Detect heapdump-endpoint via OPTIONS request

Since a HEAD request to the heapdump triggers a dump we need to test the
availability of the heapdump endppoint via OPTIONS-request.
To get this working we need to ensure that the OPTIONS-request are dispatched
to the zuul servlet as this wasn't done prio to this commit adding the
OptionsDispatchingZuulController.

Author: ejavexpert

spring-boot-admin-server-ui/modules/applications/module.js

@@ -92,8 +92,8 @@ module.run(function ($rootScope, $state, $filter, $sce, $http, Notification, App
       if (!application.managementUrl || !application.statusInfo.status || application.statusInfo.status === 'OFFLINE') {
         return false;
       }
-      return $http.head('api/applications/' + application.id + '/heapdump').then(function () {
-        return true;
+      return $http({ method: 'OPTIONS', url: 'api/applications/' + application.id + '/heapdump' }).then(function (response) {
+        return response.headers('Allow') === 'GET,HEAD'; //Test the exact headers, in case the DispatcherServlet responses to the request for older boot-versions
       }).catch(function () {
         return false;
       });

spring-boot-admin-server/src/main/java/de/codecentric/boot/admin/config/RevereseZuulProxyConfiguration.java

@@ -28,6 +28,7 @@
 import org.springframework.cloud.netflix.zuul.filters.TraceProxyRequestHelper;
 import org.springframework.cloud.netflix.zuul.filters.pre.PreDecorationFilter;
 import org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter;
+import org.springframework.cloud.netflix.zuul.web.ZuulController;
 import org.springframework.cloud.netflix.zuul.web.ZuulHandlerMapping;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationListener;
@@ -38,6 +39,7 @@
 import de.codecentric.boot.admin.event.RoutesOutdatedEvent;
 import de.codecentric.boot.admin.registry.ApplicationRegistry;
 import de.codecentric.boot.admin.zuul.ApplicationRouteLocator;
+import de.codecentric.boot.admin.zuul.OptionsDispatchingZuulController;
 
 @Configuration
 @AutoConfigureAfter({ AdminServerWebConfiguration.class })
@@ -63,6 +65,12 @@ public ApplicationRouteLocator routeLocator() {
 				adminServer.getContextPath() + "/api/applications/");
 	}
 
+	@Bean
+	@Override
+	public ZuulController zuulController() {
+		return new OptionsDispatchingZuulController();
+	}
+
 	@Bean
 	public ProxyRequestHelper proxyRequestHelper() {
 		TraceProxyRequestHelper helper = new TraceProxyRequestHelper();

spring-boot-admin-server/src/main/java/de/codecentric/boot/admin/zuul/OptionsDispatchingZuulController.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2014 the original author or authors.
+ *
+ * Licensed 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 de.codecentric.boot.admin.zuul;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import javax.servlet.http.HttpSession;
+
+import org.springframework.cloud.netflix.zuul.web.ZuulController;
+import org.springframework.web.servlet.ModelAndView;
+import org.springframework.web.util.WebUtils;
+
+/**
+ * This Controller behaves like the original ZuulController except it forwads also the OPTIONS
+ * request to Servlet instead of handling the request itself.
+ *
+ * @author Johannes Edmeier
+ */
+public class OptionsDispatchingZuulController extends ZuulController {
+
+	@Override
+	public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
+			throws Exception {
+		// Delegate to WebContentGenerator for checking and preparing.
+		checkRequest(request);
+		prepareResponse(response);
+
+		// Execute handleRequestInternal in synchronized block if required.
+		if (this.isSynchronizeOnSession()) {
+			HttpSession session = request.getSession(false);
+			if (session != null) {
+				Object mutex = WebUtils.getSessionMutex(session);
+				synchronized (mutex) {
+					return handleRequestInternal(request, response);
+				}
+			}
+		}
+
+		return handleRequestInternal(request, response);
+	}
+
+}