sync: a write between signing and making a message signed too

Review 4, F10: a sync message signed the node's latest change under the document's
write lock (`sign_sent`), then was made under its read lock: a write committed in
between went in the message unsigned, and under a policy requiring signatures waited at
the peer until the next signed change came with it, or a resend.

Now the message is made under a read lock taken after signing, and if a write came in
between (`AppState::sign_due` again under that lock), signed again: a few times at
most, past them it goes as before, its signature with the next message.

1 files changed, 12 insertions, 6 deletions

diff --git a/src/state/mod.rs b/src/state/mod.rs
index 2fbfd31..601febc 100644
--- a/src/state/mod.rs
+++ b/src/state/mod.rs
@@ -734,12 +734,7 @@ impl AppState {
         if self.sign_every == SignEvery::Change {
             return;
         }
-        let due = {
-            let replica = doc.blocking_read();
-            replica.signatures.pending()
-                && (self.sign_every == SignEvery::Sent
-                    || crate::access::policy::of(&replica.doc).required())
-        };
+        let due = self.sign_due(&doc.blocking_read());
         if due {
             let mut replica = doc.blocking_write();
             let replica = &mut *replica;
@@ -747,6 +742,17 @@ impl AppState {
         }
     }
 
+    /// Whether `replica`'s latest change of this node should be signed before a message
+    /// takes it (`sign_sent`): no signature vouches for it, and `--sign-every sent` or a
+    /// policy requiring signatures says so.
+    pub(crate) fn sign_due(&self, replica: &crate::document::replica::Replica) -> bool {
+        self.node_key.is_some()
+            && self.sign_every != SignEvery::Change
+            && replica.signatures.pending()
+            && (self.sign_every == SignEvery::Sent
+                || crate::access::policy::of(&replica.doc).required())
+    }
+
     pub(crate) fn publish_change(&self) {
         self.notify_store_changed();
         if let Err(error) = self.sync_events.send(SyncEvent::DocumentChanged) {