protocols/identify: Assist in peer discovery based on reported listen addresses from other peers (#2232)

Co-authored-by: Max Inden <mail@max-inden.de>

protocols/identify/CHANGELOG.md

@@ -5,6 +5,10 @@
 
 - Update dependencies.
 
+- Assist in peer discovery by returning reported listen addresses
+  of other peers from `addresses_of_peer`.
+  [PR 2232](https://github.com/libp2p/rust-libp2p/pull/2232)
+
 # 0.30.0 [2021-07-12]
 
 - Update dependencies.

protocols/identify/Cargo.toml

@@ -14,6 +14,7 @@ futures = "0.3.1"
 libp2p-core = { version = "0.30.0", path = "../../core", default-features = false }
 libp2p-swarm = { version = "0.31.0", path = "../../swarm" }
 log = "0.4.1"
+lru = "0.6"
 prost = "0.8"
 smallvec = "1.6.1"
 wasm-timer = "0.2"

protocols/identify/src/identify.rs

@@ -31,9 +31,11 @@ use libp2p_swarm::{
     NetworkBehaviour, NetworkBehaviourAction, NotifyHandler, PollParameters, ProtocolsHandler,
     ProtocolsHandlerUpgrErr,
 };
+use lru::LruCache;
 use std::{
     collections::{HashMap, HashSet, VecDeque},
     io,
+    iter::FromIterator,
     pin::Pin,
     task::Context,
     task::Poll,
@@ -57,6 +59,8 @@ pub struct Identify {
     /// Peers to which an active push with current information about
     /// the local peer should be sent.
     pending_push: HashSet<PeerId>,
+    /// The addresses of all peers that we have discovered.
+    discovered_peers: LruCache<PeerId, HashSet<Multiaddr>>,
 }
 
 /// A pending reply to an inbound identification request.
@@ -109,6 +113,10 @@ pub struct IdentifyConfig {
     ///
     /// Disabled by default.
     pub push_listen_addr_updates: bool,
+
+    /// How many entries of discovered peers to keep before we discard
+    /// the least-recently used one.
+    pub cache_size: usize,
 }
 
 impl IdentifyConfig {
@@ -122,6 +130,7 @@ impl IdentifyConfig {
             initial_delay: Duration::from_millis(500),
             interval: Duration::from_secs(5 * 60),
             push_listen_addr_updates: false,
+            cache_size: 100,
         }
     }
 
@@ -152,17 +161,29 @@ impl IdentifyConfig {
         self.push_listen_addr_updates = b;
         self
     }
+
+    /// Configures the size of the LRU cache, caching addresses of discovered peers.
+    ///
+    /// The [`Swarm`](libp2p_swarm::Swarm) may extend the set of addresses of an outgoing connection attempt via
+    ///  [`Identify::addresses_of_peer`].
+    pub fn with_cache_size(mut self, cache_size: usize) -> Self {
+        self.cache_size = cache_size;
+        self
+    }
 }
 
 impl Identify {
     /// Creates a new `Identify` network behaviour.
     pub fn new(config: IdentifyConfig) -> Self {
+        let discovered_peers = LruCache::new(config.cache_size);
+
         Identify {
             config,
             connected: HashMap::new(),
             pending_replies: VecDeque::new(),
             events: VecDeque::new(),
             pending_push: HashSet::new(),
+            discovered_peers,
         }
     }
 
@@ -254,6 +275,10 @@ impl NetworkBehaviour for Identify {
     ) {
         match event {
             IdentifyHandlerEvent::Identified(info) => {
+                // Replace existing addresses to prevent other peer from filling up our memory.
+                self.discovered_peers
+                    .put(peer_id, HashSet::from_iter(info.listen_addrs.clone()));
+
                 let observed = info.observed_addr.clone();
                 self.events.push_back(NetworkBehaviourAction::GenerateEvent(
                     IdentifyEvent::Received { peer_id, info },
@@ -388,6 +413,27 @@ impl NetworkBehaviour for Identify {
 
         Poll::Pending
     }
+
+    fn addresses_of_peer(&mut self, peer: &PeerId) -> Vec<Multiaddr> {
+        self.discovered_peers
+            .get(peer)
+            .cloned()
+            .map(|addr| Vec::from_iter(addr))
+            .unwrap_or_default()
+    }
+
+    fn inject_addr_reach_failure(
+        &mut self,
+        peer_id: Option<&PeerId>,
+        addr: &Multiaddr,
+        _: &dyn std::error::Error,
+    ) {
+        if let Some(peer) = peer_id {
+            if let Some(entry) = self.discovered_peers.get_mut(peer) {
+                entry.remove(addr);
+            }
+        }
+    }
 }
 
 /// Event emitted  by the `Identify` behaviour.
@@ -552,11 +598,7 @@ mod tests {
 
         let (mut swarm1, pubkey1) = {
             let (pubkey, transport) = transport();
-            let protocol = Identify::new(
+            let protocol = Identify::new(IdentifyConfig::new("a".to_string(), pubkey.clone()));
-                IdentifyConfig::new("a".to_string(), pubkey.clone())
-                    // Delay identification requests so we can test the push protocol.
-                    .with_initial_delay(Duration::from_secs(u32::MAX as u64)),
-            );
             let swarm = Swarm::new(transport, protocol, pubkey.to_peer_id());
             (swarm, pubkey)
         };
@@ -565,9 +607,7 @@ mod tests {
             let (pubkey, transport) = transport();
             let protocol = Identify::new(
                 IdentifyConfig::new("a".to_string(), pubkey.clone())
-                    .with_agent_version("b".to_string())
+                    .with_agent_version("b".to_string()),
-                    // Delay identification requests so we can test the push protocol.
-                    .with_initial_delay(Duration::from_secs(u32::MAX as u64)),
             );
             let swarm = Swarm::new(transport, protocol, pubkey.to_peer_id());
             (swarm, pubkey)
@@ -626,4 +666,80 @@ mod tests {
             }
         })
     }
+
+    #[test]
+    fn discover_peer_after_disconnect() {
+        let _ = env_logger::try_init();
+
+        let mut swarm1 = {
+            let (pubkey, transport) = transport();
+            let protocol = Identify::new(IdentifyConfig::new("a".to_string(), pubkey.clone()));
+
+            Swarm::new(transport, protocol, pubkey.to_peer_id())
+        };
+
+        let mut swarm2 = {
+            let (pubkey, transport) = transport();
+            let protocol = Identify::new(
+                IdentifyConfig::new("a".to_string(), pubkey.clone())
+                    .with_agent_version("b".to_string()),
+            );
+
+            Swarm::new(transport, protocol, pubkey.to_peer_id())
+        };
+
+        let swarm1_peer_id = *swarm1.local_peer_id();
+
+        let listener = swarm1
+            .listen_on("/ip4/127.0.0.1/tcp/0".parse().unwrap())
+            .unwrap();
+
+        let listen_addr = async_std::task::block_on(async {
+            loop {
+                match swarm1.select_next_some().await {
+                    SwarmEvent::NewListenAddr {
+                        address,
+                        listener_id,
+                    } if listener_id == listener => return address,
+                    _ => {}
+                }
+            }
+        });
+
+        async_std::task::spawn(async move {
+            loop {
+                swarm1.next().await;
+            }
+        });
+
+        swarm2.dial_addr(listen_addr).unwrap();
+
+        // wait until we identified
+        async_std::task::block_on(async {
+            loop {
+                if let SwarmEvent::Behaviour(IdentifyEvent::Received { .. }) =
+                    swarm2.select_next_some().await
+                {
+                    break;
+                }
+            }
+        });
+
+        swarm2.disconnect_peer_id(swarm1_peer_id).unwrap();
+
+        // we should still be able to dial now!
+        swarm2.dial(&swarm1_peer_id).unwrap();
+
+        let connected_peer = async_std::task::block_on(async {
+            loop {
+                if let SwarmEvent::ConnectionEstablished { peer_id, .. } =
+                    swarm2.select_next_some().await
+                {
+                    break peer_id;
+                }
+            }
+        });
+
+        assert_eq!(connected_peer, swarm1_peer_id);
+    }
 }