GUACAMOLE-364: listener interfaces now extend a common marker interface

guacamole-ext/src/main/java/org/apache/guacamole/net/event/listener/AuthenticationFailureListener.java

@@ -27,8 +27,7 @@ import org.apache.guacamole.net.event.AuthenticationFailureEvent;
  * after a user's authentication attempt fails. Note that this hook cannot
  * be used to cancel the authentication failure.
  */
-public interface AuthenticationFailureListener  {
-
+public interface AuthenticationFailureListener extends Listener {
     /**
      * Event hook which fires immediately after a user's authentication attempt
      * fails.

guacamole-ext/src/main/java/org/apache/guacamole/net/event/listener/AuthenticationSuccessListener.java

@@ -28,7 +28,7 @@ import org.apache.guacamole.net.event.AuthenticationSuccessEvent;
  * the authenticationSucceeded() hook has the opportunity to cancel the
  * authentication and force it to fail.
  */
-public interface AuthenticationSuccessListener {
+public interface AuthenticationSuccessListener extends Listener {
 
     /**
      * Event hook which fires immediately after a user's authentication attempt

guacamole-ext/src/main/java/org/apache/guacamole/net/event/listener/Listener.java

@@ -0,0 +1,29 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.guacamole.net.event.listener;
+
+/**
+ * A marker interface extended by all listener types. This interface is used
+ * simply to validate that a listener class identified in an extension
+ * actually implements some listener interface.
+ */
+public interface Listener {
+}

guacamole-ext/src/main/java/org/apache/guacamole/net/event/listener/TunnelCloseListener.java

@@ -26,10 +26,10 @@ import org.apache.guacamole.net.event.TunnelCloseEvent;
  * A listener whose tunnelClosed() hook will fire immediately after an
  * existing tunnel is closed.
  */
-public interface TunnelCloseListener {
+public interface TunnelCloseListener extends Listener {
 
     /**
-     * Event hook which fires immediately after an existing tunnel is closed.
+     * Event hook which fires immediately before an existing tunnel is closed.
      * The return value of this hook dictates whether the tunnel is allowed to
      * be closed.
      *

guacamole-ext/src/main/java/org/apache/guacamole/net/event/listener/TunnelConnectListener.java

@@ -26,7 +26,7 @@ import org.apache.guacamole.net.event.TunnelConnectEvent;
  * A listener whose tunnelConnected() hook will fire immediately after a new
  * tunnel is connected.
  */
-public interface TunnelConnectListener {
+public interface TunnelConnectListener extends Listener {
 
    /**
      * Event hook which fires immediately after a new tunnel is connected.