offer answers

2 files changed, 21 insertions, 0 deletions

diff --git a/src/document/sync.rs b/src/document/sync.rs
index 7695b82..c703300 100644
--- a/src/document/sync.rs
+++ b/src/document/sync.rs
@@ -870,6 +870,16 @@ impl SyncSession {
         self.reply_backoff.reset();
     }
 
+    /// The peer answered our message with a delta offer (`SyncBody::Delta`): the wait
+    /// ends, and to Automerge no message of ours is in flight any more, as an answer of
+    /// its own would have told it. Else, with our heads unchanged (an offer we don't
+    /// fetch, or a download that fails), it would say nothing again, and the peer would
+    /// never hear what we have to offer afresh.
+    pub(crate) fn answered_by_offer(&mut self) {
+        self.reply_settled();
+        self.state.in_flight = false;
+    }
+
     /// If the answer is overdue: forgets that the unanswered changes were sent and that
     /// a message is in flight, so the next sync pass sends them again. Returns how many
     /// changes that concerns.
diff --git a/src/swarm/sync.rs b/src/swarm/sync.rs
index e551cb8..0edc277 100644
--- a/src/swarm/sync.rs
+++ b/src/swarm/sync.rs
@@ -487,6 +487,17 @@ pub(crate) async fn handle_sync(
             )
         }
         transport::SyncBody::Delta(spec) => {
+            // An offer answers what we sent as much as a message would: the wait for an
+            // answer ends here, not when the download does (its reply timeout would
+            // otherwise count against a peer that answered, suspect its path and give it
+            // up as the source to catch up from). What it offers is what it has.
+            {
+                let mut peer_state = peer_state_mutex.lock().await;
+                peer_state.reports_ready = Some(from_ready);
+                peer_state.last_heads = Some((epoch, transport::HeadsSummary::of(spec.to.clone())));
+                peer_state.last_sync_rx = Some(Instant::now());
+                peer_state.sync.answered_by_offer();
+            }
             fetch_delta(state, peer, epoch, spec);
             return Ok(());
         }