From d221491377b7e170e8ace28336be79e9de290306 Mon Sep 17 00:00:00 2001
From: nexy7574 <git@nexy7574.co.uk>
Date: Tue, 2 Sep 2025 02:21:34 +0100
Subject: [PATCH] fix(hydra): Backfill server selection in v12

---
 src/service/rooms/timeline/backfill.rs | 56 ++++++++++++++++++++++----
 1 file changed, 49 insertions(+), 7 deletions(-)

diff --git a/src/service/rooms/timeline/backfill.rs b/src/service/rooms/timeline/backfill.rs
index 391e7545..5b70a02e 100644
--- a/src/service/rooms/timeline/backfill.rs
+++ b/src/service/rooms/timeline/backfill.rs
@@ -1,20 +1,23 @@
 use std::iter::once;
 
+use conduwuit::RoomVersion;
 use conduwuit_core::{
 	Result, debug, debug_warn, implement, info,
 	matrix::{
 		event::Event,
 		pdu::{PduCount, PduId, RawPduId},
 	},
+	trace,
 	utils::{IterStream, ReadyExt},
 	validated, warn,
 };
 use futures::{FutureExt, StreamExt};
 use ruma::{
-	RoomId, ServerName,
+	Int, RoomId, ServerName,
 	api::federation,
 	events::{
-		StateEventType, TimelineEventType, room::power_levels::RoomPowerLevelsEventContent,
+		StateEventType, TimelineEventType,
+		room::{create::RoomCreateEventContent, power_levels::RoomPowerLevelsEventContent},
 	},
 	uint,
 };
@@ -23,7 +26,7 @@ use serde_json::value::RawValue as RawJsonValue;
 use super::ExtractBody;
 
 #[implement(super::Service)]
-#[tracing::instrument(name = "backfill", level = "debug", skip(self))]
+#[tracing::instrument(name = "backfill", level = "trace", skip(self))]
 pub async fn backfill_if_required(&self, room_id: &RoomId, from: PduCount) -> Result<()> {
 	if self
 		.services
@@ -59,11 +62,47 @@ pub async fn backfill_if_required(&self, room_id: &RoomId, from: PduCount) -> Re
 		.room_state_get_content(room_id, &StateEventType::RoomPowerLevels, "")
 		.await
 		.unwrap_or_default();
+	let create_event_content: RoomCreateEventContent = self
+		.services
+		.state_accessor
+		.room_state_get_content(room_id, &StateEventType::RoomCreate, "")
+		.await?;
+	let create_event = self
+		.services
+		.state_accessor
+		.room_state_get(room_id, &StateEventType::RoomCreate, "")
+		.await?;
 
-	let room_mods = power_levels.users.iter().filter_map(|(user_id, level)| {
-		if level > &power_levels.users_default && !self.services.globals.user_is_local(user_id) {
+	let room_version =
+		RoomVersion::new(&create_event_content.room_version).expect("supported room version");
+	let mut users = power_levels.users.clone();
+	if room_version.explicitly_privilege_room_creators {
+		users.insert(create_event.sender().to_owned(), Int::MAX);
+		if let Some(additional_creators) = &create_event_content.additional_creators {
+			for user_id in additional_creators {
+				users.insert(user_id.to_owned(), Int::MAX);
+			}
+		}
+	}
+
+	let room_mods = users.iter().filter_map(|(user_id, level)| {
+		let remote_powered =
+			level > &power_levels.users_default && !self.services.globals.user_is_local(user_id);
+		let creator = if room_version.explicitly_privilege_room_creators {
+			create_event.sender() == user_id
+				|| create_event_content
+					.additional_creators
+					.as_ref()
+					.is_some_and(|c| c.contains(user_id))
+		} else {
+			false
+		};
+
+		if remote_powered || creator {
+			debug!(%remote_powered, %creator, "User {user_id} can backfill in room {room_id}");
 			Some(user_id.server_name())
 		} else {
+			debug!(%remote_powered, %creator, "User {user_id} cannot backfill in room {room_id}");
 			None
 		}
 	});
@@ -93,11 +132,14 @@ pub async fn backfill_if_required(&self, room_id: &RoomId, from: PduCount) -> Re
 		)
 		.ready_filter(|server_name| !self.services.globals.server_is_ours(server_name))
 		.filter_map(|server_name| async move {
-			self.services
+			let sn = self
+				.services
 				.state_cache
 				.server_in_room(&server_name, room_id)
 				.await
-				.then_some(server_name)
+				.then_some(server_name.clone());
+			trace!(server_name = ?server_name.clone(), "Considering server for backfill");
+			sn
 		})
 		.boxed();