From 4b6e257263f7bb6eaebb9be672f88bda85c77586 Mon Sep 17 00:00:00 2001
From: Aria <me@aria.rip>
Date: Fri, 20 Oct 2023 00:33:52 +0100
Subject: broadcast batching with minimal set of messages needed

---
 broadcast/src/topology.rs | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

(limited to 'broadcast/src/topology.rs')

diff --git a/broadcast/src/topology.rs b/broadcast/src/topology.rs
index 5e16666..bb10466 100644
--- a/broadcast/src/topology.rs
+++ b/broadcast/src/topology.rs
@@ -14,16 +14,40 @@ impl Topology {
         for node_id in node_ids.iter() {
             top.insert(node_id.clone(), node_ids.iter().cloned().collect());
         }
+        Self::filter_desc(&mut top);
 
         Topology(RwLock::new(top))
     }
 
     /// Replace the current topology with a new one.
-    pub async fn replace(&self, new: TopologyDesc) {
+    pub async fn replace(&self, mut new: TopologyDesc) {
+        Self::filter_desc(&mut new);
         *self.0.write().await = new;
     }
 
-    pub async fn all_targets(&self, node_id: &NodeId) -> HashSet<String> {
-        self.0.read().await.get(node_id).unwrap().clone()
+    fn filter_desc(desc: &mut TopologyDesc) {
+        for (node_id, neighbours) in desc.iter_mut() {
+            neighbours.remove(node_id);
+        }
+    }
+
+    /// Get the next targets from the given topology, for a message
+    /// which has travelled across the given path and is now at node_id.
+    pub async fn targets(&self, node_id: &String, last_node_id: &String) -> HashSet<String> {
+        // Ensure we don't keep holding the read lock
+        let topology = self.0.read().await;
+
+        // Get all nodes the last node sent it to
+        let visited = topology.get(last_node_id);
+
+        let neighbours = topology.get(node_id).unwrap();
+        match visited {
+            Some(visited) => neighbours
+                .difference(&visited)
+                .cloned()
+                .filter(|n| n != node_id)
+                .collect(),
+            None => neighbours.clone(),
+        }
     }
 }
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