Handle empty body in add_router_interface

when passing an empty dict body {} to add_router_interface[1], internal
server error will be raised.
There is argument check in the cli which checks either subnet or port id
is needed, but not in the server side when the body is empty.

[1]:
https://developer.openstack.org/api-ref/networking/v2/?expanded=add-interface-to-router-detail

Change-Id: Iad48dadb1235bc45787a1e87ff3f0d7a21df18af
Closes-bug: #1674069

neutron/db/l3_db.py

@@ -822,7 +822,7 @@ class L3_NAT_dbonly_mixin(l3.RouterPluginBase,
         }
 
     @db_api.retry_if_session_inactive()
-    def add_router_interface(self, context, router_id, interface_info):
+    def add_router_interface(self, context, router_id, interface_info=None):
         router = self._get_router(context, router_id)
         add_by_port, add_by_sub = self._validate_interface_info(interface_info)
         device_owner = self._get_device_owner(context, router_id)
@@ -1852,7 +1852,7 @@ class L3_NAT_db_mixin(L3_NAT_dbonly_mixin, L3RpcNotifierMixin):
         notifier.info(context, router_event,
                       {'router_interface': router_interface_info})
 
-    def add_router_interface(self, context, router_id, interface_info):
+    def add_router_interface(self, context, router_id, interface_info=None):
         router_interface_info = super(
             L3_NAT_db_mixin, self).add_router_interface(
                 context, router_id, interface_info)

neutron/extensions/l3.py

@@ -235,7 +235,7 @@ class RouterPluginBase(object):
         pass
 
     @abc.abstractmethod
-    def add_router_interface(self, context, router_id, interface_info):
+    def add_router_interface(self, context, router_id, interface_info=None):
         pass
 
     @abc.abstractmethod

neutron/tests/unit/db/test_l3_db.py

@@ -288,3 +288,11 @@ class L3_NAT_db_mixin(base.BaseTestCase):
                                 {'subnet_id': 'subnet-id',
                                  'ip_address': 'ip'}]}
         self._test_create_router(ext_gateway_info)
+
+    def test_add_router_interface_no_interface_info(self):
+        router_db = l3_models.Router(id='123')
+        with mock.patch.object(l3_db.L3_NAT_dbonly_mixin, '_get_router',
+                               return_value=router_db):
+            self.assertRaises(
+                n_exc.BadRequest,
+                self.db.add_router_interface, mock.Mock(), router_db.id)

neutron/tests/unit/extensions/test_l3.py

@@ -226,6 +226,17 @@ class L3NatExtensionTestCase(test_extensions_base.ExtensionTestCase):
         self.assertEqual(port_id, res['port_id'])
         self.assertEqual(subnet_id, res['subnet_id'])
 
+    def test_router_add_interface_empty_body(self):
+        router_id = _uuid()
+        instance = self.plugin.return_value
+
+        path = _get_path('routers', id=router_id,
+                         action="add_router_interface",
+                         fmt=self.fmt)
+        res = self.api.put(path)
+        self.assertEqual(exc.HTTPOk.code, res.status_int)
+        instance.add_router_interface.assert_called_with(mock.ANY, router_id)
+
 
 # This base plugin class is for tests.
 class TestL3NatBasePlugin(db_base_plugin_v2.NeutronDbPluginV2,