7 files changed, 39 insertions, 0 deletions
diff --git a/src/transport/identity.rs b/src/transport/identity.rs
index 7b4a8c7..1df84ec 100644
--- a/src/transport/identity.rs
+++ b/src/transport/identity.rs
@@ -642,6 +642,10 @@ impl Transport for IdentityTransport {
         self.shared.paths.on_seeds_found(found)
     }
 
+    fn on_reachable(&self, reachable: std::sync::Arc<tokio::sync::Notify>) {
+        self.shared.paths.on_reachable(reachable)
+    }
+
     /// A node ID resolves to itself if this node knows where it is; anything else is
     /// an address (`<scheme>:...`) or what one of the transports resolves to one (the
     /// first that does), asked WHO.
diff --git a/src/transport/libp2p/book.rs b/src/transport/libp2p/book.rs
index 3de8cef..0c61714 100644
--- a/src/transport/libp2p/book.rs
+++ b/src/transport/libp2p/book.rs
@@ -113,6 +113,9 @@ pub(super) struct Book {
     pub(super) discovered: Vec<Multiaddr>,
     /// Told when a seed is found (`Transport::on_seeds_found`).
     pub(super) seeds_found: Option<Arc<tokio::sync::Notify>>,
+    /// Told when others may reach this node where they couldn't before
+    /// (`Transport::on_reachable`).
+    pub(super) reachable: Option<Arc<tokio::sync::Notify>>,
 }
 
 /// What `Libp2pStats` counts since start.
diff --git a/src/transport/libp2p/driver.rs b/src/transport/libp2p/driver.rs
index 39a2a5d..6ef04e7 100644
--- a/src/transport/libp2p/driver.rs
+++ b/src/transport/libp2p/driver.rs
@@ -420,6 +420,10 @@ pub(super) async fn run(
                         book.failed_relays.remove(&relay_peer_id);
                         if !renewal {
                             book.counts.slots_granted += 1;
+                            // Peers that couldn't reach us may now, through it.
+                            if let Some(reachable) = &book.reachable {
+                                reachable.notify_one();
+                            }
                         }
                     }
                     if !renewal {
@@ -440,6 +444,12 @@ pub(super) async fn run(
                                 (Reachability::Public, Some(address.clone()))
                             }
                         };
+                        if matches!(new, NatStatus::Public(_))
+                            && !matches!(old, NatStatus::Public(_))
+                            && let Some(reachable) = &book.reachable
+                        {
+                            reachable.notify_one();
+                        }
                     }
                     nat = new;
                 }
diff --git a/src/transport/libp2p/mod.rs b/src/transport/libp2p/mod.rs
index 3ebe7f6..056b1b2 100644
--- a/src/transport/libp2p/mod.rs
+++ b/src/transport/libp2p/mod.rs
@@ -500,6 +500,10 @@ impl Transport for Libp2pTransport {
         lock(&self.book).seeds_found = Some(found);
     }
 
+    fn on_reachable(&self, reachable: Arc<tokio::sync::Notify>) {
+        lock(&self.book).reachable = Some(reachable);
+    }
+
     /// Nodes found on the LAN (mDNS) that speak continuum.
     fn discovered_seeds(&self) -> Vec<String> {
         std::mem::take(&mut lock(&self.book).discovered)
diff --git a/src/transport/mod.rs b/src/transport/mod.rs
index 1de0633..96f7651 100644
--- a/src/transport/mod.rs
+++ b/src/transport/mod.rs
@@ -831,6 +831,13 @@ pub(crate) trait Transport: Send + Sync {
         let _ = found;
     }
 
+    /// Has the transport tell `reachable` whenever others may reach this node where they
+    /// couldn't before (libp2p: a relay granted it a slot, or AutoNAT found it public).
+    /// By default it never does.
+    fn on_reachable(&self, reachable: std::sync::Arc<tokio::sync::Notify>) {
+        let _ = reachable;
+    }
+
     /// Whether this node has a way to reach `peer` at all: an address of it on one of
     /// its transports. Members it can't reach aren't its neighbours (`swarm::topology`).
     /// By default yes, as for `local_addresses`.
diff --git a/src/transport/paths.rs b/src/transport/paths.rs
index ba8581f..164574d 100644
--- a/src/transport/paths.rs
+++ b/src/transport/paths.rs
@@ -708,6 +708,13 @@ impl Paths {
         }
     }
 
+    /// Each transport's (`Transport::on_reachable`).
+    pub(crate) fn on_reachable(&self, reachable: std::sync::Arc<tokio::sync::Notify>) {
+        for link in &self.links {
+            link.inner.on_reachable(reachable.clone());
+        }
+    }
+
     /// The address of the node a seed leads to, as paths keep it: an address of ours
     /// (`<scheme>:...`) whose transport reads it at once; with a scheme of ours, what
     /// that transport resolves the rest to (an address the transport can't read as an
diff --git a/src/transport/traffic.rs b/src/transport/traffic.rs
index 21acca6..bf9438f 100644
--- a/src/transport/traffic.rs
+++ b/src/transport/traffic.rs
@@ -351,6 +351,10 @@ impl Transport for CountingTransport {
         self.inner.on_seeds_found(found)
     }
 
+    fn on_reachable(&self, reachable: std::sync::Arc<tokio::sync::Notify>) {
+        self.inner.on_reachable(reachable)
+    }
+
     fn transports(&self) -> Vec<String> {
         self.inner.transports()
     }