decode sync messages lazily

Sync messages are now being decoded only where they are applied: after
membership has been checked, in the sync lane's blocking task.

Debug now shows only the size instead of the whole message.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/swarm/sync.rs b/src/swarm/sync.rs
index 0fbff05..ca54fae 100644
--- a/src/swarm/sync.rs
+++ b/src/swarm/sync.rs
@@ -159,7 +159,7 @@ async fn deliver_sync_to_peer(state: &AppState, peer: &str) -> Result<()> {
                     swarm_id,
                     epoch,
                     epoch_seq,
-                    message,
+                    message: transport::SyncPayload::encode(message),
                     ready,
                 };
                 let encoded = transport
@@ -336,6 +336,8 @@ pub(crate) async fn handle_sync(
         // Some((caught_up, heads changed)) when applied, None when the message belongs
         // to another epoch.
         tokio::task::spawn_blocking(move || -> Result<Option<(bool, bool)>> {
+            // Before the lock: decoding a large message takes a while.
+            let message = message.decode()?;
             let mut replica = doc.blocking_write();
 
             // Authoritative check, under the same lock as the apply: the document may