Avoid NPE in NodeService#stats if HTTP is disabled

This commit adds safety against an NPE if HTTP stats are requested but
HTTP is disabled on a node.

Relates #22060

core/src/main/java/org/elasticsearch/node/service/NodeService.java

@@ -19,9 +19,6 @@
 
 package org.elasticsearch.node.service;
 
-import java.io.Closeable;
-import java.io.IOException;
-
 import org.elasticsearch.Build;
 import org.elasticsearch.Version;
 import org.elasticsearch.action.admin.cluster.node.info.NodeInfo;
@@ -44,6 +41,9 @@ import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
 
+import java.io.Closeable;
+import java.io.IOException;
+
 public class NodeService extends AbstractComponent implements Closeable {
 
     private final ThreadPool threadPool;
@@ -111,7 +111,7 @@ public class NodeService extends AbstractComponent implements Closeable {
                 threadPool ? this.threadPool.stats() : null,
                 fs ? monitorService.fsService().stats() : null,
                 transport ? transportService.stats() : null,
-                http ? httpServer.stats() : null,
+                http ? (httpServer == null ? null : httpServer.stats()) : null,
                 circuitBreaker ? circuitBreakerService.stats() : null,
                 script ? scriptService.stats() : null,
                 discoveryStats ? discovery.stats() : null,
@@ -127,4 +127,5 @@ public class NodeService extends AbstractComponent implements Closeable {
     public void close() throws IOException {
         indicesService.close();
     }
+
 }

core/src/test/java/org/elasticsearch/node/service/NodeServiceTests.java

@@ -0,0 +1,43 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.node.service;
+
+import org.elasticsearch.action.admin.cluster.node.stats.NodesStatsRequest;
+import org.elasticsearch.action.admin.cluster.node.stats.NodesStatsResponse;
+import org.elasticsearch.common.network.NetworkModule;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.test.ESSingleNodeTestCase;
+
+import static org.hamcrest.Matchers.hasSize;
+
+public class NodeServiceTests extends ESSingleNodeTestCase {
+
+    @Override
+    protected Settings nodeSettings() {
+        return Settings.builder().put(NetworkModule.HTTP_ENABLED.getKey(), false).build();
+    }
+
+    public void testHttpServerDisabled() {
+        // test for a bug where if HTTP stats were requested but HTTP was disabled, NodeService would hit a NullPointerException
+        NodesStatsResponse response = client().admin().cluster().nodesStats(new NodesStatsRequest().http(true)).actionGet();
+        assertThat(response.getNodes(), hasSize(1));
+    }
+
+}