feat(swarm): replace address scoring with explicit candidates

Previously, a `NetworkBehaviour` could report an `AddressScore` for an external address. This score was a `u32` and addresses would be ranked amongst those.

In reality, an address is either confirmed to be publicly reachable (via a protocol such as AutoNAT) or merely represents a candidate that might be an external address. In a way, addresses are guilty (private) until proven innocent (publicly reachable).

When a `NetworkBehaviour` reports an address candidate, we perform address translation on it to potentially correct for ephemeral ports of TCP. These candidates are then injected back into the `NetworkBehaviour`. Protocols such as AutoNAT can use these addresses as a source for probing their NAT status. Once confirmed, they can emit a `ToSwarm::ExternalAddrConfirmed` event which again will be passed to all `NetworkBehaviour`s.

This simplified approach will allow us implement Kademlia's client-mode (libp2p#2032) without additional configuration options: As soon as an address is reported as publicly reachable, we can activate server-mode for that connection.

Related: libp2p#3877.
Related: libp2p#3953.
Related: libp2p#2032.
Related: libp2p/go-libp2p#2229.

Co-authored-by: Max Inden <[email protected]>

Pull-Request: libp2p#3954.

Author: thomaseizinger

src/behaviour.rs

@@ -36,10 +36,10 @@ use libp2p_request_response::{
 };
 use libp2p_swarm::{
     behaviour::{
-        AddressChange, ConnectionClosed, ConnectionEstablished, DialFailure, ExpiredExternalAddr,
-        ExpiredListenAddr, FromSwarm,
+        AddressChange, ConnectionClosed, ConnectionEstablished, DialFailure, ExpiredListenAddr,
+        ExternalAddrExpired, FromSwarm,
     },
-    ConnectionDenied, ConnectionId, ExternalAddresses, ListenAddresses, NetworkBehaviour,
+    ConnectionDenied, ConnectionId, ListenAddresses, NetworkBehaviour, NewExternalAddrCandidate,
     PollParameters, THandler, THandlerInEvent, THandlerOutEvent, ToSwarm,
 };
 use std::{
@@ -214,7 +214,7 @@ pub struct Behaviour {
     probe_id: ProbeId,
 
     listen_addresses: ListenAddresses,
-    external_addresses: ExternalAddresses,
+    other_candidates: HashSet<Multiaddr>,
 }
 
 impl Behaviour {
@@ -240,7 +240,7 @@ impl Behaviour {
             pending_actions: VecDeque::new(),
             probe_id: ProbeId(0),
             listen_addresses: Default::default(),
-            external_addresses: Default::default(),
+            other_candidates: Default::default(),
         }
     }
 
@@ -279,6 +279,12 @@ impl Behaviour {
         self.servers.retain(|p| p != peer);
     }
 
+    /// Explicitly probe the provided address for external reachability.
+    pub fn probe_address(&mut self, candidate: Multiaddr) {
+        self.other_candidates.insert(candidate);
+        self.as_client().on_new_address();
+    }
+
     fn as_client(&mut self) -> AsClient {
         AsClient {
             inner: &mut self.inner,
@@ -294,7 +300,7 @@ impl Behaviour {
             last_probe: &mut self.last_probe,
             schedule_probe: &mut self.schedule_probe,
             listen_addresses: &self.listen_addresses,
-            external_addresses: &self.external_addresses,
+            other_candidates: &self.other_candidates,
         }
     }
 
@@ -532,7 +538,6 @@ impl NetworkBehaviour for Behaviour {
 
     fn on_swarm_event(&mut self, event: FromSwarm<Self::ConnectionHandler>) {
         self.listen_addresses.on_swarm_event(&event);
-        self.external_addresses.on_swarm_event(&event);
 
         match event {
             FromSwarm::ConnectionEstablished(connection_established) => {
@@ -561,14 +566,17 @@ impl NetworkBehaviour for Behaviour {
                     }));
                 self.as_client().on_expired_address(addr);
             }
-            FromSwarm::ExpiredExternalAddr(ExpiredExternalAddr { addr }) => {
+            FromSwarm::ExternalAddrExpired(ExternalAddrExpired { addr }) => {
                 self.inner
-                    .on_swarm_event(FromSwarm::ExpiredExternalAddr(ExpiredExternalAddr { addr }));
+                    .on_swarm_event(FromSwarm::ExternalAddrExpired(ExternalAddrExpired { addr }));
                 self.as_client().on_expired_address(addr);
             }
-            external_addr @ FromSwarm::NewExternalAddr(_) => {
-                self.inner.on_swarm_event(external_addr);
-                self.as_client().on_new_address();
+            FromSwarm::NewExternalAddrCandidate(NewExternalAddrCandidate { addr }) => {
+                self.inner
+                    .on_swarm_event(FromSwarm::NewExternalAddrCandidate(
+                        NewExternalAddrCandidate { addr },
+                    ));
+                self.probe_address(addr.to_owned());
             }
             listen_failure @ FromSwarm::ListenFailure(_) => {
                 self.inner.on_swarm_event(listen_failure)
@@ -580,6 +588,7 @@ impl NetworkBehaviour for Behaviour {
             listener_closed @ FromSwarm::ListenerClosed(_) => {
                 self.inner.on_swarm_event(listener_closed)
             }
+            confirmed @ FromSwarm::ExternalAddrConfirmed(_) => self.inner.on_swarm_event(confirmed),
         }
     }
 

src/behaviour/as_client.rs

@@ -30,9 +30,7 @@ use instant::Instant;
 use libp2p_core::Multiaddr;
 use libp2p_identity::PeerId;
 use libp2p_request_response::{self as request_response, OutboundFailure, RequestId};
-use libp2p_swarm::{
-    AddressScore, ConnectionId, ExternalAddresses, ListenAddresses, PollParameters, ToSwarm,
-};
+use libp2p_swarm::{ConnectionId, ListenAddresses, PollParameters, ToSwarm};
 use rand::{seq::SliceRandom, thread_rng};
 use std::{
     collections::{HashMap, HashSet, VecDeque},
@@ -97,13 +95,13 @@ pub(crate) struct AsClient<'a> {
     pub(crate) last_probe: &'a mut Option<Instant>,
     pub(crate) schedule_probe: &'a mut Delay,
     pub(crate) listen_addresses: &'a ListenAddresses,
-    pub(crate) external_addresses: &'a ExternalAddresses,
+    pub(crate) other_candidates: &'a HashSet<Multiaddr>,
 }
 
 impl<'a> HandleInnerEvent for AsClient<'a> {
     fn handle_event(
         &mut self,
-        params: &mut impl PollParameters,
+        _: &mut impl PollParameters,
         event: request_response::Event<DialRequest, DialResponse>,
     ) -> VecDeque<Action> {
         match event {
@@ -147,19 +145,7 @@ impl<'a> HandleInnerEvent for AsClient<'a> {
                 }
 
                 if let Ok(address) = response.result {
-                    // Update observed address score if it is finite.
-                    #[allow(deprecated)]
-                    // TODO: Fix once we report `AddressScore` through `FromSwarm` event.
-                    let score = params
-                        .external_addresses()
-                        .find_map(|r| (r.addr == address).then_some(r.score))
-                        .unwrap_or(AddressScore::Finite(0));
-                    if let AddressScore::Finite(finite_score) = score {
-                        actions.push_back(ToSwarm::ReportObservedAddr {
-                            address,
-                            score: AddressScore::Finite(finite_score + 1),
-                        });
-                    }
+                    actions.push_back(ToSwarm::ExternalAddrConfirmed(address));
                 }
 
                 actions
@@ -201,7 +187,7 @@ impl<'a> AsClient<'a> {
                 self.schedule_probe.reset(self.config.retry_interval);
 
                 let addresses = self
-                    .external_addresses
+                    .other_candidates
                     .iter()
                     .chain(self.listen_addresses.iter())
                     .cloned()

tests/test_client.rs

@@ -24,7 +24,7 @@ use libp2p_autonat::{
 };
 use libp2p_core::Multiaddr;
 use libp2p_identity::PeerId;
-use libp2p_swarm::{AddressScore, Swarm, SwarmEvent};
+use libp2p_swarm::{Swarm, SwarmEvent};
 use libp2p_swarm_test::SwarmExt as _;
 use std::time::Duration;
 
@@ -70,48 +70,6 @@ async fn test_auto_probe() {
     assert!(client.behaviour().public_address().is_none());
     assert_eq!(client.behaviour().confidence(), 0);
 
-    // Test Private NAT Status
-
-    // Artificially add a faulty address.
-    let unreachable_addr: Multiaddr = "/ip4/127.0.0.1/tcp/42".parse().unwrap();
-    client.add_external_address(unreachable_addr.clone(), AddressScore::Infinite);
-
-    let id = match client.next_behaviour_event().await {
-        Event::OutboundProbe(OutboundProbeEvent::Request { probe_id, peer }) => {
-            assert_eq!(peer, server_id);
-            probe_id
-        }
-        other => panic!("Unexpected behaviour event: {other:?}."),
-    };
-
-    match client.next_behaviour_event().await {
-        Event::OutboundProbe(OutboundProbeEvent::Error {
-            probe_id,
-            peer,
-            error,
-        }) => {
-            assert_eq!(peer.unwrap(), server_id);
-            assert_eq!(probe_id, id);
-            assert_eq!(
-                error,
-                OutboundProbeError::Response(ResponseError::DialError)
-            );
-        }
-        other => panic!("Unexpected behaviour event: {other:?}."),
-    }
-
-    match client.next_behaviour_event().await {
-        Event::StatusChanged { old, new } => {
-            assert_eq!(old, NatStatus::Unknown);
-            assert_eq!(new, NatStatus::Private);
-        }
-        other => panic!("Unexpected behaviour event: {other:?}."),
-    }
-
-    assert_eq!(client.behaviour().confidence(), 0);
-    assert_eq!(client.behaviour().nat_status(), NatStatus::Private);
-    assert!(client.behaviour().public_address().is_none());
-
     // Test new public listening address
     client.listen().await;
 
@@ -142,12 +100,14 @@ async fn test_auto_probe() {
             }
             SwarmEvent::Behaviour(Event::StatusChanged { old, new }) => {
                 // Expect to flip status to public
-                assert_eq!(old, NatStatus::Private);
+                assert_eq!(old, NatStatus::Unknown);
                 assert!(matches!(new, NatStatus::Public(_)));
                 assert!(new.is_public());
                 break;
             }
             SwarmEvent::IncomingConnection { .. }
+            | SwarmEvent::ConnectionEstablished { .. }
+            | SwarmEvent::Dialing { .. }
             | SwarmEvent::NewListenAddr { .. }
             | SwarmEvent::ExpiredListenAddr { .. } => {}
             other => panic!("Unexpected swarm event: {other:?}."),
@@ -198,7 +158,7 @@ async fn test_confidence() {
         client.listen().await;
     } else {
         let unreachable_addr = "/ip4/127.0.0.1/tcp/42".parse().unwrap();
-        client.add_external_address(unreachable_addr, AddressScore::Infinite);
+        client.behaviour_mut().probe_address(unreachable_addr);
     }
 
     for i in 0..MAX_CONFIDENCE + 1 {

tests/test_server.rs

@@ -24,7 +24,7 @@ use libp2p_autonat::{
 use libp2p_core::{multiaddr::Protocol, ConnectedPoint, Endpoint, Multiaddr};
 use libp2p_identity::PeerId;
 use libp2p_swarm::DialError;
-use libp2p_swarm::{AddressScore, Swarm, SwarmEvent};
+use libp2p_swarm::{Swarm, SwarmEvent};
 use libp2p_swarm_test::SwarmExt as _;
 use std::{num::NonZeroU32, time::Duration};
 
@@ -131,10 +131,9 @@ async fn test_dial_back() {
 async fn test_dial_error() {
     let (mut server, server_id, server_addr) = new_server_swarm(None).await;
     let (mut client, client_id) = new_client_swarm(server_id, server_addr).await;
-    client.add_external_address(
-        "/ip4/127.0.0.1/tcp/12345".parse().unwrap(),
-        AddressScore::Infinite,
-    );
+    client
+        .behaviour_mut()
+        .probe_address("/ip4/127.0.0.1/tcp/12345".parse().unwrap());
     async_std::task::spawn(client.loop_on_next());
 
     let request_probe_id = match server.next_behaviour_event().await {
@@ -274,10 +273,9 @@ async fn test_dial_multiple_addr() {
 
     let (mut client, client_id) = new_client_swarm(server_id, server_addr.clone()).await;
     client.listen().await;
-    client.add_external_address(
-        "/ip4/127.0.0.1/tcp/12345".parse().unwrap(),
-        AddressScore::Infinite,
-    );
+    client
+        .behaviour_mut()
+        .probe_address("/ip4/127.0.0.1/tcp/12345".parse().unwrap());
     async_std::task::spawn(client.loop_on_next());
 
     let dial_addresses = match server.next_behaviour_event().await {