Return index name and empty map for /{index}/_alias with no aliases

Previously in #24723 we changed the `_alias` API to not go through the
`RestGetIndicesAction` endpoint, instead creating a `RestGetAliasesAction` that
did the same thing.

This changes the formatting so that it matches the old formatting of the
endpoint, before:

```
GET /test-1/_alias

{ }
```

And after this change:

```
GET /test-1/_alias

{
  "test-1": {
    "aliases": {}
  }
}
```

This is related to #25090

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

@@ -243,7 +243,8 @@ public class MetaData implements Iterable<IndexMetaData>, Diffable<MetaData>, To
      *
      * @param aliases         The names of the index aliases to find
      * @param concreteIndices The concrete indexes the index aliases must point to order to be returned.
-     * @return the found index aliases grouped by index
+     * @return a map of index to a list of alias metadata, the list corresponding to a concrete index will be empty if no aliases are
+     * present for that index
      */
     public ImmutableOpenMap<String, List<AliasMetaData>> findAliases(final String[] aliases, String[] concreteIndices) {
         assert aliases != null;
@@ -273,8 +274,8 @@ public class MetaData implements Iterable<IndexMetaData>, Diffable<MetaData>, To
                         return o1.alias().compareTo(o2.alias());
                     }
                 });
-                mapBuilder.put(index, Collections.unmodifiableList(filteredValues));
             }
+            mapBuilder.put(index, Collections.unmodifiableList(filteredValues));
         }
         return mapBuilder.build();
     }

core/src/main/java/org/elasticsearch/rest/action/admin/indices/RestGetAliasesAction.java

@@ -76,6 +76,7 @@ public class RestGetAliasesAction extends BaseRestHandler {
 
     @Override
     public RestChannelConsumer prepareRequest(final RestRequest request, final NodeClient client) throws IOException {
+        final boolean namesProvided = request.hasParam("name");
         final String[] aliases = request.paramAsStringArrayOrEmptyIfAll("name");
         final GetAliasesRequest getAliasesRequest = new GetAliasesRequest(aliases);
         final String[] indices = Strings.splitStringByCommaToArray(request.param("index"));
@@ -89,9 +90,13 @@ public class RestGetAliasesAction extends BaseRestHandler {
                 final ImmutableOpenMap<String, List<AliasMetaData>> aliasMap = response.getAliases();
 
                 final Set<String> aliasNames = new HashSet<>();
-                for (final ObjectCursor<List<AliasMetaData>> cursor : aliasMap.values()) {
+                final Set<String> indicesToDisplay = new HashSet<>();
+                for (final ObjectObjectCursor<String, List<AliasMetaData>> cursor : aliasMap) {
                     for (final AliasMetaData aliasMetaData : cursor.value) {
                         aliasNames.add(aliasMetaData.alias());
+                        if (namesProvided) {
+                            indicesToDisplay.add(cursor.key);
+                        }
                     }
                 }
 
@@ -131,6 +136,7 @@ public class RestGetAliasesAction extends BaseRestHandler {
                     }
 
                     for (final ObjectObjectCursor<String, List<AliasMetaData>> entry : response.getAliases()) {
+                        if (namesProvided == false || (namesProvided && indicesToDisplay.contains(entry.key))) {
                             builder.startObject(entry.key);
                             {
                                 builder.startObject("aliases");
@@ -144,6 +150,7 @@ public class RestGetAliasesAction extends BaseRestHandler {
                             builder.endObject();
                         }
                     }
+                }
                 builder.endObject();
                 return new BytesRestResponse(status, builder);
             }

core/src/test/java/org/elasticsearch/action/admin/indices/get/GetIndexIT.java

@@ -19,6 +19,7 @@
 
 package org.elasticsearch.action.admin.indices.get;
 
+import com.carrotsearch.hppc.cursors.ObjectObjectCursor;
 import org.elasticsearch.action.admin.indices.alias.Alias;
 import org.elasticsearch.action.admin.indices.get.GetIndexRequest.Feature;
 import org.elasticsearch.cluster.metadata.AliasMetaData;
@@ -281,6 +282,8 @@ public class GetIndexIT extends ESIntegTestCase {
 
     private void assertEmptyAliases(GetIndexResponse response) {
         assertThat(response.aliases(), notNullValue());
-        assertThat(response.aliases().isEmpty(), equalTo(true));
+        for (final ObjectObjectCursor<String, List<AliasMetaData>> entry : response.getAliases()) {
+            assertTrue(entry.value.isEmpty());
+        }
     }
 }

core/src/test/java/org/elasticsearch/aliases/IndexAliasesIT.java

@@ -19,6 +19,7 @@
 
 package org.elasticsearch.aliases;
 
+import com.carrotsearch.hppc.cursors.ObjectObjectCursor;
 import org.elasticsearch.action.admin.indices.alias.Alias;
 import org.elasticsearch.action.admin.indices.alias.IndicesAliasesRequest.AliasActions;
 import org.elasticsearch.action.admin.indices.alias.exists.AliasesExistResponse;
@@ -32,6 +33,7 @@ import org.elasticsearch.cluster.metadata.AliasMetaData;
 import org.elasticsearch.cluster.metadata.AliasOrIndex;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.common.StopWatch;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.xcontent.XContentType;
@@ -49,6 +51,7 @@ import org.elasticsearch.test.ESIntegTestCase;
 
 import java.util.Arrays;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Set;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
@@ -567,20 +570,24 @@ public class IndexAliasesIT extends ESIntegTestCase {
         logger.info("--> getting alias1");
         GetAliasesResponse getResponse = admin().indices().prepareGetAliases("alias1").get();
         assertThat(getResponse, notNullValue());
-        assertThat(getResponse.getAliases().size(), equalTo(1));
+        assertThat(getResponse.getAliases().size(), equalTo(5));
         assertThat(getResponse.getAliases().get("foobar").size(), equalTo(1));
         assertThat(getResponse.getAliases().get("foobar").get(0), notNullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).alias(), equalTo("alias1"));
         assertThat(getResponse.getAliases().get("foobar").get(0).getFilter(), nullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).getIndexRouting(), nullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).getSearchRouting(), nullValue());
+        assertTrue(getResponse.getAliases().get("test").isEmpty());
+        assertTrue(getResponse.getAliases().get("test123").isEmpty());
+        assertTrue(getResponse.getAliases().get("foobarbaz").isEmpty());
+        assertTrue(getResponse.getAliases().get("bazbar").isEmpty());
         AliasesExistResponse existsResponse = admin().indices().prepareAliasesExist("alias1").get();
         assertThat(existsResponse.exists(), equalTo(true));
 
         logger.info("--> getting all aliases that start with alias*");
         getResponse = admin().indices().prepareGetAliases("alias*").get();
         assertThat(getResponse, notNullValue());
-        assertThat(getResponse.getAliases().size(), equalTo(1));
+        assertThat(getResponse.getAliases().size(), equalTo(5));
         assertThat(getResponse.getAliases().get("foobar").size(), equalTo(2));
         assertThat(getResponse.getAliases().get("foobar").get(0), notNullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).alias(), equalTo("alias1"));
@@ -592,6 +599,10 @@ public class IndexAliasesIT extends ESIntegTestCase {
         assertThat(getResponse.getAliases().get("foobar").get(1).getFilter(), nullValue());
         assertThat(getResponse.getAliases().get("foobar").get(1).getIndexRouting(), nullValue());
         assertThat(getResponse.getAliases().get("foobar").get(1).getSearchRouting(), nullValue());
+        assertTrue(getResponse.getAliases().get("test").isEmpty());
+        assertTrue(getResponse.getAliases().get("test123").isEmpty());
+        assertTrue(getResponse.getAliases().get("foobarbaz").isEmpty());
+        assertTrue(getResponse.getAliases().get("bazbar").isEmpty());
         existsResponse = admin().indices().prepareAliasesExist("alias*").get();
         assertThat(existsResponse.exists(), equalTo(true));
 
@@ -676,12 +687,13 @@ public class IndexAliasesIT extends ESIntegTestCase {
         logger.info("--> getting f* for index *bar");
         getResponse = admin().indices().prepareGetAliases("f*").addIndices("*bar").get();
         assertThat(getResponse, notNullValue());
-        assertThat(getResponse.getAliases().size(), equalTo(1));
+        assertThat(getResponse.getAliases().size(), equalTo(2));
         assertThat(getResponse.getAliases().get("foobar").get(0), notNullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).alias(), equalTo("foo"));
         assertThat(getResponse.getAliases().get("foobar").get(0).getFilter(), nullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).getIndexRouting(), nullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).getSearchRouting(), nullValue());
+        assertTrue(getResponse.getAliases().get("bazbar").isEmpty());
         existsResponse = admin().indices().prepareAliasesExist("f*")
                 .addIndices("*bar").get();
         assertThat(existsResponse.exists(), equalTo(true));
@@ -690,13 +702,14 @@ public class IndexAliasesIT extends ESIntegTestCase {
         logger.info("--> getting f* for index *bac");
         getResponse = admin().indices().prepareGetAliases("foo").addIndices("*bac").get();
         assertThat(getResponse, notNullValue());
-        assertThat(getResponse.getAliases().size(), equalTo(1));
+        assertThat(getResponse.getAliases().size(), equalTo(2));
         assertThat(getResponse.getAliases().get("foobar").size(), equalTo(1));
         assertThat(getResponse.getAliases().get("foobar").get(0), notNullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).alias(), equalTo("foo"));
         assertThat(getResponse.getAliases().get("foobar").get(0).getFilter(), nullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).getIndexRouting(), nullValue());
         assertThat(getResponse.getAliases().get("foobar").get(0).getSearchRouting(), nullValue());
+        assertTrue(getResponse.getAliases().get("bazbar").isEmpty());
         existsResponse = admin().indices().prepareAliasesExist("foo")
                 .addIndices("*bac").get();
         assertThat(existsResponse.exists(), equalTo(true));
@@ -729,7 +742,9 @@ public class IndexAliasesIT extends ESIntegTestCase {
                 .removeAlias("foobar", "foo"));
 
         getResponse = admin().indices().prepareGetAliases("foo").addIndices("foobar").get();
-        assertThat(getResponse.getAliases().isEmpty(), equalTo(true));
+        for (final ObjectObjectCursor<String, List<AliasMetaData>> entry : getResponse.getAliases()) {
+            assertTrue(entry.value.isEmpty());
+        }
         existsResponse = admin().indices().prepareAliasesExist("foo").addIndices("foobar").get();
         assertThat(existsResponse.exists(), equalTo(false));
     }

rest-api-spec/src/main/resources/rest-api-spec/test/indices.delete_alias/all_path_options.yml

@@ -84,6 +84,10 @@ setup:
 
 ---
 "check delete with index list":
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
+
   - do:
       indices.delete_alias:
         index: "test_index1,test_index2"
@@ -106,6 +110,10 @@ setup:
 
 ---
 "check delete with prefix* index":
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
+
   - do:
       indices.delete_alias:
         index: "test_*"
@@ -129,6 +137,10 @@ setup:
 
 ---
 "check delete with index list and * aliases":
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
+
   - do:
       indices.delete_alias:
         index: "test_index1,test_index2"
@@ -152,6 +164,10 @@ setup:
 
 ---
 "check delete with index list and _all aliases":
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
+
   - do:
       indices.delete_alias:
         index: "test_index1,test_index2"
@@ -175,6 +191,10 @@ setup:
 
 ---
 "check delete with index list and wildcard aliases":
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
+
   - do:
       indices.delete_alias:
         index: "test_index1,test_index2"

rest-api-spec/src/main/resources/rest-api-spec/test/indices.get_alias/10_basic.yml

@@ -40,6 +40,62 @@ setup:
   - match: {test_index.aliases.test_blias: {}}
   - is_false: test_index_2
 
+---
+"Get aliases via /_all/_alias/":
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
+
+  - do:
+      indices.create:
+        index: myindex
+
+  - do:
+      indices.get_alias:
+        index: _all
+
+  - match: {test_index.aliases.test_alias: {}}
+  - match: {test_index.aliases.test_blias: {}}
+  - match: {test_index_2.aliases.test_alias: {}}
+  - match: {test_index_2.aliases.test_blias: {}}
+  - match: {myindex.aliases: {}}
+
+---
+"Get aliases via /*/_alias/":
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
+
+  - do:
+      indices.create:
+        index: myindex
+
+  - do:
+      indices.get_alias:
+        index: "*"
+
+  - match: {test_index.aliases.test_alias: {}}
+  - match: {test_index.aliases.test_blias: {}}
+  - match: {test_index_2.aliases.test_alias: {}}
+  - match: {test_index_2.aliases.test_blias: {}}
+  - match: {myindex.aliases: {}}
+
+---
+"Get and index with no aliases via /{index}/_alias/":
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
+
+  - do:
+      indices.create:
+        index: myindex
+
+  - do:
+      indices.get_alias:
+        index: myindex
+
+  - match: {myindex.aliases: {}}
+
 ---
 "Get specific alias via /{index}/_alias/{name}":
 

rest-api-spec/src/main/resources/rest-api-spec/test/indices.put_alias/all_path_options.yml

@@ -14,6 +14,9 @@ setup:
 
 ---
 "put alias per index":
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
 
   - do:
       indices.put_alias:
@@ -69,7 +72,9 @@ setup:
 
 ---
 "put alias prefix* index":
-
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
 
   - do:
       indices.put_alias:
@@ -86,7 +91,9 @@ setup:
 
 ---
 "put alias in list of indices":
-
+  - skip:
+      version: " - 5.99.99"
+      reason:  only requested indices are included in 6.x
 
   - do:
       indices.put_alias: