diff --git a/synapse/events/presence_router.py b/synapse/events/presence_router.py
new file mode 100644
index 0000000000..24cd389d80
--- /dev/null
+++ b/synapse/events/presence_router.py
@@ -0,0 +1,104 @@
+# -*- coding: utf-8 -*-
+# Copyright 2021 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 typing import TYPE_CHECKING, Dict, Iterable, Set, Union
+
+from synapse.api.presence import UserPresenceState
+
+if TYPE_CHECKING:
+ from synapse.server import HomeServer
+
+
+class PresenceRouter:
+ """
+ A module that the homeserver will call upon to help route user presence updates to
+ additional destinations. If a custom presence router is configured, calls will be
+ passed to that instead.
+ """
+
+ ALL_USERS = "ALL"
+
+ def __init__(self, hs: "HomeServer"):
+ self.custom_presence_router = None
+
+ # Check whether a custom presence router module has been configured
+ if hs.config.presence_router_module_class:
+ # Initialise the module
+ self.custom_presence_router = hs.config.presence_router_module_class(
+ config=hs.config.presence_router_config, module_api=hs.get_module_api()
+ )
+
+ # Ensure the module has implemented the required methods
+ required_methods = ["get_users_for_states", "get_interested_users"]
+ for method_name in required_methods:
+ if not hasattr(self.custom_presence_router, method_name):
+ raise Exception(
+ "PresenceRouter module '%s' must implement all required methods: %s"
+ % (
+ hs.config.presence_router_module_class.__name__,
+ ", ".join(required_methods),
+ )
+ )
+
+ async def get_users_for_states(
+ self,
+ state_updates: Iterable[UserPresenceState],
+ ) -> Dict[str, Set[UserPresenceState]]:
+ """
+ Given an iterable of user presence updates, determine where each one
+ needs to go.
+
+ Args:
+ state_updates: An iterable of user presence state updates.
+
+ Returns:
+ A dictionary of user_id -> set of UserPresenceState, indicating which
+ presence updates each user should receive.
+ """
+ if self.custom_presence_router is not None:
+ # Ask the custom module
+ return await self.custom_presence_router.get_users_for_states(
+ state_updates=state_updates
+ )
+
+ # Don't include any extra destinations for presence updates
+ return {}
+
+ async def get_interested_users(self, user_id: str) -> Union[Set[str], ALL_USERS]:
+ """
+ Retrieve a list of users that `user_id` is interested in receiving the
+ presence of. This will be in addition to those they share a room with.
+ Optionally, the object PresenceRouter.ALL_USERS can be returned to indicate
+ that this user should receive all incoming local and remote presence updates.
+
+ Note that this method will only be called for local users, but can return users
+ that are local or remote.
+
+ Args:
+ user_id: A user requesting presence updates.
+
+ Returns:
+ A set of user IDs to return presence updates for, or ALL_USERS to return all
+ known updates.
+ """
+ if self.custom_presence_router is not None:
+ # Ask the custom module for interested users
+ return await self.custom_presence_router.get_interested_users(
+ user_id=user_id
+ )
+
+ # A custom presence router is not defined.
+ # Don't report any additional interested users
+ return set()
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