Pecan: strip duplicate and empty user fields

Remove duplicated and empty fields from users requests
in Pecan to preserve the old legacy API controller behavior.

Closes-Bug: #1714384
Change-Id: I1afc24b146a8fcc6c8ebae708f32dd7c1795292e
(cherry picked from commit 700d609ace)

neutron/pecan_wsgi/controllers/utils.py

@@ -181,11 +181,13 @@ class NeutronPecanController(object):
     def build_field_list(self, request_fields):
         added_fields = []
         combined_fields = []
-        if request_fields:
-            req_fields_set = set(request_fields)
+        req_fields_set = {f for f in request_fields if f}
+        if req_fields_set:
             added_fields = self._mandatory_fields - req_fields_set
             combined_fields = req_fields_set | self._mandatory_fields
-        return list(combined_fields), list(added_fields)
+        # field sorting is to match old behavior of legacy API and to make
+        # this drop-in compatible with the old API unit tests
+        return sorted(combined_fields), list(added_fields)
 
     @property
     def plugin(self):

neutron/tests/functional/pecan_wsgi/test_controllers.py

@@ -386,6 +386,17 @@ class TestResourceController(TestRootController):
         self._check_item(['id', 'tenant_id'],
                          jsonutils.loads(item_resp.body)['port'])
 
+    def test_duped_and_empty_fields_stripped(self):
+        mock_get = mock.patch.object(self.plugin, 'get_ports',
+                                     return_value=[]).start()
+        self.app.get(
+            '/v2.0/ports.json?fields=id&fields=name&fields=&fields=name',
+            headers={'X-Project-Id': 'tenid'}
+        )
+        received = mock_get.mock_calls[-1][2]['fields']
+        self.assertNotIn('', received)
+        self.assertEqual(len(received), len(set(received)))
+
     def test_post(self):
         response = self.app.post_json(
             '/v2.0/ports.json',