feat(identify): push changed listen protocols to remote

protocols/identify/CHANGELOG.md

@@ -10,10 +10,14 @@
 - Fix aborting the answering of an identify request in rare situations.
   See [PR 3876].
 
+- Actively push changes in listen protocols to remote.
+  See [PR 3980].
+
+[PR 3545]: https://github.com/libp2p/rust-libp2p/pull/3545
 [PR 3698]: https://github.com/libp2p/rust-libp2p/pull/3698
 [PR 3715]: https://github.com/libp2p/rust-libp2p/pull/3715
-[PR 3545]: https://github.com/libp2p/rust-libp2p/pull/3545
 [PR 3876]: https://github.com/libp2p/rust-libp2p/pull/3876
+[PR 3980]: https://github.com/libp2p/rust-libp2p/pull/3980
 
 ## 0.42.2
 

protocols/identify/src/handler.rs

@@ -36,7 +36,7 @@ use libp2p_swarm::{
     ConnectionHandler, ConnectionHandlerEvent, KeepAlive, StreamProtocol, StreamUpgradeError,
     SubstreamProtocol, SupportedProtocols,
 };
-use log::warn;
+use log::{warn, Level};
 use smallvec::SmallVec;
 use std::collections::HashSet;
 use std::{io, task::Context, task::Poll, time::Duration};
@@ -60,6 +60,9 @@ pub struct Handler {
     /// Future that fires when we need to identify the node again.
     trigger_next_identify: Delay,
 
+    /// Whether we have exchanged at least one periodic identify.
+    exchanged_one_periodic_identify: bool,
+
     /// The interval of `trigger_next_identify`, i.e. the recurrent delay.
     interval: Duration,
 
@@ -122,6 +125,7 @@ impl Handler {
             events: SmallVec::new(),
             pending_replies: FuturesUnordered::new(),
             trigger_next_identify: Delay::new(initial_delay),
+            exchanged_one_periodic_identify: false,
             interval,
             public_key,
             protocol_version,
@@ -238,6 +242,14 @@ impl Handler {
 
         self.remote_supported_protocols = new_remote_protocols;
     }
+
+    fn local_protocols_to_string(&mut self) -> String {
+        self.local_supported_protocols
+            .iter()
+            .map(|p| p.to_string())
+            .collect::<Vec<_>>()
+            .join(", ")
+    }
 }
 
 impl ConnectionHandler for Handler {
@@ -319,6 +331,7 @@ impl ConnectionHandler for Handler {
             let event = result
                 .map(|()| Event::Identification)
                 .unwrap_or_else(|err| Event::IdentificationError(StreamUpgradeError::Apply(err)));
+            self.exchanged_one_periodic_identify = true;
 
             return Poll::Ready(ConnectionHandlerEvent::NotifyBehaviour(event));
         }
@@ -349,7 +362,29 @@ impl ConnectionHandler for Handler {
             | ConnectionEvent::ListenUpgradeError(_)
             | ConnectionEvent::RemoteProtocolsChange(_) => {}
             ConnectionEvent::LocalProtocolsChange(change) => {
-                self.local_supported_protocols.on_protocols_change(change);
+                let before = log::log_enabled!(Level::Debug)
+                    .then(|| self.local_protocols_to_string())
+                    .unwrap_or_default();
+                let protocols_changed = self.local_supported_protocols.on_protocols_change(change);
+                let after = log::log_enabled!(Level::Debug)
+                    .then(|| self.local_protocols_to_string())
+                    .unwrap_or_default();
+
+                if protocols_changed && self.exchanged_one_periodic_identify {
+                    log::debug!(
+                        "Supported listen protocols changed from [{before}] to [{after}], pushing to {}",
+                        self.remote_peer_id
+                    );
+
+                    let info = self.build_info();
+                    self.events
+                        .push(ConnectionHandlerEvent::OutboundSubstreamRequest {
+                            protocol: SubstreamProtocol::new(
+                                Either::Right(Push::outbound(info)),
+                                (),
+                            ),
+                        });
+                }
             }
         }
     }