number handshakes

This prevents late hellos from resetting the session.

1 files changed, 14 insertions, 1 deletions

diff --git a/src/swarm/peer/inbound.rs b/src/swarm/peer/inbound.rs
index 040cafb..684a358 100644
--- a/src/swarm/peer/inbound.rs
+++ b/src/swarm/peer/inbound.rs
@@ -84,7 +84,20 @@ pub(crate) async fn handle_message(
                     bail!("Incompatible swarm at {peer}: ours is {swarm_id}, it claims {theirs}");
                 }
             }
-            establish_peer(state, &peer, swarm_id, true, hello.ready).await?;
+            // A resent HELLO (our reply was lost) or a late copy of one repeats a
+            // handshake we answered already: it must not reset the session again.
+            let new_handshake = {
+                let peer_state = state.get_or_create_peer_state(&peer).await;
+                let mut peer_state = peer_state.lock().await;
+                let new = peer_state.last_hello.is_none_or(|(run, handshake)| {
+                    run != hello.run_id || hello.handshake > handshake
+                });
+                if new {
+                    peer_state.last_hello = Some((hello.run_id, hello.handshake));
+                }
+                new
+            };
+            establish_peer(state, &peer, swarm_id, new_handshake, hello.ready).await?;
 
             let away = previously_seen.map(|seen| seen.elapsed());
             if let Err(error) = send_hello_reply(state, &peer, hello.run_id, away).await {