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, 4 insertions, 3 deletions

diff --git a/synapse/federation/transport/server/federation.py b/synapse/federation/transport/server/federation.py
index 17c427387e..f7ca87adc4 100644
--- a/synapse/federation/transport/server/federation.py
+++ b/synapse/federation/transport/server/federation.py
@@ -26,7 +26,7 @@ from typing import (
 
 from typing_extensions import Literal
 
-from synapse.api.constants import EduTypes
+from synapse.api.constants import Direction, EduTypes
 from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import RoomVersions
 from synapse.api.urls import FEDERATION_UNSTABLE_PREFIX, FEDERATION_V2_PREFIX
@@ -234,9 +234,10 @@ class FederationTimestampLookupServlet(BaseFederationServerServlet):
         room_id: str,
     ) -> Tuple[int, JsonDict]:
         timestamp = parse_integer_from_args(query, "ts", required=True)
-        direction = parse_string_from_args(
-            query, "dir", default="f", allowed_values=["f", "b"], required=True
+        direction_str = parse_string_from_args(
+            query, "dir", allowed_values=["f", "b"], required=True
         )
+        direction = Direction(direction_str)
 
         return await self.handler.on_timestamp_to_event_request(
             origin, room_id, timestamp, direction