-                        .putMapping("mapping2", MAPPING_SOURCE2)
-                        .putAlias(newAliasMetaDataBuilder("alias1"))
-                        .putAlias(newAliasMetaDataBuilder("alias2")))
-                .put(IndexMetaData.builder("test9")
-                        .settings(settings(Version.CURRENT).put("setting1", "value1").put("setting2", "value2"))
-                        .creationDate(2L)
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .putMapping("mapping1", MAPPING_SOURCE1)
-                        .putMapping("mapping2", MAPPING_SOURCE2)
-                        .putAlias(newAliasMetaDataBuilder("alias1"))
-                        .putAlias(newAliasMetaDataBuilder("alias2")))
-                .put(IndexMetaData.builder("test10")
-                        .settings(settings(Version.CURRENT)
-                                .put("setting1", "value1")
-                                .put("setting2", "value2"))
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .putMapping("mapping1", MAPPING_SOURCE1)
-                        .putMapping("mapping2", MAPPING_SOURCE2)
-                        .putAlias(newAliasMetaDataBuilder("alias1"))
-                        .putAlias(newAliasMetaDataBuilder("alias2")))
-                .put(IndexMetaData.builder("test11")
-                        .settings(settings(Version.CURRENT)
-                                .put("setting1", "value1")
-                                .put("setting2", "value2"))
-                        .numberOfShards(1)
-                        .numberOfReplicas(2)
-                        .putMapping("mapping1", MAPPING_SOURCE1)
-                        .putMapping("mapping2", MAPPING_SOURCE2)
-                        .putAlias(newAliasMetaDataBuilder("alias1").filter(ALIAS_FILTER1))
-                        .putAlias(newAliasMetaDataBuilder("alias2").writeIndex(randomBoolean() ? null : randomBoolean()))
-                        .putAlias(newAliasMetaDataBuilder("alias4").filter(ALIAS_FILTER2)))
                 .put(IndexTemplateMetaData.builder("foo")
                         .patterns(Collections.singletonList("bar"))
                         .order(1)
@@ -162,154 +98,12 @@ public class ToAndFromJsonMetaDataTests extends ESTestCase {
                 .put(new DataStream("data-stream2", "@timestamp2", Collections.emptyList()))
                 .build();
 
-        String metaDataSource = MetaData.Builder.toXContent(metaData);
+        XContentBuilder builder = JsonXContent.contentBuilder();
+        builder.startObject();
+        MetaData.FORMAT.toXContent(builder, metaData);
+        builder.endObject();
 
-        MetaData parsedMetaData = MetaData.Builder.fromXContent(createParser(JsonXContent.jsonXContent, metaDataSource));
+        MetaData parsedMetaData = MetaData.Builder.fromXContent(createParser(builder));
-
-        IndexMetaData indexMetaData = parsedMetaData.index("test1");
-        assertThat(indexMetaData.primaryTerm(0), equalTo(1L));
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(-1L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(3));
-        assertThat(indexMetaData.getMappings().size(), equalTo(0));
-
-        indexMetaData = parsedMetaData.index("test2");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(2));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(3));
-        assertThat(indexMetaData.primaryTerm(0), equalTo(2L));
-        assertThat(indexMetaData.primaryTerm(1), equalTo(2L));
-        assertThat(indexMetaData.getCreationDate(), equalTo(-1L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(5));
-        assertThat(indexMetaData.getSettings().get("setting1"), equalTo("value1"));
-        assertThat(indexMetaData.getSettings().get("setting2"), equalTo("value2"));
-        assertThat(indexMetaData.getMappings().size(), equalTo(0));
-
-        indexMetaData = parsedMetaData.index("test3");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(-1L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(3));
-        assertThat(indexMetaData.getMappings().size(), equalTo(1));
-        assertThat(indexMetaData.getMappings().get("mapping1").source().string(), equalTo(MAPPING_SOURCE1));
-
-        indexMetaData = parsedMetaData.index("test4");
-        assertThat(indexMetaData.getCreationDate(), equalTo(2L));
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getSettings().size(), equalTo(4));
-        assertThat(indexMetaData.getMappings().size(), equalTo(0));
-
-        indexMetaData = parsedMetaData.index("test5");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(-1L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(5));
-        assertThat(indexMetaData.getSettings().get("setting1"), equalTo("value1"));
-        assertThat(indexMetaData.getSettings().get("setting2"), equalTo("value2"));
-        assertThat(indexMetaData.getMappings().size(), equalTo(2));
-        assertThat(indexMetaData.getMappings().get("mapping1").source().string(), equalTo(MAPPING_SOURCE1));
-        assertThat(indexMetaData.getMappings().get("mapping2").source().string(), equalTo(MAPPING_SOURCE2));
-
-        indexMetaData = parsedMetaData.index("test6");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(2L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(6));
-        assertThat(indexMetaData.getSettings().get("setting1"), equalTo("value1"));
-        assertThat(indexMetaData.getSettings().get("setting2"), equalTo("value2"));
-        assertThat(indexMetaData.getMappings().size(), equalTo(0));
-
-        indexMetaData = parsedMetaData.index("test7");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(2L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(4));
-        assertThat(indexMetaData.getMappings().size(), equalTo(2));
-        assertThat(indexMetaData.getMappings().get("mapping1").source().string(), equalTo(MAPPING_SOURCE1));
-        assertThat(indexMetaData.getMappings().get("mapping2").source().string(), equalTo(MAPPING_SOURCE2));
-
-        indexMetaData = parsedMetaData.index("test8");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(-1L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(5));
-        assertThat(indexMetaData.getSettings().get("setting1"), equalTo("value1"));
-        assertThat(indexMetaData.getSettings().get("setting2"), equalTo("value2"));
-        assertThat(indexMetaData.getMappings().size(), equalTo(2));
-        assertThat(indexMetaData.getMappings().get("mapping1").source().string(), equalTo(MAPPING_SOURCE1));
-        assertThat(indexMetaData.getMappings().get("mapping2").source().string(), equalTo(MAPPING_SOURCE2));
-        assertThat(indexMetaData.getAliases().size(), equalTo(2));
-        assertThat(indexMetaData.getAliases().get("alias1").alias(), equalTo("alias1"));
-        assertThat(indexMetaData.getAliases().get("alias2").alias(), equalTo("alias2"));
-
-        indexMetaData = parsedMetaData.index("test9");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(2L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(6));
-        assertThat(indexMetaData.getSettings().get("setting1"), equalTo("value1"));
-        assertThat(indexMetaData.getSettings().get("setting2"), equalTo("value2"));
-        assertThat(indexMetaData.getMappings().size(), equalTo(2));
-        assertThat(indexMetaData.getMappings().get("mapping1").source().string(), equalTo(MAPPING_SOURCE1));
-        assertThat(indexMetaData.getMappings().get("mapping2").source().string(), equalTo(MAPPING_SOURCE2));
-        assertThat(indexMetaData.getAliases().size(), equalTo(2));
-        assertThat(indexMetaData.getAliases().get("alias1").alias(), equalTo("alias1"));
-        assertThat(indexMetaData.getAliases().get("alias2").alias(), equalTo("alias2"));
-
-        indexMetaData = parsedMetaData.index("test10");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(-1L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(5));
-        assertThat(indexMetaData.getSettings().get("setting1"), equalTo("value1"));
-        assertThat(indexMetaData.getSettings().get("setting2"), equalTo("value2"));
-        assertThat(indexMetaData.getMappings().size(), equalTo(2));
-        assertThat(indexMetaData.getMappings().get("mapping1").source().string(), equalTo(MAPPING_SOURCE1));
-        assertThat(indexMetaData.getMappings().get("mapping2").source().string(), equalTo(MAPPING_SOURCE2));
-        assertThat(indexMetaData.getAliases().size(), equalTo(2));
-        assertThat(indexMetaData.getAliases().get("alias1").alias(), equalTo("alias1"));
-        assertThat(indexMetaData.getAliases().get("alias2").alias(), equalTo("alias2"));
-
-        indexMetaData = parsedMetaData.index("test11");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(-1L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(5));
-        assertThat(indexMetaData.getSettings().get("setting1"), equalTo("value1"));
-        assertThat(indexMetaData.getSettings().get("setting2"), equalTo("value2"));
-        assertThat(indexMetaData.getMappings().size(), equalTo(2));
-        assertThat(indexMetaData.getMappings().get("mapping1").source().string(), equalTo(MAPPING_SOURCE1));
-        assertThat(indexMetaData.getMappings().get("mapping2").source().string(), equalTo(MAPPING_SOURCE2));
-        assertThat(indexMetaData.getAliases().size(), equalTo(3));
-        assertThat(indexMetaData.getAliases().get("alias1").alias(), equalTo("alias1"));
-        assertThat(indexMetaData.getAliases().get("alias1").filter().string(), equalTo(ALIAS_FILTER1));
-        assertThat(indexMetaData.getAliases().get("alias2").alias(), equalTo("alias2"));
-        assertThat(indexMetaData.getAliases().get("alias2").filter(), nullValue());
-        assertThat(indexMetaData.getAliases().get("alias2").writeIndex(),
-            equalTo(metaData.index("test11").getAliases().get("alias2").writeIndex()));
-        assertThat(indexMetaData.getAliases().get("alias4").alias(), equalTo("alias4"));
-        assertThat(indexMetaData.getAliases().get("alias4").filter().string(), equalTo(ALIAS_FILTER2));
-
-        indexMetaData = parsedMetaData.index("test12");
-        assertThat(indexMetaData.getNumberOfShards(), equalTo(1));
-        assertThat(indexMetaData.getNumberOfReplicas(), equalTo(2));
-        assertThat(indexMetaData.getCreationDate(), equalTo(2L));
-        assertThat(indexMetaData.getSettings().size(), equalTo(6));
-        assertThat(indexMetaData.getSettings().get("setting1"), equalTo("value1"));
-        assertThat(indexMetaData.getSettings().get("setting2"), equalTo("value2"));
-        assertThat(indexMetaData.getMappings().size(), equalTo(2));
-        assertThat(indexMetaData.getMappings().get("mapping1").source().string(), equalTo(MAPPING_SOURCE1));
-        assertThat(indexMetaData.getMappings().get("mapping2").source().string(), equalTo(MAPPING_SOURCE2));
-        assertThat(indexMetaData.getAliases().size(), equalTo(3));
-        assertThat(indexMetaData.getAliases().get("alias1").alias(), equalTo("alias1"));
-        assertThat(indexMetaData.getAliases().get("alias1").filter().string(), equalTo(ALIAS_FILTER1));
-        assertThat(indexMetaData.getAliases().get("alias3").alias(), equalTo("alias3"));
-        assertThat(indexMetaData.getAliases().get("alias3").filter(), nullValue());
-        assertThat(indexMetaData.getAliases().get("alias3").writeIndex(),
-            equalTo(metaData.index("test12").getAliases().get("alias3").writeIndex()));
-        assertThat(indexMetaData.getAliases().get("alias4").alias(), equalTo("alias4"));
-        assertThat(indexMetaData.getAliases().get("alias4").filter().string(), equalTo(ALIAS_FILTER2));
 
         // templates
         assertThat(parsedMetaData.templates().get("foo").name(), is("foo"));
@@ -363,4 +157,482 @@ public class ToAndFromJsonMetaDataTests extends ESTestCase {
     private static final String MAPPING_SOURCE2 = "{\"mapping2\":{\"text2\":{\"type\":\"string\"}}}";
     private static final String ALIAS_FILTER1 = "{\"field1\":\"value1\"}";
     private static final String ALIAS_FILTER2 = "{\"field2\":\"value2\"}";
+
+    public void testToXContentGateway_FlatSettingTrue_ReduceMappingFalse() throws IOException {
+        Map<String, String> mapParams = new HashMap<String,String>(){{
+            put(MetaData.CONTEXT_MODE_PARAM, CONTEXT_MODE_GATEWAY);
+            put("flat_settings", "true");
+            put("reduce_mappings", "false");
+        }};
+
+        MetaData metaData = buildMetaData();
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        builder.startObject();
+        metaData.toXContent(builder, new ToXContent.MapParams(mapParams));
+        builder.endObject();
+
+        assertEquals("{\n" +
+            "  \"meta-data\" : {\n" +
+            "    \"version\" : 0,\n" +
+            "    \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "    \"cluster_uuid_committed\" : false,\n" +
+            "    \"cluster_coordination\" : {\n" +
+            "      \"term\" : 1,\n" +
+            "      \"last_committed_config\" : [\n" +
+            "        \"commitedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"last_accepted_config\" : [\n" +
+            "        \"acceptedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"voting_config_exclusions\" : [\n" +
+            "        {\n" +
+            "          \"node_id\" : \"exlucdedNodeId\",\n" +
+            "          \"node_name\" : \"excludedNodeName\"\n" +
+            "        }\n" +
+            "      ]\n" +
+            "    },\n" +
+            "    \"settings\" : {\n" +
+            "      \"index.version.created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "    },\n" +
+            "    \"templates\" : {\n" +
+            "      \"template\" : {\n" +
+            "        \"order\" : 0,\n" +
+            "        \"index_patterns\" : [\n" +
+            "          \"pattern1\",\n" +
+            "          \"pattern2\"\n" +
+            "        ],\n" +
+            "        \"settings\" : {\n" +
+            "          \"index.version.created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "        },\n" +
+            "        \"mappings\" : [\n" +
+            "          {\n" +
+            "            \"key1\" : { }\n" +
+            "          }\n" +
+            "        ],\n" +
+            "        \"aliases\" : { }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"index-graveyard\" : {\n" +
+            "      \"tombstones\" : [ ]\n" +
+            "    }\n" +
+            "  }\n" +
+            "}", Strings.toString(builder));
+    }
+
+    public void testToXContentAPI_SameTypeName() throws IOException {
+        Map<String, String> mapParams = new HashMap<String,String>(){{
+            put(MetaData.CONTEXT_MODE_PARAM, CONTEXT_MODE_API);
+        }};
+
+        MetaData metaData = MetaData.builder()
+            .clusterUUID("clusterUUID")
+            .coordinationMetaData(CoordinationMetaData.builder()
+                .build())
+            .put(IndexMetaData.builder("index")
+                .state(IndexMetaData.State.OPEN)
+                .settings(Settings.builder()
+                    .put(SETTING_VERSION_CREATED, Version.CURRENT.id))
+                .putMapping(new MappingMetaData("type",
+                    // the type name is the root value,
+                    // the original logic in ClusterState.toXContent will reduce
+                    new HashMap<String,Object>(){{
+                        put("type", new HashMap<String, Object>(){{
+                            put("key", "value");
+                        }});
+                    }}))
+                .numberOfShards(1)
+                .primaryTerm(0, 1L)
+                .numberOfReplicas(2))
+            .build();
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        builder.startObject();
+        metaData.toXContent(builder, new ToXContent.MapParams(mapParams));
+        builder.endObject();
+
+        assertEquals("{\n" +
+            "  \"metadata\" : {\n" +
+            "    \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "    \"cluster_uuid_committed\" : false,\n" +
+            "    \"cluster_coordination\" : {\n" +
+            "      \"term\" : 0,\n" +
+            "      \"last_committed_config\" : [ ],\n" +
+            "      \"last_accepted_config\" : [ ],\n" +
+            "      \"voting_config_exclusions\" : [ ]\n" +
+            "    },\n" +
+            "    \"templates\" : { },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"version\" : 2,\n" +
+            "        \"mapping_version\" : 1,\n" +
+            "        \"settings_version\" : 1,\n" +
+            "        \"aliases_version\" : 1,\n" +
+            "        \"routing_num_shards\" : 1,\n" +
+            "        \"state\" : \"open\",\n" +
+            "        \"settings\" : {\n" +
+            "          \"index\" : {\n" +
+            "            \"number_of_shards\" : \"1\",\n" +
+            "            \"number_of_replicas\" : \"2\",\n" +
+            "            \"version\" : {\n" +
+            "              \"created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"key\" : \"value\"\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : [ ],\n" +
+            "        \"primary_terms\" : {\n" +
+            "          \"0\" : 1\n" +
+            "        },\n" +
+            "        \"in_sync_allocations\" : {\n" +
+            "          \"0\" : [ ]\n" +
+            "        },\n" +
+            "        \"rollover_info\" : { }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"index-graveyard\" : {\n" +
+            "      \"tombstones\" : [ ]\n" +
+            "    }\n" +
+            "  }\n" +
+            "}", Strings.toString(builder));
+    }
+
+    public void testToXContentGateway_FlatSettingFalse_ReduceMappingTrue() throws IOException {
+        Map<String, String> mapParams = new HashMap<String,String>(){{
+            put(MetaData.CONTEXT_MODE_PARAM, CONTEXT_MODE_GATEWAY);
+            put("flat_settings", "false");
+            put("reduce_mappings", "true");
+        }};
+
+        MetaData metaData = buildMetaData();
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        builder.startObject();
+        metaData.toXContent(builder, new ToXContent.MapParams(mapParams));
+        builder.endObject();
+
+        assertEquals("{\n" +
+            "  \"meta-data\" : {\n" +
+            "    \"version\" : 0,\n" +
+            "    \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "    \"cluster_uuid_committed\" : false,\n" +
+            "    \"cluster_coordination\" : {\n" +
+            "      \"term\" : 1,\n" +
+            "      \"last_committed_config\" : [\n" +
+            "        \"commitedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"last_accepted_config\" : [\n" +
+            "        \"acceptedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"voting_config_exclusions\" : [\n" +
+            "        {\n" +
+            "          \"node_id\" : \"exlucdedNodeId\",\n" +
+            "          \"node_name\" : \"excludedNodeName\"\n" +
+            "        }\n" +
+            "      ]\n" +
+            "    },\n" +
+            "    \"settings\" : {\n" +
+            "      \"index.version.created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "    },\n" +
+            "    \"templates\" : {\n" +
+            "      \"template\" : {\n" +
+            "        \"order\" : 0,\n" +
+            "        \"index_patterns\" : [\n" +
+            "          \"pattern1\",\n" +
+            "          \"pattern2\"\n" +
+            "        ],\n" +
+            "        \"settings\" : {\n" +
+            "          \"index\" : {\n" +
+            "            \"version\" : {\n" +
+            "              \"created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"key1\" : { }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : { }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"index-graveyard\" : {\n" +
+            "      \"tombstones\" : [ ]\n" +
+            "    }\n" +
+            "  }\n" +
+            "}", Strings.toString(builder));
+    }
+
+    public void testToXContentAPI_FlatSettingTrue_ReduceMappingFalse() throws IOException {
+        Map<String, String> mapParams = new HashMap<String,String>(){{
+            put(MetaData.CONTEXT_MODE_PARAM, CONTEXT_MODE_API);
+            put("flat_settings", "true");
+            put("reduce_mappings", "false");
+        }};
+
+        final MetaData metaData = buildMetaData();
+
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        builder.startObject();
+        metaData.toXContent(builder, new ToXContent.MapParams(mapParams));
+        builder.endObject();
+
+        assertEquals("{\n" +
+            "  \"metadata\" : {\n" +
+            "    \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "    \"cluster_uuid_committed\" : false,\n" +
+            "    \"cluster_coordination\" : {\n" +
+            "      \"term\" : 1,\n" +
+            "      \"last_committed_config\" : [\n" +
+            "        \"commitedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"last_accepted_config\" : [\n" +
+            "        \"acceptedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"voting_config_exclusions\" : [\n" +
+            "        {\n" +
+            "          \"node_id\" : \"exlucdedNodeId\",\n" +
+            "          \"node_name\" : \"excludedNodeName\"\n" +
+            "        }\n" +
+            "      ]\n" +
+            "    },\n" +
+            "    \"templates\" : {\n" +
+            "      \"template\" : {\n" +
+            "        \"order\" : 0,\n" +
+            "        \"index_patterns\" : [\n" +
+            "          \"pattern1\",\n" +
+            "          \"pattern2\"\n" +
+            "        ],\n" +
+            "        \"settings\" : {\n" +
+            "          \"index.version.created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"key1\" : { }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : { }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"version\" : 2,\n" +
+            "        \"mapping_version\" : 1,\n" +
+            "        \"settings_version\" : 1,\n" +
+            "        \"aliases_version\" : 1,\n" +
+            "        \"routing_num_shards\" : 1,\n" +
+            "        \"state\" : \"open\",\n" +
+            "        \"settings\" : {\n" +
+            "          \"index.number_of_replicas\" : \"2\",\n" +
+            "          \"index.number_of_shards\" : \"1\",\n" +
+            "          \"index.version.created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"type1\" : {\n" +
+            "              \"key\" : \"value\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : [\n" +
+            "          \"alias\"\n" +
+            "        ],\n" +
+            "        \"primary_terms\" : {\n" +
+            "          \"0\" : 1\n" +
+            "        },\n" +
+            "        \"in_sync_allocations\" : {\n" +
+            "          \"0\" : [\n" +
+            "            \"allocationId\"\n" +
+            "          ]\n" +
+            "        },\n" +
+            "        \"rollover_info\" : {\n" +
+            "          \"rolloveAlias\" : {\n" +
+            "            \"met_conditions\" : { },\n" +
+            "            \"time\" : 1\n" +
+            "          }\n" +
+            "        }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"index-graveyard\" : {\n" +
+            "      \"tombstones\" : [ ]\n" +
+            "    }\n" +
+            "  }\n" +
+            "}", Strings.toString(builder));
+    }
+
+    public void testToXContentAPI_FlatSettingFalse_ReduceMappingTrue() throws IOException {
+        Map<String, String> mapParams = new HashMap<String,String>(){{
+            put(MetaData.CONTEXT_MODE_PARAM, CONTEXT_MODE_API);
+            put("flat_settings", "false");
+            put("reduce_mappings", "true");
+        }};
+
+        final MetaData metaData = buildMetaData();
+
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        builder.startObject();
+        metaData.toXContent(builder, new ToXContent.MapParams(mapParams));
+        builder.endObject();
+
+        assertEquals("{\n" +
+            "  \"metadata\" : {\n" +
+            "    \"cluster_uuid\" : \"clusterUUID\",\n" +
+            "    \"cluster_uuid_committed\" : false,\n" +
+            "    \"cluster_coordination\" : {\n" +
+            "      \"term\" : 1,\n" +
+            "      \"last_committed_config\" : [\n" +
+            "        \"commitedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"last_accepted_config\" : [\n" +
+            "        \"acceptedConfigurationNodeId\"\n" +
+            "      ],\n" +
+            "      \"voting_config_exclusions\" : [\n" +
+            "        {\n" +
+            "          \"node_id\" : \"exlucdedNodeId\",\n" +
+            "          \"node_name\" : \"excludedNodeName\"\n" +
+            "        }\n" +
+            "      ]\n" +
+            "    },\n" +
+            "    \"templates\" : {\n" +
+            "      \"template\" : {\n" +
+            "        \"order\" : 0,\n" +
+            "        \"index_patterns\" : [\n" +
+            "          \"pattern1\",\n" +
+            "          \"pattern2\"\n" +
+            "        ],\n" +
+            "        \"settings\" : {\n" +
+            "          \"index\" : {\n" +
+            "            \"version\" : {\n" +
+            "              \"created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"key1\" : { }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : { }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"indices\" : {\n" +
+            "      \"index\" : {\n" +
+            "        \"version\" : 2,\n" +
+            "        \"mapping_version\" : 1,\n" +
+            "        \"settings_version\" : 1,\n" +
+            "        \"aliases_version\" : 1,\n" +
+            "        \"routing_num_shards\" : 1,\n" +
+            "        \"state\" : \"open\",\n" +
+            "        \"settings\" : {\n" +
+            "          \"index\" : {\n" +
+            "            \"number_of_shards\" : \"1\",\n" +
+            "            \"number_of_replicas\" : \"2\",\n" +
+            "            \"version\" : {\n" +
+            "              \"created\" : \"" + Version.CURRENT.id + "\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"mappings\" : {\n" +
+            "          \"type\" : {\n" +
+            "            \"type1\" : {\n" +
+            "              \"key\" : \"value\"\n" +
+            "            }\n" +
+            "          }\n" +
+            "        },\n" +
+            "        \"aliases\" : [\n" +
+            "          \"alias\"\n" +
+            "        ],\n" +
+            "        \"primary_terms\" : {\n" +
+            "          \"0\" : 1\n" +
+            "        },\n" +
+            "        \"in_sync_allocations\" : {\n" +
+            "          \"0\" : [\n" +
+            "            \"allocationId\"\n" +
+            "          ]\n" +
+            "        },\n" +
+            "        \"rollover_info\" : {\n" +
+            "          \"rolloveAlias\" : {\n" +
+            "            \"met_conditions\" : { },\n" +
+            "            \"time\" : 1\n" +
+            "          }\n" +
+            "        }\n" +
+            "      }\n" +
+            "    },\n" +
+            "    \"index-graveyard\" : {\n" +
+            "      \"tombstones\" : [ ]\n" +
+            "    }\n" +
+            "  }\n" +
+            "}", Strings.toString(builder));
+    }
+
+
+    private MetaData buildMetaData() throws IOException {
+        return MetaData.builder()
+            .clusterUUID("clusterUUID")
+            .coordinationMetaData(CoordinationMetaData.builder()
+                .term(1)
+                .lastCommittedConfiguration(new CoordinationMetaData.VotingConfiguration(new HashSet<String>(){{
+                    add("commitedConfigurationNodeId");
+                }}))
+                .lastAcceptedConfiguration(new CoordinationMetaData.VotingConfiguration(new HashSet<String>(){{
+                    add("acceptedConfigurationNodeId");
+                }}))
+                .addVotingConfigExclusion(new CoordinationMetaData.VotingConfigExclusion("exlucdedNodeId", "excludedNodeName"))
+                .build())
+            .persistentSettings(Settings.builder()
+                .put(SETTING_VERSION_CREATED, Version.CURRENT.id).build())
+            .transientSettings(Settings.builder()
+                .put(SETTING_VERSION_CREATED, Version.CURRENT.id).build())
+            .put(IndexMetaData.builder("index")
+                .state(IndexMetaData.State.OPEN)
+                .settings(Settings.builder()
+                    .put(SETTING_VERSION_CREATED, Version.CURRENT.id))
+                .putMapping(new MappingMetaData("type",
+                    new HashMap<String,Object>(){{
+                        put("type1", new HashMap<String, Object>(){{
+                            put("key", "value");
+                        }});
+                    }}))
+                .putAlias(AliasMetaData.builder("alias")
+                    .indexRouting("indexRouting")
+                    .build())
+                .numberOfShards(1)
+                .primaryTerm(0, 1L)
+                .putInSyncAllocationIds(0, new HashSet<String>(){{
+                    add("allocationId");
+                }})
+                .numberOfReplicas(2)
+                .putRolloverInfo(new RolloverInfo("rolloveAlias", new ArrayList<>(), 1L)))
+            .put(IndexTemplateMetaData.builder("template")
+                .patterns(Arrays.asList("pattern1", "pattern2"))
+                .order(0)
+                .settings(Settings.builder().put(SETTING_VERSION_CREATED, Version.CURRENT.id))
+                .putMapping("type", "{ \"key1\": {} }")
+                .build())
+            .build();
+    }
+
+    public static class CustomMetaData extends TestCustomMetaData {
+        public static final String TYPE = "custom_md";
+
+        CustomMetaData(String data) {
+            super(data);
+        }
+
+        @Override
+        public String getWriteableName() {
+            return TYPE;
+        }
+
+        @Override
+        public Version getMinimalSupportedVersion() {
+            return Version.CURRENT;
+        }
+
+        @Override
+        public EnumSet<MetaData.XContentContext> context() {
+            return EnumSet.of(MetaData.XContentContext.GATEWAY, MetaData.XContentContext.SNAPSHOT);
+        }
+    }
 }

test/framework/src/main/java/org/elasticsearch/test/ESIntegTestCase.java

@@ -102,9 +102,10 @@ import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.XContentType;
-import org.elasticsearch.common.xcontent.json.JsonXContent;
+import org.elasticsearch.common.xcontent.smile.SmileXContent;
 import org.elasticsearch.core.internal.io.IOUtils;
 import org.elasticsearch.discovery.Discovery;
 import org.elasticsearch.discovery.zen.ElectMasterService;
@@ -1104,20 +1105,85 @@ public abstract class ESIntegTestCase extends ESTestCase {
         if (cluster() != null && cluster().size() > 0) {
             final Client masterClient = client();
             MetaData metaData = masterClient.admin().cluster().prepareState().all().get().getState().metaData();
-            final XContentBuilder builder = JsonXContent.contentBuilder();
+            final Map<String, String> serializationParams = new HashMap<>(2);
+            serializationParams.put("binary", "true");
+            serializationParams.put(MetaData.CONTEXT_MODE_PARAM, MetaData.CONTEXT_MODE_GATEWAY);
+            final ToXContent.Params serializationFormatParams = new ToXContent.MapParams(serializationParams);
+
+            // when comparing XContent output, do not use binary format
+            final Map<String, String> compareParams = new HashMap<>(2);
+            compareParams.put(MetaData.CONTEXT_MODE_PARAM, MetaData.CONTEXT_MODE_GATEWAY);
+            final ToXContent.Params compareFormatParams = new ToXContent.MapParams(compareParams);
+
+            {
+                MetaData metaDataWithoutIndices = MetaData.builder(metaData).removeAllIndices().build();
+
+                XContentBuilder builder = SmileXContent.contentBuilder();
                 builder.startObject();
-            metaData.toXContent(builder, ToXContent.EMPTY_PARAMS);
+                metaDataWithoutIndices.toXContent(builder, serializationFormatParams);
                 builder.endObject();
+                final BytesReference originalBytes = BytesReference.bytes(builder);
+
+                XContentBuilder compareBuilder = SmileXContent.contentBuilder();
+                compareBuilder.startObject();
+                metaDataWithoutIndices.toXContent(compareBuilder, compareFormatParams);
+                compareBuilder.endObject();
+                final BytesReference compareOriginalBytes = BytesReference.bytes(compareBuilder);
 
                 final MetaData loadedMetaData;
                 try (XContentParser parser = createParser(ElasticsearchNodeCommand.namedXContentRegistry,
-                JsonXContent.jsonXContent, BytesReference.bytes(builder))) {
+                    SmileXContent.smileXContent, originalBytes)) {
                     loadedMetaData = MetaData.fromXContent(parser);
                 }
+                builder = SmileXContent.contentBuilder();
+                builder.startObject();
+                loadedMetaData.toXContent(builder, compareFormatParams);
+                builder.endObject();
+                final BytesReference parsedBytes = BytesReference.bytes(builder);
 
                 assertNull(
-                "cluster state JSON serialization does not match",
+                    "cluster state XContent serialization does not match, expected " +
-                differenceBetweenMapsIgnoringArrayOrder(convertToMap(metaData), convertToMap(loadedMetaData)));
+                        XContentHelper.convertToMap(compareOriginalBytes, false, XContentType.SMILE) +
+                        " but got " +
+                        XContentHelper.convertToMap(parsedBytes, false, XContentType.SMILE),
+                    differenceBetweenMapsIgnoringArrayOrder(
+                        XContentHelper.convertToMap(compareOriginalBytes, false, XContentType.SMILE).v2(),
+                        XContentHelper.convertToMap(parsedBytes, false, XContentType.SMILE).v2()));
+            }
+
+            for (IndexMetaData indexMetaData : metaData) {
+                XContentBuilder builder = SmileXContent.contentBuilder();
+                builder.startObject();
+                indexMetaData.toXContent(builder, serializationFormatParams);
+                builder.endObject();
+                final BytesReference originalBytes = BytesReference.bytes(builder);
+
+                XContentBuilder compareBuilder = SmileXContent.contentBuilder();
+                compareBuilder.startObject();
+                indexMetaData.toXContent(compareBuilder, compareFormatParams);
+                compareBuilder.endObject();
+                final BytesReference compareOriginalBytes = BytesReference.bytes(compareBuilder);
+
+                final IndexMetaData loadedIndexMetaData;
+                try (XContentParser parser = createParser(ElasticsearchNodeCommand.namedXContentRegistry,
+                    SmileXContent.smileXContent, originalBytes)) {
+                    loadedIndexMetaData = IndexMetaData.fromXContent(parser);
+                }
+                builder = SmileXContent.contentBuilder();
+                builder.startObject();
+                loadedIndexMetaData.toXContent(builder, compareFormatParams);
+                builder.endObject();
+                final BytesReference parsedBytes = BytesReference.bytes(builder);
+
+                assertNull(
+                    "cluster state XContent serialization does not match, expected " +
+                        XContentHelper.convertToMap(compareOriginalBytes, false, XContentType.SMILE) +
+                        " but got " +
+                        XContentHelper.convertToMap(parsedBytes, false, XContentType.SMILE),
+                    differenceBetweenMapsIgnoringArrayOrder(
+                        XContentHelper.convertToMap(compareOriginalBytes, false, XContentType.SMILE).v2(),
+                        XContentHelper.convertToMap(parsedBytes, false, XContentType.SMILE).v2()));
+            }
         }
     }