added callbacks to notify when a node goes temporarily offlien

core/src/main/java/hudson/model/Computer.java

@@ -41,6 +41,7 @@ import hudson.security.Permission;
 import hudson.security.PermissionGroup;
 import hudson.security.PermissionScope;
 import hudson.slaves.ComputerLauncher;
+import hudson.slaves.ComputerListener;
 import hudson.slaves.RetentionStrategy;
 import hudson.slaves.WorkspaceList;
 import hudson.slaves.OfflineCause;
@@ -539,6 +540,10 @@ public /*transient*/ abstract class Computer extends Actionable implements Acces
         synchronized (statusChangeLock) {
             statusChangeLock.notifyAll();
         }
+        for (ComputerListener cl : ComputerListener.all()) {
+            if (temporarilyOffline)     cl.onTemporarilyOffline(this,cause);
+            else                        cl.onTemporarilyOnline(this);
+        }
     }
 
     @Exported

core/src/main/java/hudson/slaves/ComputerListener.java

@@ -164,6 +164,21 @@ public abstract class ComputerListener implements ExtensionPoint {
      */
     public void onOffline(Computer c) {}
 
+    /**
+     * Indicates that the computer was marked as temporarily online by the administrator.
+     * This is the reverse operation of {@link #onTemporarilyOffline(Computer)}
+     *
+     * @since 1.452
+     */
+    public void onTemporarilyOnline(Computer c) {}
+    /**
+     * Indicates that the computer was marked as temporarily online by the administrator.
+     * This is the reverse operation of {@link #onTemporarilyOffline(Computer)}
+     *
+     * @since 1.452
+     */
+    public void onTemporarilyOffline(Computer c, OfflineCause cause) {}
+
     /**
      * Called when configuration of the node was changed, a node is added/removed, etc.
      * @since 1.377