subscription: return parent node to oper_state callback

The only way to differentiate two calls when there is a subscription
on an internal element of a list is by using the parent node. Moreover,
in these cases, it is on this parent node that the data structure to
be returned must be built.

sysrepo/session.py

@@ -372,13 +372,17 @@ def subscribe_module_change(
 
         self.subscriptions.append(sub)
 
-    OperDataCallbackType = Callable[[str, Any], Optional[Dict]]
+    OperDataCallbackType = Callable[[str, Optional[libyang.DNode], Any], Optional[Dict]]
     """
     Callback to be called when the operational data are requested.
 
     :arg xpath:
         The XPath requested by a client. Can be None if the client requested for all the
         module operational data.
+    :arg parent:
+        Pointer to an existing parent of the requested nodes. It is None for top-level
+        nodes. Caller is supposed to append the requested nodes to this data subtree
+        and return either the original parent or a top-level node.
     :arg private_data:
         Private context opaque to sysrepo used when subscribing.
     :arg kwargs (optional):

sysrepo/subscription.py

@@ -360,12 +360,17 @@ def oper_data_callback(session, sub_id, module, xpath, req_xpath, req_id, parent
         else:
             extra_info = {}
 
+        parent_node = None
+        if parent[0]:
+            with session.get_ly_ctx() as ly_ctx:
+                parent_node = DNode.new(ly_ctx, parent[0])
+
         if is_async_func(callback):
             task_id = req_id
 
             if task_id not in subscription.tasks:
                 task = subscription.loop.create_task(
-                    callback(req_xpath, private_data, **extra_info)
+                    callback(req_xpath, parent_node, private_data, **extra_info)
                 )
                 task.add_done_callback(
                     functools.partial(subscription.task_done, task_id, "oper")
@@ -382,7 +387,7 @@ def oper_data_callback(session, sub_id, module, xpath, req_xpath, req_id, parent
             oper_data = task.result()
 
         else:
-            oper_data = callback(req_xpath, private_data, **extra_info)
+            oper_data = callback(req_xpath, parent_node, private_data, **extra_info)
 
         if isinstance(oper_data, dict):
             # convert oper_data to a libyang.DNode object

tests/test_subs_oper.py

@@ -39,8 +39,9 @@ def test_oper_sub(self):
         priv = object()
         state = None
 
-        def oper_data_cb(xpath, private_data):
+        def oper_data_cb(xpath, path, private_data):
             self.assertEqual(xpath, "/sysrepo-example:state")
+            self.assertIsNone(path)
             self.assertEqual(private_data, priv)
             return state
 
@@ -77,8 +78,9 @@ def test_oper_sub_with_extra_info(self):
         priv = object()
         calls = []
 
-        def oper_data_cb(xpath, private_data, **kwargs):
+        def oper_data_cb(xpath, path, private_data, **kwargs):
             self.assertEqual(xpath, "/sysrepo-example:state")
+            self.assertIsNone(path)
             self.assertEqual(private_data, priv)
             self.assertIn("user", kwargs)
             self.assertEqual(getpass.getuser(), kwargs["user"])