Expose some homeserver functionality to spam checkers (#6259)

* Offer the homeserver instance to the spam checker

* Newsfile

* Linting

* Expose a Spam Checker API instead of passing the homeserver object

* Alter changelog

* s/hs/api

changelog.d/6259.misc

@@ -0,0 +1 @@
+Expose some homeserver functionality to spam checkers.

synapse/events/spamcheck.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2017 New Vector Ltd
+# 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.
@@ -13,6 +14,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import inspect
+
+from synapse.spam_checker_api import SpamCheckerApi
+
 
 class SpamChecker(object):
     def __init__(self, hs):
@@ -26,7 +31,14 @@ class SpamChecker(object):
             pass
 
         if module is not None:
-            self.spam_checker = module(config=config)
+            # Older spam checkers don't accept the `api` argument, so we
+            # try and detect support.
+            spam_args = inspect.getfullargspec(module)
+            if "api" in spam_args.args:
+                api = SpamCheckerApi(hs)
+                self.spam_checker = module(config=config, api=api)
+            else:
+                self.spam_checker = module(config=config)
 
     def check_event_for_spam(self, event):
         """Checks if a given event is considered "spammy" by this server.

synapse/spam_checker_api/__init__.py

@@ -0,0 +1,51 @@
+# -*- 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.
+import logging
+
+from twisted.internet import defer
+
+from synapse.storage.state import StateFilter
+
+logger = logging.getLogger(__name__)
+
+
+class SpamCheckerApi(object):
+    """A proxy object that gets passed to spam checkers so they can get
+    access to rooms and other relevant information.
+    """
+
+    def __init__(self, hs):
+        self.hs = hs
+
+        self._store = hs.get_datastore()
+
+    @defer.inlineCallbacks
+    def get_state_events_in_room(self, room_id, types):
+        """Gets state events for the given room.
+
+        Args:
+            room_id (string): The room ID to get state events in.
+            types (tuple): The event type and state key (using None
+                to represent 'any') of the room state to acquire.
+
+        Returns:
+            twisted.internet.defer.Deferred[list(synapse.events.FrozenEvent)]:
+                The filtered state events in the room.
+        """
+        state_ids = yield self._store.get_filtered_current_state_ids(
+            room_id=room_id, state_filter=StateFilter.from_types(types)
+        )
+        state = yield self._store.get_events(state_ids.values())
+        return state.values()