Fixes to the federation rate limiter (#5621)

- Put the default window_size back to 1000ms (broken by #5181)
- Make the `rc_federation` config actually do something
- fix an off-by-one error in the 'concurrent' limit
- Avoid creating an unused `_PerHostRatelimiter` object for every single
  incoming request

tests/config/test_ratelimiting.py

@@ -0,0 +1,40 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from synapse.config.homeserver import HomeServerConfig
+
+from tests.unittest import TestCase
+from tests.utils import default_config
+
+
+class RatelimitConfigTestCase(TestCase):
+    def test_parse_rc_federation(self):
+        config_dict = default_config("test")
+        config_dict["rc_federation"] = {
+            "window_size": 20000,
+            "sleep_limit": 693,
+            "sleep_delay": 252,
+            "reject_limit": 198,
+            "concurrent": 7,
+        }
+
+        config = HomeServerConfig()
+        config.parse_config_dict(config_dict, "", "")
+        config_obj = config.rc_federation
+
+        self.assertEqual(config_obj.window_size, 20000)
+        self.assertEqual(config_obj.sleep_limit, 693)
+        self.assertEqual(config_obj.sleep_delay, 252)
+        self.assertEqual(config_obj.reject_limit, 198)
+        self.assertEqual(config_obj.concurrent, 7)