delta known to sender

2 files changed, 14 insertions, 6 deletions

diff --git a/src/document/sync.rs b/src/document/sync.rs
index e921b22..2921bb9 100644
--- a/src/document/sync.rs
+++ b/src/document/sync.rs
@@ -347,11 +347,13 @@ impl SyncSession {
     }
 
     /// The changes since `before` in `doc` came from the peer (we just applied its
-    /// message): it has them, so they never go back to it. Automerge goes by what it
-    /// last heard the peer has, and a message that overtook another makes that older
-    /// than what the peer sent since: the answer would carry the peer's own changes
-    /// back. Counted as sent (`sent_hashes`), they don't; Automerge forgets them as sent
-    /// once the peer's heads cover them. (Changes kept until their predecessors came,
+    /// message, or a delta it offered): it has them, so they never go back to it.
+    /// Automerge goes by what it last heard the peer has, and a message that overtook
+    /// another makes that older than what the peer sent since: the answer would carry
+    /// the peer's own changes back. A delta comes outside the sync protocol, so
+    /// Automerge would think the peer lacks all of it, and offer it back as a delta of
+    /// our own. Counted as sent (`sent_hashes`), they don't; Automerge forgets them as
+    /// sent once the peer's heads cover them. (Changes kept until their predecessors came,
     /// from another peer, count too: should this one lack them, it asks, and gets them,
     /// `resend_if_needed`.)
     pub(crate) fn came_from_peer(
diff --git a/src/swarm/sync.rs b/src/swarm/sync.rs
index dcb29a7..8059fe2 100644
--- a/src/swarm/sync.rs
+++ b/src/swarm/sync.rs
@@ -663,8 +663,14 @@ async fn download_and_apply_delta(
             stats.propagated(delays);
         }
         if let Some(peer_state) = peer_state {
+            let mut peer_state = peer_state.blocking_lock();
             // Sync from it made progress: no heal for a while (`keepalive`).
-            peer_state.blocking_lock().last_sync_rx = Some(Instant::now());
+            peer_state.last_sync_rx = Some(Instant::now());
+            if changed {
+                // From its history: none goes back (`SyncSession::came_from_peer`), nor
+                // is offered back as a delta.
+                peer_state.sync.came_from_peer(&replica.doc, &heads_before);
+            }
         }
         Ok(changed)
     })