announcements answered only if heads differ

3 files changed, 24 insertions, 2 deletions

diff --git a/src/swarm/peer/inbound.rs b/src/swarm/peer/inbound.rs
index 18d29d5..1454c3e 100644
--- a/src/swarm/peer/inbound.rs
+++ b/src/swarm/peer/inbound.rs
@@ -143,8 +143,15 @@ pub(crate) async fn handle_message(
             crate::swarm::blob::handle(state, &peer, blob).await;
         }
         transport::ParsedMessage::Status(remote) => {
-            status_received(state, &peer).await;
+            // An announcement is no keepalive; it is answered only if our heads differ,
+            // so the announcer learns what we have that it lacks.
+            if !remote.announcing {
+                status_received(state, &peer).await;
+            }
             let local = on_status(state, &peer, &remote, reactivated).await;
+            if remote.announcing && local.heads == remote.heads {
+                return Ok(());
+            }
             if let Err(error) = state
                 .transport
                 .send_message(&peer, &ParsedMessage::StatusReply(local))
diff --git a/src/swarm/peer/keepalive.rs b/src/swarm/peer/keepalive.rs
index 8597dcd..196b8b6 100644
--- a/src/swarm/peer/keepalive.rs
+++ b/src/swarm/peer/keepalive.rs
@@ -32,6 +32,20 @@ pub(crate) async fn send_status(state: &AppState, peer: &str) -> Result<()> {
         .await
 }
 
+/// Sends `peer` a STATUS announcing our new heads (`swarm::relay`): no keepalive, so it
+/// leaves the keepalives' schedule as it is, and it is answered only if the peer's heads
+/// differ (`Status::announcing`).
+pub(crate) async fn announce_heads(state: &AppState, peer: &str) -> Result<()> {
+    let status = transport::Status {
+        announcing: true,
+        ..local_status(state, peer).await
+    };
+    state
+        .transport
+        .send_message(peer, &ParsedMessage::Status(status))
+        .await
+}
+
 /// Sends `peer` a PING (the paths layer measures the path with it).
 pub(crate) async fn send_ping(state: &AppState, peer: &str) -> Result<()> {
     let nonce = crate::transport::paths::random_nonce();
@@ -173,6 +187,7 @@ pub(crate) async fn local_status(state: &AppState, peer: &str) -> transport::Sta
         ready: state.is_ready().await && !state.is_closing(),
         syncs_with_you,
         leaving: state.is_closing(),
+        announcing: false,
     }
 }
 
diff --git a/src/swarm/peer/mod.rs b/src/swarm/peer/mod.rs
index cf427a2..1826ec6 100644
--- a/src/swarm/peer/mod.rs
+++ b/src/swarm/peer/mod.rs
@@ -26,6 +26,6 @@ pub(crate) use handshake::{
     send_hello_once,
 };
 pub(crate) use inbound::handle_message;
-pub(crate) use keepalive::{announce, farewell, send_status};
+pub(crate) use keepalive::{announce, announce_heads, farewell, send_status};
 pub(crate) use lanes::SyncLanes;
 pub(crate) use worker::{Due, run_peer_worker};