federation-api: Add support to get an event by timestamp

According to MSC3030

crates/ruma-federation-api/CHANGELOG.md

@@ -4,6 +4,10 @@ Bug fixes:
 
 * Add the `event` field to `RoomState` according to MSC3083 / Matrix v1.2
 
+Improvements:
+
+* Add unstable support to get an event by timestamp (MSC3030)
+
 # 0.6.0
 
 Breaking changes:

crates/ruma-federation-api/Cargo.toml

@@ -21,6 +21,7 @@ client = []
 server = []
 unstable-exhaustive-types = []
 unstable-msc2448 = []
+unstable-msc3030 = []
 unstable-msc3618 = []
 unstable-msc3723 = []
 unstable-unspecified = []

crates/ruma-federation-api/src/event.rs

@@ -1,6 +1,8 @@
 //! Endpoints to get general information about events
 
 pub mod get_event;
+#[cfg(feature = "unstable-msc3030")]
+pub mod get_event_by_timestamp;
 pub mod get_missing_events;
 pub mod get_room_state;
 pub mod get_room_state_ids;

crates/ruma-federation-api/src/event/get_event_by_timestamp.rs

@@ -0,0 +1,63 @@
+//! `GET /_matrix/federation/*/timestamp_to_event/{roomId}`
+//!
+//! Get the ID of the event closest to the given timestamp.
+
+pub mod unstable {
+    //! `/unstable/` ([spec])
+    //!
+    //! [spec]: https://github.com/matrix-org/matrix-spec-proposals/pull/3030
+
+    use ruma_common::{
+        api::{request, response, Direction, Metadata},
+        metadata, MilliSecondsSinceUnixEpoch, OwnedEventId, OwnedRoomId,
+    };
+
+    const METADATA: Metadata = metadata! {
+        method: GET,
+        rate_limited: false,
+        authentication: ServerSignatures,
+        history: {
+            unstable => "/_matrix/federation/unstable/org.matrix.msc3030/timestamp_to_event/:room_id",
+        }
+    };
+
+    /// Request type for the `get_event_by_timestamp` endpoint.
+    #[request]
+    pub struct Request {
+        /// The ID of the room the event is in.
+        #[ruma_api(path)]
+        pub room_id: OwnedRoomId,
+
+        /// The timestamp to search from.
+        #[ruma_api(query)]
+        pub ts: MilliSecondsSinceUnixEpoch,
+
+        /// The direction in which to search.
+        #[ruma_api(query)]
+        pub dir: Direction,
+    }
+
+    /// Response type for the `get_event_by_timestamp` endpoint.
+    #[response]
+    pub struct Response {
+        /// The ID of the event found.
+        pub event_id: OwnedEventId,
+
+        /// The event's timestamp.
+        pub origin_server_ts: MilliSecondsSinceUnixEpoch,
+    }
+
+    impl Request {
+        /// Creates a new `Request` with the given room ID, timestamp and direction.
+        pub fn new(room_id: OwnedRoomId, ts: MilliSecondsSinceUnixEpoch, dir: Direction) -> Self {
+            Self { room_id, ts, dir }
+        }
+    }
+
+    impl Response {
+        /// Creates a new `Response` with the given event ID and timestamp.
+        pub fn new(event_id: OwnedEventId, origin_server_ts: MilliSecondsSinceUnixEpoch) -> Self {
+            Self { event_id, origin_server_ts }
+        }
+    }
+}

crates/ruma/Cargo.toml

@@ -135,7 +135,10 @@ unstable-msc2746 = ["ruma-common/unstable-msc2746"]
 unstable-msc2870 = ["ruma-common/unstable-msc2870"]
 unstable-msc2965 = ["ruma-client-api?/unstable-msc2965"]
 unstable-msc2967 = ["ruma-client-api?/unstable-msc2967"]
-unstable-msc3030 = ["ruma-client-api?/unstable-msc3030"]
+unstable-msc3030 = [
+    "ruma-client-api?/unstable-msc3030",
+    "ruma-federation-api?/unstable-msc3030",
+]
 unstable-msc3202 = ["ruma-appservice-api?/unstable-msc3202"]
 unstable-msc3245 = ["ruma-common/unstable-msc3245"]
 unstable-msc3246 = ["ruma-common/unstable-msc3246"]