diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
new file mode 100644
index 0000000000..8c091d07c9
--- /dev/null
+++ b/synapse/state/__init__.py
@@ -0,0 +1,574 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014-2016 OpenMarket Ltd
+# 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 collections import namedtuple
+
+from six import iteritems, itervalues
+
+from frozendict import frozendict
+
+from twisted.internet import defer
+
+from synapse.api.constants import EventTypes
+from synapse.events.snapshot import EventContext
+from synapse.util.async import Linearizer
+from synapse.util.caches import CACHE_SIZE_FACTOR
+from synapse.util.caches.expiringcache import ExpiringCache
+from synapse.util.logutils import log_function
+from synapse.util.metrics import Measure
+
+from .v1 import resolve_events_with_factory, resolve_events_with_state_map
+
+logger = logging.getLogger(__name__)
+
+
+KeyStateTuple = namedtuple("KeyStateTuple", ("context", "type", "state_key"))
+
+
+SIZE_OF_CACHE = int(100000 * CACHE_SIZE_FACTOR)
+EVICTION_TIMEOUT_SECONDS = 60 * 60
+
+
+_NEXT_STATE_ID = 1
+
+POWER_KEY = (EventTypes.PowerLevels, "")
+
+
+def _gen_state_id():
+ global _NEXT_STATE_ID
+ s = "X%d" % (_NEXT_STATE_ID,)
+ _NEXT_STATE_ID += 1
+ return s
+
+
+class _StateCacheEntry(object):
+ __slots__ = ["state", "state_group", "state_id", "prev_group", "delta_ids"]
+
+ def __init__(self, state, state_group, prev_group=None, delta_ids=None):
+ # dict[(str, str), str] map from (type, state_key) to event_id
+ self.state = frozendict(state)
+
+ # the ID of a state group if one and only one is involved.
+ # otherwise, None otherwise?
+ self.state_group = state_group
+
+ self.prev_group = prev_group
+ self.delta_ids = frozendict(delta_ids) if delta_ids is not None else None
+
+ # The `state_id` is a unique ID we generate that can be used as ID for
+ # this collection of state. Usually this would be the same as the
+ # state group, but on worker instances we can't generate a new state
+ # group each time we resolve state, so we generate a separate one that
+ # isn't persisted and is used solely for caches.
+ # `state_id` is either a state_group (and so an int) or a string. This
+ # ensures we don't accidentally persist a state_id as a stateg_group
+ if state_group:
+ self.state_id = state_group
+ else:
+ self.state_id = _gen_state_id()
+
+ def __len__(self):
+ return len(self.state)
+
+
+class StateHandler(object):
+ """Fetches bits of state from the stores, and does state resolution
+ where necessary
+ """
+
+ def __init__(self, hs):
+ self.clock = hs.get_clock()
+ self.store = hs.get_datastore()
+ self.hs = hs
+ self._state_resolution_handler = hs.get_state_resolution_handler()
+
+ def start_caching(self):
+ # TODO: remove this shim
+ self._state_resolution_handler.start_caching()
+
+ @defer.inlineCallbacks
+ def get_current_state(self, room_id, event_type=None, state_key="",
+ latest_event_ids=None):
+ """ Retrieves the current state for the room. This is done by
+ calling `get_latest_events_in_room` to get the leading edges of the
+ event graph and then resolving any of the state conflicts.
+
+ This is equivalent to getting the state of an event that were to send
+ next before receiving any new events.
+
+ If `event_type` is specified, then the method returns only the one
+ event (or None) with that `event_type` and `state_key`.
+
+ Returns:
+ map from (type, state_key) to event
+ """
+ if not latest_event_ids:
+ latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
+
+ logger.debug("calling resolve_state_groups from get_current_state")
+ ret = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
+ state = ret.state
+
+ if event_type:
+ event_id = state.get((event_type, state_key))
+ event = None
+ if event_id:
+ event = yield self.store.get_event(event_id, allow_none=True)
+ defer.returnValue(event)
+ return
+
+ state_map = yield self.store.get_events(list(state.values()),
+ get_prev_content=False)
+ state = {
+ key: state_map[e_id] for key, e_id in iteritems(state) if e_id in state_map
+ }
+
+ defer.returnValue(state)
+
+ @defer.inlineCallbacks
+ def get_current_state_ids(self, room_id, latest_event_ids=None):
+ """Get the current state, or the state at a set of events, for a room
+
+ Args:
+ room_id (str):
+
+ latest_event_ids (iterable[str]|None): if given, the forward
+ extremities to resolve. If None, we look them up from the
+ database (via a cache)
+
+ Returns:
+ Deferred[dict[(str, str), str)]]: the state dict, mapping from
+ (event_type, state_key) -> event_id
+ """
+ if not latest_event_ids:
+ latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
+
+ logger.debug("calling resolve_state_groups from get_current_state_ids")
+ ret = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
+ state = ret.state
+
+ defer.returnValue(state)
+
+ @defer.inlineCallbacks
+ def get_current_user_in_room(self, room_id, latest_event_ids=None):
+ if not latest_event_ids:
+ latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
+ logger.debug("calling resolve_state_groups from get_current_user_in_room")
+ entry = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
+ joined_users = yield self.store.get_joined_users_from_state(room_id, entry)
+ defer.returnValue(joined_users)
+
+ @defer.inlineCallbacks
+ def get_current_hosts_in_room(self, room_id, latest_event_ids=None):
+ if not latest_event_ids:
+ latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
+ logger.debug("calling resolve_state_groups from get_current_hosts_in_room")
+ entry = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
+ joined_hosts = yield self.store.get_joined_hosts(room_id, entry)
+ defer.returnValue(joined_hosts)
+
+ @defer.inlineCallbacks
+ def compute_event_context(self, event, old_state=None):
+ """Build an EventContext structure for the event.
+
+ This works out what the current state should be for the event, and
+ generates a new state group if necessary.
+
+ Args:
+ event (synapse.events.EventBase):
+ old_state (dict|None): The state at the event if it can't be
+ calculated from existing events. This is normally only specified
+ when receiving an event from federation where we don't have the
+ prev events for, e.g. when backfilling.
+ Returns:
+ synapse.events.snapshot.EventContext:
+ """
+
+ if event.internal_metadata.is_outlier():
+ # If this is an outlier, then we know it shouldn't have any current
+ # state. Certainly store.get_current_state won't return any, and
+ # persisting the event won't store the state group.
+ if old_state:
+ prev_state_ids = {
+ (s.type, s.state_key): s.event_id for s in old_state
+ }
+ if event.is_state():
+ current_state_ids = dict(prev_state_ids)
+ key = (event.type, event.state_key)
+ current_state_ids[key] = event.event_id
+ else:
+ current_state_ids = prev_state_ids
+ else:
+ current_state_ids = {}
+ prev_state_ids = {}
+
+ # We don't store state for outliers, so we don't generate a state
+ # group for it.
+ context = EventContext.with_state(
+ state_group=None,
+ current_state_ids=current_state_ids,
+ prev_state_ids=prev_state_ids,
+ )
+
+ defer.returnValue(context)
+
+ if old_state:
+ # We already have the state, so we don't need to calculate it.
+ # Let's just correctly fill out the context and create a
+ # new state group for it.
+
+ prev_state_ids = {
+ (s.type, s.state_key): s.event_id for s in old_state
+ }
+
+ if event.is_state():
+ key = (event.type, event.state_key)
+ if key in prev_state_ids:
+ replaces = prev_state_ids[key]
+ if replaces != event.event_id: # Paranoia check
+ event.unsigned["replaces_state"] = replaces
+ current_state_ids = dict(prev_state_ids)
+ current_state_ids[key] = event.event_id
+ else:
+ current_state_ids = prev_state_ids
+
+ state_group = yield self.store.store_state_group(
+ event.event_id,
+ event.room_id,
+ prev_group=None,
+ delta_ids=None,
+ current_state_ids=current_state_ids,
+ )
+
+ context = EventContext.with_state(
+ state_group=state_group,
+ current_state_ids=current_state_ids,
+ prev_state_ids=prev_state_ids,
+ )
+
+ defer.returnValue(context)
+
+ logger.debug("calling resolve_state_groups from compute_event_context")
+ entry = yield self.resolve_state_groups_for_events(
+ event.room_id, [e for e, _ in event.prev_events],
+ )
+
+ prev_state_ids = entry.state
+ prev_group = None
+ delta_ids = None
+
+ if event.is_state():
+ # If this is a state event then we need to create a new state
+ # group for the state after this event.
+
+ key = (event.type, event.state_key)
+ if key in prev_state_ids:
+ replaces = prev_state_ids[key]
+ event.unsigned["replaces_state"] = replaces
+
+ current_state_ids = dict(prev_state_ids)
+ current_state_ids[key] = event.event_id
+
+ if entry.state_group:
+ # If the state at the event has a state group assigned then
+ # we can use that as the prev group
+ prev_group = entry.state_group
+ delta_ids = {
+ key: event.event_id
+ }
+ elif entry.prev_group:
+ # If the state at the event only has a prev group, then we can
+ # use that as a prev group too.
+ prev_group = entry.prev_group
+ delta_ids = dict(entry.delta_ids)
+ delta_ids[key] = event.event_id
+
+ state_group = yield self.store.store_state_group(
+ event.event_id,
+ event.room_id,
+ prev_group=prev_group,
+ delta_ids=delta_ids,
+ current_state_ids=current_state_ids,
+ )
+ else:
+ current_state_ids = prev_state_ids
+ prev_group = entry.prev_group
+ delta_ids = entry.delta_ids
+
+ if entry.state_group is None:
+ entry.state_group = yield self.store.store_state_group(
+ event.event_id,
+ event.room_id,
+ prev_group=entry.prev_group,
+ delta_ids=entry.delta_ids,
+ current_state_ids=current_state_ids,
+ )
+ entry.state_id = entry.state_group
+
+ state_group = entry.state_group
+
+ context = EventContext.with_state(
+ state_group=state_group,
+ current_state_ids=current_state_ids,
+ prev_state_ids=prev_state_ids,
+ prev_group=prev_group,
+ delta_ids=delta_ids,
+ )
+
+ defer.returnValue(context)
+
+ @defer.inlineCallbacks
+ def resolve_state_groups_for_events(self, room_id, event_ids):
+ """ Given a list of event_ids this method fetches the state at each
+ event, resolves conflicts between them and returns them.
+
+ Args:
+ room_id (str):
+ event_ids (list[str]):
+
+ Returns:
+ Deferred[_StateCacheEntry]: resolved state
+ """
+ logger.debug("resolve_state_groups event_ids %s", event_ids)
+
+ # map from state group id to the state in that state group (where
+ # 'state' is a map from state key to event id)
+ # dict[int, dict[(str, str), str]]
+ state_groups_ids = yield self.store.get_state_groups_ids(
+ room_id, event_ids
+ )
+
+ if len(state_groups_ids) == 1:
+ name, state_list = list(state_groups_ids.items()).pop()
+
+ prev_group, delta_ids = yield self.store.get_state_group_delta(name)
+
+ defer.returnValue(_StateCacheEntry(
+ state=state_list,
+ state_group=name,
+ prev_group=prev_group,
+ delta_ids=delta_ids,
+ ))
+
+ result = yield self._state_resolution_handler.resolve_state_groups(
+ room_id, state_groups_ids, None, self._state_map_factory,
+ )
+ defer.returnValue(result)
+
+ def _state_map_factory(self, ev_ids):
+ return self.store.get_events(
+ ev_ids, get_prev_content=False, check_redacted=False,
+ )
+
+ def resolve_events(self, state_sets, event):
+ logger.info(
+ "Resolving state for %s with %d groups", event.room_id, len(state_sets)
+ )
+ state_set_ids = [{
+ (ev.type, ev.state_key): ev.event_id
+ for ev in st
+ } for st in state_sets]
+
+ state_map = {
+ ev.event_id: ev
+ for st in state_sets
+ for ev in st
+ }
+
+ with Measure(self.clock, "state._resolve_events"):
+ new_state = resolve_events_with_state_map(state_set_ids, state_map)
+
+ new_state = {
+ key: state_map[ev_id] for key, ev_id in iteritems(new_state)
+ }
+
+ return new_state
+
+
+class StateResolutionHandler(object):
+ """Responsible for doing state conflict resolution.
+
+ Note that the storage layer depends on this handler, so all functions must
+ be storage-independent.
+ """
+ def __init__(self, hs):
+ self.clock = hs.get_clock()
+
+ # dict of set of event_ids -> _StateCacheEntry.
+ self._state_cache = None
+ self.resolve_linearizer = Linearizer(name="state_resolve_lock")
+
+ def start_caching(self):
+ logger.debug("start_caching")
+
+ self._state_cache = ExpiringCache(
+ cache_name="state_cache",
+ clock=self.clock,
+ max_len=SIZE_OF_CACHE,
+ expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
+ iterable=True,
+ reset_expiry_on_get=True,
+ )
+
+ self._state_cache.start()
+
+ @defer.inlineCallbacks
+ @log_function
+ def resolve_state_groups(
+ self, room_id, state_groups_ids, event_map, state_map_factory,
+ ):
+ """Resolves conflicts between a set of state groups
+
+ Always generates a new state group (unless we hit the cache), so should
+ not be called for a single state group
+
+ Args:
+ room_id (str): room we are resolving for (used for logging)
+ state_groups_ids (dict[int, dict[(str, str), str]]):
+ map from state group id to the state in that state group
+ (where 'state' is a map from state key to event id)
+
+ event_map(dict[str,FrozenEvent]|None):
+ a dict from event_id to event, for any events that we happen to
+ have in flight (eg, those currently being persisted). This will be
+ used as a starting point fof finding the state we need; any missing
+ events will be requested via state_map_factory.
+
+ If None, all events will be fetched via state_map_factory.
+
+ Returns:
+ Deferred[_StateCacheEntry]: resolved state
+ """
+ logger.debug(
+ "resolve_state_groups state_groups %s",
+ state_groups_ids.keys()
+ )
+
+ group_names = frozenset(state_groups_ids.keys())
+
+ with (yield self.resolve_linearizer.queue(group_names)):
+ if self._state_cache is not None:
+ cache = self._state_cache.get(group_names, None)
+ if cache:
+ defer.returnValue(cache)
+
+ logger.info(
+ "Resolving state for %s with %d groups", room_id, len(state_groups_ids)
+ )
+
+ # start by assuming we won't have any conflicted state, and build up the new
+ # state map by iterating through the state groups. If we discover a conflict,
+ # we give up and instead use `resolve_events_with_factory`.
+ #
+ # XXX: is this actually worthwhile, or should we just let
+ # resolve_events_with_factory do it?
+ new_state = {}
+ conflicted_state = False
+ for st in itervalues(state_groups_ids):
+ for key, e_id in iteritems(st):
+ if key in new_state:
+ conflicted_state = True
+ break
+ new_state[key] = e_id
+ if conflicted_state:
+ break
+
+ if conflicted_state:
+ logger.info("Resolving conflicted state for %r", room_id)
+ with Measure(self.clock, "state._resolve_events"):
+ new_state = yield resolve_events_with_factory(
+ list(itervalues(state_groups_ids)),
+ event_map=event_map,
+ state_map_factory=state_map_factory,
+ )
+
+ # if the new state matches any of the input state groups, we can
+ # use that state group again. Otherwise we will generate a state_id
+ # which will be used as a cache key for future resolutions, but
+ # not get persisted.
+
+ with Measure(self.clock, "state.create_group_ids"):
+ cache = _make_state_cache_entry(new_state, state_groups_ids)
+
+ if self._state_cache is not None:
+ self._state_cache[group_names] = cache
+
+ defer.returnValue(cache)
+
+
+def _make_state_cache_entry(
+ new_state,
+ state_groups_ids,
+):
+ """Given a resolved state, and a set of input state groups, pick one to base
+ a new state group on (if any), and return an appropriately-constructed
+ _StateCacheEntry.
+
+ Args:
+ new_state (dict[(str, str), str]): resolved state map (mapping from
+ (type, state_key) to event_id)
+
+ state_groups_ids (dict[int, dict[(str, str), str]]):
+ map from state group id to the state in that state group
+ (where 'state' is a map from state key to event id)
+
+ Returns:
+ _StateCacheEntry
+ """
+ # if the new state matches any of the input state groups, we can
+ # use that state group again. Otherwise we will generate a state_id
+ # which will be used as a cache key for future resolutions, but
+ # not get persisted.
+
+ # first look for exact matches
+ new_state_event_ids = set(itervalues(new_state))
+ for sg, state in iteritems(state_groups_ids):
+ if len(new_state_event_ids) != len(state):
+ continue
+
+ old_state_event_ids = set(itervalues(state))
+ if new_state_event_ids == old_state_event_ids:
+ # got an exact match.
+ return _StateCacheEntry(
+ state=new_state,
+ state_group=sg,
+ )
+
+ # TODO: We want to create a state group for this set of events, to
+ # increase cache hits, but we need to make sure that it doesn't
+ # end up as a prev_group without being added to the database
+
+ # failing that, look for the closest match.
+ prev_group = None
+ delta_ids = None
+
+ for old_group, old_state in iteritems(state_groups_ids):
+ n_delta_ids = {
+ k: v
+ for k, v in iteritems(new_state)
+ if old_state.get(k) != v
+ }
+ if not delta_ids or len(n_delta_ids) < len(delta_ids):
+ prev_group = old_group
+ delta_ids = n_delta_ids
+
+ return _StateCacheEntry(
+ state=new_state,
+ state_group=None,
+ prev_group=prev_group,
+ delta_ids=delta_ids,
+ )
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