Do not increase notfication counter for keep alive publishrequests

examples/example-server.py

@@ -59,8 +59,8 @@ if __name__ == "__main__":
     # logger.setLevel(logging.DEBUG)
     #logger = logging.getLogger("opcua.uaprocessor")
     # logger.setLevel(logging.DEBUG)
-    #logger = logging.getLogger("opcua.subscription_service")
-    # logger.setLevel(logging.DEBUG)
+    logger = logging.getLogger("opcua.subscription_service")
+    logger.setLevel(logging.DEBUG)
 
     # now setup our server
     server = Server()

opcua/internal_subscription.py

@@ -256,10 +256,11 @@ class InternalSubscription(object):
         self._keep_alive_count = 0
         self._startup = False
         result.NotificationMessage.SequenceNumber = self._notification_seq
-        self._notification_seq += 1
+        if len(result.NotificationMessage.NotificationData) != 0:
+            self._notification_seq += 1
+            self._not_acknowledged_results[result.NotificationMessage.SequenceNumber] = result
         result.MoreNotifications = False
         result.AvailableSequenceNumbers = list(self._not_acknowledged_results.keys())
-        self._not_acknowledged_results[result.NotificationMessage.SequenceNumber] = result
         return result
 
     def _pop_triggered_datachanges(self, result):