Merge remote-tracking branch 'origin/develop' into matrix-org-hotfixes

16 files changed, 2693 insertions, 1248 deletions

diff --git a/changelog.d/17447.feature b/changelog.d/17447.feature
new file mode 100644
index 0000000000..6f80e298ae
--- /dev/null
+++ b/changelog.d/17447.feature
@@ -0,0 +1 @@
+Track which rooms have been sent to clients in the experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync `/sync` endpoint.
diff --git a/changelog.d/17476.doc b/changelog.d/17476.doc
new file mode 100644
index 0000000000..89d8d490bb
--- /dev/null
+++ b/changelog.d/17476.doc
@@ -0,0 +1 @@
+Update the [`allowed_local_3pids`](https://element-hq.github.io/synapse/v1.112/usage/configuration/config_documentation.html#allowed_local_3pids) config option's msisdn address to a working example.
diff --git a/changelog.d/17477.feature b/changelog.d/17477.feature
new file mode 100644
index 0000000000..9785a2ef7b
--- /dev/null
+++ b/changelog.d/17477.feature
@@ -0,0 +1 @@
+Add Account Data extension support to experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync `/sync` endpoint.
diff --git a/changelog.d/17479.misc b/changelog.d/17479.misc
new file mode 100644
index 0000000000..4502f71662
--- /dev/null
+++ b/changelog.d/17479.misc
@@ -0,0 +1 @@
+Do not send down empty room entries down experimental sliding sync endpoint.
diff --git a/changelog.d/17481.misc b/changelog.d/17481.misc
new file mode 100644
index 0000000000..ac55538424
--- /dev/null
+++ b/changelog.d/17481.misc
@@ -0,0 +1 @@
+Refactor Sliding Sync tests to better utilize the `SlidingSyncBase`.
diff --git a/changelog.d/17482.misc b/changelog.d/17482.misc
new file mode 100644
index 0000000000..ac55538424
--- /dev/null
+++ b/changelog.d/17482.misc
@@ -0,0 +1 @@
+Refactor Sliding Sync tests to better utilize the `SlidingSyncBase`.
diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md
index 649f4f71c7..40f64be856 100644
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -2386,7 +2386,7 @@ enable_registration_without_verification: true
 ---
 ### `registrations_require_3pid`
 
-If this is set, users must provide all of the specified types of 3PID when registering an account.
+If this is set, users must provide all of the specified types of [3PID](https://spec.matrix.org/latest/appendices/#3pid-types) when registering an account.
 
 Note that [`enable_registration`](#enable_registration) must also be set to allow account registration.
 
@@ -2411,6 +2411,9 @@ disable_msisdn_registration: true
 
 Mandate that users are only allowed to associate certain formats of
 3PIDs with accounts on this server, as specified by the `medium` and `pattern` sub-options.
+`pattern` is a [Perl-like regular expression](https://docs.python.org/3/library/re.html#module-re).
+
+More information about 3PIDs, allowed `medium` types and their `address` syntax can be found [in the Matrix spec](https://spec.matrix.org/latest/appendices/#3pid-types).
 
 Example configuration:
 ```yaml
@@ -2420,7 +2423,7 @@ allowed_local_3pids:
   - medium: email
     pattern: '^[^@]+@vector\.im$'
   - medium: msisdn
-    pattern: '\+44'
+    pattern: '^44\d{10}$'
 ```
 ---
 ### `enable_3pid_lookup`
diff --git a/pyproject.toml b/pyproject.toml
index 0b5dc418e4..1adf8e087f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -201,8 +201,8 @@ netaddr = ">=0.7.18"
 # add a lower bound to the Jinja2 dependency.
 Jinja2 = ">=3.0"
 bleach = ">=1.4.3"
-# We use `Self`, which were added in `typing-extensions` 4.0.
-typing-extensions = ">=4.0"
+# We use `assert_never`, which were added in `typing-extensions` 4.1.
+typing-extensions = ">=4.1"
 # We enforce that we have a `cryptography` version that bundles an `openssl`
 # with the latest security patches.
 cryptography = ">=3.4.7"
diff --git a/synapse/handlers/sliding_sync.py b/synapse/handlers/sliding_sync.py
index f1f6f30b95..84f2fa18ff 100644
--- a/synapse/handlers/sliding_sync.py
+++ b/synapse/handlers/sliding_sync.py
@@ -18,6 +18,7 @@
 #
 #
 import logging
+from enum import Enum
 from itertools import chain
 from typing import (
     TYPE_CHECKING,
@@ -34,6 +35,7 @@ from typing import (
 
 import attr
 from immutabledict import immutabledict
+from typing_extensions import assert_never
 
 from synapse.api.constants import AccountDataTypes, Direction, EventTypes, Membership
 from synapse.events import EventBase
@@ -46,11 +48,13 @@ from synapse.storage.roommember import MemberSummary
 from synapse.types import (
     DeviceListUpdates,
     JsonDict,
+    JsonMapping,
     PersistedEventPosition,
     Requester,
     RoomStreamToken,
     SlidingSyncStreamToken,
     StateMap,
+    StrCollection,
     StreamKeyType,
     StreamToken,
     UserID,
@@ -357,8 +361,11 @@ class SlidingSyncHandler:
         self.event_sources = hs.get_event_sources()
         self.relations_handler = hs.get_relations_handler()
         self.device_handler = hs.get_device_handler()
+        self.push_rules_handler = hs.get_push_rules_handler()
         self.rooms_to_exclude_globally = hs.config.server.rooms_to_exclude_from_sync
 
+        self.connection_store = SlidingSyncConnectionStore()
+
     async def wait_for_sync_for_user(
         self,
         requester: Requester,
@@ -462,6 +469,11 @@ class SlidingSyncHandler:
             # See https://github.com/matrix-org/matrix-doc/issues/1144
             raise NotImplementedError()
 
+        await self.connection_store.mark_token_seen(
+            sync_config=sync_config,
+            from_token=from_token,
+        )
+
         # Get all of the room IDs that the user should be able to see in the sync
         # response
         has_lists = sync_config.lists is not None and len(sync_config.lists) > 0
@@ -607,11 +619,56 @@ class SlidingSyncHandler:
         # Fetch room data
         rooms: Dict[str, SlidingSyncResult.RoomResult] = {}
 
+        # Filter out rooms that haven't received updates and we've sent down
+        # previously.
+        if from_token:
+            rooms_should_send = set()
+
+            # First we check if there are rooms that match a list/room
+            # subscription and have updates we need to send (i.e. either because
+            # we haven't sent the room down, or we have but there are missing
+            # updates).
+            for room_id in relevant_room_map:
+                status = await self.connection_store.have_sent_room(
+                    sync_config,
+                    from_token.connection_position,
+                    room_id,
+                )
+                if (
+                    # The room was never sent down before so the client needs to know
+                    # about it regardless of any updates.
+                    status.status == HaveSentRoomFlag.NEVER
+                    # `PREVIOUSLY` literally means the "room was sent down before *AND*
+                    # there are updates we haven't sent down" so we already know this
+                    # room has updates.
+                    or status.status == HaveSentRoomFlag.PREVIOUSLY
+                ):
+                    rooms_should_send.add(room_id)
+                elif status.status == HaveSentRoomFlag.LIVE:
+                    # We know that we've sent all updates up until `from_token`,
+                    # so we just need to check if there have been updates since
+                    # then.
+                    pass
+                else:
+                    assert_never(status.status)
+
+            # We only need to check for new events since any state changes
+            # will also come down as new events.
+            rooms_that_have_updates = self.store.get_rooms_that_might_have_updates(
+                relevant_room_map.keys(), from_token.stream_token.room_key
+            )
+            rooms_should_send.update(rooms_that_have_updates)
+            relevant_room_map = {
+                room_id: room_sync_config
+                for room_id, room_sync_config in relevant_room_map.items()
+                if room_id in rooms_should_send
+            }
+
         @trace
         @tag_args
         async def handle_room(room_id: str) -> None:
             room_sync_result = await self.get_room_sync_data(
-                user=sync_config.user,
+                sync_config=sync_config,
                 room_id=room_id,
                 room_sync_config=relevant_room_map[room_id],
                 room_membership_for_user_at_to_token=room_membership_for_user_map[
@@ -621,22 +678,36 @@ class SlidingSyncHandler:
                 to_token=to_token,
             )
 
-            rooms[room_id] = room_sync_result
+            # Filter out empty room results during incremental sync
+            if room_sync_result or not from_token:
+                rooms[room_id] = room_sync_result
 
         with start_active_span("sliding_sync.generate_room_entries"):
             await concurrently_execute(handle_room, relevant_room_map, 10)
 
         extensions = await self.get_extensions_response(
             sync_config=sync_config,
+            lists=lists,
             from_token=from_token,
             to_token=to_token,
         )
 
-        # TODO: Update this when we implement per-connection state
-        connection_token = 0
+        if has_lists or has_room_subscriptions:
+            connection_position = await self.connection_store.record_rooms(
+                sync_config=sync_config,
+                from_token=from_token,
+                sent_room_ids=relevant_room_map.keys(),
+                # TODO: We need to calculate which rooms have had updates since the `from_token` but were not included in the `sent_room_ids`
+                unsent_room_ids=[],
+            )
+        elif from_token:
+            connection_position = from_token.connection_position
+        else:
+            # Initial sync without a `from_token` starts at `0`
+            connection_position = 0
 
         return SlidingSyncResult(
-            next_pos=SlidingSyncStreamToken(to_token, connection_token),
+            next_pos=SlidingSyncStreamToken(to_token, connection_position),
             lists=lists,
             rooms=rooms,
             extensions=extensions,
@@ -1367,7 +1438,7 @@ class SlidingSyncHandler:
 
     async def get_room_sync_data(
         self,
-        user: UserID,
+        sync_config: SlidingSyncConfig,
         room_id: str,
         room_sync_config: RoomSyncConfig,
         room_membership_for_user_at_to_token: _RoomMembershipForUser,
@@ -1389,6 +1460,37 @@ class SlidingSyncHandler:
             from_token: The point in the stream to sync from.
             to_token: The point in the stream to sync up to.
         """
+        user = sync_config.user
+
+        # Determine whether we should limit the timeline to the token range.
+        #
+        # We should return historical messages (before token range) in the
+        # following cases because we want clients to be able to show a basic
+        # screen of information:
+        #  - Initial sync (because no `from_token` to limit us anyway)
+        #  - When users `newly_joined`
+        #  - For an incremental sync where we haven't sent it down this
+        #    connection before
+        from_bound = None
+        initial = True
+        if from_token and not room_membership_for_user_at_to_token.newly_joined:
+            room_status = await self.connection_store.have_sent_room(
+                sync_config=sync_config,
+                connection_token=from_token.connection_position,
+                room_id=room_id,
+            )
+            if room_status.status == HaveSentRoomFlag.LIVE:
+                from_bound = from_token.stream_token.room_key
+                initial = False
+            elif room_status.status == HaveSentRoomFlag.PREVIOUSLY:
+                assert room_status.last_token is not None
+                from_bound = room_status.last_token
+                initial = False
+            elif room_status.status == HaveSentRoomFlag.NEVER:
+                from_bound = None
+                initial = True
+            else:
+                assert_never(room_status.status)
 
         # Assemble the list of timeline events
         #
@@ -1415,36 +1517,23 @@ class SlidingSyncHandler:
             prev_batch_token = to_token
 
             # We're going to paginate backwards from the `to_token`
-            from_bound = to_token.room_key
+            to_bound = to_token.room_key
             # People shouldn't see past their leave/ban event
             if room_membership_for_user_at_to_token.membership in (
                 Membership.LEAVE,
                 Membership.BAN,
             ):
-                from_bound = (
+                to_bound = (
                     room_membership_for_user_at_to_token.event_pos.to_room_stream_token()
                 )
 
-            # Determine whether we should limit the timeline to the token range.
-            #
-            # We should return historical messages (before token range) in the
-            # following cases because we want clients to be able to show a basic
-            # screen of information:
-            #  - Initial sync (because no `from_token` to limit us anyway)
-            #  - When users `newly_joined`
-            #  - TODO: For an incremental sync where we haven't sent it down this
-            #    connection before
-            to_bound = (
-                from_token.stream_token.room_key
-                if from_token is not None
-                and not room_membership_for_user_at_to_token.newly_joined
-                else None
-            )
-
             timeline_events, new_room_key = await self.store.paginate_room_events(
                 room_id=room_id,
-                from_key=from_bound,
-                to_key=to_bound,
+                # The bounds are reversed so we can paginate backwards
+                # (from newer to older events) starting at to_bound.
+                # This ensures we fill the `limit` with the newest events first,
+                from_key=to_bound,
+                to_key=from_bound,
                 direction=Direction.BACKWARDS,
                 # We add one so we can determine if there are enough events to saturate
                 # the limit or not (see `limited`)
@@ -1561,12 +1650,6 @@ class SlidingSyncHandler:
         # indicate to the client that a state reset happened. Perhaps we should indicate
         # this by setting `initial: True` and empty `required_state`.
 
-        # TODO: Since we can't determine whether we've already sent a room down this
-        # Sliding Sync connection before (we plan to add this optimization in the
-        # future), we're always returning the requested room state instead of
-        # updates.
-        initial = True
-
         # Check whether the room has a name set
         name_state_ids = await self.get_current_state_ids_at(
             room_id=room_id,
@@ -1712,9 +1795,22 @@ class SlidingSyncHandler:
                 to_token=to_token,
             )
         else:
-            # TODO: Once we can figure out if we've sent a room down this connection before,
-            # we can return updates instead of the full required state.
-            raise NotImplementedError()
+            assert from_bound is not None
+
+            # TODO: Limit the number of state events we're about to send down
+            # the room, if its too many we should change this to an
+            # `initial=True`?
+            deltas = await self.store.get_current_state_deltas_for_room(
+                room_id=room_id,
+                from_token=from_bound,
+                to_token=to_token.room_key,
+            )
+            # TODO: Filter room state before fetching events
+            # TODO: Handle state resets where event_id is None
+            events = await self.store.get_events(
+                [d.event_id for d in deltas if d.event_id]
+            )
+            room_state = {(s.type, s.state_key): s for s in events.values()}
 
         required_room_state: StateMap[EventBase] = {}
         if required_state_filter != StateFilter.none():
@@ -1797,6 +1893,7 @@ class SlidingSyncHandler:
     async def get_extensions_response(
         self,
         sync_config: SlidingSyncConfig,
+        lists: Dict[str, SlidingSyncResult.SlidingWindowList],
         to_token: StreamToken,
         from_token: Optional[SlidingSyncStreamToken],
     ) -> SlidingSyncResult.Extensions:
@@ -1804,6 +1901,7 @@ class SlidingSyncHandler:
 
         Args:
             sync_config: Sync configuration
+            lists: Sliding window API. A map of list key to list results.
             to_token: The point in the stream to sync up to.
             from_token: The point in the stream to sync from.
         """
@@ -1828,9 +1926,20 @@ class SlidingSyncHandler:
                 from_token=from_token,
             )
 
+        account_data_response = None
+        if sync_config.extensions.account_data is not None:
+            account_data_response = await self.get_account_data_extension_response(
+                sync_config=sync_config,
+                lists=lists,
+                account_data_request=sync_config.extensions.account_data,
+                to_token=to_token,
+                from_token=from_token,
+            )
+
         return SlidingSyncResult.Extensions(
             to_device=to_device_response,
             e2ee=e2ee_response,
+            account_data=account_data_response,
         )
 
     async def get_to_device_extension_response(
@@ -1847,7 +1956,7 @@ class SlidingSyncHandler:
             to_token: The point in the stream to sync up to.
         """
         user_id = sync_config.user.to_string()
-        device_id = sync_config.device_id
+        device_id = sync_config.requester.device_id
 
         # Skip if the extension is not enabled
         if not to_device_request.enabled:
@@ -1923,7 +2032,7 @@ class SlidingSyncHandler:
             from_token: The point in the stream to sync from.
         """
         user_id = sync_config.user.to_string()
-        device_id = sync_config.device_id
+        device_id = sync_config.requester.device_id
 
         # Skip if the extension is not enabled
         if not e2ee_request.enabled:
@@ -1956,3 +2065,357 @@ class SlidingSyncHandler:
             device_one_time_keys_count=device_one_time_keys_count,
             device_unused_fallback_key_types=device_unused_fallback_key_types,
         )
+
+    async def get_account_data_extension_response(
+        self,
+        sync_config: SlidingSyncConfig,
+        lists: Dict[str, SlidingSyncResult.SlidingWindowList],
+        account_data_request: SlidingSyncConfig.Extensions.AccountDataExtension,
+        to_token: StreamToken,
+        from_token: Optional[SlidingSyncStreamToken],
+    ) -> Optional[SlidingSyncResult.Extensions.AccountDataExtension]:
+        """Handle Account Data extension (MSC3959)
+
+        Args:
+            sync_config: Sync configuration
+            lists: Sliding window API. A map of list key to list results.
+            account_data_request: The account_data extension from the request
+            to_token: The point in the stream to sync up to.
+            from_token: The point in the stream to sync from.
+        """
+        user_id = sync_config.user.to_string()
+
+        # Skip if the extension is not enabled
+        if not account_data_request.enabled:
+            return None
+
+        global_account_data_map: Mapping[str, JsonMapping] = {}
+        if from_token is not None:
+            global_account_data_map = (
+                await self.store.get_updated_global_account_data_for_user(
+                    user_id, from_token.stream_token.account_data_key
+                )
+            )
+
+            have_push_rules_changed = await self.store.have_push_rules_changed_for_user(
+                user_id, from_token.stream_token.push_rules_key
+            )
+            if have_push_rules_changed:
+                global_account_data_map = dict(global_account_data_map)
+                global_account_data_map[AccountDataTypes.PUSH_RULES] = (
+                    await self.push_rules_handler.push_rules_for_user(sync_config.user)
+                )
+        else:
+            all_global_account_data = await self.store.get_global_account_data_for_user(
+                user_id
+            )
+
+            global_account_data_map = dict(all_global_account_data)
+            global_account_data_map[AccountDataTypes.PUSH_RULES] = (
+                await self.push_rules_handler.push_rules_for_user(sync_config.user)
+            )
+
+        # We only want to include account data for rooms that are already in the sliding
+        # sync response AND that were requested in the account data request.
+        relevant_room_ids: Set[str] = set()
+
+        # See what rooms from the room subscriptions we should get account data for
+        if (
+            account_data_request.rooms is not None
+            and sync_config.room_subscriptions is not None
+        ):
+            actual_room_ids = sync_config.room_subscriptions.keys()
+
+            for room_id in account_data_request.rooms:
+                # A wildcard means we process all rooms from the room subscriptions
+                if room_id == "*":
+                    relevant_room_ids.update(sync_config.room_subscriptions.keys())
+                    break
+
+                if room_id in actual_room_ids:
+                    relevant_room_ids.add(room_id)
+
+        # See what rooms from the sliding window lists we should get account data for
+        if account_data_request.lists is not None:
+            for list_key in account_data_request.lists:
+                # Just some typing because we share the variable name in multiple places
+                actual_list: Optional[SlidingSyncResult.SlidingWindowList] = None
+
+                # A wildcard means we process rooms from all lists
+                if list_key == "*":
+                    for actual_list in lists.values():
+                        # We only expect a single SYNC operation for any list
+                        assert len(actual_list.ops) == 1
+                        sync_op = actual_list.ops[0]
+                        assert sync_op.op == OperationType.SYNC
+
+                        relevant_room_ids.update(sync_op.room_ids)
+
+                    break
+
+                actual_list = lists.get(list_key)
+                if actual_list is not None:
+                    # We only expect a single SYNC operation for any list
+                    assert len(actual_list.ops) == 1
+                    sync_op = actual_list.ops[0]
+                    assert sync_op.op == OperationType.SYNC
+
+                    relevant_room_ids.update(sync_op.room_ids)
+
+        # Fetch room account data
+        account_data_by_room_map: Mapping[str, Mapping[str, JsonMapping]] = {}
+        if len(relevant_room_ids) > 0:
+            if from_token is not None:
+                account_data_by_room_map = (
+                    await self.store.get_updated_room_account_data_for_user(
+                        user_id, from_token.stream_token.account_data_key
+                    )
+                )
+            else:
+                account_data_by_room_map = (
+                    await self.store.get_room_account_data_for_user(user_id)
+                )
+
+        # Filter down to the relevant rooms
+        account_data_by_room_map = {
+            room_id: account_data_map
+            for room_id, account_data_map in account_data_by_room_map.items()
+            if room_id in relevant_room_ids
+        }
+
+        return SlidingSyncResult.Extensions.AccountDataExtension(
+            global_account_data_map=global_account_data_map,
+            account_data_by_room_map=account_data_by_room_map,
+        )
+
+
+class HaveSentRoomFlag(Enum):
+    """Flag for whether we have sent the room down a sliding sync connection.
+
+    The valid state changes here are:
+        NEVER -> LIVE
+        LIVE -> PREVIOUSLY
+        PREVIOUSLY -> LIVE
+    """
+
+    # The room has never been sent down (or we have forgotten we have sent it
+    # down).
+    NEVER = 1
+
+    # We have previously sent the room down, but there are updates that we
+    # haven't sent down.
+    PREVIOUSLY = 2
+
+    # We have sent the room down and the client has received all updates.
+    LIVE = 3
+
+
+@attr.s(auto_attribs=True, slots=True, frozen=True)
+class HaveSentRoom:
+    """Whether we have sent the room down a sliding sync connection.
+
+    Attributes:
+        status: Flag of if we have or haven't sent down the room
+        last_token: If the flag is `PREVIOUSLY` then this is non-null and
+            contains the last stream token of the last updates we sent down
+            the room, i.e. we still need to send everything since then to the
+            client.
+    """
+
+    status: HaveSentRoomFlag
+    last_token: Optional[RoomStreamToken]
+
+    @staticmethod
+    def previously(last_token: RoomStreamToken) -> "HaveSentRoom":
+        """Constructor for `PREVIOUSLY` flag."""
+        return HaveSentRoom(HaveSentRoomFlag.PREVIOUSLY, last_token)
+
+
+HAVE_SENT_ROOM_NEVER = HaveSentRoom(HaveSentRoomFlag.NEVER, None)
+HAVE_SENT_ROOM_LIVE = HaveSentRoom(HaveSentRoomFlag.LIVE, None)
+
+
+@attr.s(auto_attribs=True)
+class SlidingSyncConnectionStore:
+    """In-memory store of per-connection state, including what rooms we have
+    previously sent down a sliding sync connection.
+
+    Note: This is NOT safe to run in a worker setup because connection positions will
+    point to different sets of rooms on different workers. e.g. for the same connection,
+    a connection position of 5 might have totally different states on worker A and
+    worker B.
+
+    One complication that we need to deal with here is needing to handle requests being
+    resent, i.e. if we sent down a room in a response that the client received, we must
+    consider the room *not* sent when we get the request again.
+
+    This is handled by using an integer "token", which is returned to the client
+    as part of the sync token. For each connection we store a mapping from
+    tokens to the room states, and create a new entry when we send down new
+    rooms.
+
+    Note that for any given sliding sync connection we will only store a maximum
+    of two different tokens: the previous token from the request and a new token
+    sent in the response. When we receive a request with a given token, we then
+    clear out all other entries with a different token.
+
+    Attributes:
+        _connections: Mapping from `(user_id, conn_id)` to mapping of `token`
+            to mapping of room ID to `HaveSentRoom`.
+    """
+
+    # `(user_id, conn_id)` -> `token` -> `room_id` -> `HaveSentRoom`
+    _connections: Dict[Tuple[str, str], Dict[int, Dict[str, HaveSentRoom]]] = (
+        attr.Factory(dict)
+    )
+
+    async def have_sent_room(
+        self, sync_config: SlidingSyncConfig, connection_token: int, room_id: str
+    ) -> HaveSentRoom:
+        """For the given user_id/conn_id/token, return whether we have
+        previously sent the room down
+        """
+
+        conn_key = self._get_connection_key(sync_config)
+        sync_statuses = self._connections.setdefault(conn_key, {})
+        room_status = sync_statuses.get(connection_token, {}).get(
+            room_id, HAVE_SENT_ROOM_NEVER
+        )
+
+        return room_status
+
+    async def record_rooms(
+        self,
+        sync_config: SlidingSyncConfig,
+        from_token: Optional[SlidingSyncStreamToken],
+        *,
+        sent_room_ids: StrCollection,
+        unsent_room_ids: StrCollection,
+    ) -> int:
+        """Record which rooms we have/haven't sent down in a new response
+
+        Attributes:
+            sync_config
+            from_token: The since token from the request, if any
+            sent_room_ids: The set of room IDs that we have sent down as
+                part of this request (only needs to be ones we didn't
+                previously sent down).
+            unsent_room_ids: The set of room IDs that have had updates
+                since the `from_token`, but which were not included in
+                this request
+        """
+        prev_connection_token = 0
+        if from_token is not None:
+            prev_connection_token = from_token.connection_position
+
+        # If there are no changes then this is a noop.
+        if not sent_room_ids and not unsent_room_ids:
+            return prev_connection_token
+
+        conn_key = self._get_connection_key(sync_config)
+        sync_statuses = self._connections.setdefault(conn_key, {})
+
+        # Generate a new token, removing any existing entries in that token
+        # (which can happen if requests get resent).
+        new_store_token = prev_connection_token + 1
+        sync_statuses.pop(new_store_token, None)
+
+        # Copy over and update the room mappings.
+        new_room_statuses = dict(sync_statuses.get(prev_connection_token, {}))
+
+        # Whether we have updated the `new_room_statuses`, if we don't by the
+        # end we can treat this as a noop.
+        have_updated = False
+        for room_id in sent_room_ids:
+            new_room_statuses[room_id] = HAVE_SENT_ROOM_LIVE
+            have_updated = True
+
+        # Whether we add/update the entries for unsent rooms depends on the
+        # existing entry:
+        #   - LIVE: We have previously sent down everything up to
+        #     `last_room_token, so we update the entry to be `PREVIOUSLY` with
+        #     `last_room_token`.
+        #   - PREVIOUSLY: We have previously sent down everything up to *a*
+        #     given token, so we don't need to update the entry.
+        #   - NEVER: We have never previously sent down the room, and we haven't
+        #     sent anything down this time either so we leave it as NEVER.
+
+        # Work out the new state for unsent rooms that were `LIVE`.
+        if from_token:
+            new_unsent_state = HaveSentRoom.previously(from_token.stream_token.room_key)
+        else:
+            new_unsent_state = HAVE_SENT_ROOM_NEVER
+
+        for room_id in unsent_room_ids:
+            prev_state = new_room_statuses.get(room_id)
+            if prev_state is not None and prev_state.status == HaveSentRoomFlag.LIVE:
+                new_room_statuses[room_id] = new_unsent_state
+                have_updated = True
+
+        if not have_updated:
+            return prev_connection_token
+
+        sync_statuses[new_store_token] = new_room_statuses
+
+        return new_store_token
+
+    async def mark_token_seen(
+        self,
+        sync_config: SlidingSyncConfig,
+        from_token: Optional[SlidingSyncStreamToken],
+    ) -> None:
+        """We have received a request with the given token, so we can clear out
+        any other tokens associated with the connection.
+
+        If there is no from token then we have started afresh, and so we delete
+        all tokens associated with the device.
+        """
+        # Clear out any tokens for the connection that doesn't match the one
+        # from the request.
+
+        conn_key = self._get_connection_key(sync_config)
+        sync_statuses = self._connections.pop(conn_key, {})
+        if from_token is None:
+            return
+
+        sync_statuses = {
+            connection_token: room_statuses
+            for connection_token, room_statuses in sync_statuses.items()
+            if connection_token == from_token.connection_position
+        }
+        if sync_statuses:
+            self._connections[conn_key] = sync_statuses
+
+    @staticmethod
+    def _get_connection_key(sync_config: SlidingSyncConfig) -> Tuple[str, str]:
+        """Return a unique identifier for this connection.
+
+        The first part is simply the user ID.
+
+        The second part is generally a combination of device ID and conn_id.
+        However, both these two are optional (e.g. puppet access tokens don't
+        have device IDs), so this handles those edge cases.
+
+        We use this over the raw `conn_id` to avoid clashes between different
+        clients that use the same `conn_id`. Imagine a user uses a web client
+        that uses `conn_id: main_sync_loop` and an Android client that also has
+        a `conn_id: main_sync_loop`.
+        """
+
+        user_id = sync_config.user.to_string()
+
+        # Only one sliding sync connection is allowed per given conn_id (empty
+        # or not).
+        conn_id = sync_config.conn_id or ""
+
+        if sync_config.requester.device_id:
+            return (user_id, f"D/{sync_config.requester.device_id}/{conn_id}")
+
+        if sync_config.requester.access_token_id:
+            # If we don't have a device, then the access token ID should be a
+            # stable ID.
+            return (user_id, f"A/{sync_config.requester.access_token_id}/{conn_id}")
+
+        # If we have neither then its likely an AS or some weird token. Either
+        # way we can just fail here.
+        raise Exception("Cannot use sliding sync with access token type")
diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index d72dfa2b10..bf3ac8d483 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -881,7 +881,6 @@ class SlidingSyncRestServlet(RestServlet):
         )
 
         user = requester.user
-        device_id = requester.device_id
 
         timeout = parse_integer(request, "timeout", default=0)
         # Position in the stream
@@ -902,11 +901,12 @@ class SlidingSyncRestServlet(RestServlet):
 
         sync_config = SlidingSyncConfig(
             user=user,
-            device_id=device_id,
+            requester=requester,
             # FIXME: Currently, we're just manually copying the fields from the
-            # `SlidingSyncBody` into the config. How can we gurantee into the future
+            # `SlidingSyncBody` into the config. How can we guarantee into the future
             # that we don't forget any? I would like something more structured like
             # `copy_attributes(from=body, to=config)`
+            conn_id=body.conn_id,
             lists=body.lists,
             room_subscriptions=body.room_subscriptions,
             extensions=body.extensions,
@@ -929,7 +929,6 @@ class SlidingSyncRestServlet(RestServlet):
 
         return 200, response_content
 
-    # TODO: Is there a better way to encode things?
     async def encode_response(
         self,
         requester: Requester,
@@ -1117,6 +1116,24 @@ class SlidingSyncRestServlet(RestServlet):
                     extensions.e2ee.device_list_updates.left
                 )
 
+        if extensions.account_data is not None:
+            serialized_extensions["account_data"] = {
+                # Same as the the top-level `account_data.events` field in Sync v2.
+                "global": [
+                    {"type": account_data_type, "content": content}
+                    for account_data_type, content in extensions.account_data.global_account_data_map.items()
+                ],
+                # Same as the joined room's account_data field in Sync v2, e.g the path
+                # `rooms.join["!foo:bar"].account_data.events`.
+                "rooms": {
+                    room_id: [
+                        {"type": account_data_type, "content": content}
+                        for account_data_type, content in event_map.items()
+                    ]
+                    for room_id, event_map in extensions.account_data.account_data_by_room_map.items()
+                },
+            }
+
         return serialized_extensions
 
 
diff --git a/synapse/server.py b/synapse/server.py
index 4a3f9ff934..46b9d83a04 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -559,6 +559,7 @@ class HomeServer(metaclass=abc.ABCMeta):
     def get_sync_handler(self) -> SyncHandler:
         return SyncHandler(self)
 
+    @cache_in_self
     def get_sliding_sync_handler(self) -> SlidingSyncHandler:
         return SlidingSyncHandler(self)
 
diff --git a/synapse/storage/databases/main/state_deltas.py b/synapse/storage/databases/main/state_deltas.py
index 036972ac25..da3ebe66b8 100644
--- a/synapse/storage/databases/main/state_deltas.py
+++ b/synapse/storage/databases/main/state_deltas.py
@@ -26,6 +26,8 @@ import attr
 
 from synapse.storage._base import SQLBaseStore
 from synapse.storage.database import LoggingTransaction
+from synapse.storage.databases.main.stream import _filter_results_by_stream
+from synapse.types import RoomStreamToken
 from synapse.util.caches.stream_change_cache import StreamChangeCache
 
 logger = logging.getLogger(__name__)
@@ -156,3 +158,38 @@ class StateDeltasStore(SQLBaseStore):
             "get_max_stream_id_in_current_state_deltas",
             self._get_max_stream_id_in_current_state_deltas_txn,
         )
+
+    async def get_current_state_deltas_for_room(
+        self, room_id: str, from_token: RoomStreamToken, to_token: RoomStreamToken
+    ) -> List[StateDelta]:
+        """Get the state deltas between two tokens."""
+
+        def get_current_state_deltas_for_room_txn(
+            txn: LoggingTransaction,
+        ) -> List[StateDelta]:
+            sql = """
+                SELECT instance_name, stream_id, type, state_key, event_id, prev_event_id
+                FROM current_state_delta_stream
+                WHERE room_id = ? AND ? < stream_id AND stream_id <= ?
+                ORDER BY stream_id ASC
+            """
+            txn.execute(
+                sql, (room_id, from_token.stream, to_token.get_max_stream_pos())
+            )
+
+            return [
+                StateDelta(
+                    stream_id=row[1],
+                    room_id=room_id,
+                    event_type=row[2],
+                    state_key=row[3],
+                    event_id=row[4],
+                    prev_event_id=row[5],
+                )
+                for row in txn
+                if _filter_results_by_stream(from_token, to_token, row[0], row[1])
+            ]
+
+        return await self.db_pool.runInteraction(
+            "get_current_state_deltas_for_room", get_current_state_deltas_for_room_txn
+        )
diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py
index b034361aec..4207e73c7f 100644
--- a/synapse/storage/databases/main/stream.py
+++ b/synapse/storage/databases/main/stream.py
@@ -2104,3 +2104,13 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             return RoomStreamToken(stream=last_position.stream - 1)
 
         return None
+
+    def get_rooms_that_might_have_updates(
+        self, room_ids: StrCollection, from_token: RoomStreamToken
+    ) -> StrCollection:
+        """Filters given room IDs down to those that might have updates, i.e.
+        removes rooms that definitely do not have updates.
+        """
+        return self._events_stream_cache.get_entities_changed(
+            room_ids, from_token.stream
+        )
diff --git a/synapse/types/handlers/__init__.py b/synapse/types/handlers/__init__.py
index 59eb0963ee..f26cc0e903 100644
--- a/synapse/types/handlers/__init__.py
+++ b/synapse/types/handlers/__init__.py
@@ -35,6 +35,7 @@ from synapse.types import (
     DeviceListUpdates,
     JsonDict,
     JsonMapping,
+    Requester,
     SlidingSyncStreamToken,
     StreamToken,
     UserID,
@@ -109,7 +110,7 @@ class SlidingSyncConfig(SlidingSyncBody):
     """
 
     user: UserID
-    device_id: Optional[str]
+    requester: Requester
 
     # Pydantic config
     class Config:
@@ -237,6 +238,17 @@ class SlidingSyncResult:
         notification_count: int
         highlight_count: int
 
+        def __bool__(self) -> bool:
+            return (
+                # If this is the first time the client is seeing the room, we should not filter it out
+                # under any circumstance.
+                self.initial
+                # We need to let the client know if there are any new events
+                or bool(self.required_state)
+                or bool(self.timeline_events)
+                or bool(self.stripped_state)
+            )
+
     @attr.s(slots=True, frozen=True, auto_attribs=True)
     class SlidingWindowList:
         """
@@ -330,11 +342,31 @@ class SlidingSyncResult:
                     or self.device_unused_fallback_key_types
                 )
 
+        @attr.s(slots=True, frozen=True, auto_attribs=True)
+        class AccountDataExtension:
+            """The Account Data extension (MSC3959)
+
+            Attributes:
+                global_account_data_map: Mapping from `type` to `content` of global account
+                    data events.
+                account_data_by_room_map: Mapping from room_id to mapping of `type` to
+                    `content` of room account data events.
+            """
+
+            global_account_data_map: Mapping[str, JsonMapping]
+            account_data_by_room_map: Mapping[str, Mapping[str, JsonMapping]]
+
+            def __bool__(self) -> bool:
+                return bool(
+                    self.global_account_data_map or self.account_data_by_room_map
+                )
+
         to_device: Optional[ToDeviceExtension] = None
         e2ee: Optional[E2eeExtension] = None
+        account_data: Optional[AccountDataExtension] = None
 
         def __bool__(self) -> bool:
-            return bool(self.to_device or self.e2ee)
+            return bool(self.to_device or self.e2ee or self.account_data)
 
     next_pos: SlidingSyncStreamToken
     lists: Dict[str, SlidingWindowList]
@@ -346,7 +378,11 @@ class SlidingSyncResult:
         to tell if the notifier needs to wait for more events when polling for
         events.
         """
-        return bool(self.lists or self.rooms or self.extensions)
+        # We don't include `self.lists` here, as a) `lists` is always non-empty even if
+        # there are no changes, and b) since we're sorting rooms by `stream_ordering` of
+        # the latest activity, anything that would cause the order to change would end
+        # up in `self.rooms` and cause us to send down the change.
+        return bool(self.rooms or self.extensions)
 
     @staticmethod
     def empty(next_pos: SlidingSyncStreamToken) -> "SlidingSyncResult":
diff --git a/synapse/types/rest/client/__init__.py b/synapse/types/rest/client/__init__.py
index f3c45a0d6a..dfe3b1e0f7 100644
--- a/synapse/types/rest/client/__init__.py
+++ b/synapse/types/rest/client/__init__.py
@@ -120,6 +120,9 @@ class SlidingSyncBody(RequestBodyModel):
     Sliding Sync API request body.
 
     Attributes:
+        conn_id: An optional string to identify this connection to the server.
+            Only one sliding sync connection is allowed per given conn_id (empty
+            or not).
         lists: Sliding window API. A map of list key to list information
             (:class:`SlidingSyncList`). Max lists: 100. The list keys should be
             arbitrary strings which the client is using to refer to the list. Keep this
@@ -322,8 +325,28 @@ class SlidingSyncBody(RequestBodyModel):
 
             enabled: Optional[StrictBool] = False
 
+        class AccountDataExtension(RequestBodyModel):
+            """The Account Data extension (MSC3959)
+
+            Attributes:
+                enabled
+                lists: List of list keys (from the Sliding Window API) to apply this
+                    extension to.
+                rooms: List of room IDs (from the Room Subscription API) to apply this
+                    extension to.
+            """
+
+            enabled: Optional[StrictBool] = False
+            # Process all lists defined in the Sliding Window API. (This is the default.)
+            lists: Optional[List[StrictStr]] = ["*"]
+            # Process all room subscriptions defined in the Room Subscription API. (This is the default.)
+            rooms: Optional[List[StrictStr]] = ["*"]
+
         to_device: Optional[ToDeviceExtension] = None
         e2ee: Optional[E2eeExtension] = None
+        account_data: Optional[AccountDataExtension] = None
+
+    conn_id: Optional[str]
 
     # mypy workaround via https://github.com/pydantic/pydantic/issues/156#issuecomment-1130883884
     if TYPE_CHECKING:
diff --git a/tests/rest/client/test_sync.py b/tests/rest/client/test_sync.py
index 6c73f4ec33..5abf1041be 100644
--- a/tests/rest/client/test_sync.py
+++ b/tests/rest/client/test_sync.py
@@ -21,7 +21,7 @@
 import json
 import logging
 from http import HTTPStatus
-from typing import Any, Dict, Iterable, List, Optional, Tuple
+from typing import Any, Dict, Iterable, List, Literal, Optional, Tuple
 
 from parameterized import parameterized, parameterized_class
 
@@ -59,15 +59,16 @@ from synapse.types import (
     StreamToken,
     UserID,
 )
+from synapse.types.handlers import SlidingSyncConfig
 from synapse.util import Clock
+from synapse.util.stringutils import random_string
 
 from tests import unittest
 from tests.federation.transport.test_knocking import (
     KnockingStrippedStateEventHelperMixin,
 )
-from tests.server import FakeChannel, TimedOutException
+from tests.server import TimedOutException
 from tests.test_utils.event_injection import create_event, mark_event_as_partial_state
-from tests.unittest import skip_unless
 
 logger = logging.getLogger(__name__)
 
@@ -1238,6 +1239,12 @@ class SlidingSyncBase(unittest.HomeserverTestCase):
 
     sync_endpoint = "/_matrix/client/unstable/org.matrix.simplified_msc3575/sync"
 
+    def default_config(self) -> JsonDict:
+        config = super().default_config()
+        # Enable sliding sync
+        config["experimental_features"] = {"msc3575_enabled": True}
+        return config
+
     def do_sync(
         self, sync_body: JsonDict, *, since: Optional[str] = None, tok: str
     ) -> Tuple[JsonDict, str]:
@@ -1268,6 +1275,88 @@ class SlidingSyncBase(unittest.HomeserverTestCase):
 
         return channel.json_body, channel.json_body["pos"]
 
+    def _bump_notifier_wait_for_events(
+        self,
+        user_id: str,
+        wake_stream_key: Literal[
+            StreamKeyType.ACCOUNT_DATA,
+            StreamKeyType.PRESENCE,
+        ],
+    ) -> None:
+        """
+        Wake-up a `notifier.wait_for_events(user_id)` call without affecting the Sliding
+        Sync results.
+
+        Args:
+            user_id: The user ID to wake up the notifier for
+            wake_stream_key: The stream key to wake up. This will create an actual new
+                entity in that stream so it's best to choose one that won't affect the
+                Sliding Sync results you're testing for. In other words, if your testing
+                account data, choose `StreamKeyType.PRESENCE` instead. We support two
+                possible stream keys because you're probably testing one or the other so
+                one is always a "safe" option.
+        """
+        # We're expecting some new activity from this point onwards
+        from_token = self.hs.get_event_sources().get_current_token()
+
+        triggered_notifier_wait_for_events = False
+
+        async def _on_new_acivity(
+            before_token: StreamToken, after_token: StreamToken
+        ) -> bool:
+            nonlocal triggered_notifier_wait_for_events
+            triggered_notifier_wait_for_events = True
+            return True
+
+        notifier = self.hs.get_notifier()
+
+        # Listen for some new activity for the user. We're just trying to confirm that
+        # our bump below actually does what we think it does (triggers new activity for
+        # the user).
+        result_awaitable = notifier.wait_for_events(
+            user_id,
+            1000,
+            _on_new_acivity,
+            from_token=from_token,
+        )
+
+        # Update the account data or presence so that `notifier.wait_for_events(...)`
+        # wakes up. We chose these two options because they're least likely to show up
+        # in the Sliding Sync response so it won't affect whether we have results.
+        if wake_stream_key == StreamKeyType.ACCOUNT_DATA:
+            self.get_success(
+                self.hs.get_account_data_handler().add_account_data_for_user(
+                    user_id,
+                    "org.matrix.foobarbaz",
+                    {"foo": "bar"},
+                )
+            )
+        elif wake_stream_key == StreamKeyType.PRESENCE:
+            sending_user_id = self.register_user(
+                "user_bump_notifier_wait_for_events_" + random_string(10), "pass"
+            )
+            sending_user_tok = self.login(sending_user_id, "pass")
+            test_msg = {"foo": "bar"}
+            chan = self.make_request(
+                "PUT",
+                "/_matrix/client/r0/sendToDevice/m.test/1234",
+                content={"messages": {user_id: {"d1": test_msg}}},
+                access_token=sending_user_tok,
+            )
+            self.assertEqual(chan.code, 200, chan.result)
+        else:
+            raise AssertionError(
+                "Unable to wake that stream in _bump_notifier_wait_for_events(...)"
+            )
+
+        # Wait for our notifier result
+        self.get_success(result_awaitable)
+
+        if not triggered_notifier_wait_for_events:
+            raise AssertionError(
+                "Expected `notifier.wait_for_events(...)` to be triggered"
+            )
+
 
 class SlidingSyncTestCase(SlidingSyncBase):
     """
@@ -1282,18 +1371,10 @@ class SlidingSyncTestCase(SlidingSyncBase):
         devices.register_servlets,
     ]
 
-    def default_config(self) -> JsonDict:
-        config = super().default_config()
-        # Enable sliding sync
-        config["experimental_features"] = {"msc3575_enabled": True}
-        return config
-
     def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.store = hs.get_datastores().main
         self.event_sources = hs.get_event_sources()
         self.storage_controllers = hs.get_storage_controllers()
-        self.account_data_handler = hs.get_account_data_handler()
-        self.notifier = hs.get_notifier()
 
     def _assertRequiredStateIncludes(
         self,
@@ -1419,94 +1500,41 @@ class SlidingSyncTestCase(SlidingSyncBase):
 
         return room_id
 
-    def _bump_notifier_wait_for_events(self, user_id: str) -> None:
-        """
-        Wake-up a `notifier.wait_for_events(user_id)` call without affecting the Sliding
-        Sync results.
-        """
-        # We're expecting some new activity from this point onwards
-        from_token = self.event_sources.get_current_token()
-
-        triggered_notifier_wait_for_events = False
-
-        async def _on_new_acivity(
-            before_token: StreamToken, after_token: StreamToken
-        ) -> bool:
-            nonlocal triggered_notifier_wait_for_events
-            triggered_notifier_wait_for_events = True
-            return True
-
-        # Listen for some new activity for the user. We're just trying to confirm that
-        # our bump below actually does what we think it does (triggers new activity for
-        # the user).
-        result_awaitable = self.notifier.wait_for_events(
-            user_id,
-            1000,
-            _on_new_acivity,
-            from_token=from_token,
-        )
-
-        # Update the account data so that `notifier.wait_for_events(...)` wakes up.
-        # We're bumping account data because it won't show up in the Sliding Sync
-        # response so it won't affect whether we have results.
-        self.get_success(
-            self.account_data_handler.add_account_data_for_user(
-                user_id,
-                "org.matrix.foobarbaz",
-                {"foo": "bar"},
-            )
-        )
-
-        # Wait for our notifier result
-        self.get_success(result_awaitable)
-
-        if not triggered_notifier_wait_for_events:
-            raise AssertionError(
-                "Expected `notifier.wait_for_events(...)` to be triggered"
-            )
-
     def test_sync_list(self) -> None:
         """
         Test that room IDs show up in the Sliding Sync `lists`
         """
-        alice_user_id = self.register_user("alice", "correcthorse")
-        alice_access_token = self.login(alice_user_id, "correcthorse")
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
 
-        room_id = self.helper.create_room_as(
-            alice_user_id, tok=alice_access_token, is_public=True
-        )
+        room_id = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 99]],
-                        "required_state": [
-                            ["m.room.join_rules", ""],
-                            ["m.room.history_visibility", ""],
-                            ["m.space.child", "*"],
-                        ],
-                        "timeline_limit": 1,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 99]],
+                    "required_state": [
+                        ["m.room.join_rules", ""],
+                        ["m.room.history_visibility", ""],
+                        ["m.space.child", "*"],
+                    ],
+                    "timeline_limit": 1,
                 }
-            },
-            access_token=alice_access_token,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Make sure it has the foo-list we requested
         self.assertListEqual(
-            list(channel.json_body["lists"].keys()),
+            list(response_body["lists"].keys()),
             ["foo-list"],
-            channel.json_body["lists"].keys(),
+            response_body["lists"].keys(),
         )
 
         # Make sure the list includes the room we are joined to
         self.assertListEqual(
-            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            list(response_body["lists"]["foo-list"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -1514,15 +1542,15 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [room_id],
                 }
             ],
-            channel.json_body["lists"]["foo-list"],
+            response_body["lists"]["foo-list"],
         )
 
     def test_wait_for_sync_token(self) -> None:
         """
         Test that worker will wait until it catches up to the given token
         """
-        alice_user_id = self.register_user("alice", "correcthorse")
-        alice_access_token = self.login(alice_user_id, "correcthorse")
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
 
         # Create a future token that will cause us to wait. Since we never send a new
         # event to reach that future stream_ordering, the worker will wait until the
@@ -1540,23 +1568,24 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 99]],
+                    "required_state": [
+                        ["m.room.join_rules", ""],
+                        ["m.room.history_visibility", ""],
+                        ["m.space.child", "*"],
+                    ],
+                    "timeline_limit": 1,
+                }
+            }
+        }
         channel = self.make_request(
             "POST",
             self.sync_endpoint + f"?pos={future_position_token_serialized}",
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 99]],
-                        "required_state": [
-                            ["m.room.join_rules", ""],
-                            ["m.room.history_visibility", ""],
-                            ["m.space.child", "*"],
-                        ],
-                        "timeline_limit": 1,
-                    }
-                }
-            },
-            access_token=alice_access_token,
+            content=sync_body,
+            access_token=user1_tok,
             await_result=False,
         )
         # Block for 10 seconds to make `notifier.wait_for_stream_token(from_token)`
@@ -1626,12 +1655,6 @@ class SlidingSyncTestCase(SlidingSyncBase):
             channel.json_body["rooms"][room_id]["timeline"],
         )
 
-    # TODO: Once we remove `ops`, we should be able to add a `RoomResult.__bool__` to
-    # check if there are any updates since the `from_token`.
-    @skip_unless(
-        False,
-        "Once we remove ops from the Sliding Sync response, this test should pass",
-    )
     def test_wait_for_new_data_timeout(self) -> None:
         """
         Test to make sure that the Sliding Sync request waits for new data to arrive but
@@ -1646,23 +1669,22 @@ class SlidingSyncTestCase(SlidingSyncBase):
         room_id = self.helper.create_room_as(user2_id, tok=user2_tok)
         self.helper.join(room_id, user1_id, tok=user1_tok)
 
-        from_token = self.event_sources.get_current_token()
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 0]],
+                    "required_state": [],
+                    "timeline_limit": 1,
+                }
+            }
+        }
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
 
         # Make the Sliding Sync request
         channel = self.make_request(
             "POST",
-            self.sync_endpoint
-            + "?timeout=10000"
-            + f"&pos={self.get_success(from_token.to_string(self.store))}",
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 0]],
-                        "required_state": [],
-                        "timeline_limit": 1,
-                    }
-                }
-            },
+            self.sync_endpoint + f"?timeout=10000&pos={from_token}",
+            content=sync_body,
             access_token=user1_tok,
             await_result=False,
         )
@@ -1671,7 +1693,9 @@ class SlidingSyncTestCase(SlidingSyncBase):
             channel.await_result(timeout_ms=5000)
         # Wake-up `notifier.wait_for_events(...)` that will cause us test
         # `SlidingSyncResult.__bool__` for new results.
-        self._bump_notifier_wait_for_events(user1_id)
+        self._bump_notifier_wait_for_events(
+            user1_id, wake_stream_key=StreamKeyType.ACCOUNT_DATA
+        )
         # Block for a little bit more to ensure we don't see any new results.
         with self.assertRaises(TimedOutException):
             channel.await_result(timeout_ms=4000)
@@ -1680,12 +1704,8 @@ class SlidingSyncTestCase(SlidingSyncBase):
         channel.await_result(timeout_ms=1200)
         self.assertEqual(channel.code, 200, channel.json_body)
 
-        # We still see rooms because that's how Sliding Sync lists work but we reached
-        # the timeout before seeing them
-        self.assertEqual(
-            [event["event_id"] for event in channel.json_body["rooms"].keys()],
-            [room_id],
-        )
+        # There should be no room sent down.
+        self.assertFalse(channel.json_body["rooms"])
 
     def test_filter_list(self) -> None:
         """
@@ -1721,55 +1741,50 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.invite(invite_room_id, src=user2_id, targ=user1_id, tok=user2_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    # Absense of filters does not imply "False" values
-                    "all": {
-                        "ranges": [[0, 99]],
-                        "required_state": [],
-                        "timeline_limit": 1,
-                        "filters": {},
-                    },
-                    # Test single truthy filter
-                    "dms": {
-                        "ranges": [[0, 99]],
-                        "required_state": [],
-                        "timeline_limit": 1,
-                        "filters": {"is_dm": True},
-                    },
-                    # Test single falsy filter
-                    "non-dms": {
-                        "ranges": [[0, 99]],
-                        "required_state": [],
-                        "timeline_limit": 1,
-                        "filters": {"is_dm": False},
-                    },
-                    # Test how multiple filters should stack (AND'd together)
-                    "room-invites": {
-                        "ranges": [[0, 99]],
-                        "required_state": [],
-                        "timeline_limit": 1,
-                        "filters": {"is_dm": False, "is_invite": True},
-                    },
-                }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        sync_body = {
+            "lists": {
+                # Absense of filters does not imply "False" values
+                "all": {
+                    "ranges": [[0, 99]],
+                    "required_state": [],
+                    "timeline_limit": 1,
+                    "filters": {},
+                },
+                # Test single truthy filter
+                "dms": {
+                    "ranges": [[0, 99]],
+                    "required_state": [],
+                    "timeline_limit": 1,
+                    "filters": {"is_dm": True},
+                },
+                # Test single falsy filter
+                "non-dms": {
+                    "ranges": [[0, 99]],
+                    "required_state": [],
+                    "timeline_limit": 1,
+                    "filters": {"is_dm": False},
+                },
+                # Test how multiple filters should stack (AND'd together)
+                "room-invites": {
+                    "ranges": [[0, 99]],
+                    "required_state": [],
+                    "timeline_limit": 1,
+                    "filters": {"is_dm": False, "is_invite": True},
+                },
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Make sure it has the foo-list we requested
         self.assertListEqual(
-            list(channel.json_body["lists"].keys()),
+            list(response_body["lists"].keys()),
             ["all", "dms", "non-dms", "room-invites"],
-            channel.json_body["lists"].keys(),
+            response_body["lists"].keys(),
         )
 
         # Make sure the lists have the correct rooms
         self.assertListEqual(
-            list(channel.json_body["lists"]["all"]["ops"]),
+            list(response_body["lists"]["all"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -1782,10 +1797,10 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     ],
                 }
             ],
-            list(channel.json_body["lists"]["all"]),
+            list(response_body["lists"]["all"]),
         )
         self.assertListEqual(
-            list(channel.json_body["lists"]["dms"]["ops"]),
+            list(response_body["lists"]["dms"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -1793,10 +1808,10 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [invited_dm_room_id, joined_dm_room_id],
                 }
             ],
-            list(channel.json_body["lists"]["dms"]),
+            list(response_body["lists"]["dms"]),
         )
         self.assertListEqual(
-            list(channel.json_body["lists"]["non-dms"]["ops"]),
+            list(response_body["lists"]["non-dms"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -1804,10 +1819,10 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [invite_room_id, room_id],
                 }
             ],
-            list(channel.json_body["lists"]["non-dms"]),
+            list(response_body["lists"]["non-dms"]),
         )
         self.assertListEqual(
-            list(channel.json_body["lists"]["room-invites"]["ops"]),
+            list(response_body["lists"]["room-invites"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -1815,14 +1830,14 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [invite_room_id],
                 }
             ],
-            list(channel.json_body["lists"]["room-invites"]),
+            list(response_body["lists"]["room-invites"]),
         )
 
         # Ensure DM's are correctly marked
         self.assertDictEqual(
             {
                 room_id: room.get("is_dm")
-                for room_id, room in channel.json_body["rooms"].items()
+                for room_id, room in response_body["rooms"].items()
             },
             {
                 invite_room_id: None,
@@ -1849,36 +1864,31 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.send(room_id2, "activity in room2", tok=user1_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 99]],
-                        "required_state": [
-                            ["m.room.join_rules", ""],
-                            ["m.room.history_visibility", ""],
-                            ["m.space.child", "*"],
-                        ],
-                        "timeline_limit": 1,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 99]],
+                    "required_state": [
+                        ["m.room.join_rules", ""],
+                        ["m.room.history_visibility", ""],
+                        ["m.space.child", "*"],
+                    ],
+                    "timeline_limit": 1,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Make sure it has the foo-list we requested
         self.assertListEqual(
-            list(channel.json_body["lists"].keys()),
+            list(response_body["lists"].keys()),
             ["foo-list"],
-            channel.json_body["lists"].keys(),
+            response_body["lists"].keys(),
         )
 
         # Make sure the list is sorted in the way we expect
         self.assertListEqual(
-            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            list(response_body["lists"]["foo-list"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -1886,7 +1896,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [room_id2, room_id1, room_id3],
                 }
             ],
-            channel.json_body["lists"]["foo-list"],
+            response_body["lists"]["foo-list"],
         )
 
     def test_sliced_windows(self) -> None:
@@ -1902,35 +1912,26 @@ class SlidingSyncTestCase(SlidingSyncBase):
         room_id3 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
 
         # Make the Sliding Sync request for a single room
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 0]],
-                        "required_state": [
-                            ["m.room.join_rules", ""],
-                            ["m.room.history_visibility", ""],
-                            ["m.space.child", "*"],
-                        ],
-                        "timeline_limit": 1,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 0]],
+                    "required_state": [],
+                    "timeline_limit": 1,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Make sure it has the foo-list we requested
         self.assertListEqual(
-            list(channel.json_body["lists"].keys()),
+            list(response_body["lists"].keys()),
             ["foo-list"],
-            channel.json_body["lists"].keys(),
+            response_body["lists"].keys(),
         )
         # Make sure the list is sorted in the way we expect
         self.assertListEqual(
-            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            list(response_body["lists"]["foo-list"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -1938,39 +1939,30 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [room_id3],
                 }
             ],
-            channel.json_body["lists"]["foo-list"],
+            response_body["lists"]["foo-list"],
         )
 
         # Make the Sliding Sync request for the first two rooms
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            ["m.room.join_rules", ""],
-                            ["m.room.history_visibility", ""],
-                            ["m.space.child", "*"],
-                        ],
-                        "timeline_limit": 1,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 1,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Make sure it has the foo-list we requested
         self.assertListEqual(
-            list(channel.json_body["lists"].keys()),
+            list(response_body["lists"].keys()),
             ["foo-list"],
-            channel.json_body["lists"].keys(),
+            response_body["lists"].keys(),
         )
         # Make sure the list is sorted in the way we expect
         self.assertListEqual(
-            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            list(response_body["lists"]["foo-list"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -1978,7 +1970,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [room_id3, room_id2],
                 }
             ],
-            channel.json_body["lists"]["foo-list"],
+            response_body["lists"]["foo-list"],
         )
 
     def test_rooms_meta_when_joined(self) -> None:
@@ -2009,43 +2001,38 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.join(room_id1, user1_id, tok=user1_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Reflect the current state of the room
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["name"],
+            response_body["rooms"][room_id1]["name"],
             "my super room",
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["avatar"],
+            response_body["rooms"][room_id1]["avatar"],
             "mxc://DUMMY_MEDIA_ID",
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["joined_count"],
+            response_body["rooms"][room_id1]["joined_count"],
             2,
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["invited_count"],
+            response_body["rooms"][room_id1]["invited_count"],
             0,
         )
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("is_dm"),
+            response_body["rooms"][room_id1].get("is_dm"),
         )
 
     def test_rooms_meta_when_invited(self) -> None:
@@ -2092,44 +2079,39 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # This should still reflect the current state of the room even when the user is
         # invited.
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["name"],
+            response_body["rooms"][room_id1]["name"],
             "my super duper room",
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["avatar"],
+            response_body["rooms"][room_id1]["avatar"],
             "mxc://UPDATED_DUMMY_MEDIA_ID",
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["joined_count"],
+            response_body["rooms"][room_id1]["joined_count"],
             1,
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["invited_count"],
+            response_body["rooms"][room_id1]["invited_count"],
             1,
         )
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("is_dm"),
+            response_body["rooms"][room_id1].get("is_dm"),
         )
 
     def test_rooms_meta_when_banned(self) -> None:
@@ -2176,45 +2158,40 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Reflect the state of the room at the time of leaving
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["name"],
+            response_body["rooms"][room_id1]["name"],
             "my super room",
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["avatar"],
+            response_body["rooms"][room_id1]["avatar"],
             "mxc://DUMMY_MEDIA_ID",
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["joined_count"],
+            response_body["rooms"][room_id1]["joined_count"],
             # FIXME: The actual number should be "1" (user2) but we currently don't
             # support this for rooms where the user has left/been banned.
             0,
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["invited_count"],
+            response_body["rooms"][room_id1]["invited_count"],
             0,
         )
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("is_dm"),
+            response_body["rooms"][room_id1].get("is_dm"),
         )
 
     def test_rooms_meta_heroes(self) -> None:
@@ -2254,61 +2231,56 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.invite(room_id2, src=user2_id, targ=user3_id, tok=user2_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Room1 has a name so we shouldn't see any `heroes` which the client would use
         # the calculate the room name themselves.
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["name"],
+            response_body["rooms"][room_id1]["name"],
             "my super room",
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("heroes"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("heroes"))
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["joined_count"],
+            response_body["rooms"][room_id1]["joined_count"],
             2,
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["invited_count"],
+            response_body["rooms"][room_id1]["invited_count"],
             1,
         )
 
         # Room2 doesn't have a name so we should see `heroes` populated
-        self.assertIsNone(channel.json_body["rooms"][room_id2].get("name"))
+        self.assertIsNone(response_body["rooms"][room_id2].get("name"))
         self.assertCountEqual(
             [
                 hero["user_id"]
-                for hero in channel.json_body["rooms"][room_id2].get("heroes", [])
+                for hero in response_body["rooms"][room_id2].get("heroes", [])
             ],
             # Heroes shouldn't include the user themselves (we shouldn't see user1)
             [user2_id, user3_id],
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id2]["joined_count"],
+            response_body["rooms"][room_id2]["joined_count"],
             2,
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id2]["invited_count"],
+            response_body["rooms"][room_id2]["invited_count"],
             1,
         )
 
         # We didn't request any state so we shouldn't see any `required_state`
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("required_state"))
-        self.assertIsNone(channel.json_body["rooms"][room_id2].get("required_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("required_state"))
+        self.assertIsNone(response_body["rooms"][room_id2].get("required_state"))
 
     def test_rooms_meta_heroes_max(self) -> None:
         """
@@ -2347,44 +2319,39 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.join(room_id1, user7_id, tok=user7_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Room2 doesn't have a name so we should see `heroes` populated
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("name"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("name"))
         self.assertCountEqual(
             [
                 hero["user_id"]
-                for hero in channel.json_body["rooms"][room_id1].get("heroes", [])
+                for hero in response_body["rooms"][room_id1].get("heroes", [])
             ],
             # Heroes should be the first 5 users in the room (excluding the user
             # themselves, we shouldn't see `user1`)
             [user2_id, user3_id, user4_id, user5_id, user6_id],
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["joined_count"],
+            response_body["rooms"][room_id1]["joined_count"],
             7,
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["invited_count"],
+            response_body["rooms"][room_id1]["invited_count"],
             0,
         )
 
         # We didn't request any state so we shouldn't see any `required_state`
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("required_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("required_state"))
 
     def test_rooms_meta_heroes_when_banned(self) -> None:
         """
@@ -2425,28 +2392,23 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.invite(room_id1, src=user2_id, targ=user5_id, tok=user2_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Room2 doesn't have a name so we should see `heroes` populated
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("name"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("name"))
         self.assertCountEqual(
             [
                 hero["user_id"]
-                for hero in channel.json_body["rooms"][room_id1].get("heroes", [])
+                for hero in response_body["rooms"][room_id1].get("heroes", [])
             ],
             # Heroes shouldn't include the user themselves (we shouldn't see user1). We
             # also shouldn't see user4 since they joined after user1 was banned.
@@ -2457,13 +2419,13 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["joined_count"],
+            response_body["rooms"][room_id1]["joined_count"],
             # FIXME: The actual number should be "1" (user2) but we currently don't
             # support this for rooms where the user has left/been banned.
             0,
         )
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["invited_count"],
+            response_body["rooms"][room_id1]["invited_count"],
             # We shouldn't see user5 since they were invited after user1 was banned.
             #
             # FIXME: The actual number should be "1" (user3) but we currently don't
@@ -2496,46 +2458,41 @@ class SlidingSyncTestCase(SlidingSyncBase):
         user1_join_response = self.helper.join(room_id1, user1_id, tok=user1_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 3,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 3,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # We expect to saturate the `timeline_limit` (there are more than 3 messages in the room)
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["limited"],
+            response_body["rooms"][room_id1]["limited"],
             True,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         # Check to make sure the latest events are returned
         self.assertEqual(
             [
                 event["event_id"]
-                for event in channel.json_body["rooms"][room_id1]["timeline"]
+                for event in response_body["rooms"][room_id1]["timeline"]
             ],
             [
                 event_response4["event_id"],
                 event_response5["event_id"],
                 user1_join_response["event_id"],
             ],
-            channel.json_body["rooms"][room_id1]["timeline"],
+            response_body["rooms"][room_id1]["timeline"],
         )
 
         # Check to make sure the `prev_batch` points at the right place
         prev_batch_token = self.get_success(
             StreamToken.from_string(
-                self.store, channel.json_body["rooms"][room_id1]["prev_batch"]
+                self.store, response_body["rooms"][room_id1]["prev_batch"]
             )
         )
         prev_batch_room_stream_token_serialized = self.get_success(
@@ -2559,9 +2516,9 @@ class SlidingSyncTestCase(SlidingSyncBase):
         # With no `from_token` (initial sync), it's all historical since there is no
         # "live" range
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["num_live"],
+            response_body["rooms"][room_id1]["num_live"],
             0,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
 
     def test_rooms_not_limited_initial_sync(self) -> None:
@@ -2582,44 +2539,39 @@ class SlidingSyncTestCase(SlidingSyncBase):
 
         # Make the Sliding Sync request
         timeline_limit = 100
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": timeline_limit,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": timeline_limit,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # The timeline should be `limited=False` because we have all of the events (no
         # more to paginate to)
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["limited"],
+            response_body["rooms"][room_id1]["limited"],
             False,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         expected_number_of_events = 9
         # We're just looking to make sure we got all of the events before hitting the `timeline_limit`
         self.assertEqual(
-            len(channel.json_body["rooms"][room_id1]["timeline"]),
+            len(response_body["rooms"][room_id1]["timeline"]),
             expected_number_of_events,
-            channel.json_body["rooms"][room_id1]["timeline"],
+            response_body["rooms"][room_id1]["timeline"],
         )
         self.assertLessEqual(expected_number_of_events, timeline_limit)
 
         # With no `from_token` (initial sync), it's all historical since there is no
         # "live" token range.
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["num_live"],
+            response_body["rooms"][room_id1]["num_live"],
             0,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
 
     def test_rooms_incremental_sync(self) -> None:
@@ -2637,7 +2589,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
 
         # Make an initial Sliding Sync request to grab a token. This is also a sanity
         # check that we can go from initial to incremental sync.
-        sync_params = {
+        sync_body = {
             "lists": {
                 "foo-list": {
                     "ranges": [[0, 1]],
@@ -2646,14 +2598,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
                 }
             }
         }
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            sync_params,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
-        next_pos = channel.json_body["pos"]
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
 
         # Send some events but don't send enough to saturate the `timeline_limit`.
         # We want to later test that we only get the new events since the `next_pos`
@@ -2661,41 +2606,35 @@ class SlidingSyncTestCase(SlidingSyncBase):
         event_response3 = self.helper.send(room_id1, "activity after3", tok=user2_tok)
 
         # Make an incremental Sliding Sync request (what we're trying to test)
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={next_pos}",
-            sync_params,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
         # We only expect to see the new events since the last sync which isn't enough to
         # fill up the `timeline_limit`.
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["limited"],
+            response_body["rooms"][room_id1]["limited"],
             False,
-            f'Our `timeline_limit` was {sync_params["lists"]["foo-list"]["timeline_limit"]} '
-            + f'and {len(channel.json_body["rooms"][room_id1]["timeline"])} events were returned in the timeline. '
-            + str(channel.json_body["rooms"][room_id1]),
+            f'Our `timeline_limit` was {sync_body["lists"]["foo-list"]["timeline_limit"]} '
+            + f'and {len(response_body["rooms"][room_id1]["timeline"])} events were returned in the timeline. '
+            + str(response_body["rooms"][room_id1]),
         )
         # Check to make sure the latest events are returned
         self.assertEqual(
             [
                 event["event_id"]
-                for event in channel.json_body["rooms"][room_id1]["timeline"]
+                for event in response_body["rooms"][room_id1]["timeline"]
             ],
             [
                 event_response2["event_id"],
                 event_response3["event_id"],
             ],
-            channel.json_body["rooms"][room_id1]["timeline"],
+            response_body["rooms"][room_id1]["timeline"],
         )
 
         # All events are "live"
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["num_live"],
+            response_body["rooms"][room_id1]["num_live"],
             2,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
 
     def test_rooms_bump_stamp(self) -> None:
@@ -2740,33 +2679,27 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request
-        timeline_limit = 100
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": timeline_limit,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 100,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Make sure it has the foo-list we requested
         self.assertListEqual(
-            list(channel.json_body["lists"].keys()),
+            list(response_body["lists"].keys()),
             ["foo-list"],
-            channel.json_body["lists"].keys(),
+            response_body["lists"].keys(),
         )
 
         # Make sure the list includes the rooms in the right order
         self.assertListEqual(
-            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            list(response_body["lists"]["foo-list"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -2776,22 +2709,22 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [room_id1, room_id2],
                 }
             ],
-            channel.json_body["lists"]["foo-list"],
+            response_body["lists"]["foo-list"],
         )
 
         # The `bump_stamp` for room1 should point at the latest message (not the
         # reaction since it's not one of the `DEFAULT_BUMP_EVENT_TYPES`)
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["bump_stamp"],
+            response_body["rooms"][room_id1]["bump_stamp"],
             event_pos1.stream,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
 
         # The `bump_stamp` for room2 should point at the latest message
         self.assertEqual(
-            channel.json_body["rooms"][room_id2]["bump_stamp"],
+            response_body["rooms"][room_id2]["bump_stamp"],
             event_pos2.stream,
-            channel.json_body["rooms"][room_id2],
+            response_body["rooms"][room_id2],
         )
 
     def test_rooms_bump_stamp_backfill(self) -> None:
@@ -2895,23 +2828,18 @@ class SlidingSyncTestCase(SlidingSyncBase):
         # Doing an SS request should return a positive `bump_stamp`, even though
         # the only event that matches the bump types has as negative stream
         # ordering.
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            content={
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 5,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 5,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
-        self.assertGreater(channel.json_body["rooms"][room_id]["bump_stamp"], 0)
+        self.assertGreater(response_body["rooms"][room_id]["bump_stamp"], 0)
 
     def test_rooms_newly_joined_incremental_sync(self) -> None:
         """
@@ -2958,28 +2886,22 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make an incremental Sliding Sync request (what we're trying to test)
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={from_token}",
-            content=sync_body,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
         # We should see the new events and the rest should be filled with historical
         # events which will make us `limited=True` since there are more to paginate to.
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["limited"],
+            response_body["rooms"][room_id1]["limited"],
             True,
             f"Our `timeline_limit` was {timeline_limit} "
-            + f'and {len(channel.json_body["rooms"][room_id1]["timeline"])} events were returned in the timeline. '
-            + str(channel.json_body["rooms"][room_id1]),
+            + f'and {len(response_body["rooms"][room_id1]["timeline"])} events were returned in the timeline. '
+            + str(response_body["rooms"][room_id1]),
         )
         # Check to make sure that the "live" and historical events are returned
         self.assertEqual(
             [
                 event["event_id"]
-                for event in channel.json_body["rooms"][room_id1]["timeline"]
+                for event in response_body["rooms"][room_id1]["timeline"]
             ],
             [
                 event_response2["event_id"],
@@ -2987,14 +2909,14 @@ class SlidingSyncTestCase(SlidingSyncBase):
                 event_response3["event_id"],
                 event_response4["event_id"],
             ],
-            channel.json_body["rooms"][room_id1]["timeline"],
+            response_body["rooms"][room_id1]["timeline"],
         )
 
         # Only events after the `from_token` are "live" (join, event3, event4)
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["num_live"],
+            response_body["rooms"][room_id1]["num_live"],
             3,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
 
     def test_rooms_invite_shared_history_initial_sync(self) -> None:
@@ -3031,51 +2953,46 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.send(room_id1, "activity after4", tok=user2_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 3,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 3,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # `timeline` is omitted for `invite` rooms with `stripped_state`
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("timeline"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("timeline"),
+            response_body["rooms"][room_id1],
         )
         # `num_live` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("num_live"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("num_live"),
+            response_body["rooms"][room_id1],
         )
         # `limited` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("limited"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("limited"),
+            response_body["rooms"][room_id1],
         )
         # `prev_batch` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("prev_batch"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("prev_batch"),
+            response_body["rooms"][room_id1],
         )
         # `required_state` is omitted for `invite` rooms with `stripped_state`
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("required_state"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("required_state"),
+            response_body["rooms"][room_id1],
         )
         # We should have some `stripped_state` so the potential joiner can identify the
         # room (we don't care about the order).
         self.assertCountEqual(
-            channel.json_body["rooms"][room_id1]["invite_state"],
+            response_body["rooms"][room_id1]["invite_state"],
             [
                 {
                     "content": {"creator": user2_id, "room_version": "10"},
@@ -3102,7 +3019,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "type": "m.room.member",
                 },
             ],
-            channel.json_body["rooms"][room_id1]["invite_state"],
+            response_body["rooms"][room_id1]["invite_state"],
         )
 
     def test_rooms_invite_shared_history_incremental_sync(self) -> None:
@@ -3153,43 +3070,39 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.send(room_id1, "activity after toekn6", tok=user2_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={from_token}",
-            content=sync_body,
-            access_token=user1_tok,
+        response_body, from_token = self.do_sync(
+            sync_body, since=from_token, tok=user1_tok
         )
-        self.assertEqual(channel.code, 200, channel.json_body)
 
         # `timeline` is omitted for `invite` rooms with `stripped_state`
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("timeline"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("timeline"),
+            response_body["rooms"][room_id1],
         )
         # `num_live` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("num_live"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("num_live"),
+            response_body["rooms"][room_id1],
         )
         # `limited` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("limited"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("limited"),
+            response_body["rooms"][room_id1],
         )
         # `prev_batch` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("prev_batch"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("prev_batch"),
+            response_body["rooms"][room_id1],
         )
         # `required_state` is omitted for `invite` rooms with `stripped_state`
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("required_state"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("required_state"),
+            response_body["rooms"][room_id1],
         )
         # We should have some `stripped_state` so the potential joiner can identify the
         # room (we don't care about the order).
         self.assertCountEqual(
-            channel.json_body["rooms"][room_id1]["invite_state"],
+            response_body["rooms"][room_id1]["invite_state"],
             [
                 {
                     "content": {"creator": user2_id, "room_version": "10"},
@@ -3216,7 +3129,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "type": "m.room.member",
                 },
             ],
-            channel.json_body["rooms"][room_id1]["invite_state"],
+            response_body["rooms"][room_id1]["invite_state"],
         )
 
     def test_rooms_invite_world_readable_history_initial_sync(self) -> None:
@@ -3270,52 +3183,47 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.send(room_id1, "activity after4", tok=user2_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        # Large enough to see the latest events and before the invite
-                        "timeline_limit": 4,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    # Large enough to see the latest events and before the invite
+                    "timeline_limit": 4,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # `timeline` is omitted for `invite` rooms with `stripped_state`
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("timeline"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("timeline"),
+            response_body["rooms"][room_id1],
         )
         # `num_live` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("num_live"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("num_live"),
+            response_body["rooms"][room_id1],
         )
         # `limited` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("limited"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("limited"),
+            response_body["rooms"][room_id1],
         )
         # `prev_batch` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("prev_batch"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("prev_batch"),
+            response_body["rooms"][room_id1],
         )
         # `required_state` is omitted for `invite` rooms with `stripped_state`
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("required_state"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("required_state"),
+            response_body["rooms"][room_id1],
         )
         # We should have some `stripped_state` so the potential joiner can identify the
         # room (we don't care about the order).
         self.assertCountEqual(
-            channel.json_body["rooms"][room_id1]["invite_state"],
+            response_body["rooms"][room_id1]["invite_state"],
             [
                 {
                     "content": {"creator": user2_id, "room_version": "10"},
@@ -3342,7 +3250,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "type": "m.room.member",
                 },
             ],
-            channel.json_body["rooms"][room_id1]["invite_state"],
+            response_body["rooms"][room_id1]["invite_state"],
         )
 
     def test_rooms_invite_world_readable_history_incremental_sync(self) -> None:
@@ -3410,44 +3318,38 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.send(room_id1, "activity after token5", tok=user2_tok)
         self.helper.send(room_id1, "activity after toekn6", tok=user2_tok)
 
-        # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={from_token}",
-            content=sync_body,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        # Make the incremental Sliding Sync request
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
         # `timeline` is omitted for `invite` rooms with `stripped_state`
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("timeline"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("timeline"),
+            response_body["rooms"][room_id1],
         )
         # `num_live` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("num_live"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("num_live"),
+            response_body["rooms"][room_id1],
         )
         # `limited` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("limited"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("limited"),
+            response_body["rooms"][room_id1],
         )
         # `prev_batch` is omitted for `invite` rooms with `stripped_state` (no timeline anyway)
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("prev_batch"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("prev_batch"),
+            response_body["rooms"][room_id1],
         )
         # `required_state` is omitted for `invite` rooms with `stripped_state`
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("required_state"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("required_state"),
+            response_body["rooms"][room_id1],
         )
         # We should have some `stripped_state` so the potential joiner can identify the
         # room (we don't care about the order).
         self.assertCountEqual(
-            channel.json_body["rooms"][room_id1]["invite_state"],
+            response_body["rooms"][room_id1]["invite_state"],
             [
                 {
                     "content": {"creator": user2_id, "room_version": "10"},
@@ -3474,7 +3376,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "type": "m.room.member",
                 },
             ],
-            channel.json_body["rooms"][room_id1]["invite_state"],
+            response_body["rooms"][room_id1]["invite_state"],
         )
 
     def test_rooms_ban_initial_sync(self) -> None:
@@ -3502,47 +3404,42 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.send(room_id1, "activity after6", tok=user2_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [],
-                        "timeline_limit": 3,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 3,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # We should see events before the ban but not after
         self.assertEqual(
             [
                 event["event_id"]
-                for event in channel.json_body["rooms"][room_id1]["timeline"]
+                for event in response_body["rooms"][room_id1]["timeline"]
             ],
             [
                 event_response3["event_id"],
                 event_response4["event_id"],
                 user1_ban_response["event_id"],
             ],
-            channel.json_body["rooms"][room_id1]["timeline"],
+            response_body["rooms"][room_id1]["timeline"],
         )
         # No "live" events in an initial sync (no `from_token` to define the "live"
         # range)
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["num_live"],
+            response_body["rooms"][room_id1]["num_live"],
             0,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         # There are more events to paginate to
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["limited"],
+            response_body["rooms"][room_id1]["limited"],
             True,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
 
     def test_rooms_ban_incremental_sync1(self) -> None:
@@ -3582,39 +3479,33 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.send(room_id1, "activity after5", tok=user2_tok)
         self.helper.send(room_id1, "activity after6", tok=user2_tok)
 
-        # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={from_token}",
-            content=sync_body,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        # Make the incremental Sliding Sync request
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
         # We should see events before the ban but not after
         self.assertEqual(
             [
                 event["event_id"]
-                for event in channel.json_body["rooms"][room_id1]["timeline"]
+                for event in response_body["rooms"][room_id1]["timeline"]
             ],
             [
                 event_response3["event_id"],
                 event_response4["event_id"],
                 user1_ban_response["event_id"],
             ],
-            channel.json_body["rooms"][room_id1]["timeline"],
+            response_body["rooms"][room_id1]["timeline"],
         )
         # All live events in the incremental sync
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["num_live"],
+            response_body["rooms"][room_id1]["num_live"],
             3,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         # There aren't anymore events to paginate to in this range
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["limited"],
+            response_body["rooms"][room_id1]["limited"],
             False,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
 
     def test_rooms_ban_incremental_sync2(self) -> None:
@@ -3650,29 +3541,11 @@ class SlidingSyncTestCase(SlidingSyncBase):
 
         self.helper.send(room_id1, "activity after4", tok=user2_tok)
 
-        # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={from_token}",
-            content=sync_body,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        # Make the incremental Sliding Sync request
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
         # Nothing to see for this banned user in the room in the token range
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("timeline"))
-        # No events returned in the timeline so nothing is "live"
-        self.assertEqual(
-            channel.json_body["rooms"][room_id1]["num_live"],
-            0,
-            channel.json_body["rooms"][room_id1],
-        )
-        # There aren't anymore events to paginate to in this range
-        self.assertEqual(
-            channel.json_body["rooms"][room_id1]["limited"],
-            False,
-            channel.json_body["rooms"][room_id1],
-        )
+        self.assertIsNone(response_body["rooms"].get(room_id1))
 
     def test_rooms_no_required_state(self) -> None:
         """
@@ -3687,27 +3560,22 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.join(room_id1, user1_id, tok=user1_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        # Empty `required_state`
-                        "required_state": [],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    # Empty `required_state`
+                    "required_state": [],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # No `required_state` in response
         self.assertIsNone(
-            channel.json_body["rooms"][room_id1].get("required_state"),
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1].get("required_state"),
+            response_body["rooms"][room_id1],
         )
 
     def test_rooms_required_state_initial_sync(self) -> None:
@@ -3724,40 +3592,35 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.join(room_id1, user1_id, tok=user1_tok)
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [EventTypes.Create, ""],
-                            [EventTypes.RoomHistoryVisibility, ""],
-                            # This one doesn't exist in the room
-                            [EventTypes.Tombstone, ""],
-                        ],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        [EventTypes.RoomHistoryVisibility, ""],
+                        # This one doesn't exist in the room
+                        [EventTypes.Tombstone, ""],
+                    ],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         state_map = self.get_success(
             self.storage_controllers.state.get_current_state(room_id1)
         )
 
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[(EventTypes.Create, "")],
                 state_map[(EventTypes.RoomHistoryVisibility, "")],
             },
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     def test_rooms_required_state_incremental_sync(self) -> None:
         """
@@ -3782,37 +3645,73 @@ class SlidingSyncTestCase(SlidingSyncBase):
                         # This one doesn't exist in the room
                         [EventTypes.Tombstone, ""],
                     ],
-                    "timeline_limit": 0,
+                    "timeline_limit": 1,
+                }
+            }
+        }
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Send a message so the room comes down sync.
+        self.helper.send(room_id1, "msg", tok=user1_tok)
+
+        # Make the incremental Sliding Sync request
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+
+        # We only return updates but only if we've sent the room down the
+        # connection before.
+        self.assertIsNone(response_body["rooms"][room_id1].get("required_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
+
+    def test_rooms_required_state_incremental_sync_restart(self) -> None:
+        """
+        Test `rooms.required_state` returns requested state events in the room during an
+        incremental sync, after a restart (and so the in memory caches are reset).
+        """
+
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok)
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        [EventTypes.RoomHistoryVisibility, ""],
+                        # This one doesn't exist in the room
+                        [EventTypes.Tombstone, ""],
+                    ],
+                    "timeline_limit": 1,
                 }
             }
         }
-        _, after_room_token = self.do_sync(sync_body, tok=user1_tok)
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Reset the in-memory cache
+        self.hs.get_sliding_sync_handler().connection_store._connections.clear()
 
         # Make the Sliding Sync request
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={after_room_token}",
-            content=sync_body,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
+        # If the cache has been cleared then we do expect the state to come down
         state_map = self.get_success(
             self.storage_controllers.state.get_current_state(room_id1)
         )
 
-        # The returned state doesn't change from initial to incremental sync. In the
-        # future, we will only return updates but only if we've sent the room down the
-        # connection before.
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[(EventTypes.Create, "")],
                 state_map[(EventTypes.RoomHistoryVisibility, "")],
             },
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     def test_rooms_required_state_wildcard(self) -> None:
         """
@@ -3842,35 +3741,30 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request with wildcards for the `event_type` and `state_key`
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [StateValues.WILDCARD, StateValues.WILDCARD],
-                        ],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [StateValues.WILDCARD, StateValues.WILDCARD],
+                    ],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         state_map = self.get_success(
             self.storage_controllers.state.get_current_state(room_id1)
         )
 
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             # We should see all the state events in the room
             state_map.values(),
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     def test_rooms_required_state_wildcard_event_type(self) -> None:
         """
@@ -3901,23 +3795,18 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request with wildcards for the `event_type`
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [StateValues.WILDCARD, user2_id],
-                        ],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [StateValues.WILDCARD, user2_id],
+                    ],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         state_map = self.get_success(
             self.storage_controllers.state.get_current_state(room_id1)
@@ -3925,7 +3814,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
 
         # We expect at-least any state event with the `user2_id` as the `state_key`
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[(EventTypes.Member, user2_id)],
                 state_map[("org.matrix.foo_state", user2_id)],
@@ -3934,7 +3823,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
             # events when the `event_type` is a wildcard.
             exact=False,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     def test_rooms_required_state_wildcard_state_key(self) -> None:
         """
@@ -3950,37 +3839,32 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.join(room_id1, user1_id, tok=user1_tok)
 
         # Make the Sliding Sync request with wildcards for the `state_key`
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [EventTypes.Member, StateValues.WILDCARD],
-                        ],
-                        "timeline_limit": 0,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Member, StateValues.WILDCARD],
+                    ],
+                    "timeline_limit": 0,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         state_map = self.get_success(
             self.storage_controllers.state.get_current_state(room_id1)
         )
 
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[(EventTypes.Member, user1_id)],
                 state_map[(EventTypes.Member, user2_id)],
             },
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     def test_rooms_required_state_lazy_loading_room_members(self) -> None:
         """
@@ -4003,24 +3887,19 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.send(room_id1, "3", tok=user2_tok)
 
         # Make the Sliding Sync request with lazy loading for the room members
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [EventTypes.Create, ""],
-                            [EventTypes.Member, StateValues.LAZY],
-                        ],
-                        "timeline_limit": 3,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        [EventTypes.Member, StateValues.LAZY],
+                    ],
+                    "timeline_limit": 3,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         state_map = self.get_success(
             self.storage_controllers.state.get_current_state(room_id1)
@@ -4028,7 +3907,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
 
         # Only user2 and user3 sent events in the 3 events we see in the `timeline`
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[(EventTypes.Create, "")],
                 state_map[(EventTypes.Member, user2_id)],
@@ -4036,7 +3915,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
             },
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     def test_rooms_required_state_me(self) -> None:
         """
@@ -4076,25 +3955,20 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request with a request for '$ME'.
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [EventTypes.Create, ""],
-                            [EventTypes.Member, StateValues.ME],
-                            ["org.matrix.foo", StateValues.ME],
-                        ],
-                        "timeline_limit": 3,
-                    }
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        [EventTypes.Member, StateValues.ME],
+                        ["org.matrix.foo", StateValues.ME],
+                    ],
+                    "timeline_limit": 3,
                 }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         state_map = self.get_success(
             self.storage_controllers.state.get_current_state(room_id1)
@@ -4102,7 +3976,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
 
         # Only user2 and user3 sent events in the 3 events we see in the `timeline`
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[(EventTypes.Create, "")],
                 state_map[(EventTypes.Member, user1_id)],
@@ -4110,7 +3984,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
             },
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     @parameterized.expand([(Membership.LEAVE,), (Membership.BAN,)])
     def test_rooms_required_state_leave_ban(self, stop_membership: str) -> None:
@@ -4173,17 +4047,11 @@ class SlidingSyncTestCase(SlidingSyncBase):
         self.helper.leave(room_id1, user3_id, tok=user3_tok)
 
         # Make the Sliding Sync request with lazy loading for the room members
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={from_token}",
-            content=sync_body,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
         # Only user2 and user3 sent events in the 3 events we see in the `timeline`
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[(EventTypes.Create, "")],
                 state_map[(EventTypes.Member, user1_id)],
@@ -4193,7 +4061,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
             },
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     def test_rooms_required_state_combine_superset(self) -> None:
         """
@@ -4223,45 +4091,40 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request with wildcards for the `state_key`
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [EventTypes.Create, ""],
-                            [EventTypes.Member, user1_id],
-                        ],
-                        "timeline_limit": 0,
-                    },
-                    "bar-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [EventTypes.Member, StateValues.WILDCARD],
-                            ["org.matrix.foo_state", ""],
-                        ],
-                        "timeline_limit": 0,
-                    },
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        [EventTypes.Member, user1_id],
+                    ],
+                    "timeline_limit": 0,
                 },
-                "room_subscriptions": {
-                    room_id1: {
-                        "required_state": [["org.matrix.bar_state", ""]],
-                        "timeline_limit": 0,
-                    }
+                "bar-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Member, StateValues.WILDCARD],
+                        ["org.matrix.foo_state", ""],
+                    ],
+                    "timeline_limit": 0,
                 },
             },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [["org.matrix.bar_state", ""]],
+                    "timeline_limit": 0,
+                }
+            },
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         state_map = self.get_success(
             self.storage_controllers.state.get_current_state(room_id1)
         )
 
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[(EventTypes.Create, "")],
                 state_map[(EventTypes.Member, user1_id)],
@@ -4271,7 +4134,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
             },
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     def test_rooms_required_state_partial_state(self) -> None:
         """
@@ -4294,28 +4157,23 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request (NOT lazy-loading room members)
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [EventTypes.Create, ""],
-                        ],
-                        "timeline_limit": 0,
-                    },
-                }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                    ],
+                    "timeline_limit": 0,
+                },
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Make sure the list includes room1 but room2 is excluded because it's still
         # partially-stated
         self.assertListEqual(
-            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            list(response_body["lists"]["foo-list"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -4323,33 +4181,28 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [room_id1],
                 }
             ],
-            channel.json_body["lists"]["foo-list"],
+            response_body["lists"]["foo-list"],
         )
 
         # Make the Sliding Sync request (with lazy-loading room members)
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {
-                    "foo-list": {
-                        "ranges": [[0, 1]],
-                        "required_state": [
-                            [EventTypes.Create, ""],
-                            # Lazy-load room members
-                            [EventTypes.Member, StateValues.LAZY],
-                        ],
-                        "timeline_limit": 0,
-                    },
-                }
-            },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        # Lazy-load room members
+                        [EventTypes.Member, StateValues.LAZY],
+                    ],
+                    "timeline_limit": 0,
+                },
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # The list should include both rooms now because we're lazy-loading room members
         self.assertListEqual(
-            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            list(response_body["lists"]["foo-list"]["ops"]),
             [
                 {
                     "op": "SYNC",
@@ -4357,7 +4210,7 @@ class SlidingSyncTestCase(SlidingSyncBase):
                     "room_ids": [room_id2, room_id1],
                 }
             ],
-            channel.json_body["lists"]["foo-list"],
+            response_body["lists"]["foo-list"],
         )
 
     def test_room_subscriptions_with_join_membership(self) -> None:
@@ -4374,22 +4227,17 @@ class SlidingSyncTestCase(SlidingSyncBase):
         join_response = self.helper.join(room_id1, user1_id, tok=user1_tok)
 
         # Make the Sliding Sync request with just the room subscription
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "room_subscriptions": {
-                    room_id1: {
-                        "required_state": [
-                            [EventTypes.Create, ""],
-                        ],
-                        "timeline_limit": 1,
-                    }
-                },
+        sync_body = {
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                    ],
+                    "timeline_limit": 1,
+                }
             },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         state_map = self.get_success(
             self.storage_controllers.state.get_current_state(room_id1)
@@ -4397,37 +4245,37 @@ class SlidingSyncTestCase(SlidingSyncBase):
 
         # We should see some state
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[(EventTypes.Create, "")],
             },
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
         # We should see some events
         self.assertEqual(
             [
                 event["event_id"]
-                for event in channel.json_body["rooms"][room_id1]["timeline"]
+                for event in response_body["rooms"][room_id1]["timeline"]
             ],
             [
                 join_response["event_id"],
             ],
-            channel.json_body["rooms"][room_id1]["timeline"],
+            response_body["rooms"][room_id1]["timeline"],
         )
         # No "live" events in an initial sync (no `from_token` to define the "live"
         # range)
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["num_live"],
+            response_body["rooms"][room_id1]["num_live"],
             0,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         # There are more events to paginate to
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["limited"],
+            response_body["rooms"][room_id1]["limited"],
             True,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
 
     def test_room_subscriptions_with_leave_membership(self) -> None:
@@ -4468,57 +4316,52 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request with just the room subscription
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "room_subscriptions": {
-                    room_id1: {
-                        "required_state": [
-                            ["org.matrix.foo_state", ""],
-                        ],
-                        "timeline_limit": 2,
-                    }
-                },
+        sync_body = {
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [
+                        ["org.matrix.foo_state", ""],
+                    ],
+                    "timeline_limit": 2,
+                }
             },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # We should see the state at the time of the leave
         self._assertRequiredStateIncludes(
-            channel.json_body["rooms"][room_id1]["required_state"],
+            response_body["rooms"][room_id1]["required_state"],
             {
                 state_map[("org.matrix.foo_state", "")],
             },
             exact=True,
         )
-        self.assertIsNone(channel.json_body["rooms"][room_id1].get("invite_state"))
+        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
         # We should see some before we left (nothing after)
         self.assertEqual(
             [
                 event["event_id"]
-                for event in channel.json_body["rooms"][room_id1]["timeline"]
+                for event in response_body["rooms"][room_id1]["timeline"]
             ],
             [
                 join_response["event_id"],
                 leave_response["event_id"],
             ],
-            channel.json_body["rooms"][room_id1]["timeline"],
+            response_body["rooms"][room_id1]["timeline"],
         )
         # No "live" events in an initial sync (no `from_token` to define the "live"
         # range)
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["num_live"],
+            response_body["rooms"][room_id1]["num_live"],
             0,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
         # There are more events to paginate to
         self.assertEqual(
-            channel.json_body["rooms"][room_id1]["limited"],
+            response_body["rooms"][room_id1]["limited"],
             True,
-            channel.json_body["rooms"][room_id1],
+            response_body["rooms"][room_id1],
         )
 
     def test_room_subscriptions_no_leak_private_room(self) -> None:
@@ -4539,27 +4382,20 @@ class SlidingSyncTestCase(SlidingSyncBase):
         )
 
         # Make the Sliding Sync request with just the room subscription
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "room_subscriptions": {
-                    room_id1: {
-                        "required_state": [
-                            [EventTypes.Create, ""],
-                        ],
-                        "timeline_limit": 1,
-                    }
-                },
+        sync_body = {
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                    ],
+                    "timeline_limit": 1,
+                }
             },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # We should not see the room at all (we're not in it)
-        self.assertIsNone(
-            channel.json_body["rooms"].get(room_id1), channel.json_body["rooms"]
-        )
+        self.assertIsNone(response_body["rooms"].get(room_id1), response_body["rooms"])
 
     def test_room_subscriptions_world_readable(self) -> None:
         """
@@ -4602,111 +4438,506 @@ class SlidingSyncTestCase(SlidingSyncBase):
         # Note: We never join the room
 
         # Make the Sliding Sync request with just the room subscription
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "room_subscriptions": {
-                    room_id1: {
-                        "required_state": [
-                            [EventTypes.Create, ""],
-                        ],
-                        "timeline_limit": 1,
-                    }
-                },
+        sync_body = {
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                    ],
+                    "timeline_limit": 1,
+                }
             },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # FIXME: In the future, we should be able to see the room because it's
         # `world_readable` but currently we don't support this.
-        self.assertIsNone(
-            channel.json_body["rooms"].get(room_id1), channel.json_body["rooms"]
+        self.assertIsNone(response_body["rooms"].get(room_id1), response_body["rooms"])
+
+    def test_rooms_required_state_incremental_sync_LIVE(self) -> None:
+        """Test that we only get state updates in incremental sync for rooms
+        we've already seen (LIVE).
+        """
+
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok)
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+
+        # Make the Sliding Sync request
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        [EventTypes.RoomHistoryVisibility, ""],
+                        # This one doesn't exist in the room
+                        [EventTypes.Name, ""],
+                    ],
+                    "timeline_limit": 0,
+                }
+            }
+        }
+
+        response_body, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        state_map = self.get_success(
+            self.storage_controllers.state.get_current_state(room_id1)
         )
 
+        self._assertRequiredStateIncludes(
+            response_body["rooms"][room_id1]["required_state"],
+            {
+                state_map[(EventTypes.Create, "")],
+                state_map[(EventTypes.RoomHistoryVisibility, "")],
+            },
+            exact=True,
+        )
 
-class SlidingSyncToDeviceExtensionTestCase(SlidingSyncBase):
-    """Tests for the to-device sliding sync extension"""
+        # Send a state event
+        self.helper.send_state(
+            room_id1, EventTypes.Name, body={"name": "foo"}, tok=user2_tok
+        )
 
-    servlets = [
-        synapse.rest.admin.register_servlets,
-        login.register_servlets,
-        sync.register_servlets,
-        sendtodevice.register_servlets,
-    ]
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
-    def default_config(self) -> JsonDict:
-        config = super().default_config()
-        # Enable sliding sync
-        config["experimental_features"] = {"msc3575_enabled": True}
-        return config
+        state_map = self.get_success(
+            self.storage_controllers.state.get_current_state(room_id1)
+        )
 
-    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
-        self.store = hs.get_datastores().main
-        self.event_sources = hs.get_event_sources()
-        self.account_data_handler = hs.get_account_data_handler()
-        self.notifier = hs.get_notifier()
-        self.sync_endpoint = (
-            "/_matrix/client/unstable/org.matrix.simplified_msc3575/sync"
+        self.assertNotIn("initial", response_body["rooms"][room_id1])
+        self._assertRequiredStateIncludes(
+            response_body["rooms"][room_id1]["required_state"],
+            {
+                state_map[(EventTypes.Name, "")],
+            },
+            exact=True,
         )
 
-    def _bump_notifier_wait_for_events(self, user_id: str) -> None:
+    @parameterized.expand([(False,), (True,)])
+    def test_rooms_timeline_incremental_sync_PREVIOUSLY(self, limited: bool) -> None:
         """
-        Wake-up a `notifier.wait_for_events(user_id)` call without affecting the Sliding
-        Sync results.
+        Test getting room data where we have previously sent down the room, but
+        we missed sending down some timeline events previously and so its status
+        is considered PREVIOUSLY.
+
+        There are two versions of this test, one where there are more messages
+        than the timeline limit, and one where there isn't.
         """
-        # We're expecting some new activity from this point onwards
-        from_token = self.event_sources.get_current_token()
 
-        triggered_notifier_wait_for_events = False
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
 
-        async def _on_new_acivity(
-            before_token: StreamToken, after_token: StreamToken
-        ) -> bool:
-            nonlocal triggered_notifier_wait_for_events
-            triggered_notifier_wait_for_events = True
-            return True
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok)
 
-        # Listen for some new activity for the user. We're just trying to confirm that
-        # our bump below actually does what we think it does (triggers new activity for
-        # the user).
-        result_awaitable = self.notifier.wait_for_events(
-            user_id,
-            1000,
-            _on_new_acivity,
-            from_token=from_token,
+        self.helper.send(room_id1, "msg", tok=user1_tok)
+
+        timeline_limit = 5
+        conn_id = "conn_id"
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 0]],
+                    "required_state": [],
+                    "timeline_limit": timeline_limit,
+                }
+            },
+            "conn_id": "conn_id",
+        }
+
+        # The first room gets sent down the initial sync
+        response_body, initial_from_token = self.do_sync(sync_body, tok=user1_tok)
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id1}, response_body["rooms"]
         )
 
-        # Update the account data so that `notifier.wait_for_events(...)` wakes up.
-        # We're bumping account data because it won't show up in the Sliding Sync
-        # response so it won't affect whether we have results.
-        self.get_success(
-            self.account_data_handler.add_account_data_for_user(
-                user_id,
-                "org.matrix.foobarbaz",
-                {"foo": "bar"},
+        # We now send down some events in room1 (depending on the test param).
+        expected_events = []  # The set of events in the timeline
+        if limited:
+            for _ in range(10):
+                resp = self.helper.send(room_id1, "msg1", tok=user1_tok)
+                expected_events.append(resp["event_id"])
+        else:
+            resp = self.helper.send(room_id1, "msg1", tok=user1_tok)
+            expected_events.append(resp["event_id"])
+
+        # A second messages happens in the other room, so room1 won't get sent down.
+        self.helper.send(room_id2, "msg", tok=user1_tok)
+
+        # Only the second room gets sent down sync.
+        response_body, from_token = self.do_sync(
+            sync_body, since=initial_from_token, tok=user1_tok
+        )
+
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id2}, response_body["rooms"]
+        )
+
+        # FIXME: This is a hack to record that the first room wasn't sent down
+        # sync, as we don't implement that currently.
+        sliding_sync_handler = self.hs.get_sliding_sync_handler()
+        requester = self.get_success(
+            self.hs.get_auth().get_user_by_access_token(user1_tok)
+        )
+        sync_config = SlidingSyncConfig(
+            user=requester.user,
+            requester=requester,
+            conn_id=conn_id,
+        )
+
+        parsed_initial_from_token = self.get_success(
+            SlidingSyncStreamToken.from_string(self.store, initial_from_token)
+        )
+        connection_position = self.get_success(
+            sliding_sync_handler.connection_store.record_rooms(
+                sync_config,
+                parsed_initial_from_token,
+                sent_room_ids=[],
+                unsent_room_ids=[room_id1],
             )
         )
 
-        # Wait for our notifier result
-        self.get_success(result_awaitable)
+        # FIXME: Now fix up `from_token` with new connect position above.
+        parsed_from_token = self.get_success(
+            SlidingSyncStreamToken.from_string(self.store, from_token)
+        )
+        parsed_from_token = SlidingSyncStreamToken(
+            stream_token=parsed_from_token.stream_token,
+            connection_position=connection_position,
+        )
+        from_token = self.get_success(parsed_from_token.to_string(self.store))
 
-        if not triggered_notifier_wait_for_events:
-            raise AssertionError(
-                "Expected `notifier.wait_for_events(...)` to be triggered"
+        # We now send another event to room1, so we should sync all the missing events.
+        resp = self.helper.send(room_id1, "msg2", tok=user1_tok)
+        expected_events.append(resp["event_id"])
+
+        # This sync should contain the messages from room1 not yet sent down.
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id1}, response_body["rooms"]
+        )
+        self.assertNotIn("initial", response_body["rooms"][room_id1])
+
+        self.assertEqual(
+            [ev["event_id"] for ev in response_body["rooms"][room_id1]["timeline"]],
+            expected_events[-timeline_limit:],
+        )
+        self.assertEqual(response_body["rooms"][room_id1]["limited"], limited)
+        self.assertEqual(response_body["rooms"][room_id1].get("required_state"), None)
+
+    def test_rooms_required_state_incremental_sync_PREVIOUSLY(self) -> None:
+        """
+        Test getting room data where we have previously sent down the room, but
+        we missed sending down some state previously and so its status is
+        considered PREVIOUSLY.
+        """
+
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok)
+
+        self.helper.send(room_id1, "msg", tok=user1_tok)
+
+        conn_id = "conn_id"
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 0]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        [EventTypes.RoomHistoryVisibility, ""],
+                        # This one doesn't exist in the room
+                        [EventTypes.Name, ""],
+                    ],
+                    "timeline_limit": 0,
+                }
+            },
+            "conn_id": "conn_id",
+        }
+
+        # The first room gets sent down the initial sync
+        response_body, initial_from_token = self.do_sync(sync_body, tok=user1_tok)
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id1}, response_body["rooms"]
+        )
+
+        # We now send down some state in room1
+        resp = self.helper.send_state(
+            room_id1, EventTypes.Name, {"name": "foo"}, tok=user1_tok
+        )
+        name_change_id = resp["event_id"]
+
+        # A second messages happens in the other room, so room1 won't get sent down.
+        self.helper.send(room_id2, "msg", tok=user1_tok)
+
+        # Only the second room gets sent down sync.
+        response_body, from_token = self.do_sync(
+            sync_body, since=initial_from_token, tok=user1_tok
+        )
+
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id2}, response_body["rooms"]
+        )
+
+        # FIXME: This is a hack to record that the first room wasn't sent down
+        # sync, as we don't implement that currently.
+        sliding_sync_handler = self.hs.get_sliding_sync_handler()
+        requester = self.get_success(
+            self.hs.get_auth().get_user_by_access_token(user1_tok)
+        )
+        sync_config = SlidingSyncConfig(
+            user=requester.user,
+            requester=requester,
+            conn_id=conn_id,
+        )
+
+        parsed_initial_from_token = self.get_success(
+            SlidingSyncStreamToken.from_string(self.store, initial_from_token)
+        )
+        connection_position = self.get_success(
+            sliding_sync_handler.connection_store.record_rooms(
+                sync_config,
+                parsed_initial_from_token,
+                sent_room_ids=[],
+                unsent_room_ids=[room_id1],
             )
+        )
+
+        # FIXME: Now fix up `from_token` with new connect position above.
+        parsed_from_token = self.get_success(
+            SlidingSyncStreamToken.from_string(self.store, from_token)
+        )
+        parsed_from_token = SlidingSyncStreamToken(
+            stream_token=parsed_from_token.stream_token,
+            connection_position=connection_position,
+        )
+        from_token = self.get_success(parsed_from_token.to_string(self.store))
+
+        # We now send another event to room1, so we should sync all the missing state.
+        self.helper.send(room_id1, "msg", tok=user1_tok)
+
+        # This sync should contain the state changes from room1.
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id1}, response_body["rooms"]
+        )
+        self.assertNotIn("initial", response_body["rooms"][room_id1])
+
+        # We should only see the name change.
+        self.assertEqual(
+            [
+                ev["event_id"]
+                for ev in response_body["rooms"][room_id1]["required_state"]
+            ],
+            [name_change_id],
+        )
+
+    def test_rooms_required_state_incremental_sync_NEVER(self) -> None:
+        """
+        Test getting `required_state` where we have NEVER sent down the room before
+        """
+
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok)
+
+        self.helper.send(room_id1, "msg", tok=user1_tok)
+
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 0]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        [EventTypes.RoomHistoryVisibility, ""],
+                        # This one doesn't exist in the room
+                        [EventTypes.Name, ""],
+                    ],
+                    "timeline_limit": 1,
+                }
+            },
+        }
+
+        # A message happens in the other room, so room1 won't get sent down.
+        self.helper.send(room_id2, "msg", tok=user1_tok)
+
+        # Only the second room gets sent down sync.
+        response_body, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id2}, response_body["rooms"]
+        )
+
+        # We now send another event to room1, so we should send down the full
+        # room.
+        self.helper.send(room_id1, "msg2", tok=user1_tok)
+
+        # This sync should contain the messages from room1 not yet sent down.
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id1}, response_body["rooms"]
+        )
+
+        self.assertEqual(response_body["rooms"][room_id1]["initial"], True)
+
+        state_map = self.get_success(
+            self.storage_controllers.state.get_current_state(room_id1)
+        )
+
+        self._assertRequiredStateIncludes(
+            response_body["rooms"][room_id1]["required_state"],
+            {
+                state_map[(EventTypes.Create, "")],
+                state_map[(EventTypes.RoomHistoryVisibility, "")],
+            },
+            exact=True,
+        )
+
+    def test_rooms_timeline_incremental_sync_NEVER(self) -> None:
+        """
+        Test getting timeline room data where we have NEVER sent down the room
+        before
+        """
+
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok)
+
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 0]],
+                    "required_state": [],
+                    "timeline_limit": 5,
+                }
+            },
+        }
+
+        expected_events = []
+        for _ in range(4):
+            resp = self.helper.send(room_id1, "msg", tok=user1_tok)
+            expected_events.append(resp["event_id"])
+
+        # A message happens in the other room, so room1 won't get sent down.
+        self.helper.send(room_id2, "msg", tok=user1_tok)
+
+        # Only the second room gets sent down sync.
+        response_body, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id2}, response_body["rooms"]
+        )
+
+        # We now send another event to room1 so it comes down sync
+        resp = self.helper.send(room_id1, "msg2", tok=user1_tok)
+        expected_events.append(resp["event_id"])
+
+        # This sync should contain the messages from room1 not yet sent down.
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+
+        self.assertCountEqual(
+            response_body["rooms"].keys(), {room_id1}, response_body["rooms"]
+        )
+
+        self.assertEqual(
+            [ev["event_id"] for ev in response_body["rooms"][room_id1]["timeline"]],
+            expected_events,
+        )
+        self.assertEqual(response_body["rooms"][room_id1]["limited"], True)
+        self.assertEqual(response_body["rooms"][room_id1]["initial"], True)
+
+    def test_rooms_with_no_updates_do_not_come_down_incremental_sync(self) -> None:
+        """
+        Test that rooms with no updates are returned in subsequent incremental
+        syncs.
+        """
+
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            }
+        }
+
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Make the incremental Sliding Sync request
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+
+        # Nothing has happened in the room, so the room should not come down
+        # /sync.
+        self.assertIsNone(response_body["rooms"].get(room_id1))
+
+    def test_empty_initial_room_comes_down_sync(self) -> None:
+        """
+        Test that rooms come down /sync even with empty required state and
+        timeline limit in initial sync.
+        """
+
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            }
+        }
+
+        # Make the Sliding Sync request
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+        self.assertEqual(response_body["rooms"][room_id1]["initial"], True)
+
+
+class SlidingSyncToDeviceExtensionTestCase(SlidingSyncBase):
+    """Tests for the to-device sliding sync extension"""
+
+    servlets = [
+        synapse.rest.admin.register_servlets,
+        login.register_servlets,
+        sync.register_servlets,
+        sendtodevice.register_servlets,
+    ]
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.store = hs.get_datastores().main
 
     def _assert_to_device_response(
-        self, channel: FakeChannel, expected_messages: List[JsonDict]
+        self, response_body: JsonDict, expected_messages: List[JsonDict]
     ) -> str:
         """Assert the sliding sync response was successful and has the expected
         to-device messages.
 
         Returns the next_batch token from the to-device section.
         """
-        self.assertEqual(channel.code, 200, channel.json_body)
-        extensions = channel.json_body["extensions"]
+        extensions = response_body["extensions"]
         to_device = extensions["to_device"]
         self.assertIsInstance(to_device["next_batch"], str)
         self.assertEqual(to_device["events"], expected_messages)
@@ -4720,22 +4951,18 @@ class SlidingSyncToDeviceExtensionTestCase(SlidingSyncBase):
         user1_id = self.register_user("user1", "pass")
         user1_tok = self.login(user1_id, "pass")
 
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {},
-                "extensions": {
-                    "to_device": {
-                        "enabled": True,
-                    }
-                },
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "to_device": {
+                    "enabled": True,
+                }
             },
-            access_token=user1_tok,
-        )
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # We expect no to-device messages
-        self._assert_to_device_response(channel, [])
+        self._assert_to_device_response(response_body, [])
 
     def test_data_initial_sync(self) -> None:
         """Test that we get to-device messages when we don't specify a since
@@ -4756,21 +4983,17 @@ class SlidingSyncToDeviceExtensionTestCase(SlidingSyncBase):
         )
         self.assertEqual(chan.code, 200, chan.result)
 
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {},
-                "extensions": {
-                    "to_device": {
-                        "enabled": True,
-                    }
-                },
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "to_device": {
+                    "enabled": True,
+                }
             },
-            access_token=user1_tok,
-        )
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
         self._assert_to_device_response(
-            channel,
+            response_body,
             [{"content": test_msg, "sender": user2_id, "type": "m.test"}],
         )
 
@@ -4782,21 +5005,17 @@ class SlidingSyncToDeviceExtensionTestCase(SlidingSyncBase):
         user2_id = self.register_user("u2", "pass")
         user2_tok = self.login(user2_id, "pass", "d2")
 
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {},
-                "extensions": {
-                    "to_device": {
-                        "enabled": True,
-                    }
-                },
+        sync_body: JsonDict = {
+            "lists": {},
+            "extensions": {
+                "to_device": {
+                    "enabled": True,
+                }
             },
-            access_token=user1_tok,
-        )
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
         # No to-device messages yet.
-        next_batch = self._assert_to_device_response(channel, [])
+        next_batch = self._assert_to_device_response(response_body, [])
 
         test_msg = {"foo": "bar"}
         chan = self.make_request(
@@ -4807,59 +5026,47 @@ class SlidingSyncToDeviceExtensionTestCase(SlidingSyncBase):
         )
         self.assertEqual(chan.code, 200, chan.result)
 
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {},
-                "extensions": {
-                    "to_device": {
-                        "enabled": True,
-                        "since": next_batch,
-                    }
-                },
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "to_device": {
+                    "enabled": True,
+                    "since": next_batch,
+                }
             },
-            access_token=user1_tok,
-        )
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
         next_batch = self._assert_to_device_response(
-            channel,
+            response_body,
             [{"content": test_msg, "sender": user2_id, "type": "m.test"}],
         )
 
         # The next sliding sync request should not include the to-device
         # message.
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {},
-                "extensions": {
-                    "to_device": {
-                        "enabled": True,
-                        "since": next_batch,
-                    }
-                },
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "to_device": {
+                    "enabled": True,
+                    "since": next_batch,
+                }
             },
-            access_token=user1_tok,
-        )
-        self._assert_to_device_response(channel, [])
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+        self._assert_to_device_response(response_body, [])
 
         # An initial sliding sync request should not include the to-device
         # message, as it should have been deleted
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {},
-                "extensions": {
-                    "to_device": {
-                        "enabled": True,
-                    }
-                },
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "to_device": {
+                    "enabled": True,
+                }
             },
-            access_token=user1_tok,
-        )
-        self._assert_to_device_response(channel, [])
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+        self._assert_to_device_response(response_body, [])
 
     def test_wait_for_new_data(self) -> None:
         """
@@ -4909,7 +5116,7 @@ class SlidingSyncToDeviceExtensionTestCase(SlidingSyncBase):
         self.assertEqual(channel.code, 200, channel.json_body)
 
         self._assert_to_device_response(
-            channel,
+            channel.json_body,
             [{"content": test_msg, "sender": user2_id, "type": "m.test"}],
         )
 
@@ -4945,7 +5152,9 @@ class SlidingSyncToDeviceExtensionTestCase(SlidingSyncBase):
             channel.await_result(timeout_ms=5000)
         # Wake-up `notifier.wait_for_events(...)` that will cause us test
         # `SlidingSyncResult.__bool__` for new results.
-        self._bump_notifier_wait_for_events(user1_id)
+        self._bump_notifier_wait_for_events(
+            user1_id, wake_stream_key=StreamKeyType.ACCOUNT_DATA
+        )
         # Block for a little bit more to ensure we don't see any new results.
         with self.assertRaises(TimedOutException):
             channel.await_result(timeout_ms=4000)
@@ -4954,7 +5163,7 @@ class SlidingSyncToDeviceExtensionTestCase(SlidingSyncBase):
         channel.await_result(timeout_ms=1200)
         self.assertEqual(channel.code, 200, channel.json_body)
 
-        self._assert_to_device_response(channel, [])
+        self._assert_to_device_response(channel.json_body, [])
 
 
 class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
@@ -4968,67 +5177,9 @@ class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
         devices.register_servlets,
     ]
 
-    def default_config(self) -> JsonDict:
-        config = super().default_config()
-        # Enable sliding sync
-        config["experimental_features"] = {"msc3575_enabled": True}
-        return config
-
     def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.store = hs.get_datastores().main
-        self.event_sources = hs.get_event_sources()
         self.e2e_keys_handler = hs.get_e2e_keys_handler()
-        self.account_data_handler = hs.get_account_data_handler()
-        self.notifier = hs.get_notifier()
-        self.sync_endpoint = (
-            "/_matrix/client/unstable/org.matrix.simplified_msc3575/sync"
-        )
-
-    def _bump_notifier_wait_for_events(self, user_id: str) -> None:
-        """
-        Wake-up a `notifier.wait_for_events(user_id)` call without affecting the Sliding
-        Sync results.
-        """
-        # We're expecting some new activity from this point onwards
-        from_token = self.event_sources.get_current_token()
-
-        triggered_notifier_wait_for_events = False
-
-        async def _on_new_acivity(
-            before_token: StreamToken, after_token: StreamToken
-        ) -> bool:
-            nonlocal triggered_notifier_wait_for_events
-            triggered_notifier_wait_for_events = True
-            return True
-
-        # Listen for some new activity for the user. We're just trying to confirm that
-        # our bump below actually does what we think it does (triggers new activity for
-        # the user).
-        result_awaitable = self.notifier.wait_for_events(
-            user_id,
-            1000,
-            _on_new_acivity,
-            from_token=from_token,
-        )
-
-        # Update the account data so that `notifier.wait_for_events(...)` wakes up.
-        # We're bumping account data because it won't show up in the Sliding Sync
-        # response so it won't affect whether we have results.
-        self.get_success(
-            self.account_data_handler.add_account_data_for_user(
-                user_id,
-                "org.matrix.foobarbaz",
-                {"foo": "bar"},
-            )
-        )
-
-        # Wait for our notifier result
-        self.get_success(result_awaitable)
-
-        if not triggered_notifier_wait_for_events:
-            raise AssertionError(
-                "Expected `notifier.wait_for_events(...)` to be triggered"
-            )
 
     def test_no_data_initial_sync(self) -> None:
         """
@@ -5039,27 +5190,22 @@ class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
         user1_tok = self.login(user1_id, "pass")
 
         # Make an initial Sliding Sync request with the e2ee extension enabled
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {},
-                "extensions": {
-                    "e2ee": {
-                        "enabled": True,
-                    }
-                },
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "e2ee": {
+                    "enabled": True,
+                }
             },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Device list updates are only present for incremental syncs
-        self.assertIsNone(channel.json_body["extensions"]["e2ee"].get("device_lists"))
+        self.assertIsNone(response_body["extensions"]["e2ee"].get("device_lists"))
 
         # Both of these should be present even when empty
         self.assertEqual(
-            channel.json_body["extensions"]["e2ee"]["device_one_time_keys_count"],
+            response_body["extensions"]["e2ee"]["device_one_time_keys_count"],
             {
                 # This is always present because of
                 # https://github.com/element-hq/element-android/issues/3725 and
@@ -5068,7 +5214,7 @@ class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
             },
         )
         self.assertEqual(
-            channel.json_body["extensions"]["e2ee"]["device_unused_fallback_key_types"],
+            response_body["extensions"]["e2ee"]["device_unused_fallback_key_types"],
             [],
         )
 
@@ -5091,29 +5237,21 @@ class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
         _, from_token = self.do_sync(sync_body, tok=user1_tok)
 
         # Make an incremental Sliding Sync request with the e2ee extension enabled
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={from_token}",
-            content=sync_body,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
         # Device list shows up for incremental syncs
         self.assertEqual(
-            channel.json_body["extensions"]["e2ee"]
-            .get("device_lists", {})
-            .get("changed"),
+            response_body["extensions"]["e2ee"].get("device_lists", {}).get("changed"),
             [],
         )
         self.assertEqual(
-            channel.json_body["extensions"]["e2ee"].get("device_lists", {}).get("left"),
+            response_body["extensions"]["e2ee"].get("device_lists", {}).get("left"),
             [],
         )
 
         # Both of these should be present even when empty
         self.assertEqual(
-            channel.json_body["extensions"]["e2ee"]["device_one_time_keys_count"],
+            response_body["extensions"]["e2ee"]["device_one_time_keys_count"],
             {
                 # Note that "signed_curve25519" is always returned in key count responses
                 # regardless of whether we uploaded any keys for it. This is necessary until
@@ -5126,7 +5264,7 @@ class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
             },
         )
         self.assertEqual(
-            channel.json_body["extensions"]["e2ee"]["device_unused_fallback_key_types"],
+            response_body["extensions"]["e2ee"]["device_unused_fallback_key_types"],
             [],
         )
 
@@ -5231,7 +5369,9 @@ class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
             channel.await_result(timeout_ms=5000)
         # Wake-up `notifier.wait_for_events(...)` that will cause us test
         # `SlidingSyncResult.__bool__` for new results.
-        self._bump_notifier_wait_for_events(user1_id)
+        self._bump_notifier_wait_for_events(
+            user1_id, wake_stream_key=StreamKeyType.ACCOUNT_DATA
+        )
         # Block for a little bit more to ensure we don't see any new results.
         with self.assertRaises(TimedOutException):
             channel.await_result(timeout_ms=4000)
@@ -5317,23 +5457,15 @@ class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
         self.helper.leave(room_id, user4_id, tok=user4_tok)
 
         # Make an incremental Sliding Sync request with the e2ee extension enabled
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint + f"?pos={from_token}",
-            content=sync_body,
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
 
         # Device list updates show up
         self.assertEqual(
-            channel.json_body["extensions"]["e2ee"]
-            .get("device_lists", {})
-            .get("changed"),
+            response_body["extensions"]["e2ee"].get("device_lists", {}).get("changed"),
             [user3_id],
         )
         self.assertEqual(
-            channel.json_body["extensions"]["e2ee"].get("device_lists", {}).get("left"),
+            response_body["extensions"]["e2ee"].get("device_lists", {}).get("left"),
             [user4_id],
         )
 
@@ -5375,24 +5507,19 @@ class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
         )
 
         # Make a Sliding Sync request with the e2ee extension enabled
-        channel = self.make_request(
-            "POST",
-            self.sync_endpoint,
-            {
-                "lists": {},
-                "extensions": {
-                    "e2ee": {
-                        "enabled": True,
-                    }
-                },
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "e2ee": {
+                    "enabled": True,
+                }
             },
-            access_token=user1_tok,
-        )
-        self.assertEqual(channel.code, 200, channel.json_body)
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Check for those one time key counts
         self.assertEqual(
-            channel.json_body["extensions"]["e2ee"].get("device_one_time_keys_count"),
+            response_body["extensions"]["e2ee"].get("device_one_time_keys_count"),
             {
                 "alg1": 1,
                 "alg2": 2,
@@ -5436,25 +5563,747 @@ class SlidingSyncE2eeExtensionTestCase(SlidingSyncBase):
         self.assertEqual(fallback_res, ["alg1"], fallback_res)
 
         # Make a Sliding Sync request with the e2ee extension enabled
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "e2ee": {
+                    "enabled": True,
+                }
+            },
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+
+        # Check for the unused fallback key types
+        self.assertListEqual(
+            response_body["extensions"]["e2ee"].get("device_unused_fallback_key_types"),
+            ["alg1"],
+        )
+
+
+class SlidingSyncAccountDataExtensionTestCase(SlidingSyncBase):
+    """Tests for the account_data sliding sync extension"""
+
+    servlets = [
+        synapse.rest.admin.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+        sync.register_servlets,
+        sendtodevice.register_servlets,
+    ]
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.store = hs.get_datastores().main
+        self.account_data_handler = hs.get_account_data_handler()
+
+    def test_no_data_initial_sync(self) -> None:
+        """
+        Test that enabling the account_data extension works during an intitial sync,
+        even if there is no-data.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        # Make an initial Sliding Sync request with the account_data extension enabled
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                }
+            },
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+
+        self.assertIncludes(
+            {
+                global_event["type"]
+                for global_event in response_body["extensions"]["account_data"].get(
+                    "global"
+                )
+            },
+            # Even though we don't have any global account data set, Synapse saves some
+            # default push rules for us.
+            {AccountDataTypes.PUSH_RULES},
+            exact=True,
+        )
+        self.assertIncludes(
+            response_body["extensions"]["account_data"].get("rooms").keys(),
+            set(),
+            exact=True,
+        )
+
+    def test_no_data_incremental_sync(self) -> None:
+        """
+        Test that enabling account_data extension works during an incremental sync, even
+        if there is no-data.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                }
+            },
+        }
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Make an incremental Sliding Sync request with the account_data extension enabled
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+
+        # There has been no account data changes since the `from_token` so we shouldn't
+        # see any account data here.
+        self.assertIncludes(
+            {
+                global_event["type"]
+                for global_event in response_body["extensions"]["account_data"].get(
+                    "global"
+                )
+            },
+            set(),
+            exact=True,
+        )
+        self.assertIncludes(
+            response_body["extensions"]["account_data"].get("rooms").keys(),
+            set(),
+            exact=True,
+        )
+
+    def test_global_account_data_initial_sync(self) -> None:
+        """
+        On initial sync, we should return all global account data on initial sync.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        # Update the global account data
+        self.get_success(
+            self.account_data_handler.add_account_data_for_user(
+                user_id=user1_id,
+                account_data_type="org.matrix.foobarbaz",
+                content={"foo": "bar"},
+            )
+        )
+
+        # Make an initial Sliding Sync request with the account_data extension enabled
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                }
+            },
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+
+        # It should show us all of the global account data
+        self.assertIncludes(
+            {
+                global_event["type"]
+                for global_event in response_body["extensions"]["account_data"].get(
+                    "global"
+                )
+            },
+            {AccountDataTypes.PUSH_RULES, "org.matrix.foobarbaz"},
+            exact=True,
+        )
+        self.assertIncludes(
+            response_body["extensions"]["account_data"].get("rooms").keys(),
+            set(),
+            exact=True,
+        )
+
+    def test_global_account_data_incremental_sync(self) -> None:
+        """
+        On incremental sync, we should only account data that has changed since the
+        `from_token`.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        # Add some global account data
+        self.get_success(
+            self.account_data_handler.add_account_data_for_user(
+                user_id=user1_id,
+                account_data_type="org.matrix.foobarbaz",
+                content={"foo": "bar"},
+            )
+        )
+
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                }
+            },
+        }
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Add some other global account data
+        self.get_success(
+            self.account_data_handler.add_account_data_for_user(
+                user_id=user1_id,
+                account_data_type="org.matrix.doodardaz",
+                content={"doo": "dar"},
+            )
+        )
+
+        # Make an incremental Sliding Sync request with the account_data extension enabled
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+
+        self.assertIncludes(
+            {
+                global_event["type"]
+                for global_event in response_body["extensions"]["account_data"].get(
+                    "global"
+                )
+            },
+            # We should only see the new global account data that happened after the `from_token`
+            {"org.matrix.doodardaz"},
+            exact=True,
+        )
+        self.assertIncludes(
+            response_body["extensions"]["account_data"].get("rooms").keys(),
+            set(),
+            exact=True,
+        )
+
+    def test_room_account_data_initial_sync(self) -> None:
+        """
+        On initial sync, we return all account data for a given room but only for
+        rooms that we request and are being returned in the Sliding Sync response.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        # Create a room and add some room account data
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id1,
+                account_data_type="org.matrix.roorarraz",
+                content={"roo": "rar"},
+            )
+        )
+
+        # Create another room with some room account data
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id2,
+                account_data_type="org.matrix.roorarraz",
+                content={"roo": "rar"},
+            )
+        )
+
+        # Make an initial Sliding Sync request with the account_data extension enabled
+        sync_body = {
+            "lists": {},
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            },
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                    "rooms": [room_id1, room_id2],
+                }
+            },
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+
+        self.assertIsNotNone(response_body["extensions"]["account_data"].get("global"))
+        # Even though we requested room2, we only expect room1 to show up because that's
+        # the only room in the Sliding Sync response (room2 is not one of our room
+        # subscriptions or in a sliding window list).
+        self.assertIncludes(
+            response_body["extensions"]["account_data"].get("rooms").keys(),
+            {room_id1},
+            exact=True,
+        )
+        self.assertIncludes(
+            {
+                event["type"]
+                for event in response_body["extensions"]["account_data"]
+                .get("rooms")
+                .get(room_id1)
+            },
+            {"org.matrix.roorarraz"},
+            exact=True,
+        )
+
+    def test_room_account_data_incremental_sync(self) -> None:
+        """
+        On incremental sync, we return all account data for a given room but only for
+        rooms that we request and are being returned in the Sliding Sync response.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        # Create a room and add some room account data
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id1,
+                account_data_type="org.matrix.roorarraz",
+                content={"roo": "rar"},
+            )
+        )
+
+        # Create another room with some room account data
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id2,
+                account_data_type="org.matrix.roorarraz",
+                content={"roo": "rar"},
+            )
+        )
+
+        sync_body = {
+            "lists": {},
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            },
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                    "rooms": [room_id1, room_id2],
+                }
+            },
+        }
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Add some other room account data
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id1,
+                account_data_type="org.matrix.roorarraz2",
+                content={"roo": "rar"},
+            )
+        )
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id2,
+                account_data_type="org.matrix.roorarraz2",
+                content={"roo": "rar"},
+            )
+        )
+
+        # Make an incremental Sliding Sync request with the account_data extension enabled
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+
+        self.assertIsNotNone(response_body["extensions"]["account_data"].get("global"))
+        # Even though we requested room2, we only expect room1 to show up because that's
+        # the only room in the Sliding Sync response (room2 is not one of our room
+        # subscriptions or in a sliding window list).
+        self.assertIncludes(
+            response_body["extensions"]["account_data"].get("rooms").keys(),
+            {room_id1},
+            exact=True,
+        )
+        # We should only see the new room account data that happened after the `from_token`
+        self.assertIncludes(
+            {
+                event["type"]
+                for event in response_body["extensions"]["account_data"]
+                .get("rooms")
+                .get(room_id1)
+            },
+            {"org.matrix.roorarraz2"},
+            exact=True,
+        )
+
+    def test_room_account_data_relevant_rooms(self) -> None:
+        """
+        Test out different variations of `lists`/`rooms` we are requesting account data for.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        # Create a room and add some room account data
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id1,
+                account_data_type="org.matrix.roorarraz",
+                content={"roo": "rar"},
+            )
+        )
+
+        # Create another room with some room account data
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id2,
+                account_data_type="org.matrix.roorarraz",
+                content={"roo": "rar"},
+            )
+        )
+
+        # Create another room with some room account data
+        room_id3 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id3,
+                account_data_type="org.matrix.roorarraz",
+                content={"roo": "rar"},
+            )
+        )
+
+        # Create another room with some room account data
+        room_id4 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id4,
+                account_data_type="org.matrix.roorarraz",
+                content={"roo": "rar"},
+            )
+        )
+
+        # Create another room with some room account data
+        room_id5 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.get_success(
+            self.account_data_handler.add_account_data_to_room(
+                user_id=user1_id,
+                room_id=room_id5,
+                account_data_type="org.matrix.roorarraz",
+                content={"roo": "rar"},
+            )
+        )
+
+        room_id_to_human_name_map = {
+            room_id1: "room1",
+            room_id2: "room2",
+            room_id3: "room3",
+            room_id4: "room4",
+            room_id5: "room5",
+        }
+
+        # Mix lists and rooms
+        sync_body = {
+            "lists": {
+                # We expect this list range to include room5 and room4
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                },
+                # We expect this list range to include room5, room4, room3
+                "bar-list": {
+                    "ranges": [[0, 2]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                },
+            },
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            },
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                    "lists": ["foo-list", "non-existent-list"],
+                    "rooms": [room_id1, room_id2, "!non-existent-room"],
+                }
+            },
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+
+        # room1: ✅ Requested via `rooms` and a room subscription exists
+        # room2: ❌ Requested via `rooms` but not in the response (from lists or room subscriptions)
+        # room3: ❌ Not requested
+        # room4: ✅ Shows up because requested via `lists` and list exists in the response
+        # room5: ✅ Shows up because requested via `lists` and list exists in the response
+        self.assertIncludes(
+            {
+                room_id_to_human_name_map[room_id]
+                for room_id in response_body["extensions"]["account_data"]
+                .get("rooms")
+                .keys()
+            },
+            {"room1", "room4", "room5"},
+            exact=True,
+        )
+
+        # Try wildcards (this is the default)
+        sync_body = {
+            "lists": {
+                # We expect this list range to include room5 and room4
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                },
+                # We expect this list range to include room5, room4, room3
+                "bar-list": {
+                    "ranges": [[0, 2]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                },
+            },
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            },
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                    # "lists": ["*"],
+                    # "rooms": ["*"],
+                }
+            },
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+
+        # room1: ✅ Shows up because of default `rooms` wildcard and is in one of the room subscriptions
+        # room2: ❌ Not requested
+        # room3: ✅ Shows up because of default `lists` wildcard and is in a list
+        # room4: ✅ Shows up because of default `lists` wildcard and is in a list
+        # room5: ✅ Shows up because of default `lists` wildcard and is in a list
+        self.assertIncludes(
+            {
+                room_id_to_human_name_map[room_id]
+                for room_id in response_body["extensions"]["account_data"]
+                .get("rooms")
+                .keys()
+            },
+            {"room1", "room3", "room4", "room5"},
+            exact=True,
+        )
+
+        # Empty list will return nothing
+        sync_body = {
+            "lists": {
+                # We expect this list range to include room5 and room4
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                },
+                # We expect this list range to include room5, room4, room3
+                "bar-list": {
+                    "ranges": [[0, 2]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                },
+            },
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            },
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                    "lists": [],
+                    "rooms": [],
+                }
+            },
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+
+        # room1: ❌ Not requested
+        # room2: ❌ Not requested
+        # room3: ❌ Not requested
+        # room4: ❌ Not requested
+        # room5: ❌ Not requested
+        self.assertIncludes(
+            {
+                room_id_to_human_name_map[room_id]
+                for room_id in response_body["extensions"]["account_data"]
+                .get("rooms")
+                .keys()
+            },
+            set(),
+            exact=True,
+        )
+
+        # Try wildcard and none
+        sync_body = {
+            "lists": {
+                # We expect this list range to include room5 and room4
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                },
+                # We expect this list range to include room5, room4, room3
+                "bar-list": {
+                    "ranges": [[0, 2]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                },
+            },
+            "room_subscriptions": {
+                room_id1: {
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            },
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                    "lists": ["*"],
+                    "rooms": [],
+                }
+            },
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+
+        # room1: ❌ Not requested
+        # room2: ❌ Not requested
+        # room3: ✅ Shows up because of default `lists` wildcard and is in a list
+        # room4: ✅ Shows up because of default `lists` wildcard and is in a list
+        # room5: ✅ Shows up because of default `lists` wildcard and is in a list
+        self.assertIncludes(
+            {
+                room_id_to_human_name_map[room_id]
+                for room_id in response_body["extensions"]["account_data"]
+                .get("rooms")
+                .keys()
+            },
+            {"room3", "room4", "room5"},
+            exact=True,
+        )
+
+    def test_wait_for_new_data(self) -> None:
+        """
+        Test to make sure that the Sliding Sync request waits for new data to arrive.
+
+        (Only applies to incremental syncs with a `timeout` specified)
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        room_id = self.helper.create_room_as(user2_id, tok=user2_tok)
+        self.helper.join(room_id, user1_id, tok=user1_tok)
+
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                }
+            },
+        }
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Make an incremental Sliding Sync request with the account_data extension enabled
         channel = self.make_request(
             "POST",
-            self.sync_endpoint,
+            self.sync_endpoint + f"?timeout=10000&pos={from_token}",
+            content=sync_body,
+            access_token=user1_tok,
+            await_result=False,
+        )
+        # Block for 5 seconds to make sure we are `notifier.wait_for_events(...)`
+        with self.assertRaises(TimedOutException):
+            channel.await_result(timeout_ms=5000)
+        # Bump the global account data to trigger new results
+        self.get_success(
+            self.account_data_handler.add_account_data_for_user(
+                user1_id,
+                "org.matrix.foobarbaz",
+                {"foo": "bar"},
+            )
+        )
+        # Should respond before the 10 second timeout
+        channel.await_result(timeout_ms=3000)
+        self.assertEqual(channel.code, 200, channel.json_body)
+
+        # We should see the global account data update
+        self.assertIncludes(
             {
-                "lists": {},
-                "extensions": {
-                    "e2ee": {
-                        "enabled": True,
-                    }
-                },
+                global_event["type"]
+                for global_event in channel.json_body["extensions"]["account_data"].get(
+                    "global"
+                )
+            },
+            {"org.matrix.foobarbaz"},
+            exact=True,
+        )
+        self.assertIncludes(
+            channel.json_body["extensions"]["account_data"].get("rooms").keys(),
+            set(),
+            exact=True,
+        )
+
+    def test_wait_for_new_data_timeout(self) -> None:
+        """
+        Test to make sure that the Sliding Sync request waits for new data to arrive but
+        no data ever arrives so we timeout. We're also making sure that the default data
+        from the account_data extension doesn't trigger a false-positive for new data.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "account_data": {
+                    "enabled": True,
+                }
             },
+        }
+        _, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Make the Sliding Sync request
+        channel = self.make_request(
+            "POST",
+            self.sync_endpoint + f"?timeout=10000&pos={from_token}",
+            content=sync_body,
             access_token=user1_tok,
+            await_result=False,
         )
+        # Block for 5 seconds to make sure we are `notifier.wait_for_events(...)`
+        with self.assertRaises(TimedOutException):
+            channel.await_result(timeout_ms=5000)
+        # Wake-up `notifier.wait_for_events(...)` that will cause us test
+        # `SlidingSyncResult.__bool__` for new results.
+        self._bump_notifier_wait_for_events(
+            user1_id,
+            # We choose `StreamKeyType.PRESENCE` because we're testing for account data
+            # and don't want to contaminate the account data results using
+            # `StreamKeyType.ACCOUNT_DATA`.
+            wake_stream_key=StreamKeyType.PRESENCE,
+        )
+        # Block for a little bit more to ensure we don't see any new results.
+        with self.assertRaises(TimedOutException):
+            channel.await_result(timeout_ms=4000)
+        # Wait for the sync to complete (wait for the rest of the 10 second timeout,
+        # 5000 + 4000 + 1200 > 10000)
+        channel.await_result(timeout_ms=1200)
         self.assertEqual(channel.code, 200, channel.json_body)
 
-        # Check for the unused fallback key types
-        self.assertListEqual(
-            channel.json_body["extensions"]["e2ee"].get(
-                "device_unused_fallback_key_types"
-            ),
-            ["alg1"],
+        self.assertIsNotNone(
+            channel.json_body["extensions"]["account_data"].get("global")
+        )
+        self.assertIsNotNone(
+            channel.json_body["extensions"]["account_data"].get("rooms")
         )