Add plugin APIs for implementations of custom event rules.

1 files changed, 62 insertions, 0 deletions

diff --git a/synapse/events/third_party_rules.py b/synapse/events/third_party_rules.py
new file mode 100644
index 0000000000..9f98d51523
--- /dev/null
+++ b/synapse/events/third_party_rules.py
@@ -0,0 +1,62 @@
+# -*- 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)
+
+    @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)