subscription: return parent node to oper_state callback via extra_info

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

@@ -552,6 +552,10 @@ def subscribe_module_change_unsafe(
             * netconf_id: the NETCONF session ID set for the event originator
                 sysrepo session
             * user: the effective username of the event originator sysrepo session
+            * parent_xpath: XPath 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.
 
     The callback is expected to return a python dictionary containing the operational
     data. The dictionary should be in the libyang "dict" format. It will be parsed to a

sysrepo/subscription.py

@@ -367,9 +367,14 @@ def oper_data_callback(session, sub_id, module, xpath, req_xpath, req_id, parent
         callback = subscription.callback
         private_data = subscription.private_data
         if subscription.extra_info:
+            parent_xpath = None
+            if parent[0]:
+                with session.get_ly_ctx() as ly_ctx:
+                    parent_xpath = DNode.new(ly_ctx, parent[0]).path()
             extra_info = {
                 "netconf_id": session.get_netconf_id(),
                 "user": session.get_user(),
+                "parent_xpath": parent_xpath,
             }
         else:
             extra_info = {}

tests/test_subs_oper.py

@@ -84,6 +84,8 @@ def oper_data_cb(xpath, private_data, **kwargs):
             self.assertEqual(getpass.getuser(), kwargs["user"])
             self.assertIn("netconf_id", kwargs)
             self.assertEqual(kwargs["netconf_id"], 12)
+            self.assertIn("parent_xpath", kwargs)
+            self.assertIsNone(kwargs["parent_xpath"])
             calls.append((xpath, private_data, kwargs))
             return {"state": {}}