Add new callback methods to UaSubscription.NotificationListener

Add `onNotificationDataLost` and `onSubscriptionTransferFailed` callbacks to
UaSubscription.NotificationListener. This allows registering a listener at the
subscription level for callbacks that previously required registration with
OpcUaSubscriptionManager and would be invoked for all subscriptions.

opc-ua-sdk/sdk-client/src/main/java/org/eclipse/milo/opcua/sdk/client/api/subscriptions/UaSubscription.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019 the Eclipse Milo Authors
+ * Copyright (c) 2021 the Eclipse Milo Authors
  *
  * This program and the accompanying materials are made
  * available under the terms of the Eclipse Public License 2.0
@@ -15,6 +15,7 @@
 import java.util.stream.Collectors;
 
 import com.google.common.collect.ImmutableList;
+import org.eclipse.milo.opcua.sdk.client.api.UaSession;
 import org.eclipse.milo.opcua.stack.core.types.builtin.DataValue;
 import org.eclipse.milo.opcua.stack.core.types.builtin.DateTime;
 import org.eclipse.milo.opcua.stack.core.types.builtin.StatusCode;
@@ -297,6 +298,27 @@ default void onKeepAliveNotification(UaSubscription subscription, DateTime publi
          */
         default void onStatusChangedNotification(UaSubscription subscription, StatusCode status) {}
 
+        /**
+         * Attempts to recover missed notification data have failed.
+         * <p>
+         * When a notification is missed a series of Republish requests are initiated to recover the missing data. If
+         * republishing fails, or any of the notifications are no longer available, this callback will be invoked.
+         *
+         * @param subscription the subscription that missed notification data.
+         */
+        default void onNotificationDataLost(UaSubscription subscription) {}
+
+        /**
+         * A new {@link UaSession} was established, and upon attempting to transfer an existing subscription to this
+         * new session, a failure occurred.
+         * <p>
+         * This subscription will be removed from {@link UaSubscriptionManager}'s bookkeeping. It must be re-created.
+         *
+         * @param subscription the {@link UaSubscription} that could not be transferred.
+         * @param statusCode   the {@link StatusCode} for the transfer failure.
+         */
+        default void onSubscriptionTransferFailed(UaSubscription subscription, StatusCode statusCode) {}
+
     }
 
 }

opc-ua-sdk/sdk-client/src/main/java/org/eclipse/milo/opcua/sdk/client/subscriptions/OpcUaSubscriptionManager.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019 the Eclipse Milo Authors
+ * Copyright (c) 2021 the Eclipse Milo Authors
  *
  * This program and the accompanying materials are made
  * available under the terms of the Eclipse Public License 2.0
@@ -363,6 +363,11 @@ public void transferFailed(UInteger subscriptionId, StatusCode statusCode) {
 
         if (subscription != null) {
             subscriptionListeners.forEach(l -> l.onSubscriptionTransferFailed(subscription, statusCode));
+
+            subscription.getNotificationListeners().forEach(
+                l ->
+                    l.onSubscriptionTransferFailed(subscription, statusCode)
+            );
         }
     }
 
@@ -528,10 +533,12 @@ private void onPublishComplete(PublishResponse response, AtomicLong pendingCount
                     logger.debug("Republish failed: {}", ex.getMessage(), ex);
 
                     subscriptionListeners.forEach(l -> l.onNotificationDataLost(subscription));
+                    subscription.getNotificationListeners().forEach(l -> l.onNotificationDataLost(subscription));
                 } else {
                     // Republish succeeded, possibly with some data loss, resume processing.
                     if (dataLost) {
                         subscriptionListeners.forEach(l -> l.onNotificationDataLost(subscription));
+                        subscription.getNotificationListeners().forEach(l -> l.onNotificationDataLost(subscription));
                     }
                 }