answering behind counted

1 files changed, 7 insertions, 2 deletions

diff --git a/src/swarm/sync.rs b/src/swarm/sync.rs
index c969678..5100b98 100644
--- a/src/swarm/sync.rs
+++ b/src/swarm/sync.rs
@@ -603,10 +603,15 @@ pub(crate) async fn handle_sync(
             let heads_after = replica.heads().to_vec();
             if delivered {
                 // Level with the sender now, which takes the message as delivered:
-                // nothing to answer (`SyncSession::answered_as_delivered`).
-                peer_state
+                // nothing to answer (`SyncSession::answered_as_delivered`). Unless it is
+                // behind us: then the answer brings it what it lacks.
+                let behind = peer_state.sync.peer_behind(&replica.doc, &heads_after);
+                let answered = peer_state
                     .sync
                     .answered_as_delivered(&replica.doc, &heads_after);
+                if behind && !answered {
+                    stats.answering_behind();
+                }
             }
             stats.heads_seen(heads_after.len());
             let changed = heads_after != heads_before;