Fix #423: Shield against empty array access after dead peer

Signed-off-by: Lee Smet <lee.smet@hotmail.com>

CHANGELOG.md

@@ -7,18 +7,23 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Fix a panic in the route cleanup task when a peer dies who is the last stored
+  announcer of a subnet.
+
 ## [0.5.5] - 2024-09-27
 
 ### Added
 
 - Mycelium-ui, a standalone GUI which exposes (part of) the mycelium API. This
-  does __not__ have a bundled mycelium node, so that needs to be run separately.
-  
+  does **not** have a bundled mycelium node, so that needs to be run separately.
+
 ### Changed
 
 - Default TUN name on Linux and Windows is now `mycelium`. On MacOS it is now `utun0`.
 - TUN interface name validation on MacOS. If the user supplies an invalid or already
-taken interface name, an available interface name will be automatically assigned.
+  taken interface name, an available interface name will be automatically assigned.
 
 ### Fixed
 

mycelium/src/router.rs

@@ -372,6 +372,8 @@ where
         // If there is no selected route there is nothing to do here. We keep expired routes in the
         // table for a while so updates of those should already have propagated to peers.
         let route_list = routes.routes();
+        // If we have a new selected route we must have at least 1 item in the route list so
+        // accessing the 0th list element here is fine.
         if let Some(new_selected) = self.find_best_route(&route_list).cloned() {
             if new_selected.neighbour() == route_list[0].neighbour() && route_list[0].selected() {
                 debug!(
@@ -389,7 +391,7 @@ where
             }
 
             routes.set_selected(new_selected.neighbour());
-        } else if route_list[0].selected() {
+        } else if !route_list.is_empty() && route_list[0].selected() {
             // This means we went from a selected route to a non-selected route. Unselect route and
             // trigger update.
             // At this point we also send a seqno request to all peers which advertised this route