Sliding sync: Split up handler into its own module (#17595)

That file was getting long.

The changes are non functional, and simply split things up into:
- the main class
- the connection store
- the extensions
- the types

changelog.d/17595.misc

@@ -0,0 +1 @@
+Refactor sliding sync class into multiple files.

synapse/handlers/sliding_sync/extensions.py

@@ -0,0 +1,660 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2023 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+
+import logging
+from typing import TYPE_CHECKING, Dict, List, Mapping, Optional, Sequence, Set
+
+from typing_extensions import assert_never
+
+from synapse.api.constants import AccountDataTypes
+from synapse.handlers.receipts import ReceiptEventSource
+from synapse.handlers.sliding_sync.types import (
+    HaveSentRoomFlag,
+    MutablePerConnectionState,
+    PerConnectionState,
+)
+from synapse.logging.opentracing import trace
+from synapse.types import (
+    DeviceListUpdates,
+    JsonMapping,
+    MultiWriterStreamToken,
+    SlidingSyncStreamToken,
+    StreamToken,
+)
+from synapse.types.handlers import OperationType, SlidingSyncConfig, SlidingSyncResult
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+class SlidingSyncExtensionHandler:
+    """Handles the extensions to sliding sync."""
+
+    def __init__(self, hs: "HomeServer"):
+        self.store = hs.get_datastores().main
+        self.event_sources = hs.get_event_sources()
+        self.device_handler = hs.get_device_handler()
+        self.push_rules_handler = hs.get_push_rules_handler()
+
+    @trace
+    async def get_extensions_response(
+        self,
+        sync_config: SlidingSyncConfig,
+        previous_connection_state: "PerConnectionState",
+        new_connection_state: "MutablePerConnectionState",
+        actual_lists: Dict[str, SlidingSyncResult.SlidingWindowList],
+        actual_room_ids: Set[str],
+        actual_room_response_map: Dict[str, SlidingSyncResult.RoomResult],
+        to_token: StreamToken,
+        from_token: Optional[SlidingSyncStreamToken],
+    ) -> SlidingSyncResult.Extensions:
+        """Handle extension requests.
+
+        Args:
+            sync_config: Sync configuration
+            new_connection_state: Snapshot of the current per-connection state
+            new_per_connection_state: A mutable copy of the per-connection
+                state, used to record updates to the state during this request.
+            actual_lists: Sliding window API. A map of list key to list results in the
+                Sliding Sync response.
+            actual_room_ids: The actual room IDs in the the Sliding Sync response.
+            actual_room_response_map: A map of room ID to room results in the the
+                Sliding Sync response.
+            to_token: The point in the stream to sync up to.
+            from_token: The point in the stream to sync from.
+        """
+
+        if sync_config.extensions is None:
+            return SlidingSyncResult.Extensions()
+
+        to_device_response = None
+        if sync_config.extensions.to_device is not None:
+            to_device_response = await self.get_to_device_extension_response(
+                sync_config=sync_config,
+                to_device_request=sync_config.extensions.to_device,
+                to_token=to_token,
+            )
+
+        e2ee_response = None
+        if sync_config.extensions.e2ee is not None:
+            e2ee_response = await self.get_e2ee_extension_response(
+                sync_config=sync_config,
+                e2ee_request=sync_config.extensions.e2ee,
+                to_token=to_token,
+                from_token=from_token,
+            )
+
+        account_data_response = None
+        if sync_config.extensions.account_data is not None:
+            account_data_response = await self.get_account_data_extension_response(
+                sync_config=sync_config,
+                actual_lists=actual_lists,
+                actual_room_ids=actual_room_ids,
+                account_data_request=sync_config.extensions.account_data,
+                to_token=to_token,
+                from_token=from_token,
+            )
+
+        receipts_response = None
+        if sync_config.extensions.receipts is not None:
+            receipts_response = await self.get_receipts_extension_response(
+                sync_config=sync_config,
+                previous_connection_state=previous_connection_state,
+                new_connection_state=new_connection_state,
+                actual_lists=actual_lists,
+                actual_room_ids=actual_room_ids,
+                actual_room_response_map=actual_room_response_map,
+                receipts_request=sync_config.extensions.receipts,
+                to_token=to_token,
+                from_token=from_token,
+            )
+
+        typing_response = None
+        if sync_config.extensions.typing is not None:
+            typing_response = await self.get_typing_extension_response(
+                sync_config=sync_config,
+                actual_lists=actual_lists,
+                actual_room_ids=actual_room_ids,
+                actual_room_response_map=actual_room_response_map,
+                typing_request=sync_config.extensions.typing,
+                to_token=to_token,
+                from_token=from_token,
+            )
+
+        return SlidingSyncResult.Extensions(
+            to_device=to_device_response,
+            e2ee=e2ee_response,
+            account_data=account_data_response,
+            receipts=receipts_response,
+            typing=typing_response,
+        )
+
+    def find_relevant_room_ids_for_extension(
+        self,
+        requested_lists: Optional[List[str]],
+        requested_room_ids: Optional[List[str]],
+        actual_lists: Dict[str, SlidingSyncResult.SlidingWindowList],
+        actual_room_ids: Set[str],
+    ) -> Set[str]:
+        """
+        Handle the reserved `lists`/`rooms` keys for extensions. Extensions should only
+        return results for rooms in the Sliding Sync response. This matches up the
+        requested rooms/lists with the actual lists/rooms in the Sliding Sync response.
+
+        {"lists": []}                    // Do not process any lists.
+        {"lists": ["rooms", "dms"]}      // Process only a subset of lists.
+        {"lists": ["*"]}                 // Process all lists defined in the Sliding Window API. (This is the default.)
+
+        {"rooms": []}                    // Do not process any specific rooms.
+        {"rooms": ["!a:b", "!c:d"]}      // Process only a subset of room subscriptions.
+        {"rooms": ["*"]}                 // Process all room subscriptions defined in the Room Subscription API. (This is the default.)
+
+        Args:
+            requested_lists: The `lists` from the extension request.
+            requested_room_ids: The `rooms` from the extension request.
+            actual_lists: The actual lists from the Sliding Sync response.
+            actual_room_ids: The actual room subscriptions from the Sliding Sync request.
+        """
+
+        # We only want to include account data for rooms that are already in the sliding
+        # sync response AND that were requested in the account data request.
+        relevant_room_ids: Set[str] = set()
+
+        # See what rooms from the room subscriptions we should get account data for
+        if requested_room_ids is not None:
+            for room_id in requested_room_ids:
+                # A wildcard means we process all rooms from the room subscriptions
+                if room_id == "*":
+                    relevant_room_ids.update(actual_room_ids)
+                    break
+
+                if room_id in actual_room_ids:
+                    relevant_room_ids.add(room_id)
+
+        # See what rooms from the sliding window lists we should get account data for
+        if requested_lists is not None:
+            for list_key in requested_lists:
+                # Just some typing because we share the variable name in multiple places
+                actual_list: Optional[SlidingSyncResult.SlidingWindowList] = None
+
+                # A wildcard means we process rooms from all lists
+                if list_key == "*":
+                    for actual_list in actual_lists.values():
+                        # We only expect a single SYNC operation for any list
+                        assert len(actual_list.ops) == 1
+                        sync_op = actual_list.ops[0]
+                        assert sync_op.op == OperationType.SYNC
+
+                        relevant_room_ids.update(sync_op.room_ids)
+
+                    break
+
+                actual_list = actual_lists.get(list_key)
+                if actual_list is not None:
+                    # We only expect a single SYNC operation for any list
+                    assert len(actual_list.ops) == 1
+                    sync_op = actual_list.ops[0]
+                    assert sync_op.op == OperationType.SYNC
+
+                    relevant_room_ids.update(sync_op.room_ids)
+
+        return relevant_room_ids
+
+    @trace
+    async def get_to_device_extension_response(
+        self,
+        sync_config: SlidingSyncConfig,
+        to_device_request: SlidingSyncConfig.Extensions.ToDeviceExtension,
+        to_token: StreamToken,
+    ) -> Optional[SlidingSyncResult.Extensions.ToDeviceExtension]:
+        """Handle to-device extension (MSC3885)
+
+        Args:
+            sync_config: Sync configuration
+            to_device_request: The to-device extension from the request
+            to_token: The point in the stream to sync up to.
+        """
+        user_id = sync_config.user.to_string()
+        device_id = sync_config.requester.device_id
+
+        # Skip if the extension is not enabled
+        if not to_device_request.enabled:
+            return None
+
+        # Check that this request has a valid device ID (not all requests have
+        # to belong to a device, and so device_id is None)
+        if device_id is None:
+            return SlidingSyncResult.Extensions.ToDeviceExtension(
+                next_batch=f"{to_token.to_device_key}",
+                events=[],
+            )
+
+        since_stream_id = 0
+        if to_device_request.since is not None:
+            # We've already validated this is an int.
+            since_stream_id = int(to_device_request.since)
+
+            if to_token.to_device_key < since_stream_id:
+                # The since token is ahead of our current token, so we return an
+                # empty response.
+                logger.warning(
+                    "Got to-device.since from the future. since token: %r is ahead of our current to_device stream position: %r",
+                    since_stream_id,
+                    to_token.to_device_key,
+                )
+                return SlidingSyncResult.Extensions.ToDeviceExtension(
+                    next_batch=to_device_request.since,
+                    events=[],
+                )
+
+            # Delete everything before the given since token, as we know the
+            # device must have received them.
+            deleted = await self.store.delete_messages_for_device(
+                user_id=user_id,
+                device_id=device_id,
+                up_to_stream_id=since_stream_id,
+            )
+
+            logger.debug(
+                "Deleted %d to-device messages up to %d for %s",
+                deleted,
+                since_stream_id,
+                user_id,
+            )
+
+        messages, stream_id = await self.store.get_messages_for_device(
+            user_id=user_id,
+            device_id=device_id,
+            from_stream_id=since_stream_id,
+            to_stream_id=to_token.to_device_key,
+            limit=min(to_device_request.limit, 100),  # Limit to at most 100 events
+        )
+
+        return SlidingSyncResult.Extensions.ToDeviceExtension(
+            next_batch=f"{stream_id}",
+            events=messages,
+        )
+
+    @trace
+    async def get_e2ee_extension_response(
+        self,
+        sync_config: SlidingSyncConfig,
+        e2ee_request: SlidingSyncConfig.Extensions.E2eeExtension,
+        to_token: StreamToken,
+        from_token: Optional[SlidingSyncStreamToken],
+    ) -> Optional[SlidingSyncResult.Extensions.E2eeExtension]:
+        """Handle E2EE device extension (MSC3884)
+
+        Args:
+            sync_config: Sync configuration
+            e2ee_request: The e2ee extension from the request
+            to_token: The point in the stream to sync up to.
+            from_token: The point in the stream to sync from.
+        """
+        user_id = sync_config.user.to_string()
+        device_id = sync_config.requester.device_id
+
+        # Skip if the extension is not enabled
+        if not e2ee_request.enabled:
+            return None
+
+        device_list_updates: Optional[DeviceListUpdates] = None
+        if from_token is not None:
+            # TODO: This should take into account the `from_token` and `to_token`
+            device_list_updates = await self.device_handler.get_user_ids_changed(
+                user_id=user_id,
+                from_token=from_token.stream_token,
+            )
+
+        device_one_time_keys_count: Mapping[str, int] = {}
+        device_unused_fallback_key_types: Sequence[str] = []
+        if device_id:
+            # TODO: We should have a way to let clients differentiate between the states of:
+            #   * no change in OTK count since the provided since token
+            #   * the server has zero OTKs left for this device
+            #  Spec issue: https://github.com/matrix-org/matrix-doc/issues/3298
+            device_one_time_keys_count = await self.store.count_e2e_one_time_keys(
+                user_id, device_id
+            )
+            device_unused_fallback_key_types = (
+                await self.store.get_e2e_unused_fallback_key_types(user_id, device_id)
+            )
+
+        return SlidingSyncResult.Extensions.E2eeExtension(
+            device_list_updates=device_list_updates,
+            device_one_time_keys_count=device_one_time_keys_count,
+            device_unused_fallback_key_types=device_unused_fallback_key_types,
+        )
+
+    @trace
+    async def get_account_data_extension_response(
+        self,
+        sync_config: SlidingSyncConfig,
+        actual_lists: Dict[str, SlidingSyncResult.SlidingWindowList],
+        actual_room_ids: Set[str],
+        account_data_request: SlidingSyncConfig.Extensions.AccountDataExtension,
+        to_token: StreamToken,
+        from_token: Optional[SlidingSyncStreamToken],
+    ) -> Optional[SlidingSyncResult.Extensions.AccountDataExtension]:
+        """Handle Account Data extension (MSC3959)
+
+        Args:
+            sync_config: Sync configuration
+            actual_lists: Sliding window API. A map of list key to list results in the
+                Sliding Sync response.
+            actual_room_ids: The actual room IDs in the the Sliding Sync response.
+            account_data_request: The account_data extension from the request
+            to_token: The point in the stream to sync up to.
+            from_token: The point in the stream to sync from.
+        """
+        user_id = sync_config.user.to_string()
+
+        # Skip if the extension is not enabled
+        if not account_data_request.enabled:
+            return None
+
+        global_account_data_map: Mapping[str, JsonMapping] = {}
+        if from_token is not None:
+            # TODO: This should take into account the `from_token` and `to_token`
+            global_account_data_map = (
+                await self.store.get_updated_global_account_data_for_user(
+                    user_id, from_token.stream_token.account_data_key
+                )
+            )
+
+            have_push_rules_changed = await self.store.have_push_rules_changed_for_user(
+                user_id, from_token.stream_token.push_rules_key
+            )
+            if have_push_rules_changed:
+                global_account_data_map = dict(global_account_data_map)
+                # TODO: This should take into account the `from_token` and `to_token`
+                global_account_data_map[AccountDataTypes.PUSH_RULES] = (
+                    await self.push_rules_handler.push_rules_for_user(sync_config.user)
+                )
+        else:
+            # TODO: This should take into account the `to_token`
+            all_global_account_data = await self.store.get_global_account_data_for_user(
+                user_id
+            )
+
+            global_account_data_map = dict(all_global_account_data)
+            # TODO: This should take into account the  `to_token`
+            global_account_data_map[AccountDataTypes.PUSH_RULES] = (
+                await self.push_rules_handler.push_rules_for_user(sync_config.user)
+            )
+
+        # Fetch room account data
+        account_data_by_room_map: Mapping[str, Mapping[str, JsonMapping]] = {}
+        relevant_room_ids = self.find_relevant_room_ids_for_extension(
+            requested_lists=account_data_request.lists,
+            requested_room_ids=account_data_request.rooms,
+            actual_lists=actual_lists,
+            actual_room_ids=actual_room_ids,
+        )
+        if len(relevant_room_ids) > 0:
+            if from_token is not None:
+                # TODO: This should take into account the `from_token` and `to_token`
+                account_data_by_room_map = (
+                    await self.store.get_updated_room_account_data_for_user(
+                        user_id, from_token.stream_token.account_data_key
+                    )
+                )
+            else:
+                # TODO: This should take into account the `to_token`
+                account_data_by_room_map = (
+                    await self.store.get_room_account_data_for_user(user_id)
+                )
+
+        # Filter down to the relevant rooms
+        account_data_by_room_map = {
+            room_id: account_data_map
+            for room_id, account_data_map in account_data_by_room_map.items()
+            if room_id in relevant_room_ids
+        }
+
+        return SlidingSyncResult.Extensions.AccountDataExtension(
+            global_account_data_map=global_account_data_map,
+            account_data_by_room_map=account_data_by_room_map,
+        )
+
+    @trace
+    async def get_receipts_extension_response(
+        self,
+        sync_config: SlidingSyncConfig,
+        previous_connection_state: "PerConnectionState",
+        new_connection_state: "MutablePerConnectionState",
+        actual_lists: Dict[str, SlidingSyncResult.SlidingWindowList],
+        actual_room_ids: Set[str],
+        actual_room_response_map: Dict[str, SlidingSyncResult.RoomResult],
+        receipts_request: SlidingSyncConfig.Extensions.ReceiptsExtension,
+        to_token: StreamToken,
+        from_token: Optional[SlidingSyncStreamToken],
+    ) -> Optional[SlidingSyncResult.Extensions.ReceiptsExtension]:
+        """Handle Receipts extension (MSC3960)
+
+        Args:
+            sync_config: Sync configuration
+            previous_connection_state: The current per-connection state
+            new_connection_state: A mutable copy of the per-connection
+                state, used to record updates to the state.
+            actual_lists: Sliding window API. A map of list key to list results in the
+                Sliding Sync response.
+            actual_room_ids: The actual room IDs in the the Sliding Sync response.
+            actual_room_response_map: A map of room ID to room results in the the
+                Sliding Sync response.
+            account_data_request: The account_data extension from the request
+            to_token: The point in the stream to sync up to.
+            from_token: The point in the stream to sync from.
+        """
+        # Skip if the extension is not enabled
+        if not receipts_request.enabled:
+            return None
+
+        relevant_room_ids = self.find_relevant_room_ids_for_extension(
+            requested_lists=receipts_request.lists,
+            requested_room_ids=receipts_request.rooms,
+            actual_lists=actual_lists,
+            actual_room_ids=actual_room_ids,
+        )
+
+        room_id_to_receipt_map: Dict[str, JsonMapping] = {}
+        if len(relevant_room_ids) > 0:
+            # We need to handle the different cases depending on if we have sent
+            # down receipts previously or not, so we split the relevant rooms
+            # up into different collections based on status.
+            live_rooms = set()
+            previously_rooms: Dict[str, MultiWriterStreamToken] = {}
+            initial_rooms = set()
+
+            for room_id in relevant_room_ids:
+                if not from_token:
+                    initial_rooms.add(room_id)
+                    continue
+
+                # If we're sending down the room from scratch again for some reason, we
+                # should always resend the receipts as well (regardless of if
+                # we've sent them down before). This is to mimic the behaviour
+                # of what happens on initial sync, where you get a chunk of
+                # timeline with all of the corresponding receipts for the events in the timeline.
+                room_result = actual_room_response_map.get(room_id)
+                if room_result is not None and room_result.initial:
+                    initial_rooms.add(room_id)
+                    continue
+
+                room_status = previous_connection_state.receipts.have_sent_room(room_id)
+                if room_status.status == HaveSentRoomFlag.LIVE:
+                    live_rooms.add(room_id)
+                elif room_status.status == HaveSentRoomFlag.PREVIOUSLY:
+                    assert room_status.last_token is not None
+                    previously_rooms[room_id] = room_status.last_token
+                elif room_status.status == HaveSentRoomFlag.NEVER:
+                    initial_rooms.add(room_id)
+                else:
+                    assert_never(room_status.status)
+
+            # The set of receipts that we fetched. Private receipts need to be
+            # filtered out before returning.
+            fetched_receipts = []
+
+            # For live rooms we just fetch all receipts in those rooms since the
+            # `since` token.
+            if live_rooms:
+                assert from_token is not None
+                receipts = await self.store.get_linearized_receipts_for_rooms(
+                    room_ids=live_rooms,
+                    from_key=from_token.stream_token.receipt_key,
+                    to_key=to_token.receipt_key,
+                )
+                fetched_receipts.extend(receipts)
+
+            # For rooms we've previously sent down, but aren't up to date, we
+            # need to use the from token from the room status.
+            if previously_rooms:
+                for room_id, receipt_token in previously_rooms.items():
+                    # TODO: Limit the number of receipts we're about to send down
+                    # for the room, if its too many we should TODO
+                    previously_receipts = (
+                        await self.store.get_linearized_receipts_for_room(
+                            room_id=room_id,
+                            from_key=receipt_token,
+                            to_key=to_token.receipt_key,
+                        )
+                    )
+                    fetched_receipts.extend(previously_receipts)
+
+            # For rooms we haven't previously sent down, we could send all receipts
+            # from that room but we only want to include receipts for events
+            # in the timeline to avoid bloating and blowing up the sync response
+            # as the number of users in the room increases. (this behavior is part of the spec)
+            initial_rooms_and_event_ids = [
+                (room_id, event.event_id)
+                for room_id in initial_rooms
+                if room_id in actual_room_response_map
+                for event in actual_room_response_map[room_id].timeline_events
+            ]
+            if initial_rooms_and_event_ids:
+                initial_receipts = await self.store.get_linearized_receipts_for_events(
+                    room_and_event_ids=initial_rooms_and_event_ids,
+                )
+                fetched_receipts.extend(initial_receipts)
+
+            fetched_receipts = ReceiptEventSource.filter_out_private_receipts(
+                fetched_receipts, sync_config.user.to_string()
+            )
+
+            for receipt in fetched_receipts:
+                # These fields should exist for every receipt
+                room_id = receipt["room_id"]
+                type = receipt["type"]
+                content = receipt["content"]
+
+                room_id_to_receipt_map[room_id] = {"type": type, "content": content}
+
+        # Now we update the per-connection state to track which receipts we have
+        # and haven't sent down.
+        new_connection_state.receipts.record_sent_rooms(relevant_room_ids)
+
+        if from_token:
+            # Now find the set of rooms that may have receipts that we're not sending
+            # down. We only need to check rooms that we have previously returned
+            # receipts for (in `previous_connection_state`) because we only care about
+            # updating `LIVE` rooms to `PREVIOUSLY`. The `PREVIOUSLY` rooms will just
+            # stay pointing at their previous position so we don't need to waste time
+            # checking those and since we default to `NEVER`, rooms that were `NEVER`
+            # sent before don't need to be recorded as we'll handle them correctly when
+            # they come into range for the first time.
+            rooms_no_receipts = [
+                room_id
+                for room_id, room_status in previous_connection_state.receipts._statuses.items()
+                if room_status.status == HaveSentRoomFlag.LIVE
+                and room_id not in relevant_room_ids
+            ]
+            changed_rooms = await self.store.get_rooms_with_receipts_between(
+                rooms_no_receipts,
+                from_key=from_token.stream_token.receipt_key,
+                to_key=to_token.receipt_key,
+            )
+            new_connection_state.receipts.record_unsent_rooms(
+                changed_rooms, from_token.stream_token.receipt_key
+            )
+
+        return SlidingSyncResult.Extensions.ReceiptsExtension(
+            room_id_to_receipt_map=room_id_to_receipt_map,
+        )
+
+    async def get_typing_extension_response(
+        self,
+        sync_config: SlidingSyncConfig,
+        actual_lists: Dict[str, SlidingSyncResult.SlidingWindowList],
+        actual_room_ids: Set[str],
+        actual_room_response_map: Dict[str, SlidingSyncResult.RoomResult],
+        typing_request: SlidingSyncConfig.Extensions.TypingExtension,
+        to_token: StreamToken,
+        from_token: Optional[SlidingSyncStreamToken],
+    ) -> Optional[SlidingSyncResult.Extensions.TypingExtension]:
+        """Handle Typing Notification extension (MSC3961)
+
+        Args:
+            sync_config: Sync configuration
+            actual_lists: Sliding window API. A map of list key to list results in the
+                Sliding Sync response.
+            actual_room_ids: The actual room IDs in the the Sliding Sync response.
+            actual_room_response_map: A map of room ID to room results in the the
+                Sliding Sync response.
+            account_data_request: The account_data extension from the request
+            to_token: The point in the stream to sync up to.
+            from_token: The point in the stream to sync from.
+        """
+        # Skip if the extension is not enabled
+        if not typing_request.enabled:
+            return None
+
+        relevant_room_ids = self.find_relevant_room_ids_for_extension(
+            requested_lists=typing_request.lists,
+            requested_room_ids=typing_request.rooms,
+            actual_lists=actual_lists,
+            actual_room_ids=actual_room_ids,
+        )
+
+        room_id_to_typing_map: Dict[str, JsonMapping] = {}
+        if len(relevant_room_ids) > 0:
+            # Note: We don't need to take connection tracking into account for typing
+            # notifications because they'll get anything still relevant and hasn't timed
+            # out when the room comes into range. We consider the gap where the room
+            # fell out of range, as long enough for any typing notifications to have
+            # timed out (it's not worth the 30 seconds of data we may have missed).
+            typing_source = self.event_sources.sources.typing
+            typing_notifications, _ = await typing_source.get_new_events(
+                user=sync_config.user,
+                from_key=(from_token.stream_token.typing_key if from_token else 0),
+                to_key=to_token.typing_key,
+                # This is a dummy value and isn't used in the function
+                limit=0,
+                room_ids=relevant_room_ids,
+                is_guest=False,
+            )
+
+            for typing_notification in typing_notifications:
+                # These fields should exist for every typing notification
+                room_id = typing_notification["room_id"]
+                type = typing_notification["type"]
+                content = typing_notification["content"]
+
+                room_id_to_typing_map[room_id] = {"type": type, "content": content}
+
+        return SlidingSyncResult.Extensions.TypingExtension(
+            room_id_to_typing_map=room_id_to_typing_map,
+        )

synapse/handlers/sliding_sync/store.py

@@ -0,0 +1,200 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2023 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+
+import logging
+from typing import TYPE_CHECKING, Dict, Optional, Tuple
+
+import attr
+
+from synapse.api.errors import SlidingSyncUnknownPosition
+from synapse.handlers.sliding_sync.types import (
+    MutablePerConnectionState,
+    PerConnectionState,
+)
+from synapse.logging.opentracing import trace
+from synapse.types import SlidingSyncStreamToken
+from synapse.types.handlers import SlidingSyncConfig
+
+if TYPE_CHECKING:
+    pass
+
+logger = logging.getLogger(__name__)
+
+
+@attr.s(auto_attribs=True)
+class SlidingSyncConnectionStore:
+    """In-memory store of per-connection state, including what rooms we have
+    previously sent down a sliding sync connection.
+
+    Note: This is NOT safe to run in a worker setup because connection positions will
+    point to different sets of rooms on different workers. e.g. for the same connection,
+    a connection position of 5 might have totally different states on worker A and
+    worker B.
+
+    One complication that we need to deal with here is needing to handle requests being
+    resent, i.e. if we sent down a room in a response that the client received, we must
+    consider the room *not* sent when we get the request again.
+
+    This is handled by using an integer "token", which is returned to the client
+    as part of the sync token. For each connection we store a mapping from
+    tokens to the room states, and create a new entry when we send down new
+    rooms.
+
+    Note that for any given sliding sync connection we will only store a maximum
+    of two different tokens: the previous token from the request and a new token
+    sent in the response. When we receive a request with a given token, we then
+    clear out all other entries with a different token.
+
+    Attributes:
+        _connections: Mapping from `(user_id, conn_id)` to mapping of `token`
+            to mapping of room ID to `HaveSentRoom`.
+    """
+
+    # `(user_id, conn_id)` -> `connection_position` -> `PerConnectionState`
+    _connections: Dict[Tuple[str, str], Dict[int, PerConnectionState]] = attr.Factory(
+        dict
+    )
+
+    async def is_valid_token(
+        self, sync_config: SlidingSyncConfig, connection_token: int
+    ) -> bool:
+        """Return whether the connection token is valid/recognized"""
+        if connection_token == 0:
+            return True
+
+        conn_key = self._get_connection_key(sync_config)
+        return connection_token in self._connections.get(conn_key, {})
+
+    async def get_per_connection_state(
+        self,
+        sync_config: SlidingSyncConfig,
+        from_token: Optional[SlidingSyncStreamToken],
+    ) -> PerConnectionState:
+        """Fetch the per-connection state for the token.
+
+        Raises:
+            SlidingSyncUnknownPosition if the connection_token is unknown
+        """
+        if from_token is None:
+            return PerConnectionState()
+
+        connection_position = from_token.connection_position
+        if connection_position == 0:
+            # Initial sync (request without a `from_token`) starts at `0` so
+            # there is no existing per-connection state
+            return PerConnectionState()
+
+        conn_key = self._get_connection_key(sync_config)
+        sync_statuses = self._connections.get(conn_key, {})
+        connection_state = sync_statuses.get(connection_position)
+
+        if connection_state is None:
+            raise SlidingSyncUnknownPosition()
+
+        return connection_state
+
+    @trace
+    async def record_new_state(
+        self,
+        sync_config: SlidingSyncConfig,
+        from_token: Optional[SlidingSyncStreamToken],
+        new_connection_state: MutablePerConnectionState,
+    ) -> int:
+        """Record updated per-connection state, returning the connection
+        position associated with the new state.
+        If there are no changes to the state this may return the same token as
+        the existing per-connection state.
+        """
+        prev_connection_token = 0
+        if from_token is not None:
+            prev_connection_token = from_token.connection_position
+
+        if not new_connection_state.has_updates():
+            return prev_connection_token
+
+        conn_key = self._get_connection_key(sync_config)
+        sync_statuses = self._connections.setdefault(conn_key, {})
+
+        # Generate a new token, removing any existing entries in that token
+        # (which can happen if requests get resent).
+        new_store_token = prev_connection_token + 1
+        sync_statuses.pop(new_store_token, None)
+
+        # We copy the `MutablePerConnectionState` so that the inner `ChainMap`s
+        # don't grow forever.
+        sync_statuses[new_store_token] = new_connection_state.copy()
+
+        return new_store_token
+
+    @trace
+    async def mark_token_seen(
+        self,
+        sync_config: SlidingSyncConfig,
+        from_token: Optional[SlidingSyncStreamToken],
+    ) -> None:
+        """We have received a request with the given token, so we can clear out
+        any other tokens associated with the connection.
+
+        If there is no from token then we have started afresh, and so we delete
+        all tokens associated with the device.
+        """
+        # Clear out any tokens for the connection that doesn't match the one
+        # from the request.
+
+        conn_key = self._get_connection_key(sync_config)
+        sync_statuses = self._connections.pop(conn_key, {})
+        if from_token is None:
+            return
+
+        sync_statuses = {
+            connection_token: room_statuses
+            for connection_token, room_statuses in sync_statuses.items()
+            if connection_token == from_token.connection_position
+        }
+        if sync_statuses:
+            self._connections[conn_key] = sync_statuses
+
+    @staticmethod
+    def _get_connection_key(sync_config: SlidingSyncConfig) -> Tuple[str, str]:
+        """Return a unique identifier for this connection.
+
+        The first part is simply the user ID.
+
+        The second part is generally a combination of device ID and conn_id.
+        However, both these two are optional (e.g. puppet access tokens don't
+        have device IDs), so this handles those edge cases.
+
+        We use this over the raw `conn_id` to avoid clashes between different
+        clients that use the same `conn_id`. Imagine a user uses a web client
+        that uses `conn_id: main_sync_loop` and an Android client that also has
+        a `conn_id: main_sync_loop`.
+        """
+
+        user_id = sync_config.user.to_string()
+
+        # Only one sliding sync connection is allowed per given conn_id (empty
+        # or not).
+        conn_id = sync_config.conn_id or ""
+
+        if sync_config.requester.device_id:
+            return (user_id, f"D/{sync_config.requester.device_id}/{conn_id}")
+
+        if sync_config.requester.access_token_id:
+            # If we don't have a device, then the access token ID should be a
+            # stable ID.
+            return (user_id, f"A/{sync_config.requester.access_token_id}/{conn_id}")
+
+        # If we have neither then its likely an AS or some weird token. Either
+        # way we can just fail here.
+        raise Exception("Cannot use sliding sync with access token type")

synapse/handlers/sliding_sync/types.py

@@ -0,0 +1,506 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2024 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+
+import logging
+import typing
+from collections import ChainMap
+from enum import Enum
+from typing import (
+    TYPE_CHECKING,
+    Callable,
+    Dict,
+    Final,
+    Generic,
+    Mapping,
+    MutableMapping,
+    Optional,
+    Set,
+    TypeVar,
+    cast,
+)
+
+import attr
+
+from synapse.api.constants import EventTypes
+from synapse.types import MultiWriterStreamToken, RoomStreamToken, StrCollection, UserID
+from synapse.types.handlers import SlidingSyncConfig
+
+if TYPE_CHECKING:
+    pass
+
+logger = logging.getLogger(__name__)
+
+
+class StateValues:
+    """
+    Understood values of the (type, state_key) tuple in `required_state`.
+    """
+
+    # Include all state events of the given type
+    WILDCARD: Final = "*"
+    # Lazy-load room membership events (include room membership events for any event
+    # `sender` in the timeline). We only give special meaning to this value when it's a
+    # `state_key`.
+    LAZY: Final = "$LAZY"
+    # Subsitute with the requester's user ID. Typically used by clients to get
+    # the user's membership.
+    ME: Final = "$ME"
+
+
+# We can't freeze this class because we want to update it in place with the
+# de-duplicated data.
+@attr.s(slots=True, auto_attribs=True)
+class RoomSyncConfig:
+    """
+    Holds the config for what data we should fetch for a room in the sync response.
+
+    Attributes:
+        timeline_limit: The maximum number of events to return in the timeline.
+
+        required_state_map: Map from state event type to state_keys requested for the
+            room. The values are close to `StateKey` but actually use a syntax where you
+            can provide `*` wildcard and `$LAZY` for lazy-loading room members.
+    """
+
+    timeline_limit: int
+    required_state_map: Dict[str, Set[str]]
+
+    @classmethod
+    def from_room_config(
+        cls,
+        room_params: SlidingSyncConfig.CommonRoomParameters,
+    ) -> "RoomSyncConfig":
+        """
+        Create a `RoomSyncConfig` from a `SlidingSyncList`/`RoomSubscription` config.
+
+        Args:
+            room_params: `SlidingSyncConfig.SlidingSyncList` or `SlidingSyncConfig.RoomSubscription`
+        """
+        required_state_map: Dict[str, Set[str]] = {}
+        for (
+            state_type,
+            state_key,
+        ) in room_params.required_state:
+            # If we already have a wildcard for this specific `state_key`, we don't need
+            # to add it since the wildcard already covers it.
+            if state_key in required_state_map.get(StateValues.WILDCARD, set()):
+                continue
+
+            # If we already have a wildcard `state_key` for this `state_type`, we don't need
+            # to add anything else
+            if StateValues.WILDCARD in required_state_map.get(state_type, set()):
+                continue
+
+            # If we're getting wildcards for the `state_type` and `state_key`, that's
+            # all that matters so get rid of any other entries
+            if state_type == StateValues.WILDCARD and state_key == StateValues.WILDCARD:
+                required_state_map = {StateValues.WILDCARD: {StateValues.WILDCARD}}
+                # We can break, since we don't need to add anything else
+                break
+
+            # If we're getting a wildcard for the `state_type`, get rid of any other
+            # entries with the same `state_key`, since the wildcard will cover it already.
+            elif state_type == StateValues.WILDCARD:
+                # Get rid of any entries that match the `state_key`
+                #
+                # Make a copy so we don't run into an error: `dictionary changed size
+                # during iteration`, when we remove items
+                for (
+                    existing_state_type,
+                    existing_state_key_set,
+                ) in list(required_state_map.items()):
+                    # Make a copy so we don't run into an error: `Set changed size during
+                    # iteration`, when we filter out and remove items
+                    for existing_state_key in existing_state_key_set.copy():
+                        if existing_state_key == state_key:
+                            existing_state_key_set.remove(state_key)
+
+                    # If we've the left the `set()` empty, remove it from the map
+                    if existing_state_key_set == set():
+                        required_state_map.pop(existing_state_type, None)
+
+            # If we're getting a wildcard `state_key`, get rid of any other state_keys
+            # for this `state_type` since the wildcard will cover it already.
+            if state_key == StateValues.WILDCARD:
+                required_state_map[state_type] = {state_key}
+            # Otherwise, just add it to the set
+            else:
+                if required_state_map.get(state_type) is None:
+                    required_state_map[state_type] = {state_key}
+                else:
+                    required_state_map[state_type].add(state_key)
+
+        return cls(
+            timeline_limit=room_params.timeline_limit,
+            required_state_map=required_state_map,
+        )
+
+    def deep_copy(self) -> "RoomSyncConfig":
+        required_state_map: Dict[str, Set[str]] = {
+            state_type: state_key_set.copy()
+            for state_type, state_key_set in self.required_state_map.items()
+        }
+
+        return RoomSyncConfig(
+            timeline_limit=self.timeline_limit,
+            required_state_map=required_state_map,
+        )
+
+    def combine_room_sync_config(
+        self, other_room_sync_config: "RoomSyncConfig"
+    ) -> None:
+        """
+        Combine this `RoomSyncConfig` with another `RoomSyncConfig` and take the
+        superset union of the two.
+        """
+        # Take the highest timeline limit
+        if self.timeline_limit < other_room_sync_config.timeline_limit:
+            self.timeline_limit = other_room_sync_config.timeline_limit
+
+        # Union the required state
+        for (
+            state_type,
+            state_key_set,
+        ) in other_room_sync_config.required_state_map.items():
+            # If we already have a wildcard for everything, we don't need to add
+            # anything else
+            if StateValues.WILDCARD in self.required_state_map.get(
+                StateValues.WILDCARD, set()
+            ):
+                break
+
+            # If we already have a wildcard `state_key` for this `state_type`, we don't need
+            # to add anything else
+            if StateValues.WILDCARD in self.required_state_map.get(state_type, set()):
+                continue
+
+            # If we're getting wildcards for the `state_type` and `state_key`, that's
+            # all that matters so get rid of any other entries
+            if (
+                state_type == StateValues.WILDCARD
+                and StateValues.WILDCARD in state_key_set
+            ):
+                self.required_state_map = {state_type: {StateValues.WILDCARD}}
+                # We can break, since we don't need to add anything else
+                break
+
+            for state_key in state_key_set:
+                # If we already have a wildcard for this specific `state_key`, we don't need
+                # to add it since the wildcard already covers it.
+                if state_key in self.required_state_map.get(
+                    StateValues.WILDCARD, set()
+                ):
+                    continue
+
+                # If we're getting a wildcard for the `state_type`, get rid of any other
+                # entries with the same `state_key`, since the wildcard will cover it already.
+                if state_type == StateValues.WILDCARD:
+                    # Get rid of any entries that match the `state_key`
+                    #
+                    # Make a copy so we don't run into an error: `dictionary changed size
+                    # during iteration`, when we remove items
+                    for existing_state_type, existing_state_key_set in list(
+                        self.required_state_map.items()
+                    ):
+                        # Make a copy so we don't run into an error: `Set changed size during
+                        # iteration`, when we filter out and remove items
+                        for existing_state_key in existing_state_key_set.copy():
+                            if existing_state_key == state_key:
+                                existing_state_key_set.remove(state_key)
+
+                        # If we've the left the `set()` empty, remove it from the map
+                        if existing_state_key_set == set():
+                            self.required_state_map.pop(existing_state_type, None)
+
+                # If we're getting a wildcard `state_key`, get rid of any other state_keys
+                # for this `state_type` since the wildcard will cover it already.
+                if state_key == StateValues.WILDCARD:
+                    self.required_state_map[state_type] = {state_key}
+                    break
+                # Otherwise, just add it to the set
+                else:
+                    if self.required_state_map.get(state_type) is None:
+                        self.required_state_map[state_type] = {state_key}
+                    else:
+                        self.required_state_map[state_type].add(state_key)
+
+    def must_await_full_state(
+        self,
+        is_mine_id: Callable[[str], bool],
+    ) -> bool:
+        """
+        Check if we have a we're only requesting `required_state` which is completely
+        satisfied even with partial state, then we don't need to `await_full_state` before
+        we can return it.
+
+        Also see `StateFilter.must_await_full_state(...)` for comparison
+
+        Partially-stated rooms should have all state events except for remote membership
+        events so if we require a remote membership event anywhere, then we need to
+        return `True` (requires full state).
+
+        Args:
+            is_mine_id: a callable which confirms if a given state_key matches a mxid
+               of a local user
+        """
+        wildcard_state_keys = self.required_state_map.get(StateValues.WILDCARD)
+        # Requesting *all* state in the room so we have to wait
+        if (
+            wildcard_state_keys is not None
+            and StateValues.WILDCARD in wildcard_state_keys
+        ):
+            return True
+
+        # If the wildcards don't refer to remote user IDs, then we don't need to wait
+        # for full state.
+        if wildcard_state_keys is not None:
+            for possible_user_id in wildcard_state_keys:
+                if not possible_user_id[0].startswith(UserID.SIGIL):
+                    # Not a user ID
+                    continue
+
+                localpart_hostname = possible_user_id.split(":", 1)
+                if len(localpart_hostname) < 2:
+                    # Not a user ID
+                    continue
+
+                if not is_mine_id(possible_user_id):
+                    return True
+
+        membership_state_keys = self.required_state_map.get(EventTypes.Member)
+        # We aren't requesting any membership events at all so the partial state will
+        # cover us.
+        if membership_state_keys is None:
+            return False
+
+        # If we're requesting entirely local users, the partial state will cover us.
+        for user_id in membership_state_keys:
+            if user_id == StateValues.ME:
+                continue
+            # We're lazy-loading membership so we can just return the state we have.
+            # Lazy-loading means we include membership for any event `sender` in the
+            # timeline but since we had to auth those timeline events, we will have the
+            # membership state for them (including from remote senders).
+            elif user_id == StateValues.LAZY:
+                continue
+            elif user_id == StateValues.WILDCARD:
+                return False
+            elif not is_mine_id(user_id):
+                return True
+
+        # Local users only so the partial state will cover us.
+        return False
+
+
+class HaveSentRoomFlag(Enum):
+    """Flag for whether we have sent the room down a sliding sync connection.
+
+    The valid state changes here are:
+        NEVER -> LIVE
+        LIVE -> PREVIOUSLY
+        PREVIOUSLY -> LIVE
+    """
+
+    # The room has never been sent down (or we have forgotten we have sent it
+    # down).
+    NEVER = "never"
+
+    # We have previously sent the room down, but there are updates that we
+    # haven't sent down.
+    PREVIOUSLY = "previously"
+
+    # We have sent the room down and the client has received all updates.
+    LIVE = "live"
+
+
+T = TypeVar("T")
+
+
+@attr.s(auto_attribs=True, slots=True, frozen=True)
+class HaveSentRoom(Generic[T]):
+    """Whether we have sent the room data down a sliding sync connection.
+
+    We are generic over the type of token used, e.g. `RoomStreamToken` or
+    `MultiWriterStreamToken`.
+
+    Attributes:
+        status: Flag of if we have or haven't sent down the room
+        last_token: If the flag is `PREVIOUSLY` then this is non-null and
+            contains the last stream token of the last updates we sent down
+            the room, i.e. we still need to send everything since then to the
+            client.
+    """
+
+    status: HaveSentRoomFlag
+    last_token: Optional[T]
+
+    @staticmethod
+    def live() -> "HaveSentRoom[T]":
+        return HaveSentRoom(HaveSentRoomFlag.LIVE, None)
+
+    @staticmethod
+    def previously(last_token: T) -> "HaveSentRoom[T]":
+        """Constructor for `PREVIOUSLY` flag."""
+        return HaveSentRoom(HaveSentRoomFlag.PREVIOUSLY, last_token)
+
+    @staticmethod
+    def never() -> "HaveSentRoom[T]":
+        return HaveSentRoom(HaveSentRoomFlag.NEVER, None)
+
+
+@attr.s(auto_attribs=True, slots=True, frozen=True)
+class RoomStatusMap(Generic[T]):
+    """For a given stream, e.g. events, records what we have or have not sent
+    down for that stream in a given room."""
+
+    # `room_id` -> `HaveSentRoom`
+    _statuses: Mapping[str, HaveSentRoom[T]] = attr.Factory(dict)
+
+    def have_sent_room(self, room_id: str) -> HaveSentRoom[T]:
+        """Return whether we have previously sent the room down"""
+        return self._statuses.get(room_id, HaveSentRoom.never())
+
+    def get_mutable(self) -> "MutableRoomStatusMap[T]":
+        """Get a mutable copy of this state."""
+        return MutableRoomStatusMap(
+            statuses=self._statuses,
+        )
+
+    def copy(self) -> "RoomStatusMap[T]":
+        """Make a copy of the class. Useful for converting from a mutable to
+        immutable version."""
+
+        return RoomStatusMap(statuses=dict(self._statuses))
+
+
+class MutableRoomStatusMap(RoomStatusMap[T]):
+    """A mutable version of `RoomStatusMap`"""
+
+    # We use a ChainMap here so that we can easily track what has been updated
+    # and what hasn't. Note that when we persist the per connection state this
+    # will get flattened to a normal dict (via calling `.copy()`)
+    _statuses: typing.ChainMap[str, HaveSentRoom[T]]
+
+    def __init__(
+        self,
+        statuses: Mapping[str, HaveSentRoom[T]],
+    ) -> None:
+        # ChainMap requires a mutable mapping, but we're not actually going to
+        # mutate it.
+        statuses = cast(MutableMapping, statuses)
+
+        super().__init__(
+            statuses=ChainMap({}, statuses),
+        )
+
+    def get_updates(self) -> Mapping[str, HaveSentRoom[T]]:
+        """Return only the changes that were made"""
+        return self._statuses.maps[0]
+
+    def record_sent_rooms(self, room_ids: StrCollection) -> None:
+        """Record that we have sent these rooms in the response"""
+        for room_id in room_ids:
+            current_status = self._statuses.get(room_id, HaveSentRoom.never())
+            if current_status.status == HaveSentRoomFlag.LIVE:
+                continue
+
+            self._statuses[room_id] = HaveSentRoom.live()
+
+    def record_unsent_rooms(self, room_ids: StrCollection, from_token: T) -> None:
+        """Record that we have not sent these rooms in the response, but there
+        have been updates.
+        """
+        # Whether we add/update the entries for unsent rooms depends on the
+        # existing entry:
+        #   - LIVE: We have previously sent down everything up to
+        #     `last_room_token, so we update the entry to be `PREVIOUSLY` with
+        #     `last_room_token`.
+        #   - PREVIOUSLY: We have previously sent down everything up to *a*
+        #     given token, so we don't need to update the entry.
+        #   - NEVER: We have never previously sent down the room, and we haven't
+        #     sent anything down this time either so we leave it as NEVER.
+
+        for room_id in room_ids:
+            current_status = self._statuses.get(room_id, HaveSentRoom.never())
+            if current_status.status != HaveSentRoomFlag.LIVE:
+                continue
+
+            self._statuses[room_id] = HaveSentRoom.previously(from_token)
+
+
+@attr.s(auto_attribs=True)
+class PerConnectionState:
+    """The per-connection state. A snapshot of what we've sent down the
+    connection before.
+
+    Currently, we track whether we've sent down various aspects of a given room
+    before.
+
+    We use the `rooms` field to store the position in the events stream for each
+    room that we've previously sent to the client before. On the next request
+    that includes the room, we can then send only what's changed since that
+    recorded position.
+
+    Same goes for the `receipts` field so we only need to send the new receipts
+    since the last time you made a sync request.
+
+    Attributes:
+        rooms: The status of each room for the events stream.
+        receipts: The status of each room for the receipts stream.
+        room_configs: Map from room_id to the `RoomSyncConfig` of all
+            rooms that we have previously sent down.
+    """
+
+    rooms: RoomStatusMap[RoomStreamToken] = attr.Factory(RoomStatusMap)
+    receipts: RoomStatusMap[MultiWriterStreamToken] = attr.Factory(RoomStatusMap)
+
+    room_configs: Mapping[str, RoomSyncConfig] = attr.Factory(dict)
+
+    def get_mutable(self) -> "MutablePerConnectionState":
+        """Get a mutable copy of this state."""
+        room_configs = cast(MutableMapping[str, RoomSyncConfig], self.room_configs)
+
+        return MutablePerConnectionState(
+            rooms=self.rooms.get_mutable(),
+            receipts=self.receipts.get_mutable(),
+            room_configs=ChainMap({}, room_configs),
+        )
+
+    def copy(self) -> "PerConnectionState":
+        return PerConnectionState(
+            rooms=self.rooms.copy(),
+            receipts=self.receipts.copy(),
+            room_configs=dict(self.room_configs),
+        )
+
+
+@attr.s(auto_attribs=True)
+class MutablePerConnectionState(PerConnectionState):
+    """A mutable version of `PerConnectionState`"""
+
+    rooms: MutableRoomStatusMap[RoomStreamToken]
+    receipts: MutableRoomStatusMap[MultiWriterStreamToken]
+
+    room_configs: typing.ChainMap[str, RoomSyncConfig]
+
+    def has_updates(self) -> bool:
+        return (
+            bool(self.rooms.get_updates())
+            or bool(self.receipts.get_updates())
+            or bool(self.get_room_config_updates())
+        )
+
+    def get_room_config_updates(self) -> Mapping[str, RoomSyncConfig]:
+        """Get updates to the room sync config"""
+        return self.room_configs.maps[0]