Fix `external-gateway-multihoming` API extension definition

The new field ``external-gateways`` added in the API extension
``external-gateway-multihoming`` didn't have the ``enforce_policy`` flag
defined and the validate parameters didn't provide the needed
information to the Neutron policy to build a correct rule match.
Now this field copies the ``ext-gw-mode`` extension validator used in
the ``external_gateway_info`` field.

The validator type ``list_of_dict_or_nodata`` is currently not
recognized by the Neutron policy as an iterable validator [1]; this
code must be changed in Neutron in order to accept this new defined
validator that is not a dictionary but a list of dictionaries.

[1]86f94de99a/neutron/policy.py (L142)

Closes-Bug: #2098109
Change-Id: I592f7ff0673c15276e9da0054fd38f7ad96f795a

neutron_lib/api/definitions/l3_ext_gw_multihoming.py

@@ -12,6 +12,9 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import copy
+import typing
+
 from neutron_lib.api.definitions import l3
 from neutron_lib.api.definitions import l3_ext_gw_mode
 
@@ -26,6 +29,11 @@ DESCRIPTION = 'Allow multiple external gateway ports per router'
 UPDATED_TIMESTAMP = '2023-01-18T00:00:00-00:00'
 RESOURCE_NAME = l3.ROUTER
 COLLECTION_NAME = l3.ROUTERS
+
+external_gw_info_validate: typing.Dict[str, typing.Any] = copy.deepcopy(
+    l3_ext_gw_mode.RESOURCE_ATTRIBUTE_MAP[COLLECTION_NAME][l3.EXTERNAL_GW_INFO]
+    ['validate']['type:dict_or_nodata']
+)
 RESOURCE_ATTRIBUTE_MAP = {
     COLLECTION_NAME: {
         EXTERNAL_GATEWAYS: {
@@ -33,7 +41,10 @@ RESOURCE_ATTRIBUTE_MAP = {
             'allow_put': False,
             'is_visible': True,
             'default': None,
-            'validate': {'type:external_gw_info_list': None},
+            'enforce_policy': True,
+            'validate': {
+                'type:list_of_dict_or_nodata': external_gw_info_validate
+            },
         },
     },
 }

neutron_lib/api/validators/__init__.py

@@ -28,7 +28,7 @@ from neutron_lib._i18n import _
 from neutron_lib import constants
 from neutron_lib import exceptions as n_exc
 from neutron_lib.plugins import directory
-from neutron_lib.services.qos import constants as qos_consts
+
 
 LOG = logging.getLogger(__name__)
 
@@ -1211,40 +1211,17 @@ def validate_ethertype(ethertype, valid_values=None):
         return _(msg) % msg_data
 
 
-def validate_external_gw_info(data, valid_values=None):
-    """Validate data is an external_gateway_info.
+def validate_list_of_dict_or_nodata(data, valid_values=None):
+    """Validate a list of dictionaries.
 
-    :param data: The data to validate.
-    :param valid_values: Not used!
+    :param data: The data to validate. The data could be an empty list or None.
+    :param valid_values: The optional list of keys that must be contained in
+        data.
     :returns: None if valid, error string otherwise.
     """
-    # See https://github.com/PyCQA/pylint/issues/850
-    # pylint: disable=import-outside-toplevel,cyclic-import
-    from neutron_lib.api import converters
-    return validate_dict_or_nodata(
-        data,
-        key_specs={
-            'network_id': {'type:uuid': None, 'required': True},
-            'external_fixed_ips': {'type:fixed_ips': None, 'required': False},
-            'enable_snat': {'type:boolean': None, 'required': False,
-                            'convert_to': converters.convert_to_boolean},
-            qos_consts.QOS_POLICY_ID: {
-                'type:uuid_or_none': None,
-                'required': False
-            }
-        }
-    )
-
-
-def validate_external_gw_info_list(data, valid_values=None):
-    """Validate data is a list of external_gateway_info.
-
-    :param data: The data to validate.
-    :param valid_values: Not used!
-    :returns: None if valid, error string otherwise.
-    """
-    if data is not None:
-        return _validate_list_of_items(validate_external_gw_info, data)
+    if data:
+        return _validate_list_of_items(validate_dict_or_nodata, data,
+                                       **valid_values)
 
 
 # Dictionary that maintains a list of validation functions
@@ -1298,8 +1275,7 @@ validators = {'type:dict': validate_dict,
               'type:list_of_subnets_or_none': validate_subnet_list_or_none,
               'type:list_of_subnet_service_types':
                   validate_subnet_service_types,
-              'type:external_gw_info': validate_external_gw_info,
-              'type:external_gw_info_list': validate_external_gw_info_list,
+              'type:list_of_dict_or_nodata': validate_list_of_dict_or_nodata,
               }