From 5e3174493d7dd40c5432eb55a696b8ee75923c22 Mon Sep 17 00:00:00 2001
From: timedout <git@nexy7574.co.uk>
Date: Thu, 26 Feb 2026 16:16:45 +0000
Subject: [PATCH] feat: Add method to flush senders when a server becomes
 active

---
 src/api/router/auth.rs        | 10 +++++++-
 src/service/sending/mod.rs    | 44 +++++++++++++++++++++++++++++++++--
 src/service/sending/sender.rs | 15 +++++++++++-
 3 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/src/api/router/auth.rs b/src/api/router/auth.rs
index 8f48166d..8c72cbb4 100644
--- a/src/api/router/auth.rs
+++ b/src/api/router/auth.rs
@@ -4,7 +4,7 @@ use axum_extra::{
 	headers::{Authorization, authorization::Bearer},
 	typed_header::TypedHeaderRejectionReason,
 };
-use conduwuit::{Err, Error, Result, debug_error, err, warn};
+use conduwuit::{Err, Error, Result, debug_error, debug_info, err, warn};
 use futures::{
 	TryFutureExt,
 	future::{
@@ -329,6 +329,14 @@ async fn auth_server(
 		return Err!(Request(Forbidden("Failed to verify X-Matrix signatures.")));
 	}
 
+	if services.sending.server_is_offline(destination).await {
+		debug_info!(?destination, "server returned from being offline");
+		services
+			.sending
+			.mark_server_online(destination, false)
+			.await;
+	}
+
 	Ok(Auth {
 		origin: origin.to_owned().into(),
 		sender_user: None,
diff --git a/src/service/sending/mod.rs b/src/service/sending/mod.rs
index 7997d532..c60700f9 100644
--- a/src/service/sending/mod.rs
+++ b/src/service/sending/mod.rs
@@ -5,6 +5,7 @@ mod dest;
 mod sender;
 
 use std::{
+	collections::HashSet,
 	fmt::Debug,
 	hash::{DefaultHasher, Hash, Hasher},
 	iter::once,
@@ -19,8 +20,8 @@ use conduwuit::{
 	warn,
 };
 use futures::{FutureExt, Stream, StreamExt};
-use ruma::{RoomId, ServerName, UserId, api::OutgoingRequest};
-use tokio::{task, task::JoinSet};
+use ruma::{OwnedServerName, RoomId, ServerName, UserId, api::OutgoingRequest};
+use tokio::{sync::RwLock, task, task::JoinSet};
 
 use self::data::Data;
 pub use self::{
@@ -37,6 +38,7 @@ pub struct Service {
 	server: Arc<Server>,
 	services: Services,
 	channels: Vec<(loole::Sender<Msg>, loole::Receiver<Msg>)>,
+	pub offline_servers: RwLock<HashSet<OwnedServerName>>,
 }
 
 struct Services {
@@ -52,6 +54,7 @@ struct Services {
 	account_data: Dep<account_data::Service>,
 	appservice: Dep<crate::appservice::Service>,
 	pusher: Dep<pusher::Service>,
+	resolver: Dep<crate::resolver::Service>,
 	federation: Dep<federation::Service>,
 }
 
@@ -96,9 +99,11 @@ impl crate::Service for Service {
 				account_data: args.depend::<account_data::Service>("account_data"),
 				appservice: args.depend::<crate::appservice::Service>("appservice"),
 				pusher: args.depend::<pusher::Service>("pusher"),
+				resolver: args.depend::<crate::resolver::Service>("resolver"),
 				federation: args.depend::<federation::Service>("federation"),
 			},
 			channels: (0..num_senders).map(|_| loole::unbounded()).collect(),
+			offline_servers: RwLock::new(HashSet::new()),
 		}))
 	}
 
@@ -146,6 +151,8 @@ impl crate::Service for Service {
 	fn name(&self) -> &str { crate::service::make_name(std::module_path!()) }
 
 	fn unconstrained(&self) -> bool { true }
+
+	async fn clear_cache(&self) { self.offline_servers.write().await.clear(); }
 }
 
 impl Service {
@@ -379,6 +386,39 @@ impl Service {
 		let chans = self.channels.len().max(1);
 		hash.overflowing_rem(chans).0
 	}
+
+	/// Marks a server as offline
+	pub async fn mark_server_offline(&self, server: OwnedServerName) {
+		self.offline_servers.write().await.insert(server);
+	}
+
+	/// Marks a server as online again and flushes the senders if it was
+	/// previously marked as offline
+	pub async fn mark_server_online(&self, server: &ServerName, skip_flush: bool) {
+		if self.offline_servers.write().await.remove(server) && !skip_flush {
+			// Flush the senders if this server was previously offline
+			self.services.resolver.cache.del_destination(server);
+			self.services.resolver.cache.del_override(server);
+			self.dispatch(Msg {
+				dest: Destination::Federation(server.to_owned()),
+				event: SendingEvent::Flush,
+				queue_id: Vec::<u8>::new(),
+			})
+			.inspect_err(|e| {
+				error!(
+					?server,
+					?e,
+					"failed to dispatch flush message for server coming back online"
+				);
+			})
+			.ok();
+		}
+	}
+
+	/// Checks if a server is currently marked as offline
+	pub async fn server_is_offline(&self, server: &ServerName) -> bool {
+		self.offline_servers.read().await.contains(server)
+	}
 }
 
 fn num_senders(args: &crate::Args<'_>) -> usize {
diff --git a/src/service/sending/sender.rs b/src/service/sending/sender.rs
index 2044dc51..0426a510 100644
--- a/src/service/sending/sender.rs
+++ b/src/service/sending/sender.rs
@@ -9,6 +9,7 @@ use std::{
 };
 
 use base64::{Engine as _, engine::general_purpose::URL_SAFE_NO_PAD};
+use conduwuit::debug_warn;
 use conduwuit_core::{
 	Error, Event, Result, debug, err, error,
 	result::LogErr,
@@ -135,7 +136,13 @@ impl Service {
 	) {
 		match response {
 			| Ok(dest) => self.handle_response_ok(&dest, futures, statuses).await,
-			| Err((dest, e)) => Self::handle_response_err(dest, statuses, &e),
+			| Err((dest, e)) => {
+				Self::handle_response_err(dest.clone(), statuses, &e);
+				if let Destination::Federation(server_name) = dest {
+					debug_warn!(?server_name, "marking server offline due to error: {e:?}");
+					self.mark_server_offline(server_name).await;
+				}
+			},
 		}
 	}
 
@@ -180,6 +187,12 @@ impl Service {
 		} else {
 			statuses.remove(dest);
 		}
+		if let Destination::Federation(server_name) = dest {
+			self.mark_server_online(server_name, true).await;
+			// We skip the flush here because we were already able to contact
+			// the server, and have queued any pending events, and the
+			// resolver cache will be fine.
+		}
 	}
 
 	#[allow(clippy::needless_pass_by_ref_mut)]