util: Add functions for handling leaf-list operations

1 files changed, 97 insertions, 0 deletions

diff --git a/ncserver/base/util.py b/ncserver/base/util.py
index f69c65b..5223d92 100644
--- a/ncserver/base/util.py
+++ b/ncserver/base/util.py
@@ -43,3 +43,100 @@ def node_operation(node, def_op='merge') -> str:
     nc10 = '{urn:ietf:params:xml:ns:netconf:base:1.0}operation'
     nc11 = '{urn:ietf:params:xml:ns:netconf:base:1.1}operation'
     return node.attrib.get(nc11, node.attrib.get(nc10, def_op))
+
+
+def _index_for_list_op(the_list: list, operation: str, insert_value) -> int:
+    """Determine the index for a leaf-list insertion.
+
+    :param list the_list:
+        The Python list object that represents the leaf-list.
+
+    :param str operation:
+        The insertion mode: first, last, before, after.
+
+    :param insert_value:
+        The value to insert for modes before and after.  MUST be specified.
+
+    :returns int:
+        The index in which to insert.
+    """
+    if operation == 'last':
+        return len(the_list)
+    if operation == 'first':
+        return 0
+    if operation == 'before':
+        return the_list.index(insert_value)
+    if operation == 'after':
+        return the_list.index(insert_value) + 1
+
+    return -1
+
+
+def handle_list_operation(rpc, the_list: list, node, operation: str) -> list:
+    """Perform a <edit-config/> operation on a leaf-list based on RFC 6020.
+
+    :param rpc:
+        The RPC <edit-config/> message.
+
+    :param list the_list:
+        The Python list object that represents the leaf-list.
+
+    :param node:
+        The XML node that represents the item being operated on.
+
+    :param str insert:
+        The insertion mode for non-deletion operation: first, last, before,
+        after.  Defaults to 'last' if None.
+
+    :param insert_value:
+        The value to insert the new value before or after.  Only used if
+        'insert' is before or after.
+
+    :returns list:
+        The list with the value manipulated with the desired effect.
+    """
+    value = node.text
+
+    # RFC 6020 § 7.7.7
+    val_attr = '{urn:ietf:params:xml:ns:yang:1}value'
+    insert = node.attrib.get('{urn:ietf:params:xml:ns:yang:1}insert', 'last')
+    insert_value = node.attrib.get(val_attr, None)
+
+    if operation == 'create':
+        if value in the_list:
+            raise error.DataExistsAppError(rpc)
+        if insert is None:
+            insert = 'last'
+
+    if operation in ['merge', 'replace']:
+        # Need clarification about RFC § 7.7.7.  This may be wrong.
+        # If so, change `return` to `insert = 'last'`, or move to function top.
+        if insert is None:
+            return the_list
+
+        # `insert` was specified, so we will move this item.
+        if value in the_list:
+            the_list.remove(value)
+
+    if operation in ['delete', 'remove']:
+        if value not in the_list:
+            if operation == 'delete':
+                raise error.DataMissingAppError(rpc)
+            return the_list  # Job done.
+
+        the_list.remove(value)
+        return the_list
+
+    # Okay.  We are performing an addition of some kind on this list.
+    if insert in ['before', 'after'] and (
+            insert_value is None or insert_value not in the_list):
+        raise error.BadAttributeAppError(rpc, node, val_attr)
+
+    index = _index_for_list_op(the_list, insert, insert_value)
+    if index == -1:
+        raise error.BadAttributeAppError(
+                rpc, node, '{urn:ietf:params:xml:ns:yang:1}insert'
+        )
+
+    the_list.insert(index, value)
+    return the_list