libp2p: introduce rehoming

1 files changed, 12 insertions, 10 deletions

diff --git a/src/transport/libp2p/book.rs b/src/transport/libp2p/book.rs
index 7de4be7..f466aef 100644
--- a/src/transport/libp2p/book.rs
+++ b/src/transport/libp2p/book.rs
@@ -70,6 +70,9 @@ pub(super) struct Book {
     pub(super) failed_relays: HashMap<PeerId, tokio::time::Instant>,
     /// Relays that granted us a slot we hold.
     pub(super) slots: std::collections::HashSet<PeerId>,
+    /// Relays we hold a slot on whose duplicate connections we closed, and when
+    /// (`duplicates`): a slot lost then moves to the connection kept, it isn't lost.
+    pub(super) rehoming: HashMap<PeerId, tokio::time::Instant>,
     /// Peers holding a slot on this node, as a relay.
     pub(super) slots_here: std::collections::HashSet<PeerId>,
     /// Peers connected only through a relay, dialled directly (`upgrade`): when to again
@@ -117,17 +120,16 @@ impl Book {
         book_connection(&self.connections, peer)
     }
 
-    /// The connections to `peer` to close, of several: all but one, the oldest direct
-    /// one (the oldest relayed one if none is direct).
+    /// The connections to `peer` to close, of several: all but the one to keep
+    /// (`ranked`).
     ///
-    /// None between a relay and a node with a slot on it, or reserving one (`reserving`):
-    /// a slot lives on one connection, which libp2p doesn't tell, and closing it would
-    /// end the slot, and with it every circuit to the node (the relay then answers
-    /// `NoReservation`).
-    pub(super) fn duplicates(&self, peer: &PeerId, reserving: bool) -> Vec<ConnectionId> {
-        if reserving || self.slots.contains(peer) || self.slots_here.contains(peer) {
-            return Vec::new();
-        }
+    /// Between a relay and a node with a slot on it too: messages go over any of the
+    /// connections (libp2p-stream picks one at random for each), so a slower one kept
+    /// would carry half of them. A slot lives on one connection, which libp2p doesn't
+    /// tell; if that one closes, the slot ends, and the node reserves it again at once,
+    /// over the connection kept (`Book::rehoming`, not counted as lost); circuits
+    /// through it end, and are made again with the next message.
+    pub(super) fn duplicates(&self, peer: &PeerId) -> Vec<ConnectionId> {
         self.ranked(peer).into_iter().skip(1).collect()
     }