Refactor state module

We split out the actual state resolution algorithm to prepare for having
multiple versions.

1 files changed, 0 insertions, 866 deletions

diff --git a/synapse/state.py b/synapse/state.py
deleted file mode 100644
index e1092b97a9..0000000000
--- a/synapse/state.py
+++ /dev/null
@@ -1,866 +0,0 @@
-# -*- coding: utf-8 -*-
-# Copyright 2014-2016 OpenMarket 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 hashlib
-import logging
-from collections import namedtuple
-
-from six import iteritems, iterkeys, itervalues
-
-from frozendict import frozendict
-
-from twisted.internet import defer
-
-from synapse import event_auth
-from synapse.api.constants import EventTypes
-from synapse.api.errors import AuthError
-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
-
-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,
-    )
-
-
-def _ordered_events(events):
-    def key_func(e):
-        return -int(e.depth), hashlib.sha1(e.event_id.encode('ascii')).hexdigest()
-
-    return sorted(events, key=key_func)
-
-
-def resolve_events_with_state_map(state_sets, state_map):
-    """
-    Args:
-        state_sets(list): List of dicts of (type, state_key) -> event_id,
-            which are the different state groups to resolve.
-        state_map(dict): a dict from event_id to event, for all events in
-            state_sets.
-
-    Returns
-        dict[(str, str), str]:
-            a map from (type, state_key) to event_id.
-    """
-    if len(state_sets) == 1:
-        return state_sets[0]
-
-    unconflicted_state, conflicted_state = _seperate(
-        state_sets,
-    )
-
-    auth_events = _create_auth_events_from_maps(
-        unconflicted_state, conflicted_state, state_map
-    )
-
-    return _resolve_with_state(
-        unconflicted_state, conflicted_state, auth_events, state_map
-    )
-
-
-def _seperate(state_sets):
-    """Takes the state_sets and figures out which keys are conflicted and
-    which aren't. i.e., which have multiple different event_ids associated
-    with them in different state sets.
-
-    Args:
-        state_sets(iterable[dict[(str, str), str]]):
-            List of dicts of (type, state_key) -> event_id, which are the
-            different state groups to resolve.
-
-    Returns:
-        (dict[(str, str), str], dict[(str, str), set[str]]):
-            A tuple of (unconflicted_state, conflicted_state), where:
-
-            unconflicted_state is a dict mapping (type, state_key)->event_id
-            for unconflicted state keys.
-
-            conflicted_state is a dict mapping (type, state_key) to a set of
-            event ids for conflicted state keys.
-    """
-    state_set_iterator = iter(state_sets)
-    unconflicted_state = dict(next(state_set_iterator))
-    conflicted_state = {}
-
-    for state_set in state_set_iterator:
-        for key, value in iteritems(state_set):
-            # Check if there is an unconflicted entry for the state key.
-            unconflicted_value = unconflicted_state.get(key)
-            if unconflicted_value is None:
-                # There isn't an unconflicted entry so check if there is a
-                # conflicted entry.
-                ls = conflicted_state.get(key)
-                if ls is None:
-                    # There wasn't a conflicted entry so haven't seen this key before.
-                    # Therefore it isn't conflicted yet.
-                    unconflicted_state[key] = value
-                else:
-                    # This key is already conflicted, add our value to the conflict set.
-                    ls.add(value)
-            elif unconflicted_value != value:
-                # If the unconflicted value is not the same as our value then we
-                # have a new conflict. So move the key from the unconflicted_state
-                # to the conflicted state.
-                conflicted_state[key] = {value, unconflicted_value}
-                unconflicted_state.pop(key, None)
-
-    return unconflicted_state, conflicted_state
-
-
-@defer.inlineCallbacks
-def resolve_events_with_factory(state_sets, event_map, state_map_factory):
-    """
-    Args:
-        state_sets(list): List of dicts of (type, state_key) -> event_id,
-            which are the different state groups to resolve.
-
-        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.
-
-        state_map_factory(func): will be called
-            with a list of event_ids that are needed, and should return with
-            a Deferred of dict of event_id to event.
-
-    Returns
-        Deferred[dict[(str, str), str]]:
-            a map from (type, state_key) to event_id.
-    """
-    if len(state_sets) == 1:
-        defer.returnValue(state_sets[0])
-
-    unconflicted_state, conflicted_state = _seperate(
-        state_sets,
-    )
-
-    needed_events = set(
-        event_id
-        for event_ids in itervalues(conflicted_state)
-        for event_id in event_ids
-    )
-    if event_map is not None:
-        needed_events -= set(iterkeys(event_map))
-
-    logger.info("Asking for %d conflicted events", len(needed_events))
-
-    # dict[str, FrozenEvent]: a map from state event id to event. Only includes
-    # the state events which are in conflict (and those in event_map)
-    state_map = yield state_map_factory(needed_events)
-    if event_map is not None:
-        state_map.update(event_map)
-
-    # get the ids of the auth events which allow us to authenticate the
-    # conflicted state, picking only from the unconflicting state.
-    #
-    # dict[(str, str), str]: a map from state key to event id
-    auth_events = _create_auth_events_from_maps(
-        unconflicted_state, conflicted_state, state_map
-    )
-
-    new_needed_events = set(itervalues(auth_events))
-    new_needed_events -= needed_events
-    if event_map is not None:
-        new_needed_events -= set(iterkeys(event_map))
-
-    logger.info("Asking for %d auth events", len(new_needed_events))
-
-    state_map_new = yield state_map_factory(new_needed_events)
-    state_map.update(state_map_new)
-
-    defer.returnValue(_resolve_with_state(
-        unconflicted_state, conflicted_state, auth_events, state_map
-    ))
-
-
-def _create_auth_events_from_maps(unconflicted_state, conflicted_state, state_map):
-    auth_events = {}
-    for event_ids in itervalues(conflicted_state):
-        for event_id in event_ids:
-            if event_id in state_map:
-                keys = event_auth.auth_types_for_event(state_map[event_id])
-                for key in keys:
-                    if key not in auth_events:
-                        event_id = unconflicted_state.get(key, None)
-                        if event_id:
-                            auth_events[key] = event_id
-    return auth_events
-
-
-def _resolve_with_state(unconflicted_state_ids, conflicted_state_ids, auth_event_ids,
-                        state_map):
-    conflicted_state = {}
-    for key, event_ids in iteritems(conflicted_state_ids):
-        events = [state_map[ev_id] for ev_id in event_ids if ev_id in state_map]
-        if len(events) > 1:
-            conflicted_state[key] = events
-        elif len(events) == 1:
-            unconflicted_state_ids[key] = events[0].event_id
-
-    auth_events = {
-        key: state_map[ev_id]
-        for key, ev_id in iteritems(auth_event_ids)
-        if ev_id in state_map
-    }
-
-    try:
-        resolved_state = _resolve_state_events(
-            conflicted_state, auth_events
-        )
-    except Exception:
-        logger.exception("Failed to resolve state")
-        raise
-
-    new_state = unconflicted_state_ids
-    for key, event in iteritems(resolved_state):
-        new_state[key] = event.event_id
-
-    return new_state
-
-
-def _resolve_state_events(conflicted_state, auth_events):
-    """ This is where we actually decide which of the conflicted state to
-    use.
-
-    We resolve conflicts in the following order:
-        1. power levels
-        2. join rules
-        3. memberships
-        4. other events.
-    """
-    resolved_state = {}
-    if POWER_KEY in conflicted_state:
-        events = conflicted_state[POWER_KEY]
-        logger.debug("Resolving conflicted power levels %r", events)
-        resolved_state[POWER_KEY] = _resolve_auth_events(
-            events, auth_events)
-
-    auth_events.update(resolved_state)
-
-    for key, events in iteritems(conflicted_state):
-        if key[0] == EventTypes.JoinRules:
-            logger.debug("Resolving conflicted join rules %r", events)
-            resolved_state[key] = _resolve_auth_events(
-                events,
-                auth_events
-            )
-
-    auth_events.update(resolved_state)
-
-    for key, events in iteritems(conflicted_state):
-        if key[0] == EventTypes.Member:
-            logger.debug("Resolving conflicted member lists %r", events)
-            resolved_state[key] = _resolve_auth_events(
-                events,
-                auth_events
-            )
-
-    auth_events.update(resolved_state)
-
-    for key, events in iteritems(conflicted_state):
-        if key not in resolved_state:
-            logger.debug("Resolving conflicted state %r:%r", key, events)
-            resolved_state[key] = _resolve_normal_events(
-                events, auth_events
-            )
-
-    return resolved_state
-
-
-def _resolve_auth_events(events, auth_events):
-    reverse = [i for i in reversed(_ordered_events(events))]
-
-    auth_keys = set(
-        key
-        for event in events
-        for key in event_auth.auth_types_for_event(event)
-    )
-
-    new_auth_events = {}
-    for key in auth_keys:
-        auth_event = auth_events.get(key, None)
-        if auth_event:
-            new_auth_events[key] = auth_event
-
-    auth_events = new_auth_events
-
-    prev_event = reverse[0]
-    for event in reverse[1:]:
-        auth_events[(prev_event.type, prev_event.state_key)] = prev_event
-        try:
-            # The signatures have already been checked at this point
-            event_auth.check(event, auth_events, do_sig_check=False, do_size_check=False)
-            prev_event = event
-        except AuthError:
-            return prev_event
-
-    return event
-
-
-def _resolve_normal_events(events, auth_events):
-    for event in _ordered_events(events):
-        try:
-            # The signatures have already been checked at this point
-            event_auth.check(event, auth_events, do_sig_check=False, do_size_check=False)
-            return event
-        except AuthError:
-            pass
-
-    # Use the last event (the one with the least depth) if they all fail
-    # the auth check.
-    return event