From 137443b9df2c7c3b2d2d7d3fb04ad0f392f7ab58 Mon Sep 17 00:00:00 2001
From: Thomas Eizinger <thomas@eizinger.io>
Date: Thu, 25 May 2023 03:09:35 +0200
Subject: [PATCH] feat(identify): push changed listen protocols to remote

Now that we have the infrastructure for notifying protocols about changes to our listen protocols, we can use this to actively push those changes to our remotes. This allows other peers to re-configure themselves with very low-latency instead of waiting for the periodic identify event.

Resolves: #3613.

Pull-Request: #3980.
---
 protocols/identify/CHANGELOG.md   |  6 ++++-
 protocols/identify/src/handler.rs | 39 +++++++++++++++++++++++++++++--
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/protocols/identify/CHANGELOG.md b/protocols/identify/CHANGELOG.md
index e86afde808e..f90d8ce3da4 100644
--- a/protocols/identify/CHANGELOG.md
+++ b/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
 
diff --git a/protocols/identify/src/handler.rs b/protocols/identify/src/handler.rs
index 4c7ae58631e..5a1712e8c3d 100644
--- a/protocols/identify/src/handler.rs
+++ b/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)),
+                                (),
+                            ),
+                        });
+                }
             }
         }
     }