Improve backfill server selection post-v12 power and creator changes.

Signed-off-by: Jason Volk <jason@zemos.net>

src/service/rooms/timeline/backfill.rs

@@ -1,15 +1,12 @@
-use std::iter::once;
+use std::{collections::HashSet, iter::once};
 
 use futures::{
 	FutureExt, StreamExt, TryFutureExt,
 	future::{join, try_join, try_join4},
 };
+use rand::seq::SliceRandom;
 use ruma::{
-	CanonicalJsonObject, EventId, RoomId, ServerName,
-	api::federation,
-	events::{
-		StateEventType, TimelineEventType, room::power_levels::RoomPowerLevelsEventContent,
-	},
+	CanonicalJsonObject, EventId, RoomId, ServerName, api::federation, events::TimelineEventType,
 	uint,
 };
 use serde_json::value::RawValue as RawJsonValue;
@@ -20,8 +17,8 @@ use tuwunel_core::{
 		pdu::{PduCount, PduId, RawPduId},
 	},
 	utils::{
-		IterStream, ReadyExt,
-		future::{BoolExt, TryExtExt},
+		BoolExt, IterStream, ReadyExt,
+		future::{BoolExt as FutureBoolExt, TryExtExt},
 	},
 	validated, warn,
 };
@@ -72,19 +69,43 @@ pub async fn backfill_if_required(&self, room_id: &RoomId, from: PduCount) -> Re
 	let power_levels = self
 		.services
 		.state_accessor
-		.room_state_get_content(room_id, &StateEventType::RoomPowerLevels, "")
-		.map_ok(|content: RoomPowerLevelsEventContent| content)
-		.unwrap_or_default();
+		.get_power_levels(room_id);
 
 	let (canonical_alias, power_levels) = join(canonical_alias, power_levels).await;
 
-	let room_mods = power_levels
-		.users
+	let power_servers = power_levels
 		.iter()
-		.filter_map(|(user_id, level)| {
-			(*level > power_levels.users_default && !self.services.globals.user_is_local(user_id))
+		.flat_map(|power| {
+			power
+				.rules
+				.privileged_creators
+				.iter()
+				.flat_map(|creators| creators.iter())
+		})
+		.chain(power_levels.iter().flat_map(|power| {
+			power
+				.users
+				.iter()
+				.filter_map(|(user_id, level)| level.gt(&power.users_default).then_some(user_id))
+		}))
+		.filter_map(|user_id| {
+			self.services
+				.globals
+				.user_is_local(user_id)
+				.is_false()
 				.then_some(user_id.server_name())
-		});
+		})
+		.collect::<HashSet<_>>();
+
+	let power_servers = {
+		let mut vec: Vec<_> = power_servers
+			.into_iter()
+			.map(ToOwned::to_owned)
+			.collect();
+
+		vec.shuffle(&mut rand::thread_rng());
+		vec.into_iter().stream()
+	};
 
 	let canonical_room_alias_server = once(canonical_alias)
 		.filter_map(Result::ok)
@@ -100,9 +121,7 @@ pub async fn backfill_if_required(&self, room_id: &RoomId, from: PduCount) -> Re
 		.map(ToOwned::to_owned)
 		.stream();
 
-	let mut servers = room_mods
-		.stream()
-		.map(ToOwned::to_owned)
+	let mut servers = power_servers
 		.chain(canonical_room_alias_server)
 		.chain(trusted_servers)
 		.ready_filter(|server_name| !self.services.globals.server_is_ours(server_name))