Revert "Revert accidental fast-forward merge from v1.49.0rc1"

This reverts commit 158d73ebdd61eef33831ae5f6990acf07244fc55.

12 files changed, 418 insertions, 185 deletions

diff --git a/synapse/rest/admin/__init__.py b/synapse/rest/admin/__init__.py
index ee4a5e481b..c499afd4be 100644
--- a/synapse/rest/admin/__init__.py
+++ b/synapse/rest/admin/__init__.py
@@ -17,6 +17,7 @@
 
 import logging
 import platform
+from http import HTTPStatus
 from typing import TYPE_CHECKING, Optional, Tuple
 
 import synapse
@@ -39,6 +40,10 @@ from synapse.rest.admin.event_reports import (
     EventReportDetailRestServlet,
     EventReportsRestServlet,
 )
+from synapse.rest.admin.federation import (
+    DestinationsRestServlet,
+    ListDestinationsRestServlet,
+)
 from synapse.rest.admin.groups import DeleteGroupAdminRestServlet
 from synapse.rest.admin.media import ListMediaInRoom, register_servlets_for_media_repo
 from synapse.rest.admin.registration_tokens import (
@@ -98,7 +103,7 @@ class VersionServlet(RestServlet):
         }
 
     def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
-        return 200, self.res
+        return HTTPStatus.OK, self.res
 
 
 class PurgeHistoryRestServlet(RestServlet):
@@ -130,7 +135,7 @@ class PurgeHistoryRestServlet(RestServlet):
             event = await self.store.get_event(event_id)
 
             if event.room_id != room_id:
-                raise SynapseError(400, "Event is for wrong room.")
+                raise SynapseError(HTTPStatus.BAD_REQUEST, "Event is for wrong room.")
 
             # RoomStreamToken expects [int] not Optional[int]
             assert event.internal_metadata.stream_ordering is not None
@@ -144,7 +149,9 @@ class PurgeHistoryRestServlet(RestServlet):
             ts = body["purge_up_to_ts"]
             if not isinstance(ts, int):
                 raise SynapseError(
-                    400, "purge_up_to_ts must be an int", errcode=Codes.BAD_JSON
+                    HTTPStatus.BAD_REQUEST,
+                    "purge_up_to_ts must be an int",
+                    errcode=Codes.BAD_JSON,
                 )
 
             stream_ordering = await self.store.find_first_stream_ordering_after_ts(ts)
@@ -160,7 +167,9 @@ class PurgeHistoryRestServlet(RestServlet):
                     stream_ordering,
                 )
                 raise SynapseError(
-                    404, "there is no event to be purged", errcode=Codes.NOT_FOUND
+                    HTTPStatus.NOT_FOUND,
+                    "there is no event to be purged",
+                    errcode=Codes.NOT_FOUND,
                 )
             (stream, topo, _event_id) = r
             token = "t%d-%d" % (topo, stream)
@@ -173,7 +182,7 @@ class PurgeHistoryRestServlet(RestServlet):
             )
         else:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "must specify purge_up_to_event_id or purge_up_to_ts",
                 errcode=Codes.BAD_JSON,
             )
@@ -182,7 +191,7 @@ class PurgeHistoryRestServlet(RestServlet):
             room_id, token, delete_local_events=delete_local_events
         )
 
-        return 200, {"purge_id": purge_id}
+        return HTTPStatus.OK, {"purge_id": purge_id}
 
 
 class PurgeHistoryStatusRestServlet(RestServlet):
@@ -201,7 +210,7 @@ class PurgeHistoryStatusRestServlet(RestServlet):
         if purge_status is None:
             raise NotFoundError("purge id '%s' not found" % purge_id)
 
-        return 200, purge_status.asdict()
+        return HTTPStatus.OK, purge_status.asdict()
 
 
 ########################################################################################
@@ -256,6 +265,8 @@ def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
     ListRegistrationTokensRestServlet(hs).register(http_server)
     NewRegistrationTokenRestServlet(hs).register(http_server)
     RegistrationTokenRestServlet(hs).register(http_server)
+    DestinationsRestServlet(hs).register(http_server)
+    ListDestinationsRestServlet(hs).register(http_server)
 
     # Some servlets only get registered for the main process.
     if hs.config.worker.worker_app is None:
diff --git a/synapse/rest/admin/_base.py b/synapse/rest/admin/_base.py
index d9a2f6ca15..399b205aaf 100644
--- a/synapse/rest/admin/_base.py
+++ b/synapse/rest/admin/_base.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import re
+from http import HTTPStatus
 from typing import Iterable, Pattern
 
 from synapse.api.auth import Auth
@@ -62,4 +63,4 @@ async def assert_user_is_admin(auth: Auth, user_id: UserID) -> None:
     """
     is_admin = await auth.is_server_admin(user_id)
     if not is_admin:
-        raise AuthError(403, "You are not a server admin")
+        raise AuthError(HTTPStatus.FORBIDDEN, "You are not a server admin")
diff --git a/synapse/rest/admin/devices.py b/synapse/rest/admin/devices.py
index 80fbf32f17..2e5a6600d3 100644
--- a/synapse/rest/admin/devices.py
+++ b/synapse/rest/admin/devices.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
+from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.errors import NotFoundError, SynapseError
@@ -53,7 +54,7 @@ class DeviceRestServlet(RestServlet):
 
         target_user = UserID.from_string(user_id)
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Can only lookup local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only lookup local users")
 
         u = await self.store.get_user_by_id(target_user.to_string())
         if u is None:
@@ -62,7 +63,7 @@ class DeviceRestServlet(RestServlet):
         device = await self.device_handler.get_device(
             target_user.to_string(), device_id
         )
-        return 200, device
+        return HTTPStatus.OK, device
 
     async def on_DELETE(
         self, request: SynapseRequest, user_id: str, device_id: str
@@ -71,14 +72,14 @@ class DeviceRestServlet(RestServlet):
 
         target_user = UserID.from_string(user_id)
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Can only lookup local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only lookup local users")
 
         u = await self.store.get_user_by_id(target_user.to_string())
         if u is None:
             raise NotFoundError("Unknown user")
 
         await self.device_handler.delete_device(target_user.to_string(), device_id)
-        return 200, {}
+        return HTTPStatus.OK, {}
 
     async def on_PUT(
         self, request: SynapseRequest, user_id: str, device_id: str
@@ -87,7 +88,7 @@ class DeviceRestServlet(RestServlet):
 
         target_user = UserID.from_string(user_id)
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Can only lookup local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only lookup local users")
 
         u = await self.store.get_user_by_id(target_user.to_string())
         if u is None:
@@ -97,7 +98,7 @@ class DeviceRestServlet(RestServlet):
         await self.device_handler.update_device(
             target_user.to_string(), device_id, body
         )
-        return 200, {}
+        return HTTPStatus.OK, {}
 
 
 class DevicesRestServlet(RestServlet):
@@ -124,14 +125,14 @@ class DevicesRestServlet(RestServlet):
 
         target_user = UserID.from_string(user_id)
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Can only lookup local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only lookup local users")
 
         u = await self.store.get_user_by_id(target_user.to_string())
         if u is None:
             raise NotFoundError("Unknown user")
 
         devices = await self.device_handler.get_devices_by_user(target_user.to_string())
-        return 200, {"devices": devices, "total": len(devices)}
+        return HTTPStatus.OK, {"devices": devices, "total": len(devices)}
 
 
 class DeleteDevicesRestServlet(RestServlet):
@@ -155,7 +156,7 @@ class DeleteDevicesRestServlet(RestServlet):
 
         target_user = UserID.from_string(user_id)
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Can only lookup local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only lookup local users")
 
         u = await self.store.get_user_by_id(target_user.to_string())
         if u is None:
@@ -167,4 +168,4 @@ class DeleteDevicesRestServlet(RestServlet):
         await self.device_handler.delete_devices(
             target_user.to_string(), body["devices"]
         )
-        return 200, {}
+        return HTTPStatus.OK, {}
diff --git a/synapse/rest/admin/event_reports.py b/synapse/rest/admin/event_reports.py
index bbfcaf723b..5ee8b11110 100644
--- a/synapse/rest/admin/event_reports.py
+++ b/synapse/rest/admin/event_reports.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import logging
+from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.errors import Codes, NotFoundError, SynapseError
@@ -66,21 +67,23 @@ class EventReportsRestServlet(RestServlet):
 
         if start < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "The start parameter must be a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
 
         if limit < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "The limit parameter must be a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
 
         if direction not in ("f", "b"):
             raise SynapseError(
-                400, "Unknown direction: %s" % (direction,), errcode=Codes.INVALID_PARAM
+                HTTPStatus.BAD_REQUEST,
+                "Unknown direction: %s" % (direction,),
+                errcode=Codes.INVALID_PARAM,
             )
 
         event_reports, total = await self.store.get_event_reports_paginate(
@@ -90,7 +93,7 @@ class EventReportsRestServlet(RestServlet):
         if (start + limit) < total:
             ret["next_token"] = start + len(event_reports)
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
 
 class EventReportDetailRestServlet(RestServlet):
@@ -127,13 +130,17 @@ class EventReportDetailRestServlet(RestServlet):
         try:
             resolved_report_id = int(report_id)
         except ValueError:
-            raise SynapseError(400, message, errcode=Codes.INVALID_PARAM)
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, message, errcode=Codes.INVALID_PARAM
+            )
 
         if resolved_report_id < 0:
-            raise SynapseError(400, message, errcode=Codes.INVALID_PARAM)
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, message, errcode=Codes.INVALID_PARAM
+            )
 
         ret = await self.store.get_event_report(resolved_report_id)
         if not ret:
             raise NotFoundError("Event report not found")
 
-        return 200, ret
+        return HTTPStatus.OK, ret
diff --git a/synapse/rest/admin/federation.py b/synapse/rest/admin/federation.py
new file mode 100644
index 0000000000..744687be35
--- /dev/null
+++ b/synapse/rest/admin/federation.py
@@ -0,0 +1,135 @@
+# Copyright 2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import logging
+from http import HTTPStatus
+from typing import TYPE_CHECKING, Tuple
+
+from synapse.api.errors import Codes, NotFoundError, SynapseError
+from synapse.http.servlet import RestServlet, parse_integer, parse_string
+from synapse.http.site import SynapseRequest
+from synapse.rest.admin._base import admin_patterns, assert_requester_is_admin
+from synapse.storage.databases.main.transactions import DestinationSortOrder
+from synapse.types import JsonDict
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+class ListDestinationsRestServlet(RestServlet):
+    """Get request to list all destinations.
+    This needs user to have administrator access in Synapse.
+
+    GET /_synapse/admin/v1/federation/destinations?from=0&limit=10
+
+    returns:
+        200 OK with list of destinations if success otherwise an error.
+
+    The parameters `from` and `limit` are required only for pagination.
+    By default, a `limit` of 100 is used.
+    The parameter `destination` can be used to filter by destination.
+    The parameter `order_by` can be used to order the result.
+    """
+
+    PATTERNS = admin_patterns("/federation/destinations$")
+
+    def __init__(self, hs: "HomeServer"):
+        self._auth = hs.get_auth()
+        self._store = hs.get_datastore()
+
+    async def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
+        await assert_requester_is_admin(self._auth, request)
+
+        start = parse_integer(request, "from", default=0)
+        limit = parse_integer(request, "limit", default=100)
+
+        if start < 0:
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST,
+                "Query parameter from must be a string representing a positive integer.",
+                errcode=Codes.INVALID_PARAM,
+            )
+
+        if limit < 0:
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST,
+                "Query parameter limit must be a string representing a positive integer.",
+                errcode=Codes.INVALID_PARAM,
+            )
+
+        destination = parse_string(request, "destination")
+
+        order_by = parse_string(
+            request,
+            "order_by",
+            default=DestinationSortOrder.DESTINATION.value,
+            allowed_values=[dest.value for dest in DestinationSortOrder],
+        )
+
+        direction = parse_string(request, "dir", default="f", allowed_values=("f", "b"))
+
+        destinations, total = await self._store.get_destinations_paginate(
+            start, limit, destination, order_by, direction
+        )
+        response = {"destinations": destinations, "total": total}
+        if (start + limit) < total:
+            response["next_token"] = str(start + len(destinations))
+
+        return HTTPStatus.OK, response
+
+
+class DestinationsRestServlet(RestServlet):
+    """Get details of a destination.
+    This needs user to have administrator access in Synapse.
+
+    GET /_synapse/admin/v1/federation/destinations/<destination>
+
+    returns:
+        200 OK with details of a destination if success otherwise an error.
+    """
+
+    PATTERNS = admin_patterns("/federation/destinations/(?P<destination>[^/]+)$")
+
+    def __init__(self, hs: "HomeServer"):
+        self._auth = hs.get_auth()
+        self._store = hs.get_datastore()
+
+    async def on_GET(
+        self, request: SynapseRequest, destination: str
+    ) -> Tuple[int, JsonDict]:
+        await assert_requester_is_admin(self._auth, request)
+
+        destination_retry_timings = await self._store.get_destination_retry_timings(
+            destination
+        )
+
+        if not destination_retry_timings:
+            raise NotFoundError("Unknown destination")
+
+        last_successful_stream_ordering = (
+            await self._store.get_destination_last_successful_stream_ordering(
+                destination
+            )
+        )
+
+        response = {
+            "destination": destination,
+            "failure_ts": destination_retry_timings.failure_ts,
+            "retry_last_ts": destination_retry_timings.retry_last_ts,
+            "retry_interval": destination_retry_timings.retry_interval,
+            "last_successful_stream_ordering": last_successful_stream_ordering,
+        }
+
+        return HTTPStatus.OK, response
diff --git a/synapse/rest/admin/groups.py b/synapse/rest/admin/groups.py
index 68a3ba3cb7..a27110388f 100644
--- a/synapse/rest/admin/groups.py
+++ b/synapse/rest/admin/groups.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
+from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.errors import SynapseError
@@ -43,7 +44,7 @@ class DeleteGroupAdminRestServlet(RestServlet):
         await assert_user_is_admin(self.auth, requester.user)
 
         if not self.is_mine_id(group_id):
-            raise SynapseError(400, "Can only delete local groups")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only delete local groups")
 
         await self.group_server.delete_group(group_id, requester.user.to_string())
-        return 200, {}
+        return HTTPStatus.OK, {}
diff --git a/synapse/rest/admin/media.py b/synapse/rest/admin/media.py
index 30a687d234..9e23e2d8fc 100644
--- a/synapse/rest/admin/media.py
+++ b/synapse/rest/admin/media.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import logging
+from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.errors import AuthError, Codes, NotFoundError, SynapseError
@@ -62,7 +63,7 @@ class QuarantineMediaInRoom(RestServlet):
             room_id, requester.user.to_string()
         )
 
-        return 200, {"num_quarantined": num_quarantined}
+        return HTTPStatus.OK, {"num_quarantined": num_quarantined}
 
 
 class QuarantineMediaByUser(RestServlet):
@@ -89,7 +90,7 @@ class QuarantineMediaByUser(RestServlet):
             user_id, requester.user.to_string()
         )
 
-        return 200, {"num_quarantined": num_quarantined}
+        return HTTPStatus.OK, {"num_quarantined": num_quarantined}
 
 
 class QuarantineMediaByID(RestServlet):
@@ -118,7 +119,7 @@ class QuarantineMediaByID(RestServlet):
             server_name, media_id, requester.user.to_string()
         )
 
-        return 200, {}
+        return HTTPStatus.OK, {}
 
 
 class UnquarantineMediaByID(RestServlet):
@@ -147,7 +148,7 @@ class UnquarantineMediaByID(RestServlet):
         # Remove from quarantine this media id
         await self.store.quarantine_media_by_id(server_name, media_id, None)
 
-        return 200, {}
+        return HTTPStatus.OK, {}
 
 
 class ProtectMediaByID(RestServlet):
@@ -170,7 +171,7 @@ class ProtectMediaByID(RestServlet):
         # Protect this media id
         await self.store.mark_local_media_as_safe(media_id, safe=True)
 
-        return 200, {}
+        return HTTPStatus.OK, {}
 
 
 class UnprotectMediaByID(RestServlet):
@@ -193,7 +194,7 @@ class UnprotectMediaByID(RestServlet):
         # Unprotect this media id
         await self.store.mark_local_media_as_safe(media_id, safe=False)
 
-        return 200, {}
+        return HTTPStatus.OK, {}
 
 
 class ListMediaInRoom(RestServlet):
@@ -211,11 +212,11 @@ class ListMediaInRoom(RestServlet):
         requester = await self.auth.get_user_by_req(request)
         is_admin = await self.auth.is_server_admin(requester.user)
         if not is_admin:
-            raise AuthError(403, "You are not a server admin")
+            raise AuthError(HTTPStatus.FORBIDDEN, "You are not a server admin")
 
         local_mxcs, remote_mxcs = await self.store.get_media_mxcs_in_room(room_id)
 
-        return 200, {"local": local_mxcs, "remote": remote_mxcs}
+        return HTTPStatus.OK, {"local": local_mxcs, "remote": remote_mxcs}
 
 
 class PurgeMediaCacheRestServlet(RestServlet):
@@ -233,13 +234,13 @@ class PurgeMediaCacheRestServlet(RestServlet):
 
         if before_ts < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter before_ts must be a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
         elif before_ts < 30000000000:  # Dec 1970 in milliseconds, Aug 2920 in seconds
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter before_ts you provided is from the year 1970. "
                 + "Double check that you are providing a timestamp in milliseconds.",
                 errcode=Codes.INVALID_PARAM,
@@ -247,7 +248,7 @@ class PurgeMediaCacheRestServlet(RestServlet):
 
         ret = await self.media_repository.delete_old_remote_media(before_ts)
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
 
 class DeleteMediaByID(RestServlet):
@@ -267,7 +268,7 @@ class DeleteMediaByID(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if self.server_name != server_name:
-            raise SynapseError(400, "Can only delete local media")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only delete local media")
 
         if await self.store.get_local_media(media_id) is None:
             raise NotFoundError("Unknown media")
@@ -277,7 +278,7 @@ class DeleteMediaByID(RestServlet):
         deleted_media, total = await self.media_repository.delete_local_media_ids(
             [media_id]
         )
-        return 200, {"deleted_media": deleted_media, "total": total}
+        return HTTPStatus.OK, {"deleted_media": deleted_media, "total": total}
 
 
 class DeleteMediaByDateSize(RestServlet):
@@ -304,26 +305,26 @@ class DeleteMediaByDateSize(RestServlet):
 
         if before_ts < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter before_ts must be a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
         elif before_ts < 30000000000:  # Dec 1970 in milliseconds, Aug 2920 in seconds
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter before_ts you provided is from the year 1970. "
                 + "Double check that you are providing a timestamp in milliseconds.",
                 errcode=Codes.INVALID_PARAM,
             )
         if size_gt < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter size_gt must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
 
         if self.server_name != server_name:
-            raise SynapseError(400, "Can only delete local media")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only delete local media")
 
         logging.info(
             "Deleting local media by timestamp: %s, size larger than: %s, keep profile media: %s"
@@ -333,7 +334,7 @@ class DeleteMediaByDateSize(RestServlet):
         deleted_media, total = await self.media_repository.delete_old_local_media(
             before_ts, size_gt, keep_profiles
         )
-        return 200, {"deleted_media": deleted_media, "total": total}
+        return HTTPStatus.OK, {"deleted_media": deleted_media, "total": total}
 
 
 class UserMediaRestServlet(RestServlet):
@@ -369,7 +370,7 @@ class UserMediaRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if not self.is_mine(UserID.from_string(user_id)):
-            raise SynapseError(400, "Can only look up local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only look up local users")
 
         user = await self.store.get_user_by_id(user_id)
         if user is None:
@@ -380,14 +381,14 @@ class UserMediaRestServlet(RestServlet):
 
         if start < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter from must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
 
         if limit < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter limit must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
@@ -425,7 +426,7 @@ class UserMediaRestServlet(RestServlet):
         if (start + limit) < total:
             ret["next_token"] = start + len(media)
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
     async def on_DELETE(
         self, request: SynapseRequest, user_id: str
@@ -436,7 +437,7 @@ class UserMediaRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if not self.is_mine(UserID.from_string(user_id)):
-            raise SynapseError(400, "Can only look up local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only look up local users")
 
         user = await self.store.get_user_by_id(user_id)
         if user is None:
@@ -447,14 +448,14 @@ class UserMediaRestServlet(RestServlet):
 
         if start < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter from must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
 
         if limit < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter limit must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
@@ -492,7 +493,7 @@ class UserMediaRestServlet(RestServlet):
             ([row["media_id"] for row in media])
         )
 
-        return 200, {"deleted_media": deleted_media, "total": total}
+        return HTTPStatus.OK, {"deleted_media": deleted_media, "total": total}
 
 
 def register_servlets_for_media_repo(hs: "HomeServer", http_server: HttpServer) -> None:
diff --git a/synapse/rest/admin/registration_tokens.py b/synapse/rest/admin/registration_tokens.py
index aba48f6e7b..891b98c088 100644
--- a/synapse/rest/admin/registration_tokens.py
+++ b/synapse/rest/admin/registration_tokens.py
@@ -14,6 +14,7 @@
 
 import logging
 import string
+from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.errors import Codes, NotFoundError, SynapseError
@@ -77,7 +78,7 @@ class ListRegistrationTokensRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
         valid = parse_boolean(request, "valid")
         token_list = await self.store.get_registration_tokens(valid)
-        return 200, {"registration_tokens": token_list}
+        return HTTPStatus.OK, {"registration_tokens": token_list}
 
 
 class NewRegistrationTokenRestServlet(RestServlet):
@@ -123,16 +124,20 @@ class NewRegistrationTokenRestServlet(RestServlet):
         if "token" in body:
             token = body["token"]
             if not isinstance(token, str):
-                raise SynapseError(400, "token must be a string", Codes.INVALID_PARAM)
+                raise SynapseError(
+                    HTTPStatus.BAD_REQUEST,
+                    "token must be a string",
+                    Codes.INVALID_PARAM,
+                )
             if not (0 < len(token) <= 64):
                 raise SynapseError(
-                    400,
+                    HTTPStatus.BAD_REQUEST,
                     "token must not be empty and must not be longer than 64 characters",
                     Codes.INVALID_PARAM,
                 )
             if not set(token).issubset(self.allowed_chars_set):
                 raise SynapseError(
-                    400,
+                    HTTPStatus.BAD_REQUEST,
                     "token must consist only of characters matched by the regex [A-Za-z0-9-_]",
                     Codes.INVALID_PARAM,
                 )
@@ -142,11 +147,13 @@ class NewRegistrationTokenRestServlet(RestServlet):
             length = body.get("length", 16)
             if not isinstance(length, int):
                 raise SynapseError(
-                    400, "length must be an integer", Codes.INVALID_PARAM
+                    HTTPStatus.BAD_REQUEST,
+                    "length must be an integer",
+                    Codes.INVALID_PARAM,
                 )
             if not (0 < length <= 64):
                 raise SynapseError(
-                    400,
+                    HTTPStatus.BAD_REQUEST,
                     "length must be greater than zero and not greater than 64",
                     Codes.INVALID_PARAM,
                 )
@@ -162,7 +169,7 @@ class NewRegistrationTokenRestServlet(RestServlet):
             or (isinstance(uses_allowed, int) and uses_allowed >= 0)
         ):
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "uses_allowed must be a non-negative integer or null",
                 Codes.INVALID_PARAM,
             )
@@ -170,11 +177,15 @@ class NewRegistrationTokenRestServlet(RestServlet):
         expiry_time = body.get("expiry_time", None)
         if not isinstance(expiry_time, (int, type(None))):
             raise SynapseError(
-                400, "expiry_time must be an integer or null", Codes.INVALID_PARAM
+                HTTPStatus.BAD_REQUEST,
+                "expiry_time must be an integer or null",
+                Codes.INVALID_PARAM,
             )
         if isinstance(expiry_time, int) and expiry_time < self.clock.time_msec():
             raise SynapseError(
-                400, "expiry_time must not be in the past", Codes.INVALID_PARAM
+                HTTPStatus.BAD_REQUEST,
+                "expiry_time must not be in the past",
+                Codes.INVALID_PARAM,
             )
 
         created = await self.store.create_registration_token(
@@ -182,7 +193,9 @@ class NewRegistrationTokenRestServlet(RestServlet):
         )
         if not created:
             raise SynapseError(
-                400, f"Token already exists: {token}", Codes.INVALID_PARAM
+                HTTPStatus.BAD_REQUEST,
+                f"Token already exists: {token}",
+                Codes.INVALID_PARAM,
             )
 
         resp = {
@@ -192,7 +205,7 @@ class NewRegistrationTokenRestServlet(RestServlet):
             "completed": 0,
             "expiry_time": expiry_time,
         }
-        return 200, resp
+        return HTTPStatus.OK, resp
 
 
 class RegistrationTokenRestServlet(RestServlet):
@@ -261,7 +274,7 @@ class RegistrationTokenRestServlet(RestServlet):
         if token_info is None:
             raise NotFoundError(f"No such registration token: {token}")
 
-        return 200, token_info
+        return HTTPStatus.OK, token_info
 
     async def on_PUT(self, request: SynapseRequest, token: str) -> Tuple[int, JsonDict]:
         """Update a registration token."""
@@ -277,7 +290,7 @@ class RegistrationTokenRestServlet(RestServlet):
                 or (isinstance(uses_allowed, int) and uses_allowed >= 0)
             ):
                 raise SynapseError(
-                    400,
+                    HTTPStatus.BAD_REQUEST,
                     "uses_allowed must be a non-negative integer or null",
                     Codes.INVALID_PARAM,
                 )
@@ -287,11 +300,15 @@ class RegistrationTokenRestServlet(RestServlet):
             expiry_time = body["expiry_time"]
             if not isinstance(expiry_time, (int, type(None))):
                 raise SynapseError(
-                    400, "expiry_time must be an integer or null", Codes.INVALID_PARAM
+                    HTTPStatus.BAD_REQUEST,
+                    "expiry_time must be an integer or null",
+                    Codes.INVALID_PARAM,
                 )
             if isinstance(expiry_time, int) and expiry_time < self.clock.time_msec():
                 raise SynapseError(
-                    400, "expiry_time must not be in the past", Codes.INVALID_PARAM
+                    HTTPStatus.BAD_REQUEST,
+                    "expiry_time must not be in the past",
+                    Codes.INVALID_PARAM,
                 )
             new_attributes["expiry_time"] = expiry_time
 
@@ -307,7 +324,7 @@ class RegistrationTokenRestServlet(RestServlet):
         if token_info is None:
             raise NotFoundError(f"No such registration token: {token}")
 
-        return 200, token_info
+        return HTTPStatus.OK, token_info
 
     async def on_DELETE(
         self, request: SynapseRequest, token: str
@@ -316,6 +333,6 @@ class RegistrationTokenRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if await self.store.delete_registration_token(token):
-            return 200, {}
+            return HTTPStatus.OK, {}
 
         raise NotFoundError(f"No such registration token: {token}")
diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index a89dda1ba5..829e86675a 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -102,10 +102,9 @@ class RoomRestV2Servlet(RestServlet):
             )
 
         if not RoomID.is_valid(room_id):
-            raise SynapseError(400, "%s is not a legal room ID" % (room_id,))
-
-        if not await self._store.get_room(room_id):
-            raise NotFoundError("Unknown room id %s" % (room_id,))
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "%s is not a legal room ID" % (room_id,)
+            )
 
         delete_id = self._pagination_handler.start_shutdown_and_purge_room(
             room_id=room_id,
@@ -118,7 +117,7 @@ class RoomRestV2Servlet(RestServlet):
             force_purge=force_purge,
         )
 
-        return 200, {"delete_id": delete_id}
+        return HTTPStatus.OK, {"delete_id": delete_id}
 
 
 class DeleteRoomStatusByRoomIdRestServlet(RestServlet):
@@ -137,7 +136,9 @@ class DeleteRoomStatusByRoomIdRestServlet(RestServlet):
         await assert_requester_is_admin(self._auth, request)
 
         if not RoomID.is_valid(room_id):
-            raise SynapseError(400, "%s is not a legal room ID" % (room_id,))
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "%s is not a legal room ID" % (room_id,)
+            )
 
         delete_ids = self._pagination_handler.get_delete_ids_by_room(room_id)
         if delete_ids is None:
@@ -153,7 +154,7 @@ class DeleteRoomStatusByRoomIdRestServlet(RestServlet):
                         **delete.asdict(),
                     }
                 ]
-        return 200, {"results": cast(JsonDict, response)}
+        return HTTPStatus.OK, {"results": cast(JsonDict, response)}
 
 
 class DeleteRoomStatusByDeleteIdRestServlet(RestServlet):
@@ -175,7 +176,7 @@ class DeleteRoomStatusByDeleteIdRestServlet(RestServlet):
         if delete_status is None:
             raise NotFoundError("delete id '%s' not found" % delete_id)
 
-        return 200, cast(JsonDict, delete_status.asdict())
+        return HTTPStatus.OK, cast(JsonDict, delete_status.asdict())
 
 
 class ListRoomRestServlet(RestServlet):
@@ -217,7 +218,7 @@ class ListRoomRestServlet(RestServlet):
             RoomSortOrder.STATE_EVENTS.value,
         ):
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Unknown value for order_by: %s" % (order_by,),
                 errcode=Codes.INVALID_PARAM,
             )
@@ -225,7 +226,7 @@ class ListRoomRestServlet(RestServlet):
         search_term = parse_string(request, "search_term", encoding="utf-8")
         if search_term == "":
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "search_term cannot be an empty string",
                 errcode=Codes.INVALID_PARAM,
             )
@@ -233,7 +234,9 @@ class ListRoomRestServlet(RestServlet):
         direction = parse_string(request, "dir", default="f")
         if direction not in ("f", "b"):
             raise SynapseError(
-                400, "Unknown direction: %s" % (direction,), errcode=Codes.INVALID_PARAM
+                HTTPStatus.BAD_REQUEST,
+                "Unknown direction: %s" % (direction,),
+                errcode=Codes.INVALID_PARAM,
             )
 
         reverse_order = True if direction == "b" else False
@@ -265,7 +268,7 @@ class ListRoomRestServlet(RestServlet):
             else:
                 response["prev_batch"] = 0
 
-        return 200, response
+        return HTTPStatus.OK, response
 
 
 class RoomRestServlet(RestServlet):
@@ -310,7 +313,7 @@ class RoomRestServlet(RestServlet):
         members = await self.store.get_users_in_room(room_id)
         ret["joined_local_devices"] = await self.store.count_devices_by_users(members)
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
     async def on_DELETE(
         self, request: SynapseRequest, room_id: str
@@ -386,7 +389,7 @@ class RoomRestServlet(RestServlet):
         # See https://github.com/python/mypy/issues/4976#issuecomment-579883622
         # for some discussion on why this is necessary. Either way,
         # `ret` is an opaque dictionary blob as far as the rest of the app cares.
-        return 200, cast(JsonDict, ret)
+        return HTTPStatus.OK, cast(JsonDict, ret)
 
 
 class RoomMembersRestServlet(RestServlet):
@@ -413,7 +416,7 @@ class RoomMembersRestServlet(RestServlet):
         members = await self.store.get_users_in_room(room_id)
         ret = {"members": members, "total": len(members)}
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
 
 class RoomStateRestServlet(RestServlet):
@@ -443,16 +446,10 @@ class RoomStateRestServlet(RestServlet):
         event_ids = await self.store.get_current_state_ids(room_id)
         events = await self.store.get_events(event_ids.values())
         now = self.clock.time_msec()
-        room_state = await self._event_serializer.serialize_events(
-            events.values(),
-            now,
-            # We don't bother bundling aggregations in when asked for state
-            # events, as clients won't use them.
-            bundle_relations=False,
-        )
+        room_state = await self._event_serializer.serialize_events(events.values(), now)
         ret = {"state": room_state}
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
 
 class JoinRoomAliasServlet(ResolveRoomIdMixin, RestServlet):
@@ -481,7 +478,10 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, RestServlet):
         target_user = UserID.from_string(content["user_id"])
 
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "This endpoint can only be used with local users")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST,
+                "This endpoint can only be used with local users",
+            )
 
         if not await self.admin_handler.get_user(target_user):
             raise NotFoundError("User not found")
@@ -527,7 +527,7 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, RestServlet):
             ratelimit=False,
         )
 
-        return 200, {"room_id": room_id}
+        return HTTPStatus.OK, {"room_id": room_id}
 
 
 class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
@@ -568,7 +568,7 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
         # Figure out which local users currently have power in the room, if any.
         room_state = await self.state_handler.get_current_state(room_id)
         if not room_state:
-            raise SynapseError(400, "Server not in room")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Server not in room")
 
         create_event = room_state[(EventTypes.Create, "")]
         power_levels = room_state.get((EventTypes.PowerLevels, ""))
@@ -582,7 +582,9 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
             admin_users.sort(key=lambda user: user_power[user])
 
             if not admin_users:
-                raise SynapseError(400, "No local admin user in room")
+                raise SynapseError(
+                    HTTPStatus.BAD_REQUEST, "No local admin user in room"
+                )
 
             admin_user_id = None
 
@@ -599,7 +601,7 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
 
             if not admin_user_id:
                 raise SynapseError(
-                    400,
+                    HTTPStatus.BAD_REQUEST,
                     "No local admin user in room",
                 )
 
@@ -610,7 +612,7 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
             admin_user_id = create_event.sender
             if not self.is_mine_id(admin_user_id):
                 raise SynapseError(
-                    400,
+                    HTTPStatus.BAD_REQUEST,
                     "No local admin user in room",
                 )
 
@@ -639,7 +641,8 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
         except AuthError:
             # The admin user we found turned out not to have enough power.
             raise SynapseError(
-                400, "No local admin user in room with power to update power levels."
+                HTTPStatus.BAD_REQUEST,
+                "No local admin user in room with power to update power levels.",
             )
 
         # Now we check if the user we're granting admin rights to is already in
@@ -653,7 +656,7 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
             )
 
         if is_joined:
-            return 200, {}
+            return HTTPStatus.OK, {}
 
         join_rules = room_state.get((EventTypes.JoinRules, ""))
         is_public = False
@@ -661,7 +664,7 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
             is_public = join_rules.content.get("join_rule") == JoinRules.PUBLIC
 
         if is_public:
-            return 200, {}
+            return HTTPStatus.OK, {}
 
         await self.room_member_handler.update_membership(
             fake_requester,
@@ -670,7 +673,7 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
             action=Membership.INVITE,
         )
 
-        return 200, {}
+        return HTTPStatus.OK, {}
 
 
 class ForwardExtremitiesRestServlet(ResolveRoomIdMixin, RestServlet):
@@ -702,7 +705,7 @@ class ForwardExtremitiesRestServlet(ResolveRoomIdMixin, RestServlet):
         room_id, _ = await self.resolve_room_id(room_identifier)
 
         deleted_count = await self.store.delete_forward_extremities_for_room(room_id)
-        return 200, {"deleted": deleted_count}
+        return HTTPStatus.OK, {"deleted": deleted_count}
 
     async def on_GET(
         self, request: SynapseRequest, room_identifier: str
@@ -713,7 +716,7 @@ class ForwardExtremitiesRestServlet(ResolveRoomIdMixin, RestServlet):
         room_id, _ = await self.resolve_room_id(room_identifier)
 
         extremities = await self.store.get_forward_extremities_for_room(room_id)
-        return 200, {"count": len(extremities), "results": extremities}
+        return HTTPStatus.OK, {"count": len(extremities), "results": extremities}
 
 
 class RoomEventContextServlet(RestServlet):
@@ -762,7 +765,9 @@ class RoomEventContextServlet(RestServlet):
         )
 
         if not results:
-            raise SynapseError(404, "Event not found.", errcode=Codes.NOT_FOUND)
+            raise SynapseError(
+                HTTPStatus.NOT_FOUND, "Event not found.", errcode=Codes.NOT_FOUND
+            )
 
         time_now = self.clock.time_msec()
         results["events_before"] = await self._event_serializer.serialize_events(
@@ -775,13 +780,10 @@ class RoomEventContextServlet(RestServlet):
             results["events_after"], time_now
         )
         results["state"] = await self._event_serializer.serialize_events(
-            results["state"],
-            time_now,
-            # No need to bundle aggregations for state events
-            bundle_relations=False,
+            results["state"], time_now
         )
 
-        return 200, results
+        return HTTPStatus.OK, results
 
 
 class BlockRoomRestServlet(RestServlet):
diff --git a/synapse/rest/admin/server_notice_servlet.py b/synapse/rest/admin/server_notice_servlet.py
index 19f84f33f2..b295fb078b 100644
--- a/synapse/rest/admin/server_notice_servlet.py
+++ b/synapse/rest/admin/server_notice_servlet.py
@@ -11,6 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from http import HTTPStatus
 from typing import TYPE_CHECKING, Awaitable, Optional, Tuple
 
 from synapse.api.constants import EventTypes
@@ -82,11 +83,15 @@ class SendServerNoticeServlet(RestServlet):
         # but worker processes still need to initialise SendServerNoticeServlet (as it is part of the
         # admin api).
         if not self.server_notices_manager.is_enabled():
-            raise SynapseError(400, "Server notices are not enabled on this server")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Server notices are not enabled on this server"
+            )
 
         target_user = UserID.from_string(body["user_id"])
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Server notices can only be sent to local users")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Server notices can only be sent to local users"
+            )
 
         if not await self.admin_handler.get_user(target_user):
             raise NotFoundError("User not found")
@@ -99,7 +104,7 @@ class SendServerNoticeServlet(RestServlet):
             txn_id=txn_id,
         )
 
-        return 200, {"event_id": event.event_id}
+        return HTTPStatus.OK, {"event_id": event.event_id}
 
     def on_PUT(
         self, request: SynapseRequest, txn_id: str
diff --git a/synapse/rest/admin/statistics.py b/synapse/rest/admin/statistics.py
index 948de94ccd..ca41fd45f2 100644
--- a/synapse/rest/admin/statistics.py
+++ b/synapse/rest/admin/statistics.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import logging
+from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.errors import Codes, SynapseError
@@ -53,7 +54,7 @@ class UserMediaStatisticsRestServlet(RestServlet):
             UserSortOrder.DISPLAYNAME.value,
         ):
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Unknown value for order_by: %s" % (order_by,),
                 errcode=Codes.INVALID_PARAM,
             )
@@ -61,7 +62,7 @@ class UserMediaStatisticsRestServlet(RestServlet):
         start = parse_integer(request, "from", default=0)
         if start < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter from must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
@@ -69,7 +70,7 @@ class UserMediaStatisticsRestServlet(RestServlet):
         limit = parse_integer(request, "limit", default=100)
         if limit < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter limit must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
@@ -77,7 +78,7 @@ class UserMediaStatisticsRestServlet(RestServlet):
         from_ts = parse_integer(request, "from_ts", default=0)
         if from_ts < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter from_ts must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
@@ -86,13 +87,13 @@ class UserMediaStatisticsRestServlet(RestServlet):
         if until_ts is not None:
             if until_ts < 0:
                 raise SynapseError(
-                    400,
+                    HTTPStatus.BAD_REQUEST,
                     "Query parameter until_ts must be a string representing a positive integer.",
                     errcode=Codes.INVALID_PARAM,
                 )
             if until_ts <= from_ts:
                 raise SynapseError(
-                    400,
+                    HTTPStatus.BAD_REQUEST,
                     "Query parameter until_ts must be greater than from_ts.",
                     errcode=Codes.INVALID_PARAM,
                 )
@@ -100,7 +101,7 @@ class UserMediaStatisticsRestServlet(RestServlet):
         search_term = parse_string(request, "search_term")
         if search_term == "":
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter search_term cannot be an empty string.",
                 errcode=Codes.INVALID_PARAM,
             )
@@ -108,7 +109,9 @@ class UserMediaStatisticsRestServlet(RestServlet):
         direction = parse_string(request, "dir", default="f")
         if direction not in ("f", "b"):
             raise SynapseError(
-                400, "Unknown direction: %s" % (direction,), errcode=Codes.INVALID_PARAM
+                HTTPStatus.BAD_REQUEST,
+                "Unknown direction: %s" % (direction,),
+                errcode=Codes.INVALID_PARAM,
             )
 
         users_media, total = await self.store.get_users_media_usage_paginate(
@@ -118,4 +121,4 @@ class UserMediaStatisticsRestServlet(RestServlet):
         if (start + limit) < total:
             ret["next_token"] = start + len(users_media)
 
-        return 200, ret
+        return HTTPStatus.OK, ret
diff --git a/synapse/rest/admin/users.py b/synapse/rest/admin/users.py
index ccd9a2a175..2a60b602b1 100644
--- a/synapse/rest/admin/users.py
+++ b/synapse/rest/admin/users.py
@@ -79,14 +79,14 @@ class UsersRestServletV2(RestServlet):
 
         if start < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter from must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
 
         if limit < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "Query parameter limit must be a string representing a positive integer.",
                 errcode=Codes.INVALID_PARAM,
             )
@@ -122,7 +122,7 @@ class UsersRestServletV2(RestServlet):
         if (start + limit) < total:
             ret["next_token"] = str(start + len(users))
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
 
 class UserRestServletV2(RestServlet):
@@ -172,14 +172,14 @@ class UserRestServletV2(RestServlet):
 
         target_user = UserID.from_string(user_id)
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Can only look up local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only look up local users")
 
         ret = await self.admin_handler.get_user(target_user)
 
         if not ret:
             raise NotFoundError("User not found")
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
     async def on_PUT(
         self, request: SynapseRequest, user_id: str
@@ -191,7 +191,10 @@ class UserRestServletV2(RestServlet):
         body = parse_json_object_from_request(request)
 
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "This endpoint can only be used with local users")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST,
+                "This endpoint can only be used with local users",
+            )
 
         user = await self.admin_handler.get_user(target_user)
         user_id = target_user.to_string()
@@ -210,7 +213,7 @@ class UserRestServletV2(RestServlet):
 
         user_type = body.get("user_type", None)
         if user_type is not None and user_type not in UserTypes.ALL_USER_TYPES:
-            raise SynapseError(400, "Invalid user type")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Invalid user type")
 
         set_admin_to = body.get("admin", False)
         if not isinstance(set_admin_to, bool):
@@ -223,11 +226,13 @@ class UserRestServletV2(RestServlet):
         password = body.get("password", None)
         if password is not None:
             if not isinstance(password, str) or len(password) > 512:
-                raise SynapseError(400, "Invalid password")
+                raise SynapseError(HTTPStatus.BAD_REQUEST, "Invalid password")
 
         deactivate = body.get("deactivated", False)
         if not isinstance(deactivate, bool):
-            raise SynapseError(400, "'deactivated' parameter is not of type boolean")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "'deactivated' parameter is not of type boolean"
+            )
 
         # convert List[Dict[str, str]] into List[Tuple[str, str]]
         if external_ids is not None:
@@ -282,7 +287,9 @@ class UserRestServletV2(RestServlet):
                         user_id,
                     )
                 except ExternalIDReuseException:
-                    raise SynapseError(409, "External id is already in use.")
+                    raise SynapseError(
+                        HTTPStatus.CONFLICT, "External id is already in use."
+                    )
 
             if "avatar_url" in body and isinstance(body["avatar_url"], str):
                 await self.profile_handler.set_avatar_url(
@@ -293,7 +300,9 @@ class UserRestServletV2(RestServlet):
                 if set_admin_to != user["admin"]:
                     auth_user = requester.user
                     if target_user == auth_user and not set_admin_to:
-                        raise SynapseError(400, "You may not demote yourself.")
+                        raise SynapseError(
+                            HTTPStatus.BAD_REQUEST, "You may not demote yourself."
+                        )
 
                     await self.store.set_server_admin(target_user, set_admin_to)
 
@@ -319,7 +328,8 @@ class UserRestServletV2(RestServlet):
                         and self.auth_handler.can_change_password()
                     ):
                         raise SynapseError(
-                            400, "Must provide a password to re-activate an account."
+                            HTTPStatus.BAD_REQUEST,
+                            "Must provide a password to re-activate an account.",
                         )
 
                     await self.deactivate_account_handler.activate_account(
@@ -332,7 +342,7 @@ class UserRestServletV2(RestServlet):
             user = await self.admin_handler.get_user(target_user)
             assert user is not None
 
-            return 200, user
+            return HTTPStatus.OK, user
 
         else:  # create user
             displayname = body.get("displayname", None)
@@ -381,7 +391,9 @@ class UserRestServletV2(RestServlet):
                             user_id,
                         )
                 except ExternalIDReuseException:
-                    raise SynapseError(409, "External id is already in use.")
+                    raise SynapseError(
+                        HTTPStatus.CONFLICT, "External id is already in use."
+                    )
 
             if "avatar_url" in body and isinstance(body["avatar_url"], str):
                 await self.profile_handler.set_avatar_url(
@@ -429,51 +441,61 @@ class UserRegisterServlet(RestServlet):
 
         nonce = secrets.token_hex(64)
         self.nonces[nonce] = int(self.reactor.seconds())
-        return 200, {"nonce": nonce}
+        return HTTPStatus.OK, {"nonce": nonce}
 
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         self._clear_old_nonces()
 
         if not self.hs.config.registration.registration_shared_secret:
-            raise SynapseError(400, "Shared secret registration is not enabled")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Shared secret registration is not enabled"
+            )
 
         body = parse_json_object_from_request(request)
 
         if "nonce" not in body:
-            raise SynapseError(400, "nonce must be specified", errcode=Codes.BAD_JSON)
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST,
+                "nonce must be specified",
+                errcode=Codes.BAD_JSON,
+            )
 
         nonce = body["nonce"]
 
         if nonce not in self.nonces:
-            raise SynapseError(400, "unrecognised nonce")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "unrecognised nonce")
 
         # Delete the nonce, so it can't be reused, even if it's invalid
         del self.nonces[nonce]
 
         if "username" not in body:
             raise SynapseError(
-                400, "username must be specified", errcode=Codes.BAD_JSON
+                HTTPStatus.BAD_REQUEST,
+                "username must be specified",
+                errcode=Codes.BAD_JSON,
             )
         else:
             if not isinstance(body["username"], str) or len(body["username"]) > 512:
-                raise SynapseError(400, "Invalid username")
+                raise SynapseError(HTTPStatus.BAD_REQUEST, "Invalid username")
 
             username = body["username"].encode("utf-8")
             if b"\x00" in username:
-                raise SynapseError(400, "Invalid username")
+                raise SynapseError(HTTPStatus.BAD_REQUEST, "Invalid username")
 
         if "password" not in body:
             raise SynapseError(
-                400, "password must be specified", errcode=Codes.BAD_JSON
+                HTTPStatus.BAD_REQUEST,
+                "password must be specified",
+                errcode=Codes.BAD_JSON,
             )
         else:
             password = body["password"]
             if not isinstance(password, str) or len(password) > 512:
-                raise SynapseError(400, "Invalid password")
+                raise SynapseError(HTTPStatus.BAD_REQUEST, "Invalid password")
 
             password_bytes = password.encode("utf-8")
             if b"\x00" in password_bytes:
-                raise SynapseError(400, "Invalid password")
+                raise SynapseError(HTTPStatus.BAD_REQUEST, "Invalid password")
 
             password_hash = await self.auth_handler.hash(password)
 
@@ -482,10 +504,12 @@ class UserRegisterServlet(RestServlet):
         displayname = body.get("displayname", None)
 
         if user_type is not None and user_type not in UserTypes.ALL_USER_TYPES:
-            raise SynapseError(400, "Invalid user type")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Invalid user type")
 
         if "mac" not in body:
-            raise SynapseError(400, "mac must be specified", errcode=Codes.BAD_JSON)
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "mac must be specified", errcode=Codes.BAD_JSON
+            )
 
         got_mac = body["mac"]
 
@@ -507,7 +531,7 @@ class UserRegisterServlet(RestServlet):
         want_mac = want_mac_builder.hexdigest()
 
         if not hmac.compare_digest(want_mac.encode("ascii"), got_mac.encode("ascii")):
-            raise SynapseError(403, "HMAC incorrect")
+            raise SynapseError(HTTPStatus.FORBIDDEN, "HMAC incorrect")
 
         # Reuse the parts of RegisterRestServlet to reduce code duplication
         from synapse.rest.client.register import RegisterRestServlet
@@ -524,7 +548,7 @@ class UserRegisterServlet(RestServlet):
         )
 
         result = await register._create_registration_details(user_id, body)
-        return 200, result
+        return HTTPStatus.OK, result
 
 
 class WhoisRestServlet(RestServlet):
@@ -552,11 +576,11 @@ class WhoisRestServlet(RestServlet):
             await assert_user_is_admin(self.auth, auth_user)
 
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Can only whois a local user")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only whois a local user")
 
         ret = await self.admin_handler.get_whois(target_user)
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
 
 class DeactivateAccountRestServlet(RestServlet):
@@ -575,7 +599,9 @@ class DeactivateAccountRestServlet(RestServlet):
         await assert_user_is_admin(self.auth, requester.user)
 
         if not self.is_mine(UserID.from_string(target_user_id)):
-            raise SynapseError(400, "Can only deactivate local users")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Can only deactivate local users"
+            )
 
         if not await self.store.get_user_by_id(target_user_id):
             raise NotFoundError("User not found")
@@ -597,7 +623,7 @@ class DeactivateAccountRestServlet(RestServlet):
         else:
             id_server_unbind_result = "no-support"
 
-        return 200, {"id_server_unbind_result": id_server_unbind_result}
+        return HTTPStatus.OK, {"id_server_unbind_result": id_server_unbind_result}
 
 
 class AccountValidityRenewServlet(RestServlet):
@@ -620,7 +646,7 @@ class AccountValidityRenewServlet(RestServlet):
 
             if "user_id" not in body:
                 raise SynapseError(
-                    400,
+                    HTTPStatus.BAD_REQUEST,
                     "Missing property 'user_id' in the request body",
                 )
 
@@ -631,7 +657,7 @@ class AccountValidityRenewServlet(RestServlet):
             )
 
         res = {"expiration_ts": expiration_ts}
-        return 200, res
+        return HTTPStatus.OK, res
 
 
 class ResetPasswordRestServlet(RestServlet):
@@ -678,7 +704,7 @@ class ResetPasswordRestServlet(RestServlet):
         await self._set_password_handler.set_password(
             target_user_id, new_password_hash, logout_devices, requester
         )
-        return 200, {}
+        return HTTPStatus.OK, {}
 
 
 class SearchUsersRestServlet(RestServlet):
@@ -712,16 +738,16 @@ class SearchUsersRestServlet(RestServlet):
 
         # To allow all users to get the users list
         # if not is_admin and target_user != auth_user:
-        #     raise AuthError(403, "You are not a server admin")
+        #     raise AuthError(HTTPStatus.FORBIDDEN, "You are not a server admin")
 
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Can only users a local user")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only users a local user")
 
         term = parse_string(request, "term", required=True)
         logger.info("term: %s ", term)
 
         ret = await self.store.search_users(term)
-        return 200, ret
+        return HTTPStatus.OK, ret
 
 
 class UserAdminServlet(RestServlet):
@@ -765,11 +791,14 @@ class UserAdminServlet(RestServlet):
         target_user = UserID.from_string(user_id)
 
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Only local users can be admins of this homeserver")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST,
+                "Only local users can be admins of this homeserver",
+            )
 
         is_admin = await self.store.is_server_admin(target_user)
 
-        return 200, {"admin": is_admin}
+        return HTTPStatus.OK, {"admin": is_admin}
 
     async def on_PUT(
         self, request: SynapseRequest, user_id: str
@@ -785,16 +814,19 @@ class UserAdminServlet(RestServlet):
         assert_params_in_dict(body, ["admin"])
 
         if not self.hs.is_mine(target_user):
-            raise SynapseError(400, "Only local users can be admins of this homeserver")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST,
+                "Only local users can be admins of this homeserver",
+            )
 
         set_admin_to = bool(body["admin"])
 
         if target_user == auth_user and not set_admin_to:
-            raise SynapseError(400, "You may not demote yourself.")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "You may not demote yourself.")
 
         await self.store.set_server_admin(target_user, set_admin_to)
 
-        return 200, {}
+        return HTTPStatus.OK, {}
 
 
 class UserMembershipRestServlet(RestServlet):
@@ -816,7 +848,7 @@ class UserMembershipRestServlet(RestServlet):
 
         room_ids = await self.store.get_rooms_for_user(user_id)
         ret = {"joined_rooms": list(room_ids), "total": len(room_ids)}
-        return 200, ret
+        return HTTPStatus.OK, ret
 
 
 class PushersRestServlet(RestServlet):
@@ -845,7 +877,7 @@ class PushersRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if not self.is_mine(UserID.from_string(user_id)):
-            raise SynapseError(400, "Can only look up local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only look up local users")
 
         if not await self.store.get_user_by_id(user_id):
             raise NotFoundError("User not found")
@@ -854,7 +886,10 @@ class PushersRestServlet(RestServlet):
 
         filtered_pushers = [p.as_dict() for p in pushers]
 
-        return 200, {"pushers": filtered_pushers, "total": len(filtered_pushers)}
+        return HTTPStatus.OK, {
+            "pushers": filtered_pushers,
+            "total": len(filtered_pushers),
+        }
 
 
 class UserTokenRestServlet(RestServlet):
@@ -887,16 +922,22 @@ class UserTokenRestServlet(RestServlet):
         auth_user = requester.user
 
         if not self.hs.is_mine_id(user_id):
-            raise SynapseError(400, "Only local users can be logged in as")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Only local users can be logged in as"
+            )
 
         body = parse_json_object_from_request(request, allow_empty_body=True)
 
         valid_until_ms = body.get("valid_until_ms")
         if valid_until_ms and not isinstance(valid_until_ms, int):
-            raise SynapseError(400, "'valid_until_ms' parameter must be an int")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "'valid_until_ms' parameter must be an int"
+            )
 
         if auth_user.to_string() == user_id:
-            raise SynapseError(400, "Cannot use admin API to login as self")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Cannot use admin API to login as self"
+            )
 
         token = await self.auth_handler.create_access_token_for_user_id(
             user_id=auth_user.to_string(),
@@ -905,7 +946,7 @@ class UserTokenRestServlet(RestServlet):
             puppets_user_id=user_id,
         )
 
-        return 200, {"access_token": token}
+        return HTTPStatus.OK, {"access_token": token}
 
 
 class ShadowBanRestServlet(RestServlet):
@@ -947,11 +988,13 @@ class ShadowBanRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if not self.hs.is_mine_id(user_id):
-            raise SynapseError(400, "Only local users can be shadow-banned")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Only local users can be shadow-banned"
+            )
 
         await self.store.set_shadow_banned(UserID.from_string(user_id), True)
 
-        return 200, {}
+        return HTTPStatus.OK, {}
 
     async def on_DELETE(
         self, request: SynapseRequest, user_id: str
@@ -959,11 +1002,13 @@ class ShadowBanRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if not self.hs.is_mine_id(user_id):
-            raise SynapseError(400, "Only local users can be shadow-banned")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Only local users can be shadow-banned"
+            )
 
         await self.store.set_shadow_banned(UserID.from_string(user_id), False)
 
-        return 200, {}
+        return HTTPStatus.OK, {}
 
 
 class RateLimitRestServlet(RestServlet):
@@ -995,7 +1040,7 @@ class RateLimitRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if not self.hs.is_mine_id(user_id):
-            raise SynapseError(400, "Can only look up local users")
+            raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only look up local users")
 
         if not await self.store.get_user_by_id(user_id):
             raise NotFoundError("User not found")
@@ -1016,7 +1061,7 @@ class RateLimitRestServlet(RestServlet):
         else:
             ret = {}
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
     async def on_POST(
         self, request: SynapseRequest, user_id: str
@@ -1024,7 +1069,9 @@ class RateLimitRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if not self.hs.is_mine_id(user_id):
-            raise SynapseError(400, "Only local users can be ratelimited")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Only local users can be ratelimited"
+            )
 
         if not await self.store.get_user_by_id(user_id):
             raise NotFoundError("User not found")
@@ -1036,14 +1083,14 @@ class RateLimitRestServlet(RestServlet):
 
         if not isinstance(messages_per_second, int) or messages_per_second < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "%r parameter must be a positive int" % (messages_per_second,),
                 errcode=Codes.INVALID_PARAM,
             )
 
         if not isinstance(burst_count, int) or burst_count < 0:
             raise SynapseError(
-                400,
+                HTTPStatus.BAD_REQUEST,
                 "%r parameter must be a positive int" % (burst_count,),
                 errcode=Codes.INVALID_PARAM,
             )
@@ -1059,7 +1106,7 @@ class RateLimitRestServlet(RestServlet):
             "burst_count": ratelimit.burst_count,
         }
 
-        return 200, ret
+        return HTTPStatus.OK, ret
 
     async def on_DELETE(
         self, request: SynapseRequest, user_id: str
@@ -1067,11 +1114,13 @@ class RateLimitRestServlet(RestServlet):
         await assert_requester_is_admin(self.auth, request)
 
         if not self.hs.is_mine_id(user_id):
-            raise SynapseError(400, "Only local users can be ratelimited")
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST, "Only local users can be ratelimited"
+            )
 
         if not await self.store.get_user_by_id(user_id):
             raise NotFoundError("User not found")
 
         await self.store.delete_ratelimit_for_user(user_id)
 
-        return 200, {}
+        return HTTPStatus.OK, {}