feat!: add sibling key to Event::EldersChanged

BREAKING CHANGE: added new field to the `Event::EldersChanged` variant.

examples/minimal.rs

@@ -243,12 +243,13 @@ async fn handle_event(index: usize, node: &mut Routing, event: Event) -> bool {
         Event::EldersChanged {
             prefix,
             key,
+            sibling_key,
             elders,
             self_status_change,
         } => {
             info!(
-                "Node #{} elders changed - prefix: {:b}, key: {:?}, elders: {:?}. Node elder status change: {:?}",
-                index, prefix, key, elders, self_status_change
+                "Node #{} elders changed - prefix: {:b}, key: {:?}, sibling key: {:?}, elders: {:?}, node elder status change: {:?}",
+                index, prefix, key, sibling_key, elders, self_status_change
             );
         }
         Event::MessageReceived { content, src, dst } => info!(

examples/stress.rs

@@ -303,6 +303,7 @@ impl Network {
                     key,
                     elders,
                     self_status_change,
+                    ..
                 } => {
                     if let Some(Node::Joined {
                         name,

src/event.rs

@@ -74,6 +74,9 @@ pub enum Event {
         prefix: Prefix,
         /// The BLS public key of our section.
         key: bls::PublicKey,
+        /// The BLS public key of the sibling section, if this event is fired during a split.
+        /// Otherwise `None`.
+        sibling_key: Option<bls::PublicKey>,
         /// The set of elders of our section.
         elders: BTreeSet<XorName>,
         /// Promoted, demoted or no change?
@@ -137,12 +140,14 @@ impl Debug for Event {
             Self::EldersChanged {
                 prefix,
                 key,
+                sibling_key,
                 elders,
                 self_status_change,
             } => formatter
                 .debug_struct("EldersChanged")
                 .field("prefix", prefix)
                 .field("key", key)
+                .field("sibling_key", sibling_key)
                 .field("elders", elders)
                 .field("self_status_change", self_status_change)
                 .finish(),

src/network/mod.rs

@@ -170,6 +170,14 @@ impl Network {
         self.keys.get_matching(name).map(|entry| &entry.value.1)
     }
 
+    /// Returns the latest known key for a section with `prefix`.
+    /// If this returns `None` that means the latest known key is the genesis key.
+    pub fn key_by_prefix(&self, prefix: &Prefix) -> Option<&bls::PublicKey> {
+        self.keys
+            .get_equal_or_ancestor(prefix)
+            .map(|entry| &entry.value.1)
+    }
+
     /// Returns the elders_info and the latest known key for the prefix that matches `name`,
     /// excluding self section.
     pub fn section_by_name(&self, name: &XorName) -> (Option<bls::PublicKey>, Option<EldersInfo>) {

src/routing/approved.rs

@@ -1691,9 +1691,21 @@ impl Approved {
                 NodeElderChange::None
             };
 
+            let sibling_key = if new_prefix != old_prefix {
+                Some(
+                    *self
+                        .network
+                        .key_by_prefix(&new_prefix.sibling())
+                        .unwrap_or_else(|| self.section.chain().last_key()),
+                )
+            } else {
+                None
+            };
+
             self.send_event(Event::EldersChanged {
                 prefix: *self.section.prefix(),
                 key: *self.section.chain().last_key(),
+                sibling_key,
                 elders: self.section.elders_info().elders.keys().copied().collect(),
                 self_status_change,
             });

src/routing/mod.rs

@@ -108,6 +108,7 @@ impl Routing {
             state.send_event(Event::EldersChanged {
                 prefix: *section.prefix(),
                 key: *section.chain().last_key(),
+                sibling_key: None,
                 elders: section.elders_info().elders.keys().copied().collect(),
                 self_status_change: NodeElderChange::Promoted,
             });