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.

3 files changed, 7 insertions, 6 deletions

diff --git a/synapse/handlers/account_data.py b/synapse/handlers/account_data.py
index d500b21809..67e789eef7 100644
--- a/synapse/handlers/account_data.py
+++ b/synapse/handlers/account_data.py
@@ -314,7 +314,7 @@ class AccountDataEventSource(EventSource[int, JsonDict]):
     def __init__(self, hs: "HomeServer"):
         self.store = hs.get_datastores().main
 
-    def get_current_key(self, direction: str = "f") -> int:
+    def get_current_key(self) -> int:
         return self.store.get_max_account_data_stream_id()
 
     async def get_new_events(
diff --git a/synapse/handlers/receipts.py b/synapse/handlers/receipts.py
index 6a4fed1156..04c61ae3dd 100644
--- a/synapse/handlers/receipts.py
+++ b/synapse/handlers/receipts.py
@@ -315,5 +315,5 @@ class ReceiptEventSource(EventSource[int, JsonDict]):
 
         return events, to_key
 
-    def get_current_key(self, direction: str = "f") -> int:
+    def get_current_key(self) -> int:
         return self.store.get_max_receipt_stream_id()
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 60a6d9cf3c..7ba7c4ff07 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -27,6 +27,7 @@ from typing_extensions import TypedDict
 
 import synapse.events.snapshot
 from synapse.api.constants import (
+    Direction,
     EventContentFields,
     EventTypes,
     GuestAccess,
@@ -1487,7 +1488,7 @@ class TimestampLookupHandler:
         requester: Requester,
         room_id: str,
         timestamp: int,
-        direction: str,
+        direction: Direction,
     ) -> Tuple[str, int]:
         """Find the closest event to the given timestamp in the given direction.
         If we can't find an event locally or the event we have locally is next to a gap,
@@ -1498,7 +1499,7 @@ class TimestampLookupHandler:
             room_id: Room to fetch the event from
             timestamp: The point in time (inclusive) we should navigate from in
                 the given direction to find the closest event.
-            direction: ["f"|"b"] to indicate whether we should navigate forward
+            direction: indicates whether we should navigate forward
                 or backward from the given timestamp to find the closest event.
 
         Returns:
@@ -1533,13 +1534,13 @@ class TimestampLookupHandler:
                 local_event_id, allow_none=False, allow_rejected=False
             )
 
-            if direction == "f":
+            if direction == Direction.FORWARDS:
                 # We only need to check for a backward gap if we're looking forwards
                 # to ensure there is nothing in between.
                 is_event_next_to_backward_gap = (
                     await self.store.is_event_next_to_backward_gap(local_event)
                 )
-            elif direction == "b":
+            elif direction == Direction.BACKWARDS:
                 # We only need to check for a forward gap if we're looking backwards
                 # to ensure there is nothing in between
                 is_event_next_to_forward_gap = (