1 files changed, 16 insertions, 7 deletions

diff --git a/src/document/sync.rs b/src/document/sync.rs
index 2a24007..2119eda 100644
--- a/src/document/sync.rs
+++ b/src/document/sync.rs
@@ -95,6 +95,9 @@ pub(crate) struct SyncReplyWait {
     pub(crate) started: (Instant, SyncBytes),
     /// Changes first sent in the unanswered messages.
     pub(crate) sent: Vec<crate::document::ChangeHash>,
+    /// The largest of them, in bytes: if they go unanswered, messages that large may
+    /// not make it to the peer whole (`PeerState::whole_failed`).
+    pub(crate) largest: usize,
 }
 
 impl SyncSession {
@@ -143,12 +146,13 @@ impl SyncSession {
             .difference(&sent_before)
             .copied()
             .collect();
+        let payload = message.map(|message| SyncPayload(message.encode().into()));
         if in_step {
             self.reply_settled();
-        } else if message.is_some() {
-            self.expect_reply(sent.clone(), now, bytes);
+        } else if let Some(payload) = &payload {
+            self.expect_reply(sent.clone(), now, bytes, payload.0.len());
         }
-        if message.is_some() {
+        if payload.is_some() {
             // Marked together with the generation, so no second message is generated
             // while this one is handed over.
             self.sending = Some(Sending {
@@ -156,7 +160,7 @@ impl SyncSession {
                 regenerate: false,
             });
         }
-        message.map(|message| SyncPayload(message.encode().into()))
+        payload
     }
 
     /// Applies a sync message from the peer to `doc`. Doesn't settle the awaited
@@ -303,22 +307,27 @@ impl SyncSession {
         Some(delay)
     }
 
-    /// A sync message went out; `sent` are the changes it carried for the first time.
-    /// `bytes` are the sync bytes exchanged with the peer before it.
+    /// A sync message of `len` bytes went out; `sent` are the changes it carried for the
+    /// first time. `bytes` are the sync bytes exchanged with the peer before it.
     pub(crate) fn expect_reply(
         &mut self,
         sent: Vec<crate::document::ChangeHash>,
         now: Instant,
         bytes: SyncBytes,
+        len: usize,
     ) {
         match &mut self.reply {
             // Still waiting for an earlier one: keep its deadline, remember these too.
-            Some(wait) => wait.sent.extend(sent),
+            Some(wait) => {
+                wait.sent.extend(sent);
+                wait.largest = wait.largest.max(len);
+            }
             None => {
                 self.reply = Some(SyncReplyWait {
                     deadline: now + self.reply_backoff.current(),
                     started: (now, bytes),
                     sent,
+                    largest: len,
                 });
             }
         }