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, 3 insertions, 9 deletions

diff --git a/synapse/streams/config.py b/synapse/streams/config.py
index 5cb7875181..a044280410 100644
--- a/synapse/streams/config.py
+++ b/synapse/streams/config.py
@@ -18,7 +18,7 @@ import attr
 
 from synapse.api.constants import Direction
 from synapse.api.errors import SynapseError
-from synapse.http.servlet import parse_integer, parse_string
+from synapse.http.servlet import parse_enum, parse_integer, parse_string
 from synapse.http.site import SynapseRequest
 from synapse.storage.databases.main import DataStore
 from synapse.types import StreamToken
@@ -44,15 +44,9 @@ class PaginationConfig:
         store: "DataStore",
         request: SynapseRequest,
         default_limit: int,
-        default_dir: str = "f",
+        default_dir: Direction = Direction.FORWARDS,
     ) -> "PaginationConfig":
-        direction_str = parse_string(
-            request,
-            "dir",
-            default=default_dir,
-            allowed_values=[Direction.FORWARDS.value, Direction.BACKWARDS.value],
-        )
-        direction = Direction(direction_str)
+        direction = parse_enum(request, "dir", Direction, default=default_dir)
 
         from_tok_str = parse_string(request, "from")
         to_tok_str = parse_string(request, "to")