Correctly state cluster is in maintenance mode when maintenance znode is empty (#2559)

helix-rest maintenanceSignal detects cluster in maintenance mode when maintenance znode is empty

Author: GrantPSpencer

helix-rest/src/main/java/org/apache/helix/rest/server/resources/helix/ClusterAccessor.java

@@ -765,12 +765,16 @@ public Response getClusterMaintenanceHistory(@PathParam("clusterId") String clus
   @GET
   @Path("{clusterId}/controller/maintenanceSignal")
   public Response getClusterMaintenanceSignal(@PathParam("clusterId") String clusterId) {
-    HelixDataAccessor dataAccessor = getDataAccssor(clusterId);
-    MaintenanceSignal maintenanceSignal =
-        dataAccessor.getProperty(dataAccessor.keyBuilder().maintenance());
-    if (maintenanceSignal != null) {
-      Map<String, String> maintenanceInfo = maintenanceSignal.getRecord().getSimpleFields();
+    boolean inMaintenanceMode = getHelixAdmin().isInMaintenanceMode(clusterId);
+
+    if (inMaintenanceMode) {
+      HelixDataAccessor dataAccessor = getDataAccssor(clusterId);
+      MaintenanceSignal maintenanceSignal = dataAccessor.getProperty(dataAccessor.keyBuilder().maintenance());
+
+      Map<String, String> maintenanceInfo = (maintenanceSignal != null) ?
+          maintenanceSignal.getRecord().getSimpleFields() : new HashMap<>();
       maintenanceInfo.put(ClusterProperties.clusterName.name(), clusterId);
+
       return JSONRepresentation(maintenanceInfo);
     }
     return notFound(String.format("Cluster %s is not in maintenance mode!", clusterId));

helix-rest/src/test/java/org/apache/helix/rest/server/TestClusterAccessor.java

@@ -523,6 +523,33 @@ public void testEnableDisableMaintenanceMode() throws IOException {
   }
 
   @Test(dependsOnMethods = "testEnableDisableMaintenanceMode")
+  public void testEmptyMaintenanceSignal() throws IOException {
+    System.out.println("Start test :" + TestHelper.getTestMethodName());
+    String cluster = _clusters.iterator().next();
+
+    // Create empty maintenance znode
+    ZNRecord record = new ZNRecord("test_maintenance_node");
+    ZKUtil.createOrUpdate(_gZkClient, "/"+cluster+"/CONTROLLER/MAINTENANCE", record, true, true);
+
+    // Verify maintenance mode enabled
+    Assert.assertTrue(isMaintenanceModeEnabled(cluster));
+    get("clusters/" + cluster + "/controller/maintenanceSignal", null,
+        Response.Status.OK.getStatusCode(), true);
+
+
+    // Disable maintenance mode
+    post("clusters/" + cluster, ImmutableMap.of("command", "disableMaintenanceMode"),
+        Entity.entity("", MediaType.APPLICATION_JSON_TYPE), Response.Status.OK.getStatusCode());
+
+    // Verify no longer in maintenance mode
+    Assert.assertFalse(isMaintenanceModeEnabled(cluster));
+    get("clusters/" + cluster + "/controller/maintenanceSignal", null,
+        Response.Status.NOT_FOUND.getStatusCode(), false);
+    System.out.println("End test :" + TestHelper.getTestMethodName());
+
+  }
+
+  @Test(dependsOnMethods = "testEmptyMaintenanceSignal")
   public void testGetControllerLeadershipHistory() throws IOException {
     System.out.println("Start test :" + TestHelper.getTestMethodName());
     String cluster = _clusters.iterator().next();