Add helper to parse an enum from query args & use it. (#14956)

The `parse_enum` helper pulls an enum value from the query string
(by delegating down to the parse_string helper with values generated
from the enum).

This is used to pull out "f" and "b" in most places and then we thread
the resulting Direction enum throughout more code.

1 files changed, 5 insertions, 11 deletions

diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index e957aa28ca..1d6e4982d7 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -16,13 +16,14 @@ from http import HTTPStatus
 from typing import TYPE_CHECKING, List, Optional, Tuple, cast
 from urllib import parse as urlparse
 
-from synapse.api.constants import EventTypes, JoinRules, Membership
+from synapse.api.constants import Direction, EventTypes, JoinRules, Membership
 from synapse.api.errors import AuthError, Codes, NotFoundError, SynapseError
 from synapse.api.filtering import Filter
 from synapse.http.servlet import (
     ResolveRoomIdMixin,
     RestServlet,
     assert_params_in_dict,
+    parse_enum,
     parse_integer,
     parse_json_object_from_request,
     parse_string,
@@ -224,15 +225,8 @@ class ListRoomRestServlet(RestServlet):
                 errcode=Codes.INVALID_PARAM,
             )
 
-        direction = parse_string(request, "dir", default="f")
-        if direction not in ("f", "b"):
-            raise SynapseError(
-                HTTPStatus.BAD_REQUEST,
-                "Unknown direction: %s" % (direction,),
-                errcode=Codes.INVALID_PARAM,
-            )
-
-        reverse_order = True if direction == "b" else False
+        direction = parse_enum(request, "dir", Direction, default=Direction.FORWARDS)
+        reverse_order = True if direction == Direction.BACKWARDS else False
 
         # Return list of rooms according to parameters
         rooms, total_rooms = await self.store.get_rooms_paginate(
@@ -949,7 +943,7 @@ class RoomTimestampToEventRestServlet(RestServlet):
         await assert_user_is_admin(self._auth, requester)
 
         timestamp = parse_integer(request, "ts", required=True)
-        direction = parse_string(request, "dir", default="f", allowed_values=["f", "b"])
+        direction = parse_enum(request, "dir", Direction, default=Direction.FORWARDS)
 
         (
             event_id,