fix: avoid selecting unknown-latency peer conns

easytier/src/peers/peer.rs

@@ -188,37 +188,45 @@ impl Peer {
 
     async fn select_conn(&self) -> Option<ArcPeerConn> {
         let default_conn_id = self.default_conn_id.load();
-        let default_conn = self.conns.get(&default_conn_id).and_then(|conn| {
-            if conn.is_closed() {
-                None
+        let latency_score = |latency_us| {
+            if latency_us == 0 {
+                u64::MAX
             } else {
-                Some((conn.priority(), conn.clone()))
+                latency_us
             }
-        });
-
-        if let Some((default_priority, default_conn)) = default_conn {
-            let has_better_conn = self.conns.iter().any(|conn| {
-                !conn.value().is_closed() && conn.value().priority() < default_priority
-            });
-            if !has_better_conn {
-                return Some(default_conn);
-            }
-        }
-
-        // Prefer lower listener priority first, then use latency to pick the
-        // initial connection within that priority class. Keep the selected conn
-        // sticky until a strictly better priority appears.
-        let selected_conn_id = self
+        };
+        let selected_conn = self
             .conns
             .iter()
             .filter(|conn| !conn.value().is_closed())
-            .min_by_key(|conn| (conn.value().priority(), conn.value().get_stats().latency_us))
-            .map(|conn| conn.get_conn_id());
-
-        selected_conn_id.and_then(|conn_id| {
-            self.default_conn_id.store(conn_id);
-            self.conns.get(&conn_id).map(|conn| conn.clone())
+            .min_by_key(|conn| {
+                (
+                    conn.value().priority(),
+                    latency_score(conn.value().get_stats().latency_us),
+                )
             })
+            .map(|conn| {
+                (
+                    conn.get_conn_id(),
+                    conn.value().priority(),
+                    latency_score(conn.value().get_stats().latency_us),
+                )
+            });
+
+        let (selected_conn_id, selected_priority, selected_latency) = selected_conn?;
+
+        if let Some(default_conn) = self.conns.get(&default_conn_id)
+            && !default_conn.is_closed()
+            && (
+                default_conn.priority(),
+                latency_score(default_conn.get_stats().latency_us),
+            ) == (selected_priority, selected_latency)
+        {
+            return Some(default_conn.clone());
+        }
+
+        self.default_conn_id.store(selected_conn_id);
+        self.conns.get(&selected_conn_id).map(|conn| conn.clone())
     }
 
     pub async fn send_msg(&self, msg: ZCPacket) -> Result<(), Error> {
@@ -409,7 +417,7 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn select_conn_prefers_lower_priority_before_latency() {
+    async fn select_conn_prefers_priority_then_latency() {
         let (packet_send, _packet_recv) = create_packet_recv_chan();
         let global_ctx = get_mock_global_ctx();
         let local_peer_id = new_peer_id();
@@ -425,6 +433,7 @@ mod tests {
             ps.clone(),
         );
         low_client_conn.set_priority(100);
+        low_client_conn.record_latency_for_test(1000);
         let low_conn_id = low_client_conn.get_conn_id();
         let mut low_server_conn = PeerConn::new(
             remote_peer_id,
@@ -449,6 +458,8 @@ mod tests {
             ps.clone(),
         );
         same_priority_client_conn.set_priority(100);
+        same_priority_client_conn.record_latency_for_test(10);
+        let same_priority_conn_id = same_priority_client_conn.get_conn_id();
         let mut same_priority_server_conn = PeerConn::new(
             remote_peer_id,
             global_ctx.clone(),
@@ -462,7 +473,39 @@ mod tests {
         client_ret.unwrap();
         server_ret.unwrap();
         peer.add_peer_conn(same_priority_client_conn).await.unwrap();
-        assert_eq!(peer.select_conn().await.unwrap().get_conn_id(), low_conn_id);
+        assert_eq!(
+            peer.select_conn().await.unwrap().get_conn_id(),
+            same_priority_conn_id
+        );
+
+        let (unknown_latency_client_tunnel, unknown_latency_server_tunnel) =
+            create_ring_tunnel_pair();
+        let mut unknown_latency_client_conn = PeerConn::new(
+            local_peer_id,
+            global_ctx.clone(),
+            unknown_latency_client_tunnel,
+            ps.clone(),
+        );
+        unknown_latency_client_conn.set_priority(100);
+        let mut unknown_latency_server_conn = PeerConn::new(
+            remote_peer_id,
+            global_ctx.clone(),
+            unknown_latency_server_tunnel,
+            ps.clone(),
+        );
+        let (client_ret, server_ret) = tokio::join!(
+            unknown_latency_client_conn.do_handshake_as_client(),
+            unknown_latency_server_conn.do_handshake_as_server()
+        );
+        client_ret.unwrap();
+        server_ret.unwrap();
+        peer.add_peer_conn(unknown_latency_client_conn)
+            .await
+            .unwrap();
+        assert_eq!(
+            peer.select_conn().await.unwrap().get_conn_id(),
+            same_priority_conn_id
+        );
 
         let (high_client_tunnel, high_server_tunnel) = create_ring_tunnel_pair();
         let mut high_client_conn = PeerConn::new(

easytier/src/peers/peer_conn.rs

@@ -452,6 +452,11 @@ impl PeerConn {
         self.priority
     }
 
+    #[cfg(test)]
+    pub(crate) fn record_latency_for_test(&self, latency_us: u32) {
+        self.latency_stats.record_latency(latency_us);
+    }
+
     pub fn is_closed(&self) -> bool {
         self.close_event_notifier.is_closed()
     }