Infrastructure for a server notices room

Server Notices use a special room which the user can't dismiss. They are
created on demand when some other bit of the code calls send_notice.

(This doesn't actually do much yet becuse we don't call send_notice anywhere)

synapse/server_notices/server_notices_manager.py

@@ -0,0 +1,110 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# 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.api.constants import EventTypes, Membership, RoomCreationPreset
+from synapse.types import create_requester
+from synapse.util.caches.descriptors import cachedInlineCallbacks
+
+logger = logging.getLogger(__name__)
+
+
+class ServerNoticesManager(object):
+    def __init__(self, hs):
+        """
+
+        Args:
+            hs (synapse.server.HomeServer):
+        """
+
+        self._store = hs.get_datastore()
+        self._config = hs.config
+        self._room_creation_handler = hs.get_room_creation_handler()
+        self._event_creation_handler = hs.get_event_creation_handler()
+
+    def is_enabled(self):
+        return self._config.server_notices_mxid is not None
+
+    @defer.inlineCallbacks
+    def send_notice(self, user_id, event_content):
+        room_id = yield self.get_notice_room_for_user(user_id)
+
+        system_mxid = self._config.server_notices_mxid
+        requester = create_requester(system_mxid)
+
+        logger.info("Sending server notice to %s", user_id)
+
+        yield self._event_creation_handler.create_and_send_nonmember_event(
+            requester, {
+                "type": EventTypes.Message,
+                "room_id": room_id,
+                "sender": system_mxid,
+                "content": event_content,
+            },
+            ratelimit=False,
+        )
+
+    @cachedInlineCallbacks()
+    def get_notice_room_for_user(self, user_id):
+        """Get the room for notices for a given user
+
+        If we have not yet created a notice room for this user, create it
+
+        Args:
+            user_id (str): complete user id for the user we want a room for
+
+        Returns:
+            str: room id of notice room.
+        """
+        if not self.is_enabled():
+            raise Exception("Server notices not enabled")
+
+        rooms = yield self._store.get_rooms_for_user_where_membership_is(
+            user_id, [Membership.INVITE, Membership.JOIN],
+        )
+        system_mxid = self._config.server_notices_mxid
+        for room in rooms:
+            user_ids = yield self._store.get_users_in_room(room.room_id)
+            if system_mxid in user_ids:
+                # we found a room which our user shares with the system notice
+                # user
+                logger.info("Using room %s", room.room_id)
+                defer.returnValue(room.room_id)
+
+        # apparently no existing notice room: create a new one
+        logger.info("Creating server notices room for %s", user_id)
+
+        requester = create_requester(system_mxid)
+        info = yield self._room_creation_handler.create_room(
+            requester,
+            config={
+                "preset": RoomCreationPreset.PRIVATE_CHAT,
+                "name": self._config.server_notices_room_name,
+                "power_level_content_override": {
+                    "users_default": -10,
+                },
+                "invite": (user_id,)
+            },
+            ratelimit=False,
+            creator_join_profile={
+                "displayname": self._config.server_notices_mxid_display_name,
+            },
+        )
+        room_id = info['room_id']
+
+        logger.info("Created server notices room %s for %s", room_id, user_id)
+        defer.returnValue(room_id)