1 files changed, 41 insertions, 0 deletions
diff --git a/synapse/federation/transport/server/federation.py b/synapse/federation/transport/server/federation.py
index 66e915228c..77bfd88ad0 100644
--- a/synapse/federation/transport/server/federation.py
+++ b/synapse/federation/transport/server/federation.py
@@ -174,6 +174,46 @@ class FederationBackfillServlet(BaseFederationServerServlet):
         return await self.handler.on_backfill_request(origin, room_id, versions, limit)
 
 
+class FederationTimestampLookupServlet(BaseFederationServerServlet):
+    """
+    API endpoint to fetch the `event_id` of the closest event to the given
+    timestamp (`ts` query parameter) in the given direction (`dir` query
+    parameter).
+
+    Useful for other homeservers when they're unable to find an event locally.
+
+    `ts` is a timestamp in milliseconds where we will find the closest event in
+    the given direction.
+
+    `dir` can be `f` or `b` to indicate forwards and backwards in time from the
+    given timestamp.
+
+    GET /_matrix/federation/unstable/org.matrix.msc3030/timestamp_to_event/<roomID>?ts=<timestamp>&dir=<direction>
+    {
+        "event_id": ...
+    }
+    """
+
+    PATH = "/timestamp_to_event/(?P<room_id>[^/]*)/?"
+    PREFIX = FEDERATION_UNSTABLE_PREFIX + "/org.matrix.msc3030"
+
+    async def on_GET(
+        self,
+        origin: str,
+        content: Literal[None],
+        query: Dict[bytes, List[bytes]],
+        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
+        )
+
+        return await self.handler.on_timestamp_to_event_request(
+            origin, room_id, timestamp, direction
+        )
+
+
 class FederationQueryServlet(BaseFederationServerServlet):
     PATH = "/query/(?P<query_type>[^/]*)"
 
@@ -683,6 +723,7 @@ FEDERATION_SERVLET_CLASSES: Tuple[Type[BaseFederationServlet], ...] = (
     FederationStateV1Servlet,
     FederationStateIdsServlet,
     FederationBackfillServlet,
+    FederationTimestampLookupServlet,
     FederationQueryServlet,
     FederationMakeJoinServlet,
     FederationMakeLeaveServlet,