Implement MSC4185

Cargo.toml

@@ -147,7 +147,10 @@ xdg = "2.5.2"
 nix = { version = "0.29", features = ["resource"] }
 
 [features]
-default = ["rocksdb", "sqlite", "systemd"]
+# needed for ruma Request/Response derives
+client = []
+server = []
+default = ["rocksdb", "sqlite", "systemd", "server"]
 
 # Keep sorted
 jemalloc = ["dep:tikv-jemallocator"]

src/api/client_server.rs

@@ -6,6 +6,7 @@ mod config;
 mod context;
 mod device;
 mod directory;
+mod event_visibility;
 mod filter;
 mod keys;
 mod media;
@@ -40,6 +41,7 @@ pub(crate) use config::*;
 pub(crate) use context::*;
 pub(crate) use device::*;
 pub(crate) use directory::*;
+pub(crate) use event_visibility::*;
 pub(crate) use filter::*;
 pub(crate) use keys::*;
 pub(crate) use media::*;

src/api/client_server/event_visibility.rs

@@ -0,0 +1,60 @@
+//! Implementation of [MSC4185](https://github.com/matrix-org/matrix-spec-proposals/pull/4185)
+
+use ruma::{
+    api::{request, response, Metadata},
+    metadata, OwnedEventId, OwnedRoomId, OwnedUserId,
+};
+
+use crate::{services, Ar, Ra, Result};
+
+const METADATA: Metadata = metadata! {
+    method: GET,
+    rate_limited: true,
+    authentication: AccessToken,
+
+    history: {
+        unstable => "/_matrix/client/unstable/net.tadzik/can_user_see_event/:room_id/:user_id/:event_id",
+    },
+};
+
+#[request]
+#[allow(clippy::struct_field_names)]
+pub(crate) struct Request {
+    #[ruma_api(path)]
+    pub(crate) room_id: OwnedRoomId,
+
+    #[ruma_api(path)]
+    pub(crate) user_id: OwnedUserId,
+
+    #[ruma_api(path)]
+    pub(crate) event_id: OwnedEventId,
+}
+
+#[response]
+pub(crate) struct Response {
+    #[ruma_api(body)]
+    pub(crate) is_visible: bool,
+}
+
+pub(crate) async fn can_user_see_event_route(
+    body: Ar<Request>,
+) -> Result<Ra<Response>> {
+    let Ok(true) = services().rooms.state_accessor.user_can_see_event(
+        body.sender_user.as_ref().expect("user is authenticated"),
+        &body.room_id,
+        &body.event_id,
+    ) else {
+        return Err(crate::Error::BadRequest(
+            ruma::api::client::error::ErrorKind::Unauthorized,
+            "event is not visible to requesting user",
+        ));
+    };
+
+    Ok(Ra(Response {
+        is_visible: services().rooms.state_accessor.user_can_see_event(
+            &body.user_id,
+            &body.room_id,
+            &body.event_id,
+        )?,
+    }))
+}

src/api/client_server/unversioned.rs

@@ -29,10 +29,10 @@ pub(crate) async fn get_supported_versions_route(
             "v1.4".to_owned(),
             "v1.5".to_owned(),
         ],
-        unstable_features: BTreeMap::from_iter([(
-            "org.matrix.e2e_cross_signing".to_owned(),
-            true,
-        )]),
+        unstable_features: BTreeMap::from_iter([
+            ("org.matrix.e2e_cross_signing".to_owned(), true),
+            ("org.matrix.msc4185".to_owned(), true),
+        ]),
     };
 
     Ok(Ra(resp))

src/main.rs

@@ -414,7 +414,8 @@ fn routes(config: &Config) -> Router {
         .ruma_route(c2s::get_relating_events_with_rel_type_and_event_type_route)
         .ruma_route(c2s::get_relating_events_with_rel_type_route)
         .ruma_route(c2s::get_relating_events_route)
-        .ruma_route(c2s::get_hierarchy_route);
+        .ruma_route(c2s::get_hierarchy_route)
+        .ruma_route(c2s::can_user_see_event_route);
 
     // Ruma doesn't have support for multiple paths for a single endpoint yet,
     // and these routes share one Ruma request / response type pair with