feat(kad): emit ToSwarm::NewExternalAddrOfPeer (libp2p#5549)

## Description

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Related https://github.com/libp2p/rust-libp2p/issues/ABCD.
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Updates `libp2p-kad` to emit new event `ToSwarm::NewExternalAddrOfPeer`
whenever it discovers a new address through the DHT.
Related: libp2p#5103 

## Notes & open questions

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## Change checklist

<!-- Please add a Changelog entry in the appropriate crates and bump the
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- [X] I have performed a self-review of my own code
- [ ] I have made corresponding changes to the documentation
- [X] I have added tests that prove my fix is effective or that my
feature works
- [ ] A changelog entry has been made in the appropriate crates

---------

Co-authored-by: Guillaume Michel <guillaumemichel@users.noreply.github.com>

Cargo.toml

@@ -86,7 +86,7 @@ libp2p-floodsub = { version = "0.45.0", path = "protocols/floodsub" }
 libp2p-gossipsub = { version = "0.47.0", path = "protocols/gossipsub" }
 libp2p-identify = { version = "0.45.0", path = "protocols/identify" }
 libp2p-identity = { version = "0.2.9" }
-libp2p-kad = { version = "0.46.1", path = "protocols/kad" }
+libp2p-kad = { version = "0.46.2", path = "protocols/kad" }
 libp2p-mdns = { version = "0.46.0", path = "protocols/mdns" }
 libp2p-memory-connection-limits = { version = "0.3.0", path = "misc/memory-connection-limits" }
 libp2p-metrics = { version = "0.15.0", path = "misc/metrics" }

protocols/kad/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.46.2
+
+- Emit `ToSwarm::NewExternalAddrOfPeer`.
+  See [PR 5549](https://github.com/libp2p/rust-libp2p/pull/5549)
+
 ## 0.46.1
 
 - Use new provider record update strategy to prevent Sybil attack.

protocols/kad/Cargo.toml

@@ -3,7 +3,7 @@ name = "libp2p-kad"
 edition = "2021"
 rust-version = { workspace = true }
 description = "Kademlia protocol for libp2p"
-version = "0.46.1"
+version = "0.46.2"
 authors = ["Parity Technologies <admin@parity.io>"]
 license = "MIT"
 repository = "https://github.com/libp2p/rust-libp2p"

protocols/kad/src/behaviour.rs

@@ -2562,13 +2562,19 @@ where
             // Drain applied pending entries from the routing table.
             if let Some(entry) = self.kbuckets.take_applied_pending() {
                 let kbucket::Node { key, value } = entry.inserted;
+                let peer_id = key.into_preimage();
+                self.queued_events
+                    .push_back(ToSwarm::NewExternalAddrOfPeer {
+                        peer_id,
+                        address: value.first().clone(),
+                    });
                 let event = Event::RoutingUpdated {
                     bucket_range: self
                         .kbuckets
                         .bucket(&key)
                         .map(|b| b.range())
                         .expect("Self to never be applied from pending."),
-                    peer: key.into_preimage(),
+                    peer: peer_id,
                     is_new_peer: true,
                     addresses: value,
                     old_peer: entry.evicted.map(|n| n.key.into_preimage()),

protocols/kad/tests/client_mode.rs

@@ -23,14 +23,21 @@ async fn server_gets_added_to_routing_table_by_client() {
     let server_peer_id = *server.local_peer_id();
     async_std::task::spawn(server.loop_on_next());
 
-    let peer = client
+    let external_event_peer = client
+        .wait(|e| match e {
+            SwarmEvent::NewExternalAddrOfPeer { peer_id, .. } => Some(peer_id),
+            _ => None,
+        })
+        .await;
+    let routing_updated_peer = client
         .wait(|e| match e {
             SwarmEvent::Behaviour(Kad(RoutingUpdated { peer, .. })) => Some(peer),
             _ => None,
         })
         .await;
 
-    assert_eq!(peer, server_peer_id);
+    assert_eq!(external_event_peer, server_peer_id);
+    assert_eq!(routing_updated_peer, server_peer_id);
 }
 
 #[async_std::test]
@@ -126,6 +133,12 @@ async fn set_client_to_server_mode() {
 
     let server_peer_id = *server.local_peer_id();
 
+    let peer_id = client
+        .wait(|e| match e {
+            SwarmEvent::NewExternalAddrOfPeer { peer_id, .. } => Some(peer_id),
+            _ => None,
+        })
+        .await;
     let client_event = client.wait(|e| match e {
         SwarmEvent::Behaviour(Kad(RoutingUpdated { peer, .. })) => Some(peer),
         _ => None,
@@ -138,6 +151,7 @@ async fn set_client_to_server_mode() {
     let (peer, info) = futures::future::join(client_event, server_event).await;
 
     assert_eq!(peer, server_peer_id);
+    assert_eq!(peer_id, server_peer_id);
     assert!(info
         .protocols
         .iter()