[ping] Refactor the ping protocol for conformity. (#1692)

* Refactor the ping protocol.

Such that pings are sent over a single substream, as it is
done in other libp2p implementations. Note that, since each
peer sends its pings over a single, dedicated substream,
every peer that participates in the protocol has effectively
two open substreams.

* Cleanup

* Update ping changelog.

* Update protocols/ping/src/protocol.rs

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

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

protocols/ping/CHANGELOG.md

@@ -1,5 +1,9 @@
 # 0.21.0 [unreleased]
 
+- Refactor the ping protocol for conformity by (re)using
+a single substream for outbound pings, addressing
+[#1601](https://github.com/libp2p/rust-libp2p/issues/1601).
+
 - Bump `libp2p-core` and `libp2p-swarm` dependencies.
 
 # 0.20.0 [2020-07-01]

protocols/ping/src/handler.rs

@@ -20,14 +20,23 @@
 
 use crate::protocol;
 use futures::prelude::*;
+use futures::future::BoxFuture;
 use libp2p_swarm::{
     KeepAlive,
+    NegotiatedSubstream,
     SubstreamProtocol,
     ProtocolsHandler,
     ProtocolsHandlerUpgrErr,
     ProtocolsHandlerEvent
 };
-use std::{error::Error, io, fmt, num::NonZeroU32, pin::Pin, task::Context, task::Poll, time::Duration};
+use std::{
+    error::Error,
+    io,
+    fmt,
+    num::NonZeroU32,
+    task::{Context, Poll},
+    time::Duration
+};
 use std::collections::VecDeque;
 use wasm_timer::Delay;
 use void::Void;
@@ -160,13 +169,21 @@ impl Error for PingFailure {
 pub struct PingHandler {
     /// Configuration options.
     config: PingConfig,
-    /// The timer for when to send the next ping.
-    next_ping: Delay,
-    /// The pending results from inbound or outbound pings, ready
-    /// to be `poll()`ed.
-    pending_results: VecDeque<PingResult>,
+    /// The timer used for the delay to the next ping as well as
+    /// the ping timeout.
+    timer: Delay,
+    /// Outbound ping failures that are pending to be processed by `poll()`.
+    pending_errors: VecDeque<PingFailure>,
     /// The number of consecutive ping failures that occurred.
+    ///
+    /// Each successful ping resets this counter to 0.
     failures: u32,
+    /// The outbound ping state.
+    outbound: Option<PingState>,
+    /// The inbound pong handler, i.e. if there is an inbound
+    /// substream, this is always a future that waits for the
+    /// next inbound ping to be answered.
+    inbound: Option<PongFuture>,
 }
 
 impl PingHandler {
@@ -174,9 +191,11 @@ impl PingHandler {
     pub fn new(config: PingConfig) -> Self {
         PingHandler {
             config,
-            next_ping: Delay::new(Duration::new(0, 0)),
-            pending_results: VecDeque::with_capacity(2),
+            timer: Delay::new(Duration::new(0, 0)),
+            pending_errors: VecDeque::with_capacity(2),
             failures: 0,
+            outbound: None,
+            inbound: None,
         }
     }
 }
@@ -193,24 +212,25 @@ impl ProtocolsHandler for PingHandler {
         SubstreamProtocol::new(protocol::Ping)
     }
 
-    fn inject_fully_negotiated_inbound(&mut self, _: ()) {
-        // A ping from a remote peer has been answered.
-        self.pending_results.push_front(Ok(PingSuccess::Pong));
+    fn inject_fully_negotiated_inbound(&mut self, stream: NegotiatedSubstream) {
+        self.inbound = Some(protocol::recv_ping(stream).boxed());
     }
 
-    fn inject_fully_negotiated_outbound(&mut self, rtt: Duration, _info: ()) {
-        // A ping initiated by the local peer was answered by the remote.
-        self.pending_results.push_front(Ok(PingSuccess::Ping { rtt }));
+    fn inject_fully_negotiated_outbound(&mut self, stream: NegotiatedSubstream, (): ()) {
+        self.timer.reset(self.config.timeout);
+        self.outbound = Some(PingState::Ping(protocol::send_ping(stream).boxed()));
     }
 
     fn inject_event(&mut self, _: Void) {}
 
-    fn inject_dial_upgrade_error(&mut self, _info: (), error: ProtocolsHandlerUpgrErr<io::Error>) {
-        self.pending_results.push_front(
-            Err(match error {
+    fn inject_dial_upgrade_error(&mut self, _info: (), error: ProtocolsHandlerUpgrErr<Void>) {
+        self.outbound = None; // Request a new substream on the next `poll`.
+        self.pending_errors.push_front(
+            match error {
+                // Note: This timeout only covers protocol negotiation.
                 ProtocolsHandlerUpgrErr::Timeout => PingFailure::Timeout,
-                e => PingFailure::Other { error: Box::new(e) }
-            }))
+                e => PingFailure::Other { error: Box::new(e) },
+            })
     }
 
     fn connection_keep_alive(&self) -> KeepAlive {
@@ -222,117 +242,117 @@ impl ProtocolsHandler for PingHandler {
     }
 
     fn poll(&mut self, cx: &mut Context<'_>) -> Poll<ProtocolsHandlerEvent<protocol::Ping, (), PingResult, Self::Error>> {
-        if let Some(result) = self.pending_results.pop_back() {
-            if let Ok(PingSuccess::Ping { .. }) = result {
-                self.failures = 0;
-                self.next_ping.reset(self.config.interval);
+        // Respond to inbound pings.
+        if let Some(fut) = self.inbound.as_mut() {
+            match fut.poll_unpin(cx) {
+                Poll::Pending => {},
+                Poll::Ready(Err(e)) => {
+                    log::debug!("Inbound ping error: {:?}", e);
+                    self.inbound = None;
                 }
-            if let Err(e) = result {
-                self.failures += 1;
-                if self.failures >= self.config.max_failures.get() {
-                    return Poll::Ready(ProtocolsHandlerEvent::Close(e))
-                } else {
-                    return Poll::Ready(ProtocolsHandlerEvent::Custom(Err(e)))
+                Poll::Ready(Ok(stream)) => {
+                    // A ping from a remote peer has been answered, wait for the next.
+                    self.inbound = Some(protocol::recv_ping(stream).boxed());
+                    return Poll::Ready(ProtocolsHandlerEvent::Custom(Ok(PingSuccess::Pong)))
                 }
             }
-            return Poll::Ready(ProtocolsHandlerEvent::Custom(result))
         }
 
-        match Future::poll(Pin::new(&mut self.next_ping), cx) {
+        loop {
+            // Check for outbound ping failures.
+            if let Some(error) = self.pending_errors.pop_back() {
+                log::debug!("Ping failure: {:?}", error);
+
+                self.failures += 1;
+
+                // Note: For backward-compatibility, with configured
+                // `max_failures == 1`, the first failure is always "free"
+                // and silent. This allows peers who still use a new substream
+                // for each ping to have successful ping exchanges with peers
+                // that use a single substream, since every successful ping
+                // resets `failures` to `0`, while at the same time emitting
+                // events only for `max_failures - 1` failures, as before.
+                if self.failures > 1 || self.config.max_failures.get() > 1 {
+                    if self.failures >= self.config.max_failures.get() {
+                        log::debug!("Too many failures ({}). Closing connection.", self.failures);
+                        return Poll::Ready(ProtocolsHandlerEvent::Close(error))
+                    }
+
+                    return Poll::Ready(ProtocolsHandlerEvent::Custom(Err(error)))
+                }
+            }
+
+            // Continue outbound pings.
+            match self.outbound.take() {
+                Some(PingState::Ping(mut ping)) => match ping.poll_unpin(cx) {
+                    Poll::Pending => {
+                        if self.timer.poll_unpin(cx).is_ready() {
+                            self.pending_errors.push_front(PingFailure::Timeout);
+                        } else {
+                            self.outbound = Some(PingState::Ping(ping));
+                            break
+                        }
+                    },
+                    Poll::Ready(Ok((stream, rtt))) => {
+                        self.failures = 0;
+                        self.timer.reset(self.config.interval);
+                        self.outbound = Some(PingState::Idle(stream));
+                        return Poll::Ready(
+                            ProtocolsHandlerEvent::Custom(
+                                Ok(PingSuccess::Ping { rtt })))
+                    }
+                    Poll::Ready(Err(e)) => {
+                        self.pending_errors.push_front(PingFailure::Other {
+                            error: Box::new(e)
+                        });
+                    }
+                },
+                Some(PingState::Idle(stream)) => match self.timer.poll_unpin(cx) {
+                    Poll::Pending => {
+                        self.outbound = Some(PingState::Idle(stream));
+                        break
+                    },
                     Poll::Ready(Ok(())) => {
-                self.next_ping.reset(self.config.timeout);
+                        self.timer.reset(self.config.timeout);
+                        self.outbound = Some(PingState::Ping(protocol::send_ping(stream).boxed()));
+                    },
+                    Poll::Ready(Err(e)) => {
+                        return Poll::Ready(ProtocolsHandlerEvent::Close(
+                            PingFailure::Other {
+                                error: Box::new(e)
+                            }))
+                    }
+                }
+                Some(PingState::OpenStream) => {
+                    self.outbound = Some(PingState::OpenStream);
+                    break
+                }
+                None => {
+                    self.outbound = Some(PingState::OpenStream);
                     let protocol = SubstreamProtocol::new(protocol::Ping)
                         .with_timeout(self.config.timeout);
-                Poll::Ready(ProtocolsHandlerEvent::OutboundSubstreamRequest {
+                    return Poll::Ready(ProtocolsHandlerEvent::OutboundSubstreamRequest {
                         protocol,
                         info: (),
                     })
-            },
-            Poll::Pending => Poll::Pending,
-            Poll::Ready(Err(e)) =>
-                Poll::Ready(ProtocolsHandlerEvent::Close(PingFailure::Other { error: Box::new(e) }))
                 }
             }
         }
 
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    use futures::future;
-    use quickcheck::*;
-    use rand::Rng;
-
-    impl Arbitrary for PingConfig {
-        fn arbitrary<G: Gen>(g: &mut G) -> PingConfig {
-            PingConfig::new()
-                .with_timeout(Duration::from_secs(g.gen_range(0, 3600)))
-                .with_interval(Duration::from_secs(g.gen_range(0, 3600)))
-                .with_max_failures(NonZeroU32::new(g.gen_range(1, 100)).unwrap())
+        Poll::Pending
     }
 }
 
-    fn tick(h: &mut PingHandler)
-        -> ProtocolsHandlerEvent<protocol::Ping, (), PingResult, PingFailure>
-    {
-        async_std::task::block_on(future::poll_fn(|cx| h.poll(cx) ))
+type PingFuture = BoxFuture<'static, Result<(NegotiatedSubstream, Duration), io::Error>>;
+type PongFuture = BoxFuture<'static, Result<NegotiatedSubstream, io::Error>>;
+
+/// The current state w.r.t. outbound pings.
+enum PingState {
+    /// A new substream is being negotiated for the ping protocol.
+    OpenStream,
+    /// The substream is idle, waiting to send the next ping.
+    Idle(NegotiatedSubstream),
+    /// A ping is being sent and the response awaited.
+    Ping(PingFuture),
 }
 
-    #[test]
-    fn ping_interval() {
-        fn prop(cfg: PingConfig, ping_rtt: Duration) -> bool {
-            let mut h = PingHandler::new(cfg);
-
-            // Send ping
-            match tick(&mut h) {
-                ProtocolsHandlerEvent::OutboundSubstreamRequest { protocol, info: _ } => {
-                    // The handler must use the configured timeout.
-                    assert_eq!(protocol.timeout(), &h.config.timeout);
-                }
-                e => panic!("Unexpected event: {:?}", e)
-            }
-
-            // Receive pong
-            h.inject_fully_negotiated_outbound(ping_rtt, ());
-            match tick(&mut h) {
-                ProtocolsHandlerEvent::Custom(Ok(PingSuccess::Ping { rtt })) => {
-                    // The handler must report the given RTT.
-                    assert_eq!(rtt, ping_rtt);
-                }
-                e => panic!("Unexpected event: {:?}", e)
-            }
-
-            true
-        }
-
-        quickcheck(prop as fn(_,_) -> _);
-    }
-
-    #[test]
-    fn max_failures() {
-        let cfg = PingConfig::arbitrary(&mut StdGen::new(rand::thread_rng(), 100));
-        let mut h = PingHandler::new(cfg);
-        for _ in 0 .. h.config.max_failures.get() - 1 {
-            h.inject_dial_upgrade_error((), ProtocolsHandlerUpgrErr::Timeout);
-            match tick(&mut h) {
-                ProtocolsHandlerEvent::Custom(Err(PingFailure::Timeout)) => {}
-                e => panic!("Unexpected event: {:?}", e)
-            }
-        }
-        h.inject_dial_upgrade_error((), ProtocolsHandlerUpgrErr::Timeout);
-        match tick(&mut h) {
-            ProtocolsHandlerEvent::Close(PingFailure::Timeout) => {
-                assert_eq!(h.failures, h.config.max_failures.get());
-            }
-            e => panic!("Unexpected event: {:?}", e)
-        }
-        h.inject_fully_negotiated_outbound(Duration::from_secs(1), ());
-        match tick(&mut h) {
-            ProtocolsHandlerEvent::Custom(Ok(PingSuccess::Ping { .. })) => {
-                // A success resets the counter for consecutive failures.
-                assert_eq!(h.failures, 0);
-            }
-            e => panic!("Unexpected event: {:?}", e)
-        }
-    }
-}

protocols/ping/src/lib.rs

@@ -28,15 +28,14 @@
 //!
 //! The [`Ping`] struct implements the [`NetworkBehaviour`] trait. When used with a [`Swarm`],
 //! it will respond to inbound ping requests and as necessary periodically send outbound
-//! ping requests on every established connection. If a configurable number of pings fail,
-//! the connection will be closed.
+//! ping requests on every established connection. If a configurable number of consecutive
+//! pings fail, the connection will be closed.
 //!
 //! The `Ping` network behaviour produces [`PingEvent`]s, which may be consumed from the `Swarm`
 //! by an application, e.g. to collect statistics.
 //!
-//! > **Note**: The ping protocol does not keep otherwise idle connections alive,
-//! > it only adds an additional condition for terminating the connection, namely
-//! > a certain number of failed ping requests.
+//! > **Note**: The ping protocol does not keep otherwise idle connections alive
+//! > by default, see [`PingConfig::with_keep_alive`] for changing this behaviour.
 //!
 //! [`Swarm`]: libp2p_swarm::Swarm
 //! [`Transport`]: libp2p_core::Transport

protocols/ping/src/protocol.rs

@@ -18,23 +18,27 @@
 // FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
-use futures::{future::BoxFuture, prelude::*};
+use futures::prelude::*;
 use libp2p_core::{InboundUpgrade, OutboundUpgrade, UpgradeInfo};
-use log::debug;
+use libp2p_swarm::NegotiatedSubstream;
 use rand::{distributions, prelude::*};
 use std::{io, iter, time::Duration};
+use void::Void;
 use wasm_timer::Instant;
 
-/// Represents a prototype for an upgrade to handle the ping protocol.
+/// The `Ping` protocol upgrade.
 ///
-/// The protocol works the following way:
+/// The ping protocol sends 32 bytes of random data in configurable
+/// intervals over a single outbound substream, expecting to receive
+/// the same bytes as a response. At the same time, incoming pings
+/// on inbound substreams are answered by sending back the received bytes.
 ///
-/// - Dialer sends 32 bytes of random data.
-/// - Listener receives the data and sends it back.
-/// - Dialer receives the data and verifies that it matches what it sent.
+/// At most a single inbound and outbound substream is kept open at
+/// any time. In case of a ping timeout or another error on a substream, the
+/// substream is dropped. If a configurable number of consecutive
+/// outbound pings fail, the connection is closed.
 ///
-/// The dialer produces a `Duration`, which corresponds to the round-trip time
-/// of the payload.
+/// Successful pings report the round-trip time.
 ///
 /// > **Note**: The round-trip time of a ping may be subject to delays induced
 /// >           by the underlying transport, e.g. in the case of TCP there is
@@ -55,59 +59,60 @@ impl UpgradeInfo for Ping {
     }
 }
 
-impl<TSocket> InboundUpgrade<TSocket> for Ping
+impl InboundUpgrade<NegotiatedSubstream> for Ping {
+    type Output = NegotiatedSubstream;
+    type Error = Void;
+    type Future = future::Ready<Result<Self::Output, Self::Error>>;
+
+    fn upgrade_inbound(self, stream: NegotiatedSubstream, _: Self::Info) -> Self::Future {
+        future::ok(stream)
+    }
+}
+
+impl OutboundUpgrade<NegotiatedSubstream> for Ping {
+    type Output = NegotiatedSubstream;
+    type Error = Void;
+    type Future = future::Ready<Result<Self::Output, Self::Error>>;
+
+    fn upgrade_outbound(self, stream: NegotiatedSubstream, _: Self::Info) -> Self::Future {
+        future::ok(stream)
+    }
+}
+
+/// Sends a ping and waits for the pong.
+pub async fn send_ping<S>(mut stream: S) -> io::Result<(S, Duration)>
 where
-    TSocket: AsyncRead + AsyncWrite + Send + Unpin + 'static,
+    S: AsyncRead + AsyncWrite + Unpin
 {
-    type Output = ();
-    type Error = io::Error;
-    type Future = BoxFuture<'static, Result<(), io::Error>>;
-
-    fn upgrade_inbound(self, mut socket: TSocket, _: Self::Info) -> Self::Future {
-        async move {
-            let mut payload = [0u8; PING_SIZE];
-            while let Ok(_) = socket.read_exact(&mut payload).await {
-                socket.write_all(&payload).await?;
-            }
-            socket.close().await?;
-            Ok(())
-        }.boxed()
-    }
-}
-
-impl<TSocket> OutboundUpgrade<TSocket> for Ping
-where
-    TSocket: AsyncRead + AsyncWrite + Send + Unpin + 'static,
-{
-    type Output = Duration;
-    type Error = io::Error;
-    type Future = BoxFuture<'static, Result<Duration, io::Error>>;
-
-    fn upgrade_outbound(self, mut socket: TSocket, _: Self::Info) -> Self::Future {
     let payload: [u8; PING_SIZE] = thread_rng().sample(distributions::Standard);
-        debug!("Preparing ping payload {:?}", payload);
-        async move {
-            socket.write_all(&payload).await?;
-            socket.close().await?;
+    log::debug!("Preparing ping payload {:?}", payload);
+    stream.write_all(&payload).await?;
     let started = Instant::now();
-
-            let mut recv_payload = [0u8; 32];
-            socket.read_exact(&mut recv_payload).await?;
+    let mut recv_payload = [0u8; PING_SIZE];
+    stream.read_exact(&mut recv_payload).await?;
     if recv_payload == payload {
-                Ok(started.elapsed())
+        Ok((stream, started.elapsed()))
     } else {
         Err(io::Error::new(io::ErrorKind::InvalidData, "Ping payload mismatch"))
     }
-        }.boxed()
 }
+
+/// Waits for a ping and sends a pong.
+pub async fn recv_ping<S>(mut stream: S) -> io::Result<S>
+where
+    S: AsyncRead + AsyncWrite + Unpin
+{
+    let mut payload = [0u8; PING_SIZE];
+    stream.read_exact(&mut payload).await?;
+    stream.write_all(&payload).await?;
+    stream.flush().await?;
+    Ok(stream)
 }
 
 #[cfg(test)]
 mod tests {
-    use super::Ping;
-    use futures::prelude::*;
+    use super::*;
     use libp2p_core::{
-        upgrade,
         multiaddr::multiaddr,
         transport::{
             Transport,
@@ -134,12 +139,12 @@ mod tests {
             let listener_event = listener.next().await.unwrap();
             let (listener_upgrade, _) = listener_event.unwrap().into_upgrade().unwrap();
             let conn = listener_upgrade.await.unwrap();
-            upgrade::apply_inbound(conn, Ping::default()).await.unwrap();
+            recv_ping(conn).await.unwrap();
         });
 
         async_std::task::block_on(async move {
             let c = MemoryTransport.dial(listener_addr).unwrap().await.unwrap();
-            let rtt = upgrade::apply_outbound(c, Ping::default(), upgrade::Version::V1).await.unwrap();
+            let (_, rtt) = send_ping(c).await.unwrap();
             assert!(rtt > Duration::from_secs(0));
         });
     }

protocols/ping/tests/ping.rs

@@ -30,14 +30,18 @@ use libp2p_core::{
 };
 use libp2p_ping::*;
 use libp2p_secio::SecioConfig;
-use libp2p_swarm::Swarm;
+use libp2p_swarm::{Swarm, SwarmEvent};
 use libp2p_tcp::TcpConfig;
 use futures::{prelude::*, channel::mpsc};
-use std::{io, time::Duration};
+use quickcheck::*;
+use std::{io, num::NonZeroU8, time::Duration};
 
 #[test]
-fn ping() {
-    let cfg = PingConfig::new().with_keep_alive(true);
+fn ping_pong() {
+    fn prop(count: NonZeroU8) {
+        let cfg = PingConfig::new()
+            .with_keep_alive(true)
+            .with_interval(Duration::from_millis(10));
 
         let (peer1_id, trans) = mk_transport();
         let mut swarm1 = Swarm::new(trans, Ping::new(cfg.clone()), peer1_id.clone());
@@ -51,6 +55,9 @@ fn ping() {
         let addr = "/ip4/127.0.0.1/tcp/0".parse().unwrap();
         Swarm::listen_on(&mut swarm1, addr).unwrap();
 
+        let mut count1 = count.get();
+        let mut count2 = count.get();
+
         let peer1 = async move {
             while let Some(_) = swarm1.next().now_or_never() {}
 
@@ -61,8 +68,12 @@ fn ping() {
             loop {
                 match swarm1.next().await {
                     PingEvent { peer, result: Ok(PingSuccess::Ping { rtt }) } => {
+                        count1 -= 1;
+                        if count1 == 0 {
                             return (pid1.clone(), peer, rtt)
+                        }
                     },
+                    PingEvent { result: Err(e), .. } => panic!("Ping failure: {:?}", e),
                     _ => {}
                 }
             }
@@ -75,8 +86,12 @@ fn ping() {
             loop {
                 match swarm2.next().await {
                     PingEvent { peer, result: Ok(PingSuccess::Ping { rtt }) } => {
+                        count2 -= 1;
+                        if count2 == 0 {
                             return (pid2.clone(), peer, rtt)
+                        }
                     },
+                    PingEvent { result: Err(e), .. } => panic!("Ping failure: {:?}", e),
                     _ => {}
                 }
             }
@@ -88,6 +103,95 @@ fn ping() {
         assert!(rtt < Duration::from_millis(50));
     }
 
+    QuickCheck::new().tests(3).quickcheck(prop as fn(_))
+}
+
+
+/// Tests that the connection is closed upon a configurable
+/// number of consecutive ping failures.
+#[test]
+fn max_failures() {
+    fn prop(max_failures: NonZeroU8) {
+        let cfg = PingConfig::new()
+            .with_keep_alive(true)
+            .with_interval(Duration::from_millis(10))
+            .with_timeout(Duration::from_millis(0))
+            .with_max_failures(max_failures.into());
+
+        let (peer1_id, trans) = mk_transport();
+        let mut swarm1 = Swarm::new(trans, Ping::new(cfg.clone()), peer1_id.clone());
+
+        let (peer2_id, trans) = mk_transport();
+        let mut swarm2 = Swarm::new(trans, Ping::new(cfg), peer2_id.clone());
+
+        let (mut tx, mut rx) = mpsc::channel::<Multiaddr>(1);
+
+        let addr = "/ip4/127.0.0.1/tcp/0".parse().unwrap();
+        Swarm::listen_on(&mut swarm1, addr).unwrap();
+
+        let peer1 = async move {
+            while let Some(_) = swarm1.next().now_or_never() {}
+
+            for l in Swarm::listeners(&swarm1) {
+                tx.send(l.clone()).await.unwrap();
+            }
+
+            let mut count1: u8 = 0;
+
+            loop {
+                match swarm1.next_event().await {
+                    SwarmEvent::Behaviour(PingEvent {
+                        result: Ok(PingSuccess::Ping { .. }), ..
+                    }) => {
+                        count1 = 0; // there may be an occasional success
+                    }
+                    SwarmEvent::Behaviour(PingEvent {
+                        result: Err(_), ..
+                    }) => {
+                        count1 += 1;
+                    }
+                    SwarmEvent::ConnectionClosed { .. } => {
+                        return count1
+                    }
+                    _ => {}
+                }
+            }
+        };
+
+        let peer2 = async move {
+            Swarm::dial_addr(&mut swarm2, rx.next().await.unwrap()).unwrap();
+
+            let mut count2: u8 = 0;
+
+            loop {
+                match swarm2.next_event().await {
+                    SwarmEvent::Behaviour(PingEvent {
+                        result: Ok(PingSuccess::Ping { .. }), ..
+                    }) => {
+                        count2 = 0; // there may be an occasional success
+                    }
+                    SwarmEvent::Behaviour(PingEvent {
+                        result: Err(_), ..
+                    }) => {
+                        count2 += 1;
+                    }
+                    SwarmEvent::ConnectionClosed { .. } => {
+                        return count2
+                    }
+                    _ => {}
+                }
+            }
+        };
+
+        let future = future::join(peer1, peer2);
+        let (count1, count2) = async_std::task::block_on(future);
+        assert_eq!(u8::max(count1, count2), max_failures.get() - 1);
+    }
+
+    QuickCheck::new().tests(3).quickcheck(prop as fn(_))
+}
+
+
 fn mk_transport() -> (
     PeerId,
     Boxed<