fix(dcutr): handle empty holepunch_candidates

Cargo.toml

@@ -80,7 +80,7 @@ libp2p-allow-block-list = { version = "0.4.1", path = "misc/allow-block-list" }
 libp2p-autonat = { version = "0.13.1", path = "protocols/autonat" }
 libp2p-connection-limits = { version = "0.4.0", path = "misc/connection-limits" }
 libp2p-core = { version = "0.42.0", path = "core" }
-libp2p-dcutr = { version = "0.12.0", path = "protocols/dcutr" }
+libp2p-dcutr = { version = "0.12.1", path = "protocols/dcutr" }
 libp2p-dns = { version = "0.42.0", path = "transports/dns" }
 libp2p-floodsub = { version = "0.45.0", path = "protocols/floodsub" }
 libp2p-gossipsub = { version = "0.47.1", path = "protocols/gossipsub" }

protocols/dcutr/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.12.1
+
+- Handle empty hole-punch candidates at relayed connection startup.
+  See [PR 5583](https://github.com/libp2p/rust-libp2p/pull/5583).
+
 ## 0.12.0
 
 <!-- Update to libp2p-swarm v0.45.0 -->

protocols/dcutr/Cargo.toml

@@ -3,7 +3,7 @@ name = "libp2p-dcutr"
 edition = "2021"
 rust-version = { workspace = true }
 description = "Direct connection upgrade through relay"
-version = "0.12.0"
+version = "0.12.1"
 authors = ["Max Inden <[email protected]>"]
 license = "MIT"
 repository = "https://github.com/libp2p/rust-libp2p"

protocols/dcutr/src/behaviour.rs

@@ -70,8 +70,8 @@ pub struct Behaviour {
     /// Queue of actions to return when polled.
     queued_events: VecDeque<ToSwarm<Event, Either<handler::relayed::Command, Void>>>,
 
-    /// All direct (non-relayed) connections.
-    direct_connections: HashMap<PeerId, HashSet<ConnectionId>>,
+    /// All relayed connections.
+    relayed_connections: HashMap<PeerId, HashSet<ConnectionId>>,
 
     address_candidates: Candidates,
 
@@ -86,15 +86,15 @@ impl Behaviour {
     pub fn new(local_peer_id: PeerId) -> Self {
         Behaviour {
             queued_events: Default::default(),
-            direct_connections: Default::default(),
+            relayed_connections: Default::default(),
             address_candidates: Candidates::new(local_peer_id),
             direct_to_relayed_connections: Default::default(),
             outgoing_direct_connection_attempts: Default::default(),
         }
     }
 
-    fn observed_addresses(&self) -> Vec<Multiaddr> {
-        self.address_candidates.iter().cloned().collect()
+    fn observed_addresses(&self) -> LruCache<Multiaddr, ()> {
+        self.address_candidates.inner.clone()
     }
 
     fn on_dial_failure(
@@ -148,17 +148,17 @@ impl Behaviour {
             ..
         }: ConnectionClosed,
     ) {
-        if !connected_point.is_relayed() {
+        if connected_point.is_relayed() {
             let connections = self
-                .direct_connections
+                .relayed_connections
                 .get_mut(&peer_id)
-                .expect("Peer of direct connection to be tracked.");
+                .expect("Peer of relayed connection to be tracked.");
             connections
                 .remove(&connection_id)
                 .then_some(())
-                .expect("Direct connection to be tracked.");
+                .expect("Relayed connection to be tracked.");
             if connections.is_empty() {
-                self.direct_connections.remove(&peer_id);
+                self.relayed_connections.remove(&peer_id);
             }
         }
     }
@@ -176,6 +176,11 @@ impl NetworkBehaviour for Behaviour {
         remote_addr: &Multiaddr,
     ) -> Result<THandler<Self>, ConnectionDenied> {
         if is_relayed(local_addr) {
+            self.relayed_connections
+                .entry(peer)
+                .or_default()
+                .insert(connection_id);
+
             let connected_point = ConnectedPoint::Listener {
                 local_addr: local_addr.clone(),
                 send_back_addr: remote_addr.clone(),
@@ -186,10 +191,6 @@ impl NetworkBehaviour for Behaviour {
 
             return Ok(Either::Left(handler)); // TODO: We could make two `handler::relayed::Handler` here, one inbound one outbound.
         }
-        self.direct_connections
-            .entry(peer)
-            .or_default()
-            .insert(connection_id);
 
         assert!(
             !self
@@ -210,6 +211,11 @@ impl NetworkBehaviour for Behaviour {
         port_use: PortUse,
     ) -> Result<THandler<Self>, ConnectionDenied> {
         if is_relayed(addr) {
+            self.relayed_connections
+                .entry(peer)
+                .or_default()
+                .insert(connection_id);
+
             return Ok(Either::Left(handler::relayed::Handler::new(
                 ConnectedPoint::Dialer {
                     address: addr.clone(),
@@ -220,11 +226,6 @@ impl NetworkBehaviour for Behaviour {
             ))); // TODO: We could make two `handler::relayed::Handler` here, one inbound one outbound.
         }
 
-        self.direct_connections
-            .entry(peer)
-            .or_default()
-            .insert(connection_id);
-
         // Whether this is a connection requested by this behaviour.
         if let Some(&relayed_connection_id) = self.direct_to_relayed_connections.get(&connection_id)
         {
@@ -336,7 +337,21 @@ impl NetworkBehaviour for Behaviour {
             }
             FromSwarm::DialFailure(dial_failure) => self.on_dial_failure(dial_failure),
             FromSwarm::NewExternalAddrCandidate(NewExternalAddrCandidate { addr }) => {
-                self.address_candidates.add(addr.clone());
+                if let Some(address) = self.address_candidates.add(addr.clone()) {
+                    for (peer, connections) in &self.relayed_connections {
+                        for connection in connections {
+                            self.queued_events.push_back(ToSwarm::NotifyHandler {
+                                handler: NotifyHandler::One(*connection),
+                                peer_id: *peer,
+                                event: Either::Left(
+                                    handler::relayed::Command::NewExternalAddrCandidate(
+                                        address.clone(),
+                                    ),
+                                ),
+                            })
+                        }
+                    }
+                }
             }
             _ => {}
         }
@@ -362,20 +377,21 @@ impl Candidates {
         }
     }
 
-    fn add(&mut self, mut address: Multiaddr) {
+    /// Format the address and push it into the LruCache if it is not relayed.
+    ///
+    /// Returns the provided address formatted if it was pushed.
+    /// Returns `None` otherwise.
+    fn add(&mut self, mut address: Multiaddr) -> Option<Multiaddr> {
         if is_relayed(&address) {
-            return;
+            return None;
         }
 
         if address.iter().last() != Some(Protocol::P2p(self.me)) {
             address.push(Protocol::P2p(self.me));
         }
 
-        self.inner.push(address, ());
-    }
-
-    fn iter(&self) -> impl Iterator<Item = &Multiaddr> {
-        self.inner.iter().map(|(a, _)| a)
+        self.inner.push(address.clone(), ());
+        Some(address)
     }
 }
 

protocols/dcutr/src/handler/relayed.rs

@@ -32,18 +32,21 @@ use libp2p_swarm::handler::{
     ListenUpgradeError,
 };
 use libp2p_swarm::{
-    ConnectionHandler, ConnectionHandlerEvent, StreamProtocol, StreamUpgradeError,
+    ConnectionHandler, ConnectionHandlerEvent, Stream, StreamProtocol, StreamUpgradeError,
     SubstreamProtocol,
 };
+use lru::LruCache;
 use protocol::{inbound, outbound};
 use std::collections::VecDeque;
 use std::io;
 use std::task::{Context, Poll};
 use std::time::Duration;
+use tracing::{debug, warn};
 
 #[derive(Debug)]
 pub enum Command {
     Connect,
+    NewExternalAddrCandidate(Multiaddr),
 }
 
 #[derive(Debug)]
@@ -67,28 +70,76 @@ pub struct Handler {
 
     // Inbound DCUtR handshakes
     inbound_stream: futures_bounded::FuturesSet<Result<Vec<Multiaddr>, inbound::Error>>,
+    pending_inbound_stream: Option<Stream>,
 
     // Outbound DCUtR handshake.
     outbound_stream: futures_bounded::FuturesSet<Result<Vec<Multiaddr>, outbound::Error>>,
 
     /// The addresses we will send to the other party for hole-punching attempts.
-    holepunch_candidates: Vec<Multiaddr>,
+    holepunch_candidates: LruCache<Multiaddr, ()>,
+    pending_outbound_stream: Option<Stream>,
 
     attempts: u8,
 }
 
 impl Handler {
-    pub fn new(endpoint: ConnectedPoint, holepunch_candidates: Vec<Multiaddr>) -> Self {
+    pub fn new(endpoint: ConnectedPoint, holepunch_candidates: LruCache<Multiaddr, ()>) -> Self {
         Self {
             endpoint,
             queued_events: Default::default(),
             inbound_stream: futures_bounded::FuturesSet::new(Duration::from_secs(10), 1),
+            pending_inbound_stream: None,
             outbound_stream: futures_bounded::FuturesSet::new(Duration::from_secs(10), 1),
+            pending_outbound_stream: None,
             holepunch_candidates,
             attempts: 0,
         }
     }
 
+    fn set_stream(&mut self, stream_type: StreamType, stream: Stream) {
+        if self.holepunch_candidates.is_empty() {
+            debug!(
+                "New {stream_type} connect stream but holepunch_candidates is empty. Buffering it."
+            );
+            let has_replaced_old_stream = match stream_type {
+                StreamType::Inbound => self.pending_inbound_stream.replace(stream).is_some(),
+                StreamType::Outbound => self.pending_outbound_stream.replace(stream).is_some(),
+            };
+            if has_replaced_old_stream {
+                warn!("New {stream_type} connect stream while still buffering previous one. Replacing previous with new.");
+            }
+        } else {
+            let holepunch_candidates = self
+                .holepunch_candidates
+                .iter()
+                .map(|(a, _)| a)
+                .cloned()
+                .collect();
+
+            let has_replaced_old_stream = match stream_type {
+                StreamType::Inbound => {
+                    // TODO: when upstreaming this fix, ask libp2p about merging the `attempts` incrementation.
+                    self.attempts += 1;
+
+                    // FIXME: actually does not replace !!
+                    self.inbound_stream
+                        .try_push(inbound::handshake(stream, holepunch_candidates))
+                        .is_err()
+                }
+                StreamType::Outbound => {
+                    // FIXME: actually does not replace !!
+                    self.outbound_stream
+                        .try_push(outbound::handshake(stream, holepunch_candidates))
+                        .is_err()
+                }
+            };
+
+            if has_replaced_old_stream {
+                warn!("New {stream_type} connect stream while still upgrading previous one. Replacing previous with new.");
+            }
+        }
+    }
+
     fn on_fully_negotiated_inbound(
         &mut self,
         FullyNegotiatedInbound {
@@ -99,21 +150,7 @@ impl Handler {
         >,
     ) {
         match output {
-            future::Either::Left(stream) => {
-                if self
-                    .inbound_stream
-                    .try_push(inbound::handshake(
-                        stream,
-                        self.holepunch_candidates.clone(),
-                    ))
-                    .is_err()
-                {
-                    tracing::warn!(
-                        "New inbound connect stream while still upgrading previous one. Replacing previous with new.",
-                    );
-                }
-                self.attempts += 1;
-            }
+            future::Either::Left(stream) => self.set_stream(StreamType::Inbound, stream),
             // A connection listener denies all incoming substreams, thus none can ever be fully negotiated.
             // TODO: remove when Rust 1.82 is MSRV
             #[allow(unreachable_patterns)]
@@ -134,18 +171,7 @@ impl Handler {
             self.endpoint.is_listener(),
             "A connection dialer never initiates a connection upgrade."
         );
-        if self
-            .outbound_stream
-            .try_push(outbound::handshake(
-                stream,
-                self.holepunch_candidates.clone(),
-            ))
-            .is_err()
-        {
-            tracing::warn!(
-                "New outbound connect stream while still upgrading previous one. Replacing previous with new.",
-            );
-        }
+        self.set_stream(StreamType::Outbound, stream);
     }
 
     fn on_listen_upgrade_error(
@@ -214,8 +240,22 @@ impl ConnectionHandler for Handler {
                     .push_back(ConnectionHandlerEvent::OutboundSubstreamRequest {
                         protocol: SubstreamProtocol::new(ReadyUpgrade::new(PROTOCOL_NAME), ()),
                     });
+
+                // TODO: when upstreaming this fix, ask libp2p about merging the `attempts` incrementation.
+                // Indeed, even if the `queued_event` above will be trigger on stream opening, it might not start
                 self.attempts += 1;
             }
+            Command::NewExternalAddrCandidate(address) => {
+                self.holepunch_candidates.push(address, ());
+
+                if let Some(stream) = self.pending_inbound_stream.take() {
+                    self.set_stream(StreamType::Inbound, stream);
+                }
+
+                if let Some(stream) = self.pending_outbound_stream.take() {
+                    self.set_stream(StreamType::Outbound, stream);
+                }
+            }
         }
     }
 
@@ -316,3 +356,17 @@ impl ConnectionHandler for Handler {
         }
     }
 }
+
+enum StreamType {
+    Inbound,
+    Outbound,
+}
+
+impl std::fmt::Display for StreamType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Inbound => write!(f, "inbound"),
+            Self::Outbound => write!(f, "outbound"),
+        }
+    }
+}