2 files changed, 38 insertions, 6 deletions

diff --git a/src/state/peer.rs b/src/state/peer.rs
index ba8379a..24f9188 100644
--- a/src/state/peer.rs
+++ b/src/state/peer.rs
@@ -76,6 +76,11 @@ pub(crate) enum HelloState {
 /// comes.
 const HELLO_RETRY: Duration = Duration::from_secs(1);
 const HELLO_RETRY_MAX: Duration = Duration::from_secs(30);
+/// How long after it became known (`added_at`) a peer never heard from is HELLOed that
+/// often, unreachable or not, rather than probed (`dormant_probe`, ten keepalives):
+/// members that restart together may fail to reach each other at first, as the others
+/// aren't up yet, and would otherwise wait for a probe to find each other.
+const FIRST_CONTACT: Duration = Duration::from_secs(300);
 
 #[derive(Clone)]
 pub(crate) struct PeerState {
@@ -341,9 +346,12 @@ impl PeerState {
         )
     }
 
-    /// The wait before the next HELLO: a probe's if unreachable.
-    pub(crate) fn next_hello_wait(&mut self) -> Duration {
-        if self.is_unreachable() {
+    /// The wait before the next HELLO: a probe's if unreachable, but while a peer never
+    /// heard from is new (`FIRST_CONTACT`).
+    pub(crate) fn next_hello_wait(&mut self, now: Instant) -> Duration {
+        let new = self.last_seen.is_none()
+            && now.saturating_duration_since(self.added_at) < FIRST_CONTACT;
+        if self.is_unreachable() && !new {
             self.probe_backoff.next()
         } else {
             self.hello_backoff.next()
@@ -691,7 +699,9 @@ mod tests {
         }
         assert!(peer.is_unreachable());
 
-        let probes: Vec<Duration> = (0..4).map(|_| peer.next_hello_wait()).collect();
+        // Known for a while: probed.
+        let later = start + FIRST_CONTACT;
+        let probes: Vec<Duration> = (0..4).map(|_| peer.next_hello_wait(later)).collect();
         let probe = timing.dormant_probe;
         assert_eq!(probes, [probe, probe * 2, probe * 4, probe * 6]);
         peer.hello_sent(start + probe * 20);
@@ -702,6 +712,28 @@ mod tests {
         peer.hello_sent(start + probe * 22);
         peer.hello_sent(start + probe * 22);
         peer.hello_sent(start + probe * 22);
-        assert_eq!(peer.next_hello_wait(), probe);
+        assert_eq!(peer.next_hello_wait(start + probe * 22), probe);
+    }
+
+    /// A peer never heard from is HELLOed at the HELLO backoff while it is new
+    /// (`FIRST_CONTACT`), unreachable or not; probed after.
+    #[test]
+    fn new_peers_retried_before_probed() {
+        let timing = Timing::from_keepalive(Duration::from_secs(60), Duration::from_secs(300));
+        let mut peer = PeerState::new(true, &timing);
+        let start = peer.added_at;
+        for _ in 0..UNREACHABLE_AFTER_HELLOS {
+            peer.hello_sent(start);
+        }
+        assert!(peer.is_unreachable());
+        let waits: Vec<Duration> = (0..7).map(|_| peer.next_hello_wait(start)).collect();
+        assert!(
+            waits.iter().all(|wait| *wait <= HELLO_RETRY_MAX),
+            "{waits:?}"
+        );
+        assert_eq!(
+            peer.next_hello_wait(start + FIRST_CONTACT),
+            timing.dormant_probe
+        );
     }
 }
diff --git a/src/swarm/peer/handshake.rs b/src/swarm/peer/handshake.rs
index 1ca955b..769b010 100644
--- a/src/swarm/peer/handshake.rs
+++ b/src/swarm/peer/handshake.rs
@@ -148,7 +148,7 @@ async fn transmit_hello(state: &AppState, peer: &str) -> Result<()> {
 
         if peer_state.hello_state == HelloState::Sending {
             topology::change_peer(state, &mut peer_state, |p| p.hello_sent(Instant::now()));
-            let wait = peer_state.next_hello_wait();
+            let wait = peer_state.next_hello_wait(Instant::now());
             let next_attempt = Instant::now() + wait;
             peer_state.hello_state = HelloState::AwaitingReply { next_attempt };
             state.peers_due.by(next_attempt);