diff --git a/synapse/events/third_party_rules.py b/synapse/events/third_party_rules.py
new file mode 100644
index 0000000000..8f5d95696b
--- /dev/null
+++ b/synapse/events/third_party_rules.py
@@ -0,0 +1,113 @@
+# -*- 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 twisted.internet import defer
+
+
+class ThirdPartyEventRules(object):
+ """Allows server admins to provide a Python module implementing an extra
+ set of rules to apply when processing events.
+
+ This is designed to help admins of closed federations with enforcing custom
+ behaviours.
+ """
+
+ def __init__(self, hs):
+ self.third_party_rules = None
+
+ self.store = hs.get_datastore()
+
+ module = None
+ config = None
+ if hs.config.third_party_event_rules:
+ module, config = hs.config.third_party_event_rules
+
+ if module is not None:
+ self.third_party_rules = module(
+ config=config, http_client=hs.get_simple_http_client()
+ )
+
+ @defer.inlineCallbacks
+ def check_event_allowed(self, event, context):
+ """Check if a provided event should be allowed in the given context.
+
+ Args:
+ event (synapse.events.EventBase): The event to be checked.
+ context (synapse.events.snapshot.EventContext): The context of the event.
+
+ Returns:
+ defer.Deferred[bool]: True if the event should be allowed, False if not.
+ """
+ if self.third_party_rules is None:
+ defer.returnValue(True)
+
+ prev_state_ids = yield context.get_prev_state_ids(self.store)
+
+ # Retrieve the state events from the database.
+ state_events = {}
+ for key, event_id in prev_state_ids.items():
+ state_events[key] = yield self.store.get_event(event_id, allow_none=True)
+
+ ret = yield self.third_party_rules.check_event_allowed(event, state_events)
+ defer.returnValue(ret)
+
+ @defer.inlineCallbacks
+ def on_create_room(self, requester, config, is_requester_admin):
+ """Intercept requests to create room to allow, deny or update the
+ request config.
+
+ Args:
+ requester (Requester)
+ config (dict): The creation config from the client.
+ is_requester_admin (bool): If the requester is an admin
+
+ Returns:
+ defer.Deferred
+ """
+
+ if self.third_party_rules is None:
+ return
+
+ yield self.third_party_rules.on_create_room(
+ requester, config, is_requester_admin
+ )
+
+ @defer.inlineCallbacks
+ def check_threepid_can_be_invited(self, medium, address, room_id):
+ """Check if a provided 3PID can be invited in the given room.
+
+ Args:
+ medium (str): The 3PID's medium.
+ address (str): The 3PID's address.
+ room_id (str): The room we want to invite the threepid to.
+
+ Returns:
+ defer.Deferred[bool], True if the 3PID can be invited, False if not.
+ """
+
+ if self.third_party_rules is None:
+ defer.returnValue(True)
+
+ state_ids = yield self.store.get_filtered_current_state_ids(room_id)
+ room_state_events = yield self.store.get_events(state_ids.values())
+
+ state_events = {}
+ for key, event_id in state_ids.items():
+ state_events[key] = room_state_events[event_id]
+
+ ret = yield self.third_party_rules.check_threepid_can_be_invited(
+ medium, address, state_events
+ )
+ defer.returnValue(ret)
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