Added index templates REST support for HEAD and proper 404

* Added HEAD support for index templates to find out of they exist
* Returning a 404 instead of a 200 if a GET hits on a non-existing index template

Closes elastic#3434

src/main/java/org/elasticsearch/rest/action/RestActionModule.java

@@ -62,6 +62,7 @@
 import org.elasticsearch.rest.action.admin.indices.status.RestIndicesStatusAction;
 import org.elasticsearch.rest.action.admin.indices.template.delete.RestDeleteIndexTemplateAction;
 import org.elasticsearch.rest.action.admin.indices.template.get.RestGetIndexTemplateAction;
+import org.elasticsearch.rest.action.admin.indices.template.head.RestHeadIndexTemplateAction;
 import org.elasticsearch.rest.action.admin.indices.template.put.RestPutIndexTemplateAction;
 import org.elasticsearch.rest.action.admin.indices.validate.query.RestValidateQueryAction;
 import org.elasticsearch.rest.action.admin.indices.warmer.delete.RestDeleteWarmerAction;
@@ -142,6 +143,7 @@ protected void configure() {
         bind(RestGetIndexTemplateAction.class).asEagerSingleton();
         bind(RestPutIndexTemplateAction.class).asEagerSingleton();
         bind(RestDeleteIndexTemplateAction.class).asEagerSingleton();
+        bind(RestHeadIndexTemplateAction.class).asEagerSingleton();
 
         bind(RestPutWarmerAction.class).asEagerSingleton();
         bind(RestDeleteWarmerAction.class).asEagerSingleton();

src/main/java/org/elasticsearch/rest/action/admin/indices/template/get/RestGetIndexTemplateAction.java

@@ -39,6 +39,7 @@
 import java.util.Map;
 
 import static org.elasticsearch.rest.RestRequest.Method.GET;
+import static org.elasticsearch.rest.RestStatus.NOT_FOUND;
 import static org.elasticsearch.rest.RestStatus.OK;
 
 /**
@@ -76,16 +77,21 @@ public void onResponse(ClusterStateResponse response) {
 
                 try {
                     MetaData metaData = response.getState().metaData();
-                    XContentBuilder builder = RestXContentBuilder.restContentBuilder(request);
-                    builder.startObject();
 
-                    for (IndexTemplateMetaData indexMetaData : metaData.templates().values()) {
-                        IndexTemplateMetaData.Builder.toXContent(indexMetaData, builder, params);
-                    }
+                    if (metaData.templates().values().size() == 0) {
+                        channel.sendResponse(new StringRestResponse(NOT_FOUND));
+                    } else {
+                        XContentBuilder builder = RestXContentBuilder.restContentBuilder(request);
+                        builder.startObject();
+
+                        for (IndexTemplateMetaData indexMetaData : metaData.templates().values()) {
+                            IndexTemplateMetaData.Builder.toXContent(indexMetaData, builder, params);
+                        }
 
-                    builder.endObject();
+                        builder.endObject();
 
-                    channel.sendResponse(new XContentRestResponse(request, OK, builder));
+                        channel.sendResponse(new XContentRestResponse(request, OK, builder));
+                    }
                 } catch (Throwable e) {
                     onFailure(e);
                 }

src/main/java/org/elasticsearch/rest/action/admin/indices/template/head/RestHeadIndexTemplateAction.java

@@ -0,0 +1,83 @@
+/*
+ * Licensed to ElasticSearch and Shay Banon under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. ElasticSearch licenses this
+ * file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.elasticsearch.rest.action.admin.indices.template.head;
+
+import org.elasticsearch.ExceptionsHelper;
+import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.admin.cluster.state.ClusterStateRequest;
+import org.elasticsearch.action.admin.cluster.state.ClusterStateResponse;
+import org.elasticsearch.client.Client;
+import org.elasticsearch.client.Requests;
+import org.elasticsearch.common.inject.Inject;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.rest.*;
+
+import static org.elasticsearch.rest.RestRequest.Method.HEAD;
+import static org.elasticsearch.rest.RestStatus.NOT_FOUND;
+import static org.elasticsearch.rest.RestStatus.OK;
+
+/**
+ *
+ */
+public class RestHeadIndexTemplateAction extends BaseRestHandler {
+
+    @Inject
+    public RestHeadIndexTemplateAction(Settings settings, Client client, RestController controller) {
+        super(settings, client);
+
+        controller.registerHandler(HEAD, "/_template/{name}", this);
+    }
+
+    @Override
+    public void handleRequest(final RestRequest request, final RestChannel channel) {
+        ClusterStateRequest clusterStateRequest = Requests.clusterStateRequest()
+                .filterRoutingTable(true)
+                .filterNodes(true)
+                .filteredIndexTemplates(request.param("name"))
+                .filterOutIndices();
+
+        clusterStateRequest.listenerThreaded(false);
+
+        client.admin().cluster().state(clusterStateRequest, new ActionListener<ClusterStateResponse>() {
+            @Override
+            public void onResponse(ClusterStateResponse response) {
+                try {
+                    boolean templateExists = response.getState().metaData().templates().size() > 0;
+
+                    if (templateExists) {
+                        channel.sendResponse(new StringRestResponse(OK));
+                    } else {
+                        channel.sendResponse(new StringRestResponse(NOT_FOUND));
+                    }
+                } catch (Throwable e) {
+                    onFailure(e);
+                }
+            }
+
+            @Override
+            public void onFailure(Throwable e) {
+                try {
+                    channel.sendResponse(new StringRestResponse(ExceptionsHelper.status(e)));
+                } catch (Exception e1) {
+                    logger.error("Failed to send failure response", e1);
+                }
+            }
+        });
+    }
+}