behaviour.rs

// Copyright 2018 Parity Technologies (UK) Ltd.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

use crate::handler::{self, Handler, InEvent};
use crate::protocol::{Info, Protocol, UpgradeError};
use libp2p_core::{multiaddr, ConnectedPoint, Endpoint, Multiaddr};
use libp2p_identity::PeerId;
use libp2p_identity::PublicKey;
use libp2p_swarm::behaviour::{ConnectionClosed, ConnectionEstablished, DialFailure, FromSwarm};
use libp2p_swarm::{
    dial_opts::DialOpts, AddressScore, ConnectionDenied, ConnectionHandlerUpgrErr, DialError,
    ExternalAddresses, ListenAddresses, NetworkBehaviour, NotifyHandler, PollParameters,
    THandlerInEvent, ToSwarm,
};
use libp2p_swarm::{ConnectionId, THandler, THandlerOutEvent};
use lru::LruCache;
use std::num::NonZeroUsize;
use std::{
    collections::{HashMap, HashSet, VecDeque},
    iter::FromIterator,
    task::Context,
    task::Poll,
    time::Duration,
};

/// Network behaviour that automatically identifies nodes periodically, returns information
/// about them, and answers identify queries from other nodes.
///
/// All external addresses of the local node supposedly observed by remotes
/// are reported via [`ToSwarm::ReportObservedAddr`] with a
/// [score](AddressScore) of `1`.
pub struct Behaviour {
    config: Config,
    /// For each peer we're connected to, the observed address to send back to it.
    connected: HashMap<PeerId, HashMap<ConnectionId, Multiaddr>>,
    /// Pending requests to be fulfilled, either `Handler` requests for `Behaviour` info
    /// to address identification requests, or push requests to peers
    /// with current information about the local peer.
    requests: Vec<Request>,
    /// Pending events to be emitted when polled.
    events: VecDeque<ToSwarm<Event, InEvent>>,
    /// The addresses of all peers that we have discovered.
    discovered_peers: PeerCache,

    listen_addresses: ListenAddresses,
    external_addresses: ExternalAddresses,
}

/// A `Behaviour` request to be fulfilled, either `Handler` requests for `Behaviour` info
/// to address identification requests, or push requests to peers
/// with current information about the local peer.
#[derive(Debug, PartialEq, Eq)]
struct Request {
    peer_id: PeerId,
    protocol: Protocol,
}

/// Configuration for the [`identify::Behaviour`](Behaviour).
#[non_exhaustive]
#[derive(Debug, Clone)]
pub struct Config {
    /// Application-specific version of the protocol family used by the peer,
    /// e.g. `ipfs/1.0.0` or `polkadot/1.0.0`.
    pub protocol_version: String,
    /// The public key of the local node. To report on the wire.
    pub local_public_key: PublicKey,
    /// Name and version of the local peer implementation, similar to the
    /// `User-Agent` header in the HTTP protocol.
    ///
    /// Defaults to `rust-libp2p/<libp2p-identify-version>`.
    pub agent_version: String,
    /// The initial delay before the first identification request
    /// is sent to a remote on a newly established connection.
    ///
    /// Defaults to 500ms.
    pub initial_delay: Duration,
    /// The interval at which identification requests are sent to
    /// the remote on established connections after the first request,
    /// i.e. the delay between identification requests.
    ///
    /// Defaults to 5 minutes.
    pub interval: Duration,

    /// Whether new or expired listen addresses of the local node should
    /// trigger an active push of an identify message to all connected peers.
    ///
    /// Enabling this option can result in connected peers being informed
    /// earlier about new or expired listen addresses of the local node,
    /// i.e. before the next periodic identify request with each peer.
    ///
    /// 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.
    ///
    /// Disabled by default.
    pub cache_size: usize,
}

impl Config {
    /// Creates a new configuration for the identify [`Behaviour`] that
    /// advertises the given protocol version and public key.
    pub fn new(protocol_version: String, local_public_key: PublicKey) -> Self {
        Self {
            protocol_version,
            agent_version: format!("rust-libp2p/{}", env!("CARGO_PKG_VERSION")),
            local_public_key,
            initial_delay: Duration::from_millis(500),
            interval: Duration::from_secs(5 * 60),
            push_listen_addr_updates: false,
            cache_size: 100,
        }
    }

    /// Configures the agent version sent to peers.
    pub fn with_agent_version(mut self, v: String) -> Self {
        self.agent_version = v;
        self
    }

    /// Configures the initial delay before the first identification
    /// request is sent on a newly established connection to a peer.
    pub fn with_initial_delay(mut self, d: Duration) -> Self {
        self.initial_delay = d;
        self
    }

    /// Configures the interval at which identification requests are
    /// sent to peers after the initial request.
    pub fn with_interval(mut self, d: Duration) -> Self {
        self.interval = d;
        self
    }

    /// Configures whether new or expired listen addresses of the local
    /// node should trigger an active push of an identify message to all
    /// connected peers.
    pub fn with_push_listen_addr_updates(mut self, b: bool) -> Self {
        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
    ///  [`Behaviour::addresses_of_peer`].
    pub fn with_cache_size(mut self, cache_size: usize) -> Self {
        self.cache_size = cache_size;
        self
    }
}

impl Behaviour {
    /// Creates a new identify [`Behaviour`].
    pub fn new(config: Config) -> Self {
        let discovered_peers = match NonZeroUsize::new(config.cache_size) {
            None => PeerCache::disabled(),
            Some(size) => PeerCache::enabled(size),
        };

        Self {
            config,
            connected: HashMap::new(),
            requests: Vec::new(),
            events: VecDeque::new(),
            discovered_peers,
            listen_addresses: Default::default(),
            external_addresses: Default::default(),
        }
    }

    /// Initiates an active push of the local peer information to the given peers.
    pub fn push<I>(&mut self, peers: I)
    where
        I: IntoIterator<Item = PeerId>,
    {
        for p in peers {
            let request = Request {
                peer_id: p,
                protocol: Protocol::Push,
            };
            if !self.requests.contains(&request) {
                self.requests.push(request);

                self.events.push_back(ToSwarm::Dial {
                    opts: DialOpts::peer_id(p).build(),
                });
            }
        }
    }

    fn on_connection_established(
        &mut self,
        ConnectionEstablished {
            peer_id,
            connection_id: conn,
            endpoint,
            failed_addresses,
            ..
        }: ConnectionEstablished,
    ) {
        let addr = match endpoint {
            ConnectedPoint::Dialer { address, .. } => address.clone(),
            ConnectedPoint::Listener { send_back_addr, .. } => send_back_addr.clone(),
        };

        self.connected
            .entry(peer_id)
            .or_default()
            .insert(conn, addr);

        if let Some(entry) = self.discovered_peers.get_mut(&peer_id) {
            for addr in failed_addresses {
                entry.remove(addr);
            }
        }
    }
}

impl NetworkBehaviour for Behaviour {
    type ConnectionHandler = Handler;
    type OutEvent = Event;

    fn handle_established_inbound_connection(
        &mut self,
        _: ConnectionId,
        peer: PeerId,
        _: &Multiaddr,
        remote_addr: &Multiaddr,
    ) -> Result<THandler<Self>, ConnectionDenied> {
        Ok(Handler::new(
            self.config.initial_delay,
            self.config.interval,
            peer,
            self.config.local_public_key.clone(),
            self.config.protocol_version.clone(),
            self.config.agent_version.clone(),
            remote_addr.clone(),
        ))
    }

    fn handle_established_outbound_connection(
        &mut self,
        _: ConnectionId,
        peer: PeerId,
        addr: &Multiaddr,
        _: Endpoint,
    ) -> Result<THandler<Self>, ConnectionDenied> {
        Ok(Handler::new(
            self.config.initial_delay,
            self.config.interval,
            peer,
            self.config.local_public_key.clone(),
            self.config.protocol_version.clone(),
            self.config.agent_version.clone(),
            addr.clone(), // TODO: This is weird? That is the public address we dialed, shouldn't need to tell the other party?
        ))
    }

    fn on_connection_handler_event(
        &mut self,
        peer_id: PeerId,
        connection_id: ConnectionId,
        event: THandlerOutEvent<Self>,
    ) {
        match event {
            handler::Event::Identified(mut info) => {
                // Remove invalid multiaddrs.
                info.listen_addrs
                    .retain(|addr| multiaddr_matches_peer_id(addr, &peer_id));

                // Replace existing addresses to prevent other peer from filling up our memory.
                self.discovered_peers
                    .put(peer_id, info.listen_addrs.iter().cloned());

                let observed = info.observed_addr.clone();
                self.events
                    .push_back(ToSwarm::GenerateEvent(Event::Received { peer_id, info }));
                self.events.push_back(ToSwarm::ReportObservedAddr {
                    address: observed,
                    score: AddressScore::Finite(1),
                });
            }
            handler::Event::Identification(peer) => {
                self.events
                    .push_back(ToSwarm::GenerateEvent(Event::Sent { peer_id: peer }));
            }
            handler::Event::IdentificationPushed => {
                self.events
                    .push_back(ToSwarm::GenerateEvent(Event::Pushed { peer_id }));
            }
            handler::Event::Identify => {
                self.requests.push(Request {
                    peer_id,
                    protocol: Protocol::Identify(connection_id),
                });
            }
            handler::Event::IdentificationError(error) => {
                self.events
                    .push_back(ToSwarm::GenerateEvent(Event::Error { peer_id, error }));
            }
        }
    }

    fn poll(
        &mut self,
        _cx: &mut Context<'_>,
        params: &mut impl PollParameters,
    ) -> Poll<ToSwarm<Self::OutEvent, THandlerInEvent<Self>>> {
        if let Some(event) = self.events.pop_front() {
            return Poll::Ready(event);
        }

        // Check for pending requests.
        match self.requests.pop() {
            Some(Request {
                peer_id,
                protocol: Protocol::Push,
            }) => Poll::Ready(ToSwarm::NotifyHandler {
                peer_id,
                handler: NotifyHandler::Any,
                event: InEvent {
                    listen_addrs: self
                        .listen_addresses
                        .iter()
                        .chain(self.external_addresses.iter())
                        .cloned()
                        .collect(),
                    supported_protocols: supported_protocols(params),
                    protocol: Protocol::Push,
                },
            }),
            Some(Request {
                peer_id,
                protocol: Protocol::Identify(connection_id),
            }) => Poll::Ready(ToSwarm::NotifyHandler {
                peer_id,
                handler: NotifyHandler::One(connection_id),
                event: InEvent {
                    listen_addrs: self
                        .listen_addresses
                        .iter()
                        .chain(self.external_addresses.iter())
                        .cloned()
                        .collect(),
                    supported_protocols: supported_protocols(params),
                    protocol: Protocol::Identify(connection_id),
                },
            }),
            None => Poll::Pending,
        }
    }

    fn handle_pending_outbound_connection(
        &mut self,
        _connection_id: ConnectionId,
        maybe_peer: Option<PeerId>,
        _addresses: &[Multiaddr],
        _effective_role: Endpoint,
    ) -> Result<Vec<Multiaddr>, ConnectionDenied> {
        let peer = match maybe_peer {
            None => return Ok(vec![]),
            Some(peer) => peer,
        };

        Ok(self.discovered_peers.get(&peer))
    }

    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) => {
                self.on_connection_established(connection_established)
            }
            FromSwarm::ConnectionClosed(ConnectionClosed {
                peer_id,
                connection_id,
                remaining_established,
                ..
            }) => {
                if remaining_established == 0 {
                    self.connected.remove(&peer_id);
                    self.requests.retain(|request| {
                        request
                            != &Request {
                                peer_id,
                                protocol: Protocol::Push,
                            }
                    });
                } else if let Some(addrs) = self.connected.get_mut(&peer_id) {
                    addrs.remove(&connection_id);
                }
            }
            FromSwarm::DialFailure(DialFailure { peer_id, error, .. }) => {
                if let Some(peer_id) = peer_id {
                    if !self.connected.contains_key(&peer_id) {
                        self.requests.retain(|request| {
                            request
                                != &Request {
                                    peer_id,
                                    protocol: Protocol::Push,
                                }
                        });
                    }
                }

                if let Some(entry) = peer_id.and_then(|id| self.discovered_peers.get_mut(&id)) {
                    if let DialError::Transport(errors) = error {
                        for (addr, _error) in errors {
                            entry.remove(addr);
                        }
                    }
                }
            }
            FromSwarm::NewListenAddr(_) | FromSwarm::ExpiredListenAddr(_) => {
                if self.config.push_listen_addr_updates {
                    for p in self.connected.keys() {
                        let request = Request {
                            peer_id: *p,
                            protocol: Protocol::Push,
                        };
                        if !self.requests.contains(&request) {
                            self.requests.push(request);
                        }
                    }
                }
            }
            FromSwarm::AddressChange(_)
            | FromSwarm::ListenFailure(_)
            | FromSwarm::NewListener(_)
            | FromSwarm::ListenerError(_)
            | FromSwarm::ListenerClosed(_)
            | FromSwarm::NewExternalAddr(_)
            | FromSwarm::ExpiredExternalAddr(_) => {}
        }
    }
}

/// Event emitted  by the `Identify` behaviour.
#[allow(clippy::large_enum_variant)]
#[derive(Debug)]
pub enum Event {
    /// Identification information has been received from a peer.
    Received {
        /// The peer that has been identified.
        peer_id: PeerId,
        /// The information provided by the peer.
        info: Info,
    },
    /// Identification information of the local node has been sent to a peer in
    /// response to an identification request.
    Sent {
        /// The peer that the information has been sent to.
        peer_id: PeerId,
    },
    /// Identification information of the local node has been actively pushed to
    /// a peer.
    Pushed {
        /// The peer that the information has been sent to.
        peer_id: PeerId,
    },
    /// Error while attempting to identify the remote.
    Error {
        /// The peer with whom the error originated.
        peer_id: PeerId,
        /// The error that occurred.
        error: ConnectionHandlerUpgrErr<UpgradeError>,
    },
}

fn supported_protocols(params: &impl PollParameters) -> Vec<String> {
    // The protocol names can be bytes, but the identify protocol except UTF-8 strings.
    // There's not much we can do to solve this conflict except strip non-UTF-8 characters.
    params
        .supported_protocols()
        .map(|p| String::from_utf8_lossy(&p).to_string())
        .collect()
}

/// If there is a given peer_id in the multiaddr, make sure it is the same as
/// the given peer_id. If there is no peer_id for the peer in the mutiaddr, this returns true.
fn multiaddr_matches_peer_id(addr: &Multiaddr, peer_id: &PeerId) -> bool {
    let last_component = addr.iter().last();
    if let Some(multiaddr::Protocol::P2p(multi_addr_peer_id)) = last_component {
        return multi_addr_peer_id == *peer_id.as_ref();
    }
    true
}

struct PeerCache(Option<LruCache<PeerId, HashSet<Multiaddr>>>);

impl PeerCache {
    fn disabled() -> Self {
        Self(None)
    }

    fn enabled(size: NonZeroUsize) -> Self {
        Self(Some(LruCache::new(size)))
    }

    fn get_mut(&mut self, peer: &PeerId) -> Option<&mut HashSet<Multiaddr>> {
        self.0.as_mut()?.get_mut(peer)
    }

    fn put(&mut self, peer: PeerId, addresses: impl Iterator<Item = Multiaddr>) {
        let cache = match self.0.as_mut() {
            None => return,
            Some(cache) => cache,
        };

        cache.put(peer, HashSet::from_iter(addresses));
    }

    fn get(&mut self, peer: &PeerId) -> Vec<Multiaddr> {
        let cache = match self.0.as_mut() {
            None => return Vec::new(),
            Some(cache) => cache,
        };

        cache
            .get(peer)
            .cloned()
            .map(Vec::from_iter)
            .unwrap_or_default()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use futures::pin_mut;
    use futures::prelude::*;
    use libp2p_core::{muxing::StreamMuxerBox, transport, upgrade, Transport};
    use libp2p_identity as identity;
    use libp2p_identity::PeerId;
    use libp2p_mplex::MplexConfig;
    use libp2p_noise as noise;
    use libp2p_swarm::{Swarm, SwarmBuilder, SwarmEvent};
    use libp2p_tcp as tcp;
    use std::time::Duration;

    fn transport() -> (
        identity::PublicKey,
        transport::Boxed<(PeerId, StreamMuxerBox)>,
    ) {
        let id_keys = identity::Keypair::generate_ed25519();
        let noise_keys = noise::Keypair::<noise::X25519Spec>::new()
            .into_authentic(&id_keys)
            .unwrap();
        let pubkey = id_keys.public();
        let transport = tcp::async_io::Transport::new(tcp::Config::default().nodelay(true))
            .upgrade(upgrade::Version::V1)
            .authenticate(noise::NoiseConfig::xx(noise_keys).into_authenticated())
            .multiplex(MplexConfig::new())
            .boxed();
        (pubkey, transport)
    }

    #[test]
    fn periodic_identify() {
        let (mut swarm1, pubkey1) = {
            let (pubkey, transport) = transport();
            let protocol = Behaviour::new(
                Config::new("a".to_string(), pubkey.clone()).with_agent_version("b".to_string()),
            );
            let swarm =
                SwarmBuilder::with_async_std_executor(transport, protocol, pubkey.to_peer_id())
                    .build();
            (swarm, pubkey)
        };

        let (mut swarm2, pubkey2) = {
            let (pubkey, transport) = transport();
            let protocol = Behaviour::new(
                Config::new("c".to_string(), pubkey.clone()).with_agent_version("d".to_string()),
            );
            let swarm =
                SwarmBuilder::with_async_std_executor(transport, protocol, pubkey.to_peer_id())
                    .build();
            (swarm, pubkey)
        };

        swarm1
            .listen_on("/ip4/127.0.0.1/tcp/0".parse().unwrap())
            .unwrap();

        let listen_addr = async_std::task::block_on(async {
            loop {
                let swarm1_fut = swarm1.select_next_some();
                pin_mut!(swarm1_fut);
                if let SwarmEvent::NewListenAddr { address, .. } = swarm1_fut.await {
                    return address;
                }
            }
        });
        swarm2.dial(listen_addr).unwrap();

        // nb. Either swarm may receive the `Identified` event first, upon which
        // it will permit the connection to be closed, as defined by
        // `Handler::connection_keep_alive`. Hence the test succeeds if
        // either `Identified` event arrives correctly.
        async_std::task::block_on(async move {
            loop {
                let swarm1_fut = swarm1.select_next_some();
                pin_mut!(swarm1_fut);
                let swarm2_fut = swarm2.select_next_some();
                pin_mut!(swarm2_fut);

                match future::select(swarm1_fut, swarm2_fut)
                    .await
                    .factor_second()
                    .0
                {
                    future::Either::Left(SwarmEvent::Behaviour(Event::Received {
                        info, ..
                    })) => {
                        assert_eq!(info.public_key, pubkey2);
                        assert_eq!(info.protocol_version, "c");
                        assert_eq!(info.agent_version, "d");
                        assert!(!info.protocols.is_empty());
                        assert!(info.listen_addrs.is_empty());
                        return;
                    }
                    future::Either::Right(SwarmEvent::Behaviour(Event::Received {
                        info, ..
                    })) => {
                        assert_eq!(info.public_key, pubkey1);
                        assert_eq!(info.protocol_version, "a");
                        assert_eq!(info.agent_version, "b");
                        assert!(!info.protocols.is_empty());
                        assert_eq!(info.listen_addrs.len(), 1);
                        return;
                    }
                    _ => {}
                }
            }
        })
    }

    #[test]
    fn identify_push() {
        let _ = env_logger::try_init();

        let (mut swarm1, pubkey1) = {
            let (pubkey, transport) = transport();
            let protocol = Behaviour::new(Config::new("a".to_string(), pubkey.clone()));
            let swarm =
                SwarmBuilder::with_async_std_executor(transport, protocol, pubkey.to_peer_id())
                    .build();
            (swarm, pubkey)
        };

        let (mut swarm2, pubkey2) = {
            let (pubkey, transport) = transport();
            let protocol = Behaviour::new(
                Config::new("a".to_string(), pubkey.clone()).with_agent_version("b".to_string()),
            );
            let swarm =
                SwarmBuilder::with_async_std_executor(transport, protocol, pubkey.to_peer_id())
                    .build();
            (swarm, pubkey)
        };

        Swarm::listen_on(&mut swarm1, "/ip4/127.0.0.1/tcp/0".parse().unwrap()).unwrap();

        let listen_addr = async_std::task::block_on(async {
            loop {
                let swarm1_fut = swarm1.select_next_some();
                pin_mut!(swarm1_fut);
                if let SwarmEvent::NewListenAddr { address, .. } = swarm1_fut.await {
                    return address;
                }
            }
        });

        swarm2.dial(listen_addr).unwrap();

        async_std::task::block_on(async move {
            loop {
                let swarm1_fut = swarm1.select_next_some();
                let swarm2_fut = swarm2.select_next_some();

                {
                    pin_mut!(swarm1_fut);
                    pin_mut!(swarm2_fut);
                    match future::select(swarm1_fut, swarm2_fut)
                        .await
                        .factor_second()
                        .0
                    {
                        future::Either::Left(SwarmEvent::Behaviour(Event::Received {
                            info,
                            ..
                        })) => {
                            assert_eq!(info.public_key, pubkey2);
                            assert_eq!(info.protocol_version, "a");
                            assert_eq!(info.agent_version, "b");
                            assert!(!info.protocols.is_empty());
                            assert!(info.listen_addrs.is_empty());
                            return;
                        }
                        future::Either::Right(SwarmEvent::ConnectionEstablished { .. }) => {
                            // Once a connection is established, we can initiate an
                            // active push below.
                        }
                        _ => continue,
                    }
                }

                swarm2
                    .behaviour_mut()
                    .push(std::iter::once(pubkey1.to_peer_id()));
            }
        })
    }

    #[test]
    fn discover_peer_after_disconnect() {
        let _ = env_logger::try_init();

        let mut swarm1 = {
            let (pubkey, transport) = transport();
            let protocol = Behaviour::new(
                Config::new("a".to_string(), pubkey.clone())
                    // `swarm1` will set `KeepAlive::No` once it identified `swarm2` and thus
                    // closes the connection. At this point in time `swarm2` might not yet have
                    // identified `swarm1`. To give `swarm2` enough time, set an initial delay on
                    // `swarm1`.
                    .with_initial_delay(Duration::from_secs(10)),
            );

            SwarmBuilder::with_async_std_executor(transport, protocol, pubkey.to_peer_id()).build()
        };

        let mut swarm2 = {
            let (pubkey, transport) = transport();
            let protocol = Behaviour::new(
                Config::new("a".to_string(), pubkey.clone()).with_agent_version("b".to_string()),
            );

            SwarmBuilder::with_async_std_executor(transport, protocol, pubkey.to_peer_id()).build()
        };

        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(listen_addr).unwrap();

        // Wait until we identified.
        async_std::task::block_on(async {
            loop {
                if let SwarmEvent::Behaviour(Event::Received { .. }) =
                    swarm2.select_next_some().await
                {
                    break;
                }
            }
        });

        swarm2.disconnect_peer_id(swarm1_peer_id).unwrap();

        // Wait for connection to close.
        async_std::task::block_on(async {
            loop {
                if let SwarmEvent::ConnectionClosed { peer_id, .. } =
                    swarm2.select_next_some().await
                {
                    break peer_id;
                }
            }
        });

        // 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);
    }

    #[test]
    fn check_multiaddr_matches_peer_id() {
        let peer_id = PeerId::random();
        let other_peer_id = PeerId::random();
        let mut addr: Multiaddr = "/ip4/147.75.69.143/tcp/4001"
            .parse()
            .expect("failed to parse multiaddr");

        let addr_without_peer_id: Multiaddr = addr.clone();
        let mut addr_with_other_peer_id = addr.clone();

        addr.push(multiaddr::Protocol::P2p(peer_id.into()));
        addr_with_other_peer_id.push(multiaddr::Protocol::P2p(other_peer_id.into()));

        assert!(multiaddr_matches_peer_id(&addr, &peer_id));
        assert!(!multiaddr_matches_peer_id(
            &addr_with_other_peer_id,
            &peer_id
        ));
        assert!(multiaddr_matches_peer_id(&addr_without_peer_id, &peer_id));
    }
}