From 119451dcd192ff5397a3f9630f14556737e82677 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 7 Aug 2018 15:22:40 +0100
Subject: [PATCH 1/8] Refactor state module

We split out the actual state resolution algorithm to prepare for having
multiple versions.
---
 synapse/{state.py => state/__init__.py} | 300 +---------------------
 synapse/state/v1.py                     | 321 ++++++++++++++++++++++++
 2 files changed, 325 insertions(+), 296 deletions(-)
 rename synapse/{state.py => state/__init__.py} (67%)
 create mode 100644 synapse/state/v1.py

diff --git a/synapse/state.py b/synapse/state/__init__.py
similarity index 67%
rename from synapse/state.py
rename to synapse/state/__init__.py
index e1092b97a..8c091d07c 100644
--- a/synapse/state.py
+++ b/synapse/state/__init__.py
@@ -1,5 +1,6 @@
 # -*- 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.
@@ -13,20 +14,16 @@
 # 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 six import iteritems, 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
@@ -34,6 +31,8 @@ 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__)
 
 
@@ -573,294 +572,3 @@ def _make_state_cache_entry(
         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
diff --git a/synapse/state/v1.py b/synapse/state/v1.py
new file mode 100644
index 000000000..3a1f7054a
--- /dev/null
+++ b/synapse/state/v1.py
@@ -0,0 +1,321 @@
+# -*- coding: utf-8 -*-
+# 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 hashlib
+import logging
+
+from six import iteritems, iterkeys, itervalues
+
+from twisted.internet import defer
+
+from synapse import event_auth
+from synapse.api.constants import EventTypes
+from synapse.api.errors import AuthError
+
+logger = logging.getLogger(__name__)
+
+
+POWER_KEY = (EventTypes.PowerLevels, "")
+
+
+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
+    )
+
+
+@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 _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
+
+
+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
+
+
+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)

From 152c0aa58edd1453f6c8c16a82cdb92165d0adba Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 7 Aug 2018 15:27:19 +0100
Subject: [PATCH 2/8] Add constants for room versions

---
 synapse/api/constants.py | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index b0da506f6..912bf024b 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -97,9 +97,14 @@ class ThirdPartyEntityKind(object):
     LOCATION = "location"
 
 
+class RoomVersions(object):
+    V1 = "1"
+    VDH_TEST = "vdh-test-version"
+
+
 # the version we will give rooms which are created on this server
-DEFAULT_ROOM_VERSION = "1"
+DEFAULT_ROOM_VERSION = RoomVersions.V1
 
 # vdh-test-version is a placeholder to get room versioning support working and tested
 # until we have a working v2.
-KNOWN_ROOM_VERSIONS = {"1", "vdh-test-version"}
+KNOWN_ROOM_VERSIONS = {RoomVersions.V1, RoomVersions.VDH_TEST}

From ce6db0e5473e31292567b11599eb334c3275c564 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 8 Aug 2018 17:01:57 +0100
Subject: [PATCH 3/8] Choose state algorithm based on room version

---
 synapse/handlers/federation.py  |   8 ++-
 synapse/handlers/room_member.py |   5 +-
 synapse/state/__init__.py       | 104 ++++++++++++++++++++++++++++----
 synapse/storage/events.py       |   4 +-
 4 files changed, 105 insertions(+), 16 deletions(-)

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 0dffd44e2..75a819dd1 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -274,8 +274,9 @@ class FederationHandler(BaseHandler):
                             ev_ids, get_prev_content=False, check_redacted=False
                         )
 
+                    room_version = yield self.store.get_room_version(pdu.room_id)
                     state_map = yield resolve_events_with_factory(
-                        state_groups, {pdu.event_id: pdu}, fetch
+                        room_version, state_groups, {pdu.event_id: pdu}, fetch
                     )
 
                     state = (yield self.store.get_events(state_map.values())).values()
@@ -1811,7 +1812,10 @@ class FederationHandler(BaseHandler):
                     (d.type, d.state_key): d for d in different_events if d
                 })
 
-                new_state = self.state_handler.resolve_events(
+                room_version = yield self.store.get_room_version(event.room_id)
+
+                new_state = yield self.state_handler.resolve_events(
+                    room_version,
                     [list(local_view.values()), list(remote_view.values())],
                     event
                 )
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 0d4a3f467..b6010bb41 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -341,9 +341,10 @@ class RoomMemberHandler(object):
         prev_events_and_hashes = yield self.store.get_prev_events_for_room(
             room_id,
         )
-        latest_event_ids = (
+        latest_event_ids = [
             event_id for (event_id, _, _) in prev_events_and_hashes
-        )
+        ]
+
         current_state_ids = yield self.state_handler.get_current_state_ids(
             room_id, latest_event_ids=latest_event_ids,
         )
diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
index 8c091d07c..222daa0b2 100644
--- a/synapse/state/__init__.py
+++ b/synapse/state/__init__.py
@@ -23,16 +23,15 @@ from frozendict import frozendict
 
 from twisted.internet import defer
 
-from synapse.api.constants import EventTypes
+from synapse.api.constants import EventTypes, RoomVersions
 from synapse.events.snapshot import EventContext
+from synapse.state import v1
 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__)
 
 
@@ -263,8 +262,14 @@ class StateHandler(object):
             defer.returnValue(context)
 
         logger.debug("calling resolve_state_groups from compute_event_context")
+        if event.type == EventTypes.Create:
+            room_version = event.content.get("room_version", RoomVersions.V1)
+        else:
+            room_version = None
+
         entry = yield self.resolve_state_groups_for_events(
             event.room_id, [e for e, _ in event.prev_events],
+            explicit_room_version=room_version,
         )
 
         prev_state_ids = entry.state
@@ -332,13 +337,17 @@ class StateHandler(object):
         defer.returnValue(context)
 
     @defer.inlineCallbacks
-    def resolve_state_groups_for_events(self, room_id, event_ids):
+    def resolve_state_groups_for_events(self, room_id, event_ids,
+                                        explicit_room_version=None):
         """ 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]):
+            room_id (str)
+            event_ids (list[str])
+            explicit_room_version (str|None): If set uses the the given room
+                version to choose the resolution algorithm. If None, then
+                checks the database for room version.
 
         Returns:
             Deferred[_StateCacheEntry]: resolved state
@@ -364,8 +373,13 @@ class StateHandler(object):
                 delta_ids=delta_ids,
             ))
 
+        room_version = explicit_room_version
+        if not room_version:
+            room_version = yield self.store.get_room_version(room_id)
+
         result = yield self._state_resolution_handler.resolve_state_groups(
-            room_id, state_groups_ids, None, self._state_map_factory,
+            room_id, room_version, state_groups_ids, None,
+            self._state_map_factory,
         )
         defer.returnValue(result)
 
@@ -374,7 +388,8 @@ class StateHandler(object):
             ev_ids, get_prev_content=False, check_redacted=False,
         )
 
-    def resolve_events(self, state_sets, event):
+    @defer.inlineCallbacks
+    def resolve_events(self, room_version, state_sets, event):
         logger.info(
             "Resolving state for %s with %d groups", event.room_id, len(state_sets)
         )
@@ -389,14 +404,18 @@ class StateHandler(object):
             for ev in st
         }
 
+        room_version = yield self.store.get_room_version(event.room_id)
+
         with Measure(self.clock, "state._resolve_events"):
-            new_state = resolve_events_with_state_map(state_set_ids, state_map)
+            new_state = resolve_events_with_state_map(
+                room_version, state_set_ids, state_map,
+            )
 
         new_state = {
             key: state_map[ev_id] for key, ev_id in iteritems(new_state)
         }
 
-        return new_state
+        defer.returnValue(new_state)
 
 
 class StateResolutionHandler(object):
@@ -429,7 +448,7 @@ class StateResolutionHandler(object):
     @defer.inlineCallbacks
     @log_function
     def resolve_state_groups(
-        self, room_id, state_groups_ids, event_map, state_map_factory,
+        self, room_id, room_version, state_groups_ids, event_map, state_map_factory,
     ):
         """Resolves conflicts between a set of state groups
 
@@ -438,6 +457,7 @@ class StateResolutionHandler(object):
 
         Args:
             room_id (str): room we are resolving for (used for logging)
+            room_version (str): version of the room
             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)
@@ -491,6 +511,7 @@ class StateResolutionHandler(object):
                 logger.info("Resolving conflicted state for %r", room_id)
                 with Measure(self.clock, "state._resolve_events"):
                     new_state = yield resolve_events_with_factory(
+                        room_version,
                         list(itervalues(state_groups_ids)),
                         event_map=event_map,
                         state_map_factory=state_map_factory,
@@ -572,3 +593,64 @@ def _make_state_cache_entry(
         prev_group=prev_group,
         delta_ids=delta_ids,
     )
+
+
+def resolve_events_with_state_map(room_version, state_sets, state_map):
+    """
+    Args:
+        room_version(str): Version of the room
+        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 room_version in (RoomVersions.V1, RoomVersions.VDH_TEST,):
+        return v1.resolve_events_with_state_map(
+            state_sets, state_map,
+        )
+    else:
+        # This should only happen if we added a version but forgot to add it to
+        # the list above.
+        raise Exception(
+            "No state resolution algorithm defined for version %r" % (room_version,)
+        )
+
+
+def resolve_events_with_factory(room_version, state_sets, event_map, state_map_factory):
+    """
+    Args:
+        room_version(str): Version of the room
+
+        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 room_version in (RoomVersions.V1, RoomVersions.VDH_TEST,):
+        return v1.resolve_events_with_factory(
+            state_sets, event_map, state_map_factory,
+        )
+    else:
+        # This should only happen if we added a version but forgot to add it to
+        # the list above.
+        raise Exception(
+            "No state resolution algorithm defined for version %r" % (room_version,)
+        )
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index ce32e8fef..dc68d365c 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -705,9 +705,11 @@ class EventsStore(EventFederationStore, EventsWorkerStore, BackgroundUpdateStore
         }
 
         events_map = {ev.event_id: ev for ev, _ in events_context}
+        room_version = yield self.get_room_version(room_id)
+
         logger.debug("calling resolve_state_groups from preserve_events")
         res = yield self._state_resolution_handler.resolve_state_groups(
-            room_id, state_groups, events_map, get_events
+            room_id, room_version, state_groups, events_map, get_events
         )
 
         defer.returnValue((res.state, None))

From bb99b1f5507e009bc32a82ba6ef29ba2d91e6b65 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 9 Aug 2018 14:44:10 +0100
Subject: [PATCH 4/8] Add fast path in state res for zero prev events

---
 synapse/state/__init__.py | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
index 222daa0b2..f1c26d107 100644
--- a/synapse/state/__init__.py
+++ b/synapse/state/__init__.py
@@ -361,7 +361,12 @@ class StateHandler(object):
             room_id, event_ids
         )
 
-        if len(state_groups_ids) == 1:
+        if len(state_groups_ids) == 0:
+            defer.returnValue(_StateCacheEntry(
+                state={},
+                state_group=None,
+            ))
+        elif 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)

From 3e19beb941f3f797262b051d47227018898bb36f Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 9 Aug 2018 14:33:49 +0100
Subject: [PATCH 5/8] Fix tests

---
 .../replication/slave/storage/test_events.py  |  3 +-
 tests/storage/test_redaction.py               |  4 ++-
 tests/storage/test_roommember.py              |  4 ++-
 tests/test_state.py                           |  6 +++-
 tests/test_visibility.py                      |  4 ++-
 tests/utils.py                                | 30 +++++++++++++++++++
 6 files changed, 46 insertions(+), 5 deletions(-)

diff --git a/tests/replication/slave/storage/test_events.py b/tests/replication/slave/storage/test_events.py
index f5b47f5ec..8c08985fa 100644
--- a/tests/replication/slave/storage/test_events.py
+++ b/tests/replication/slave/storage/test_events.py
@@ -122,6 +122,7 @@ class SlavedEventStoreTestCase(BaseSlavedStoreTestCase):
 
     @defer.inlineCallbacks
     def test_invites(self):
+        yield self.persist(type="m.room.create", key="", creator=USER_ID)
         yield self.check("get_invited_rooms_for_user", [USER_ID_2], [])
         event = yield self.persist(
             type="m.room.member", key=USER_ID_2, membership="invite"
@@ -134,7 +135,7 @@ class SlavedEventStoreTestCase(BaseSlavedStoreTestCase):
 
     @defer.inlineCallbacks
     def test_push_actions_for_user(self):
-        yield self.persist(type="m.room.create", creator=USER_ID)
+        yield self.persist(type="m.room.create", key="", creator=USER_ID)
         yield self.persist(type="m.room.join", key=USER_ID, membership="join")
         yield self.persist(
             type="m.room.join", sender=USER_ID, key=USER_ID_2, membership="join"
diff --git a/tests/storage/test_redaction.py b/tests/storage/test_redaction.py
index 475ec900c..05f40eaa9 100644
--- a/tests/storage/test_redaction.py
+++ b/tests/storage/test_redaction.py
@@ -22,7 +22,7 @@ from synapse.api.constants import EventTypes, Membership
 from synapse.types import RoomID, UserID
 
 from tests import unittest
-from tests.utils import setup_test_homeserver
+from tests.utils import create_room, setup_test_homeserver
 
 
 class RedactionTestCase(unittest.TestCase):
@@ -43,6 +43,8 @@ class RedactionTestCase(unittest.TestCase):
 
         self.room1 = RoomID.from_string("!abc123:test")
 
+        yield create_room(hs, self.room1.to_string(), self.u_alice.to_string())
+
         self.depth = 1
 
     @defer.inlineCallbacks
diff --git a/tests/storage/test_roommember.py b/tests/storage/test_roommember.py
index c5fd54f67..034ea3fbb 100644
--- a/tests/storage/test_roommember.py
+++ b/tests/storage/test_roommember.py
@@ -22,7 +22,7 @@ from synapse.api.constants import EventTypes, Membership
 from synapse.types import RoomID, UserID
 
 from tests import unittest
-from tests.utils import setup_test_homeserver
+from tests.utils import create_room, setup_test_homeserver
 
 
 class RoomMemberStoreTestCase(unittest.TestCase):
@@ -47,6 +47,8 @@ class RoomMemberStoreTestCase(unittest.TestCase):
 
         self.room = RoomID.from_string("!abc123:test")
 
+        yield create_room(hs, self.room.to_string(), self.u_alice.to_string())
+
     @defer.inlineCallbacks
     def inject_room_member(self, room, user, membership, replaces_state=None):
         builder = self.event_builder_factory.new({
diff --git a/tests/test_state.py b/tests/test_state.py
index 429a18cbf..770e94437 100644
--- a/tests/test_state.py
+++ b/tests/test_state.py
@@ -18,7 +18,7 @@ from mock import Mock
 from twisted.internet import defer
 
 from synapse.api.auth import Auth
-from synapse.api.constants import EventTypes, Membership
+from synapse.api.constants import EventTypes, Membership, RoomVersions
 from synapse.events import FrozenEvent
 from synapse.state import StateHandler, StateResolutionHandler
 
@@ -108,6 +108,9 @@ class StateGroupStore(object):
     def register_event_id_state_group(self, event_id, state_group):
         self._event_to_state_group[event_id] = state_group
 
+    def get_room_version(self, room_id):
+        return RoomVersions.V1
+
 
 class DictObj(dict):
     def __init__(self, **kwargs):
@@ -167,6 +170,7 @@ class StateTestCase(unittest.TestCase):
                 "START": DictObj(
                     type=EventTypes.Create,
                     state_key="",
+                    content={},
                     depth=1,
                 ),
                 "A": DictObj(
diff --git a/tests/test_visibility.py b/tests/test_visibility.py
index 0dc1a924d..15ebb0aa0 100644
--- a/tests/test_visibility.py
+++ b/tests/test_visibility.py
@@ -21,7 +21,7 @@ from synapse.events import FrozenEvent
 from synapse.visibility import filter_events_for_server
 
 import tests.unittest
-from tests.utils import setup_test_homeserver
+from tests.utils import create_room, setup_test_homeserver
 
 logger = logging.getLogger(__name__)
 
@@ -36,6 +36,8 @@ class FilterEventsForServerTestCase(tests.unittest.TestCase):
         self.event_builder_factory = self.hs.get_event_builder_factory()
         self.store = self.hs.get_datastore()
 
+        yield create_room(self.hs, TEST_ROOM_ID, "@someone:ROOM")
+
     @defer.inlineCallbacks
     def test_filtering(self):
         #
diff --git a/tests/utils.py b/tests/utils.py
index 3f1730493..8930a3a23 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -21,6 +21,7 @@ from six.moves.urllib import parse as urlparse
 
 from twisted.internet import defer, reactor
 
+from synapse.api.constants import EventTypes
 from synapse.api.errors import CodeMessageException, cs_error
 from synapse.federation.transport import server
 from synapse.http.server import HttpServer
@@ -445,3 +446,32 @@ class DeferredMockCallable(object):
                     "call(%s)" % _format_call(c[0], c[1]) for c in calls
                 ])
             )
+
+
+@defer.inlineCallbacks
+def create_room(hs, room_id, creator_id):
+    """Creates and persist a creation event for the given room
+
+    Args:
+        hs
+        room_id (str)
+        creator_id (str)
+    """
+
+    store = hs.get_datastore()
+    event_builder_factory = hs.get_event_builder_factory()
+    event_creation_handler = hs.get_event_creation_handler()
+
+    builder = event_builder_factory.new({
+        "type": EventTypes.Create,
+        "state_key": "",
+        "sender": creator_id,
+        "room_id": room_id,
+        "content": {},
+    })
+
+    event, context = yield event_creation_handler.create_new_client_event(
+        builder
+    )
+
+    yield store.persist_event(event, context)

From 5075e444f413b0b564dbc525a641cb5784acf2ad Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 9 Aug 2018 14:56:25 +0100
Subject: [PATCH 6/8] Newsfile

---
 changelog.d/3673.misc | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/3673.misc

diff --git a/changelog.d/3673.misc b/changelog.d/3673.misc
new file mode 100644
index 000000000..d672111fb
--- /dev/null
+++ b/changelog.d/3673.misc
@@ -0,0 +1 @@
+Refactor state module to support multiple room versions

From e21c368b8b7c62b2f626ff6c739ea33c3c2e73bb Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Mon, 20 Aug 2018 13:54:51 +0100
Subject: [PATCH 7/8] Revert spurious change

---
 synapse/handlers/room_member.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index b6010bb41..b8e1af580 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -341,9 +341,9 @@ class RoomMemberHandler(object):
         prev_events_and_hashes = yield self.store.get_prev_events_for_room(
             room_id,
         )
-        latest_event_ids = [
+        latest_event_ids = (
             event_id for (event_id, _, _) in prev_events_and_hashes
-        ]
+        )
 
         current_state_ids = yield self.state_handler.get_current_state_ids(
             room_id, latest_event_ids=latest_event_ids,

From 8dee601054089311b81efd6239b458401da063e3 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Mon, 20 Aug 2018 14:21:12 +0100
Subject: [PATCH 8/8] Remove redundant room_version checks

---
 synapse/handlers/federation.py |  2 +-
 synapse/state/__init__.py      | 17 +++--------------
 2 files changed, 4 insertions(+), 15 deletions(-)

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 75a819dd1..14a10c122 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1814,7 +1814,7 @@ class FederationHandler(BaseHandler):
 
                 room_version = yield self.store.get_room_version(event.room_id)
 
-                new_state = yield self.state_handler.resolve_events(
+                new_state = self.state_handler.resolve_events(
                     room_version,
                     [list(local_view.values()), list(remote_view.values())],
                     event
diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
index f1c26d107..a2992fd95 100644
--- a/synapse/state/__init__.py
+++ b/synapse/state/__init__.py
@@ -262,14 +262,9 @@ class StateHandler(object):
             defer.returnValue(context)
 
         logger.debug("calling resolve_state_groups from compute_event_context")
-        if event.type == EventTypes.Create:
-            room_version = event.content.get("room_version", RoomVersions.V1)
-        else:
-            room_version = None
 
         entry = yield self.resolve_state_groups_for_events(
             event.room_id, [e for e, _ in event.prev_events],
-            explicit_room_version=room_version,
         )
 
         prev_state_ids = entry.state
@@ -337,8 +332,7 @@ class StateHandler(object):
         defer.returnValue(context)
 
     @defer.inlineCallbacks
-    def resolve_state_groups_for_events(self, room_id, event_ids,
-                                        explicit_room_version=None):
+    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.
 
@@ -378,9 +372,7 @@ class StateHandler(object):
                 delta_ids=delta_ids,
             ))
 
-        room_version = explicit_room_version
-        if not room_version:
-            room_version = yield self.store.get_room_version(room_id)
+        room_version = yield self.store.get_room_version(room_id)
 
         result = yield self._state_resolution_handler.resolve_state_groups(
             room_id, room_version, state_groups_ids, None,
@@ -393,7 +385,6 @@ class StateHandler(object):
             ev_ids, get_prev_content=False, check_redacted=False,
         )
 
-    @defer.inlineCallbacks
     def resolve_events(self, room_version, state_sets, event):
         logger.info(
             "Resolving state for %s with %d groups", event.room_id, len(state_sets)
@@ -409,8 +400,6 @@ class StateHandler(object):
             for ev in st
         }
 
-        room_version = yield self.store.get_room_version(event.room_id)
-
         with Measure(self.clock, "state._resolve_events"):
             new_state = resolve_events_with_state_map(
                 room_version, state_set_ids, state_map,
@@ -420,7 +409,7 @@ class StateHandler(object):
             key: state_map[ev_id] for key, ev_id in iteritems(new_state)
         }
 
-        defer.returnValue(new_state)
+        return new_state
 
 
 class StateResolutionHandler(object):