From d26808dd854006bd26a2366c675428ce0737238c Mon Sep 17 00:00:00 2001 From: David Robertson Date: Thu, 2 Dec 2021 20:58:32 +0000 Subject: [PATCH] Comments on the /sync tentacles (#11494) This mainly consists of docstrings and inline comments. There are one or two type annotations and variable renames thrown in while I was here. Co-authored-by: Patrick Cloke --- changelog.d/11494.misc | 1 + synapse/handlers/sync.py | 156 +++++++++++++++++------ synapse/storage/databases/main/stream.py | 15 ++- 3 files changed, 129 insertions(+), 43 deletions(-) create mode 100644 changelog.d/11494.misc diff --git a/changelog.d/11494.misc b/changelog.d/11494.misc new file mode 100644 index 000000000000..7afd7d3a0727 --- /dev/null +++ b/changelog.d/11494.misc @@ -0,0 +1 @@ +Add comments to various parts of the `/sync` handler. \ No newline at end of file diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py index 891435c14daf..53d4627147d4 100644 --- a/synapse/handlers/sync.py +++ b/synapse/handlers/sync.py @@ -334,6 +334,19 @@ async def _wait_for_sync_for_user( full_state: bool, cache_context: ResponseCacheContext[SyncRequestKey], ) -> SyncResult: + """The start of the machinery that produces a /sync response. + + See https://spec.matrix.org/v1.1/client-server-api/#syncing for full details. + + This method does high-level bookkeeping: + - tracking the kind of sync in the logging context + - deleting any to_device messages whose delivery has been acknowledged. + - deciding if we should dispatch an instant or delayed response + - marking the sync as being lazily loaded, if appropriate + + Computing the body of the response begins in the next method, + `current_sync_for_user`. + """ if since_token is None: sync_type = "initial_sync" elif full_state: @@ -363,7 +376,7 @@ async def _wait_for_sync_for_user( sync_config, since_token, full_state=full_state ) else: - + # Otherwise, we wait for something to happen and report it to the user. async def current_sync_callback( before_token: StreamToken, after_token: StreamToken ) -> SyncResult: @@ -402,7 +415,12 @@ async def current_sync_for_user( since_token: Optional[StreamToken] = None, full_state: bool = False, ) -> SyncResult: - """Get the sync for client needed to match what the server has now.""" + """Generates the response body of a sync result, represented as a SyncResult. + + This is a wrapper around `generate_sync_result` which starts an open tracing + span to track the sync. See `generate_sync_result` for the next part of your + indoctrination. + """ with start_active_span("current_sync_for_user"): log_kv({"since_token": since_token}) sync_result = await self.generate_sync_result( @@ -560,7 +578,7 @@ async def _load_filtered_recents( # that have happened since `since_key` up to `end_key`, so we # can just use `get_room_events_stream_for_room`. # Otherwise, we want to return the last N events in the room - # in toplogical ordering. + # in topological ordering. if since_key: events, end_key = await self.store.get_room_events_stream_for_room( room_id, @@ -1042,7 +1060,18 @@ async def generate_sync_result( since_token: Optional[StreamToken] = None, full_state: bool = False, ) -> SyncResult: - """Generates a sync result.""" + """Generates the response body of a sync result. + + This is represented by a `SyncResult` struct, which is built from small pieces + using a `SyncResultBuilder`. See also + https://spec.matrix.org/v1.1/client-server-api/#get_matrixclientv3sync + the `sync_result_builder` is passed as a mutable ("inout") parameter to various + helper functions. These retrieve and process the data which forms the sync body, + often writing to the `sync_result_builder` to store their output. + + At the end, we transfer data from the `sync_result_builder` to a new `SyncResult` + instance to signify that the sync calculation is complete. + """ # NB: The now_token gets changed by some of the generate_sync_* methods, # this is due to some of the underlying streams not supporting the ability # to query up to a given point. @@ -1344,14 +1373,22 @@ async def _generate_sync_entry_for_to_device( async def _generate_sync_entry_for_account_data( self, sync_result_builder: "SyncResultBuilder" ) -> Dict[str, Dict[str, JsonDict]]: - """Generates the account data portion of the sync response. Populates - `sync_result_builder` with the result. + """Generates the account data portion of the sync response. + + Account data (called "Client Config" in the spec) can be set either globally + or for a specific room. Account data consists of a list of events which + accumulate state, much like a room. + + This function retrieves global and per-room account data. The former is written + to the given `sync_result_builder`. The latter is returned directly, to be + later written to the `sync_result_builder` on a room-by-room basis. Args: sync_result_builder Returns: - A dictionary containing the per room account data. + A dictionary whose keys (room ids) map to the per room account data for that + room. """ sync_config = sync_result_builder.sync_config user_id = sync_result_builder.sync_config.user.to_string() @@ -1359,7 +1396,7 @@ async def _generate_sync_entry_for_account_data( if since_token and not sync_result_builder.full_state: ( - account_data, + global_account_data, account_data_by_room, ) = await self.store.get_updated_account_data_for_user( user_id, since_token.account_data_key @@ -1370,23 +1407,23 @@ async def _generate_sync_entry_for_account_data( ) if push_rules_changed: - account_data["m.push_rules"] = await self.push_rules_for_user( + global_account_data["m.push_rules"] = await self.push_rules_for_user( sync_config.user ) else: ( - account_data, + global_account_data, account_data_by_room, ) = await self.store.get_account_data_for_user(sync_config.user.to_string()) - account_data["m.push_rules"] = await self.push_rules_for_user( + global_account_data["m.push_rules"] = await self.push_rules_for_user( sync_config.user ) account_data_for_user = await sync_config.filter_collection.filter_account_data( [ {"type": account_data_type, "content": content} - for account_data_type, content in account_data.items() + for account_data_type, content in global_account_data.items() ] ) @@ -1460,15 +1497,22 @@ async def _generate_sync_entry_for_rooms( """Generates the rooms portion of the sync response. Populates the `sync_result_builder` with the result. + In the response that reaches the client, rooms are divided into four categories: + `invite`, `join`, `knock`, `leave`. These aren't the same as the four sets of + room ids returned by this function. + Args: sync_result_builder account_data_by_room: Dictionary of per room account data Returns: - Returns a 4-tuple of - `(newly_joined_rooms, newly_joined_or_invited_users, - newly_left_rooms, newly_left_users)` + Returns a 4-tuple whose entries are: + - newly_joined_rooms + - newly_joined_or_invited_or_knocked_users + - newly_left_rooms + - newly_left_users """ + # Start by fetching all ephemeral events in rooms we've joined (if required). user_id = sync_result_builder.sync_config.user.to_string() block_all_room_ephemeral = ( sync_result_builder.since_token is None @@ -1590,6 +1634,8 @@ async def _have_rooms_changed( ) -> bool: """Returns whether there may be any new events that should be sent down the sync. Returns True if there are. + + Does not modify the `sync_result_builder`. """ user_id = sync_result_builder.sync_config.user.to_string() since_token = sync_result_builder.since_token @@ -1597,12 +1643,13 @@ async def _have_rooms_changed( assert since_token - # Get a list of membership change events that have happened. - rooms_changed = await self.store.get_membership_changes_for_user( + # Get a list of membership change events that have happened to the user + # requesting the sync. + membership_changes = await self.store.get_membership_changes_for_user( user_id, since_token.room_key, now_token.room_key ) - if rooms_changed: + if membership_changes: return True stream_id = since_token.room_key.stream @@ -1614,7 +1661,25 @@ async def _have_rooms_changed( async def _get_rooms_changed( self, sync_result_builder: "SyncResultBuilder", ignored_users: FrozenSet[str] ) -> _RoomChanges: - """Gets the the changes that have happened since the last sync.""" + """Determine the changes in rooms to report to the user. + + Ideally, we want to report all events whose stream ordering `s` lies in the + range `since_token < s <= now_token`, where the two tokens are read from the + sync_result_builder. + + If there are too many events in that range to report, things get complicated. + In this situation we return a truncated list of the most recent events, and + indicate in the response that there is a "gap" of omitted events. Additionally: + + - we include a "state_delta", to describe the changes in state over the gap, + - we include all membership events applying to the user making the request, + even those in the gap. + + See the spec for the rationale: + https://spec.matrix.org/v1.1/client-server-api/#syncing + + The sync_result_builder is not modified by this function. + """ user_id = sync_result_builder.sync_config.user.to_string() since_token = sync_result_builder.since_token now_token = sync_result_builder.now_token @@ -1622,21 +1687,36 @@ async def _get_rooms_changed( assert since_token - # Get a list of membership change events that have happened. - rooms_changed = await self.store.get_membership_changes_for_user( + # The spec + # https://spec.matrix.org/v1.1/client-server-api/#get_matrixclientv3sync + # notes that membership events need special consideration: + # + # > When a sync is limited, the server MUST return membership events for events + # > in the gap (between since and the start of the returned timeline), regardless + # > as to whether or not they are redundant. + # + # We fetch such events here, but we only seem to use them for categorising rooms + # as newly joined, newly left, invited or knocked. + # TODO: we've already called this function and ran this query in + # _have_rooms_changed. We could keep the results in memory to avoid a + # second query, at the cost of more complicated source code. + membership_change_events = await self.store.get_membership_changes_for_user( user_id, since_token.room_key, now_token.room_key ) mem_change_events_by_room_id: Dict[str, List[EventBase]] = {} - for event in rooms_changed: + for event in membership_change_events: mem_change_events_by_room_id.setdefault(event.room_id, []).append(event) - newly_joined_rooms = [] - newly_left_rooms = [] - room_entries = [] - invited = [] - knocked = [] + newly_joined_rooms: List[str] = [] + newly_left_rooms: List[str] = [] + room_entries: List[RoomSyncResultBuilder] = [] + invited: List[InvitedSyncResult] = [] + knocked: List[KnockedSyncResult] = [] for room_id, events in mem_change_events_by_room_id.items(): + # The body of this loop will add this room to at least one of the five lists + # above. Things get messy if you've e.g. joined, left, joined then left the + # room all in the same sync period. logger.debug( "Membership changes in %s: [%s]", room_id, @@ -1781,7 +1861,9 @@ async def _get_rooms_changed( timeline_limit = sync_config.filter_collection.timeline_limit() - # Get all events for rooms we're currently joined to. + # Get all events since the `from_key` in rooms we're currently joined to. + # If there are too many, we get the most recent events only. This leaves + # a "gap" in the timeline, as described by the spec for /sync. room_to_events = await self.store.get_room_events_stream_for_rooms( room_ids=sync_result_builder.joined_room_ids, from_key=since_token.room_key, @@ -1842,6 +1924,10 @@ async def _get_all_rooms( ) -> _RoomChanges: """Returns entries for all rooms for the user. + Like `_get_rooms_changed`, but assumes the `since_token` is `None`. + + This function does not modify the sync_result_builder. + Args: sync_result_builder ignored_users: Set of users ignored by user. @@ -1853,16 +1939,9 @@ async def _get_all_rooms( now_token = sync_result_builder.now_token sync_config = sync_result_builder.sync_config - membership_list = ( - Membership.INVITE, - Membership.KNOCK, - Membership.JOIN, - Membership.LEAVE, - Membership.BAN, - ) - room_list = await self.store.get_rooms_for_local_user_where_membership_is( - user_id=user_id, membership_list=membership_list + user_id=user_id, + membership_list=Membership.LIST, ) room_entries = [] @@ -2212,8 +2291,7 @@ def _calculate_state( # to only include membership events for the senders in the timeline. # In practice, we can do this by removing them from the p_ids list, # which is the list of relevant state we know we have already sent to the client. - # see https://github.com/matrix-org/synapse/pull/2970 - # /files/efcdacad7d1b7f52f879179701c7e0d9b763511f#r204732809 + # see https://github.com/matrix-org/synapse/pull/2970/files/efcdacad7d1b7f52f879179701c7e0d9b763511f#r204732809 if lazy_load_members: p_ids.difference_update( diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py index 42dc807d17ff..57aab5525937 100644 --- a/synapse/storage/databases/main/stream.py +++ b/synapse/storage/databases/main/stream.py @@ -497,7 +497,7 @@ async def get_room_events_stream_for_room( oldest `limit` events. Returns: - The list of events (in ascending order) and the token from the start + The list of events (in ascending stream order) and the token from the start of the chunk of events returned. """ if from_key == to_key: @@ -510,7 +510,7 @@ async def get_room_events_stream_for_room( if not has_changed: return [], from_key - def f(txn): + def f(txn: LoggingTransaction) -> List[_EventDictReturn]: # To handle tokens with a non-empty instance_map we fetch more # results than necessary and then filter down min_from_id = from_key.stream @@ -565,6 +565,13 @@ def f(txn): async def get_membership_changes_for_user( self, user_id: str, from_key: RoomStreamToken, to_key: RoomStreamToken ) -> List[EventBase]: + """Fetch membership events for a given user. + + All such events whose stream ordering `s` lies in the range + `from_key < s <= to_key` are returned. Events are ordered by ascending stream + order. + """ + # Start by ruling out cases where a DB query is not necessary. if from_key == to_key: return [] @@ -575,7 +582,7 @@ async def get_membership_changes_for_user( if not has_changed: return [] - def f(txn): + def f(txn: LoggingTransaction) -> List[_EventDictReturn]: # To handle tokens with a non-empty instance_map we fetch more # results than necessary and then filter down min_from_id = from_key.stream @@ -634,7 +641,7 @@ async def get_recent_events_for_room( Returns: A list of events and a token pointing to the start of the returned - events. The events returned are in ascending order. + events. The events returned are in ascending topological order. """ rows, token = await self.get_recent_event_ids_for_room(