fix(relay): send correct PeerId to client in outbound STOP message

Previously, the relay server would erroneously send its own `PeerId` in the STOP message to the client upon an incoming relay connection. This is obviously wrong and results in failed connection upgrades in other implementations.

Pull-Request: #3767.

protocols/relay/CHANGELOG.md

@@ -1,8 +1,12 @@
 ## 0.15.2 - unreleased
 
+- Send correct `PeerId` in outbound STOP message to client.
+  See [PR 3767].
+
 - As a relay, when forwarding data between relay-connection-source and -destination and vice versa, flush write side when read currently has no more data available.
   See [PR 3765].
 
+[PR 3767]: https://github.com/libp2p/rust-libp2p/pull/3767
 [PR 3765]: https://github.com/libp2p/rust-libp2p/pull/3765
 
 ## 0.15.1

protocols/relay/src/behaviour.rs

@@ -520,7 +520,6 @@ impl NetworkBehaviour for Behaviour {
                         event: Either::Left(handler::In::NegotiateOutboundConnect {
                             circuit_id,
                             inbound_circuit_req,
-                            relay_peer_id: self.local_peer_id,
                             src_peer_id: event_source,
                             src_connection_id: connection,
                         }),

protocols/relay/src/behaviour/handler.rs

@@ -69,7 +69,6 @@ pub enum In {
     NegotiateOutboundConnect {
         circuit_id: CircuitId,
         inbound_circuit_req: inbound_hop::CircuitReq,
-        relay_peer_id: PeerId,
         src_peer_id: PeerId,
         src_connection_id: ConnectionId,
     },
@@ -112,13 +111,11 @@ impl fmt::Debug for In {
             In::NegotiateOutboundConnect {
                 circuit_id,
                 inbound_circuit_req: _,
-                relay_peer_id,
                 src_peer_id,
                 src_connection_id,
             } => f
                 .debug_struct("In::NegotiateOutboundConnect")
                 .field("circuit_id", circuit_id)
-                .field("relay_peer_id", relay_peer_id)
                 .field("src_peer_id", src_peer_id)
                 .field("src_connection_id", src_connection_id)
                 .finish(),
@@ -655,7 +652,6 @@ impl ConnectionHandler for Handler {
             In::NegotiateOutboundConnect {
                 circuit_id,
                 inbound_circuit_req,
-                relay_peer_id,
                 src_peer_id,
                 src_connection_id,
             } => {
@@ -663,7 +659,7 @@ impl ConnectionHandler for Handler {
                     .push_back(ConnectionHandlerEvent::OutboundSubstreamRequest {
                         protocol: SubstreamProtocol::new(
                             outbound_stop::Upgrade {
-                                relay_peer_id,
+                                src_peer_id,
                                 max_circuit_duration: self.config.max_circuit_duration,
                                 max_circuit_bytes: self.config.max_circuit_bytes,
                             },

protocols/relay/src/priv_client/handler.rs

@@ -199,10 +199,7 @@ impl Handler {
                 });
 
                 self.queued_events.push_back(ConnectionHandlerEvent::Custom(
-                    Event::InboundCircuitEstablished {
-                        src_peer_id: self.remote_peer_id,
-                        limit,
-                    },
+                    Event::InboundCircuitEstablished { src_peer_id, limit },
                 ));
             }
             Reservation::None => {

protocols/relay/src/protocol/outbound_stop.rs

@@ -32,7 +32,7 @@ use std::time::Duration;
 use thiserror::Error;
 
 pub struct Upgrade {
-    pub relay_peer_id: PeerId,
+    pub src_peer_id: PeerId,
     pub max_circuit_duration: Duration,
     pub max_circuit_bytes: u64,
 }
@@ -55,7 +55,7 @@ impl upgrade::OutboundUpgrade<NegotiatedSubstream> for Upgrade {
         let msg = proto::StopMessage {
             type_pb: proto::StopMessageType::CONNECT,
             peer: Some(proto::Peer {
-                id: self.relay_peer_id.to_bytes(),
+                id: self.src_peer_id.to_bytes(),
                 addrs: vec![],
             }),
             limit: Some(proto::Limit {

protocols/relay/tests/lib.rs

@@ -203,34 +203,46 @@ fn connect() {
         relay_peer_id,
         false, // No renewal.
     ));
-    spawn_swarm_on_pool(&pool, dst);
 
     let mut src = build_client();
+    let src_peer_id = *src.local_peer_id();
 
     src.dial(dst_addr).unwrap();
 
-    pool.run_until(async {
+    pool.run_until(futures::future::join(
+        connection_established_to(src, relay_peer_id, dst_peer_id),
+        connection_established_to(dst, relay_peer_id, src_peer_id),
+    ));
+}
+
+async fn connection_established_to(mut swarm: Swarm<Client>, relay_peer_id: PeerId, other: PeerId) {
     loop {
-            match src.select_next_some().await {
+        match swarm.select_next_some().await {
             SwarmEvent::Dialing(peer_id) if peer_id == relay_peer_id => {}
             SwarmEvent::ConnectionEstablished { peer_id, .. } if peer_id == relay_peer_id => {}
-                SwarmEvent::Behaviour(ClientEvent::Ping(ping::Event { peer, .. }))
-                    if peer == dst_peer_id =>
-                {
+            SwarmEvent::Behaviour(ClientEvent::Ping(ping::Event { peer, .. })) if peer == other => {
                 break
             }
             SwarmEvent::Behaviour(ClientEvent::Relay(
                 relay::client::Event::OutboundCircuitEstablished { .. },
             )) => {}
+            SwarmEvent::Behaviour(ClientEvent::Relay(
+                relay::client::Event::InboundCircuitEstablished { src_peer_id, .. },
+            )) => {
+                assert_eq!(src_peer_id, other);
+            }
             SwarmEvent::Behaviour(ClientEvent::Ping(ping::Event { peer, .. }))
                 if peer == relay_peer_id => {}
-                SwarmEvent::ConnectionEstablished { peer_id, .. } if peer_id == dst_peer_id => {
-                    break
+            SwarmEvent::ConnectionEstablished { peer_id, .. } if peer_id == other => break,
+            SwarmEvent::IncomingConnection { send_back_addr, .. } => {
+                let peer_id_from_addr =
+                    PeerId::try_from_multiaddr(&send_back_addr).expect("to have /p2p");
+
+                assert_eq!(peer_id_from_addr, other)
             }
             e => panic!("{e:?}"),
         }
     }
-    })
 }
 
 #[test]