optimize the condition of enabling kcp (#1210)

easytier/src/peers/peer_manager.rs

@@ -1360,6 +1360,38 @@ impl PeerManager {
         tracing::info!("close_peer_conn in foreign network manager done: {:?}", ret);
         ret
     }
+
+    pub async fn check_allow_kcp_to_dst(&self, dst_ip: &IpAddr) -> bool {
+        let route = self.get_route();
+        let Some(dst_peer_id) = route.get_peer_id_by_ip(dst_ip).await else {
+            return false;
+        };
+        let Some(peer_info) = route.get_peer_info(dst_peer_id).await else {
+            return false;
+        };
+
+        // check dst allow kcp input
+        if !peer_info.feature_flag.map(|x| x.kcp_input).unwrap_or(false) {
+            return false;
+        }
+
+        let next_hop_policy = Self::get_next_hop_policy( self.global_ctx.get_flags().latency_first);
+        // check relay node allow relay kcp.
+        let Some(next_hop_id) = route.get_next_hop_with_policy(dst_peer_id, next_hop_policy).await else {
+            return false;
+        };
+
+        let Some(next_hop_info) = route.get_peer_info(next_hop_id).await else {
+            return false;
+        };
+
+        // check next hop allow kcp relay
+        if next_hop_info.feature_flag.map(|x| x.no_relay_kcp).unwrap_or(false) {
+            return false;
+        }
+
+        true
+    }
 }
 
 #[cfg(test)]