use only ready peers as sync source

Sync messages now carries a ready flag, telling whether the sending peer
itself is joined or is itself still (re-)joining.  In the latter case,
the peer won't be used as sync source.

2 files changed, 9 insertions, 0 deletions

diff --git a/src/transport/mod.rs b/src/transport/mod.rs
index 69d9e70..eeba47f 100644
--- a/src/transport/mod.rs
+++ b/src/transport/mod.rs
@@ -62,6 +62,10 @@ pub struct SyncEnvelope {
     /// Epoch of the document the message was generated from.
     pub epoch: Epoch,
     pub message: Message,
+    /// The sender was ready when it generated the message: its document is the swarm's,
+    /// not one it is still filling (joining, rejoining). Only such a peer can tell a
+    /// catching-up node that it has everything; an empty document says nothing else.
+    pub ready: bool,
 }
 
 /// A message serialized for the wire. Cloning is cheap (shared buffer).
diff --git a/src/transport/mycelium.rs b/src/transport/mycelium.rs
index 84a34ea..193beaa 100644
--- a/src/transport/mycelium.rs
+++ b/src/transport/mycelium.rs
@@ -818,6 +818,9 @@ pub struct SyncEnvelopeShadow<'a> {
     pub message: automerge::sync::Message,
     #[serde(default)]
     epoch: EpochShadow,
+    /// Absent from nodes that predate it: never counts as ready.
+    #[serde(default)]
+    ready: bool,
 }
 
 // =====================================================================
@@ -890,6 +893,7 @@ pub fn sync_envelope_to_bytes(msg: &SyncEnvelope) -> Result<Vec<u8>, rmp_serde::
         swarm_id: Cow::Borrowed(&msg.swarm_id),
         message: msg.message.clone(), // Clone required by automerge_msg_codec ownership rules
         epoch: epoch_to_shadow(&msg.epoch),
+        ready: msg.ready,
     };
     rmp_serde::to_vec(&shadow)
 }
@@ -899,6 +903,7 @@ pub fn bytes_to_sync_envelope(bytes: &[u8]) -> Result<SyncEnvelope, TransportErr
         swarm_id: shadow.swarm_id.into_owned(),
         epoch: epoch_from_shadow(shadow.epoch)?,
         message: shadow.message,
+        ready: shadow.ready,
     })
 }