From 120ab1d0688d82028d0ccbb041d74143a58d0a21 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Wed, 19 Nov 2025 03:07:15 +0000
Subject: [PATCH] Add config circuit-breaker for heroes calculations during
 sync.

Signed-off-by: Jason Volk <jason@zemos.net>
---
 src/api/client/sync/v3.rs       |  5 ++++-
 src/api/client/sync/v5/rooms.rs | 30 +++++++++++++++++++-----------
 src/core/config/mod.rs          | 11 +++++++++++
 tuwunel-example.toml            | 11 +++++++++++
 4 files changed, 45 insertions(+), 12 deletions(-)

diff --git a/src/api/client/sync/v3.rs b/src/api/client/sync/v3.rs
index 40430cf6..c40a73b9 100644
--- a/src/api/client/sync/v3.rs
+++ b/src/api/client/sync/v3.rs
@@ -1262,7 +1262,10 @@ async fn calculate_counts(
 
 	let small_room = joined_member_count.saturating_add(invited_member_count) <= 5;
 
-	let heroes: OptionFuture<_> = small_room
+	let heroes: OptionFuture<_> = services
+		.config
+		.calculate_heroes
+		.and_is(small_room)
 		.then(|| calculate_heroes(services, room_id, sender_user))
 		.into();
 
diff --git a/src/api/client/sync/v5/rooms.rs b/src/api/client/sync/v5/rooms.rs
index 1e1cf598..f9d9e41c 100644
--- a/src/api/client/sync/v5/rooms.rs
+++ b/src/api/client/sync/v5/rooms.rs
@@ -327,20 +327,27 @@ async fn handle_room(
 		.boxed()
 		.await;
 
-	let (heroes, hero_name, heroes_avatar) = calculate_heroes(
-		services,
-		sender_user,
-		room_id,
-		room_name.as_ref(),
-		room_avatar.as_deref(),
-	)
-	.await?;
+	let heroes: OptionFuture<_> = services
+		.config
+		.calculate_heroes
+		.then(|| {
+			calculate_heroes(
+				services,
+				sender_user,
+				room_id,
+				room_name.as_ref(),
+				room_avatar.as_deref(),
+			)
+		})
+		.into();
+
+	let (heroes, heroes_name, heroes_avatar) = heroes.await.unwrap_or_default();
 
 	Ok(response::Room {
 		initial: roomsince.eq(&0).then_some(true),
 		lists: lists.clone(),
 		membership: membership.clone(),
-		name: room_name.or(hero_name),
+		name: room_name.or(heroes_name),
 		avatar: JsOption::from_option(room_avatar.or(heroes_avatar)),
 		is_dm,
 		heroes,
@@ -365,8 +372,9 @@ async fn calculate_heroes(
 	room_id: &RoomId,
 	room_name: Option<&DisplayName>,
 	room_avatar: Option<&MxcUri>,
-) -> Result<(Option<Heroes>, Option<DisplayName>, Option<OwnedMxcUri>)> {
+) -> (Option<Heroes>, Option<DisplayName>, Option<OwnedMxcUri>) {
 	const MAX_HEROES: usize = 5;
+
 	let heroes: Heroes = services
 		.state_cache
 		.room_members(room_id)
@@ -443,5 +451,5 @@ async fn calculate_heroes(
 		})
 		.flatten();
 
-	Ok((Some(heroes), hero_name, heroes_avatar))
+	(Some(heroes), hero_name, heroes_avatar)
 }
diff --git a/src/core/config/mod.rs b/src/core/config/mod.rs
index 998b3fb1..6e7b44b3 100644
--- a/src/core/config/mod.rs
+++ b/src/core/config/mod.rs
@@ -1336,6 +1336,17 @@ pub struct Config {
 	#[serde(default)]
 	pub push_everything: bool,
 
+	/// Setting to false disables the heroes calculation made by sliding and
+	/// legacy client sync. The heroes calculation is mandated by the Matrix
+	/// specification and your client may not operate properly unless this
+	/// option is set to true.
+	///
+	/// This option is intended for custom software deployments seeking purely
+	/// to minimize unused resources; the overall savings are otherwise
+	/// negligible.
+	#[serde(default = "true_fn")]
+	pub calculate_heroes: bool,
+
 	/// Allow local (your server only) presence updates/requests.
 	///
 	/// Note that presence on tuwunel is very fast unlike Synapse's. If using
diff --git a/tuwunel-example.toml b/tuwunel-example.toml
index d7926cbb..7f10476a 100644
--- a/tuwunel-example.toml
+++ b/tuwunel-example.toml
@@ -1136,6 +1136,17 @@
 #
 #push_everything = false
 
+# Setting to false disables the heroes calculation made by sliding and
+# legacy client sync. The heroes calculation is mandated by the Matrix
+# specification and your client may not operate properly unless this
+# option is set to true.
+#
+# This option is intended for custom software deployments seeking purely
+# to minimize unused resources; the overall savings are otherwise
+# negligible.
+#
+#calculate_heroes = true
+
 # Allow local (your server only) presence updates/requests.
 #
 # Note that presence on tuwunel is very fast unlike Synapse's. If using