feat(client): implement rfc 6555 (happy eyeballs)

Update client connector to attempt a parallel connection using
alternative address family, if connection using preferred address family
takes too long.

Closes: #1316

.travis.yml

@@ -1,5 +1,5 @@
 language: rust
-sudo: false
+sudo: true # Required for functional IPv6 (forces VM instead of Docker).
 dist: trusty
 matrix:
     fast_finish: true
@@ -18,6 +18,13 @@ matrix:
 cache:
     apt: true
 
+before_script:
+  # Add an IPv6 config - see the corresponding Travis issue
+  # https://github.com/travis-ci/travis-ci/issues/8361
+  - if [ "${TRAVIS_OS_NAME}" == "linux" ]; then
+      sudo sh -c 'echo 0 > /proc/sys/net/ipv6/conf/all/disable_ipv6';
+    fi
+
 script:
   - ./.travis/readme.py
   - cargo build $FEATURES

src/client/connect.rs

@@ -386,7 +386,7 @@ mod http {
     use std::mem;
     use std::net::{IpAddr, SocketAddr};
     use std::sync::Arc;
-    use std::time::Duration;
+    use std::time::{Duration, Instant};
 
     use futures::{Async, Poll};
     use futures::future::{Executor, ExecuteError};
@@ -396,6 +396,7 @@ mod http {
     use net2::TcpBuilder;
     use tokio_reactor::Handle;
     use tokio_tcp::{TcpStream, ConnectFuture};
+    use tokio_timer::Delay;
 
     use super::super::dns;
 
@@ -444,6 +445,7 @@ mod http {
         keep_alive_timeout: Option<Duration>,
         nodelay: bool,
         local_address: Option<IpAddr>,
+        happy_eyeballs_timeout: Option<Duration>,
     }
 
     impl HttpConnector {
@@ -481,6 +483,7 @@ mod http {
                 keep_alive_timeout: None,
                 nodelay: false,
                 local_address: None,
+                happy_eyeballs_timeout: Some(Duration::from_millis(300)),
             }
         }
 
@@ -519,6 +522,23 @@ mod http {
         pub fn set_local_address(&mut self, addr: Option<IpAddr>) {
             self.local_address = addr;
         }
+
+        /// Set timeout for [RFC 6555 (Happy Eyeballs)][RFC 6555] algorithm.
+        ///
+        /// If hostname resolves to both IPv4 and IPv6 addresses and connection
+        /// cannot be established using preferred address family before timeout
+        /// elapses, then connector will in parallel attempt connection using other
+        /// address family.
+        ///
+        /// If `None`, parallel connection attempts are disabled.
+        ///
+        /// Default is 300 milliseconds.
+        ///
+        /// [RFC 6555]: https://tools.ietf.org/html/rfc6555
+        #[inline]
+        pub fn set_happy_eyeballs_timeout(&mut self, dur: Option<Duration>) {
+            self.happy_eyeballs_timeout = dur;
+        }
     }
 
     impl fmt::Debug for HttpConnector {
@@ -564,6 +584,7 @@ mod http {
                 handle: self.handle.clone(),
                 keep_alive_timeout: self.keep_alive_timeout,
                 nodelay: self.nodelay,
+                happy_eyeballs_timeout: self.happy_eyeballs_timeout,
             }
         }
     }
@@ -575,6 +596,7 @@ mod http {
             handle: handle.clone(),
             keep_alive_timeout: None,
             nodelay: false,
+            happy_eyeballs_timeout: None,
         }
     }
 
@@ -607,6 +629,7 @@ mod http {
         handle: Option<Handle>,
         keep_alive_timeout: Option<Duration>,
         nodelay: bool,
+        happy_eyeballs_timeout: Option<Duration>,
     }
 
     enum State {
@@ -628,11 +651,8 @@ mod http {
                         // If the host is already an IP addr (v4 or v6),
                         // skip resolving the dns and start connecting right away.
                         if let Some(addrs) = dns::IpAddrs::try_parse(host, port) {
-                            state = State::Connecting(ConnectingTcp {
+                            state = State::Connecting(ConnectingTcp::new(
-                                addrs: addrs,
+                                local_addr, addrs, self.happy_eyeballs_timeout));
-                                local_addr: local_addr,
-                                current: None
-                            })
                         } else {
                             let host = mem::replace(host, String::new());
                             let work = dns::Work::new(host, port);
@@ -643,11 +663,8 @@ mod http {
                         match try!(future.poll()) {
                             Async::NotReady => return Ok(Async::NotReady),
                             Async::Ready(addrs) => {
-                                state = State::Connecting(ConnectingTcp {
+                                state = State::Connecting(ConnectingTcp::new(
-                                    addrs: addrs,
+                                    local_addr, addrs, self.happy_eyeballs_timeout));
-                                    local_addr: local_addr,
-                                    current: None,
-                                })
                             }
                         };
                     },
@@ -676,14 +693,71 @@ mod http {
     }
 
     struct ConnectingTcp {
-        addrs: dns::IpAddrs,
         local_addr: Option<IpAddr>,
-        current: Option<ConnectFuture>,
+        preferred: ConnectingTcpRemote,
+        fallback: Option<ConnectingTcpFallback>,
     }
 
     impl ConnectingTcp {
+        fn new(
+            local_addr: Option<IpAddr>,
+            remote_addrs: dns::IpAddrs,
+            fallback_timeout: Option<Duration>,
+        ) -> ConnectingTcp {
+            if let Some(fallback_timeout) = fallback_timeout {
+                let (preferred_addrs, fallback_addrs) = remote_addrs.split_by_preference();
+                if fallback_addrs.is_empty() {
+                    return ConnectingTcp {
+                        local_addr,
+                        preferred: ConnectingTcpRemote::new(preferred_addrs),
+                        fallback: None,
+                    };
+                }
+
+                ConnectingTcp {
+                    local_addr,
+                    preferred: ConnectingTcpRemote::new(preferred_addrs),
+                    fallback: Some(ConnectingTcpFallback {
+                        delay: Delay::new(Instant::now() + fallback_timeout),
+                        remote: ConnectingTcpRemote::new(fallback_addrs),
+                    }),
+                }
+            } else {
+                ConnectingTcp {
+                    local_addr,
+                    preferred: ConnectingTcpRemote::new(remote_addrs),
+                    fallback: None,
+                }
+            }
+        }
+    }
+
+    struct ConnectingTcpFallback {
+        delay: Delay,
+        remote: ConnectingTcpRemote,
+    }
+
+    struct ConnectingTcpRemote {
+        addrs: dns::IpAddrs,
+        current: Option<ConnectFuture>,
+    }
+
+    impl ConnectingTcpRemote {
+        fn new(addrs: dns::IpAddrs) -> Self {
+            Self {
+                addrs,
+                current: None,
+            }
+        }
+    }
+
+    impl ConnectingTcpRemote {
         // not a Future, since passing a &Handle to poll
-        fn poll(&mut self, handle: &Option<Handle>) -> Poll<TcpStream, io::Error> {
+        fn poll(
+            &mut self,
+            local_addr: &Option<IpAddr>,
+            handle: &Option<Handle>,
+        ) -> Poll<TcpStream, io::Error> {
             let mut err = None;
             loop {
                 if let Some(ref mut current) = self.current {
@@ -694,14 +768,14 @@ mod http {
                             err = Some(e);
                             if let Some(addr) = self.addrs.next() {
                                 debug!("connecting to {}", addr);
-                                *current = connect(&addr, &self.local_addr, handle)?;
+                                *current = connect(&addr, local_addr, handle)?;
                                 continue;
                             }
                         }
                     }
                 } else if let Some(addr) = self.addrs.next() {
                     debug!("connecting to {}", addr);
-                    self.current = Some(connect(&addr, &self.local_addr, handle)?);
+                    self.current = Some(connect(&addr, local_addr, handle)?);
                     continue;
                 }
 
@@ -710,6 +784,54 @@ mod http {
         }
     }
 
+    impl ConnectingTcp {
+        // not a Future, since passing a &Handle to poll
+        fn poll(&mut self, handle: &Option<Handle>) -> Poll<TcpStream, io::Error> {
+            match self.fallback.take() {
+                None => self.preferred.poll(&self.local_addr, handle),
+                Some(mut fallback) => match self.preferred.poll(&self.local_addr, handle) {
+                    Ok(Async::Ready(stream)) => {
+                        // Preferred successful - drop fallback.
+                        Ok(Async::Ready(stream))
+                    }
+                    Ok(Async::NotReady) => match fallback.delay.poll() {
+                        Ok(Async::Ready(_)) => match fallback.remote.poll(&self.local_addr, handle) {
+                            Ok(Async::Ready(stream)) => {
+                                // Fallback successful - drop current preferred,
+                                // but keep fallback as new preferred.
+                                self.preferred = fallback.remote;
+                                Ok(Async::Ready(stream))
+                            }
+                            Ok(Async::NotReady) => {
+                                // Neither preferred nor fallback are ready.
+                                self.fallback = Some(fallback);
+                                Ok(Async::NotReady)
+                            }
+                            Err(_) => {
+                                // Fallback failed - resume with preferred only.
+                                Ok(Async::NotReady)
+                            }
+                        },
+                        Ok(Async::NotReady) => {
+                            // Too early to attempt fallback.
+                            self.fallback = Some(fallback);
+                            Ok(Async::NotReady)
+                        }
+                        Err(_) => {
+                            // Fallback delay failed - resume with preferred only.
+                            Ok(Async::NotReady)
+                        }
+                    }
+                    Err(_) => {
+                        // Preferred failed - use fallback as new preferred.
+                        self.preferred = fallback.remote;
+                        self.preferred.poll(&self.local_addr, handle)
+                    }
+                }
+            }
+        }
+    }
+
     // Make this Future unnameable outside of this crate.
     mod http_connector {
         use super::*;
@@ -783,6 +905,154 @@ mod http {
 
             assert_eq!(connector.connect(dst).wait().unwrap_err().kind(), io::ErrorKind::InvalidInput);
         }
+
+        #[test]
+        fn client_happy_eyeballs() {
+            extern crate pretty_env_logger;
+
+            use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, TcpListener};
+            use std::time::{Duration, Instant};
+
+            use futures::{Async, Poll};
+            use tokio::runtime::current_thread::Runtime;
+            use tokio_reactor::Handle;
+
+            use super::dns;
+            use super::ConnectingTcp;
+
+            let _ = pretty_env_logger::try_init();
+            let server4 = TcpListener::bind("127.0.0.1:0").unwrap();
+            let addr = server4.local_addr().unwrap();
+            let _server6 = TcpListener::bind(&format!("[::1]:{}", addr.port())).unwrap();
+            let mut rt = Runtime::new().unwrap();
+
+            let local_timeout = Duration::default();
+            let unreachable_v4_timeout = measure_connect(unreachable_ipv4_addr()).1;
+            let unreachable_v6_timeout = measure_connect(unreachable_ipv6_addr()).1;
+            let fallback_timeout = ::std::cmp::max(unreachable_v4_timeout, unreachable_v6_timeout)
+                + Duration::from_millis(250);
+
+            let scenarios = &[
+                // Fast primary, without fallback.
+                (&[local_ipv4_addr()][..],
+                    4, local_timeout, false),
+                (&[local_ipv6_addr()][..],
+                    6, local_timeout, false),
+
+                // Fast primary, with (unused) fallback.
+                (&[local_ipv4_addr(), local_ipv6_addr()][..],
+                    4, local_timeout, false),
+                (&[local_ipv6_addr(), local_ipv4_addr()][..],
+                    6, local_timeout, false),
+
+                // Unreachable + fast primary, without fallback.
+                (&[unreachable_ipv4_addr(), local_ipv4_addr()][..],
+                    4, unreachable_v4_timeout, false),
+                (&[unreachable_ipv6_addr(), local_ipv6_addr()][..],
+                    6, unreachable_v6_timeout, false),
+
+                // Unreachable + fast primary, with (unused) fallback.
+                (&[unreachable_ipv4_addr(), local_ipv4_addr(), local_ipv6_addr()][..],
+                    4, unreachable_v4_timeout, false),
+                (&[unreachable_ipv6_addr(), local_ipv6_addr(), local_ipv4_addr()][..],
+                    6, unreachable_v6_timeout, true),
+
+                // Slow primary, with (used) fallback.
+                (&[slow_ipv4_addr(), local_ipv4_addr(), local_ipv6_addr()][..],
+                    6, fallback_timeout, false),
+                (&[slow_ipv6_addr(), local_ipv6_addr(), local_ipv4_addr()][..],
+                    4, fallback_timeout, true),
+
+                // Slow primary, with (used) unreachable + fast fallback.
+                (&[slow_ipv4_addr(), unreachable_ipv6_addr(), local_ipv6_addr()][..],
+                    6, fallback_timeout + unreachable_v6_timeout, false),
+                (&[slow_ipv6_addr(), unreachable_ipv4_addr(), local_ipv4_addr()][..],
+                    4, fallback_timeout + unreachable_v4_timeout, true),
+            ];
+
+            // Scenarios for IPv6 -> IPv4 fallback require that host can access IPv6 network.
+            // Otherwise, connection to "slow" IPv6 address will error-out immediatelly.
+            let ipv6_accessible = measure_connect(slow_ipv6_addr()).0;
+
+            for &(hosts, family, timeout, needs_ipv6_access) in scenarios {
+                if needs_ipv6_access && !ipv6_accessible {
+                    continue;
+                }
+
+                let addrs = hosts.iter().map(|host| (host.clone(), addr.port()).into()).collect();
+                let connecting_tcp = ConnectingTcp::new(None, dns::IpAddrs::new(addrs), Some(fallback_timeout));
+                let fut = ConnectingTcpFuture(connecting_tcp);
+
+                let start = Instant::now();
+                let res = rt.block_on(fut).unwrap();
+                let duration = start.elapsed();
+
+                // Allow actual duration to be +/- 150ms off.
+                let min_duration = if timeout >= Duration::from_millis(150) {
+                    timeout - Duration::from_millis(150)
+                } else {
+                    Duration::default()
+                };
+                let max_duration = timeout + Duration::from_millis(150);
+
+                assert_eq!(res, family);
+                assert!(duration >= min_duration);
+                assert!(duration <= max_duration);
+            }
+
+            struct ConnectingTcpFuture(ConnectingTcp);
+
+            impl Future for ConnectingTcpFuture {
+                type Item = u8;
+                type Error = ::std::io::Error;
+
+                fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+                    match self.0.poll(&Some(Handle::default())) {
+                        Ok(Async::Ready(stream)) => Ok(Async::Ready(
+                            if stream.peer_addr().unwrap().is_ipv4() { 4 } else { 6 }
+                        )),
+                        Ok(Async::NotReady) => Ok(Async::NotReady),
+                        Err(err) => Err(err),
+                    }
+                }
+            }
+
+            fn local_ipv4_addr() -> IpAddr {
+                Ipv4Addr::new(127, 0, 0, 1).into()
+            }
+
+            fn local_ipv6_addr() -> IpAddr {
+                Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1).into()
+            }
+
+            fn unreachable_ipv4_addr() -> IpAddr {
+                Ipv4Addr::new(127, 0, 0, 2).into()
+            }
+
+            fn unreachable_ipv6_addr() -> IpAddr {
+                Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 2).into()
+            }
+
+            fn slow_ipv4_addr() -> IpAddr {
+                // RFC 6890 reserved IPv4 address.
+                Ipv4Addr::new(198, 18, 0, 25).into()
+            }
+
+            fn slow_ipv6_addr() -> IpAddr {
+                // RFC 6890 reserved IPv6 address.
+                Ipv6Addr::new(2001, 2, 0, 0, 0, 0, 0, 254).into()
+            }
+
+            fn measure_connect(addr: IpAddr) -> (bool, Duration) {
+                let start = Instant::now();
+                let result = ::std::net::TcpStream::connect_timeout(
+                    &(addr, 80).into(), Duration::from_secs(1));
+
+                let reachable = result.is_ok() || result.unwrap_err().kind() == io::ErrorKind::TimedOut;
+                let duration = start.elapsed();
+                (reachable, duration)
+            }
+        }
     }
 }
 

src/client/dns.rs

@@ -35,6 +35,10 @@ pub struct IpAddrs {
 }
 
 impl IpAddrs {
+    pub fn new(addrs: Vec<SocketAddr>) -> Self {
+        IpAddrs { iter: addrs.into_iter() }
+    }
+
     pub fn try_parse(host: &str, port: u16) -> Option<IpAddrs> {
         if let Ok(addr) = host.parse::<Ipv4Addr>() {
             let addr = SocketAddrV4::new(addr, port);
@@ -46,6 +50,23 @@ impl IpAddrs {
         }
         None
     }
+
+    pub fn split_by_preference(self) -> (IpAddrs, IpAddrs) {
+        let preferring_v6 = self.iter
+            .as_slice()
+            .first()
+            .map(SocketAddr::is_ipv6)
+            .unwrap_or(false);
+
+        let (preferred, fallback) = self.iter
+            .partition::<Vec<_>, _>(|addr| addr.is_ipv6() == preferring_v6);
+
+        (IpAddrs::new(preferred), IpAddrs::new(fallback))
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.iter.as_slice().is_empty()
+    }
 }
 
 impl Iterator for IpAddrs {
@@ -55,3 +76,25 @@ impl Iterator for IpAddrs {
         self.iter.next()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use std::net::{Ipv4Addr, Ipv6Addr};
+    use super::*;
+
+    #[test]
+    fn test_ip_addrs_split_by_preference() {
+        let v4_addr = (Ipv4Addr::new(127, 0, 0, 1), 80).into();
+        let v6_addr = (Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 80).into();
+
+        let (mut preferred, mut fallback) =
+            IpAddrs { iter: vec![v4_addr, v6_addr].into_iter() }.split_by_preference();
+        assert!(preferred.next().unwrap().is_ipv4());
+        assert!(fallback.next().unwrap().is_ipv6());
+
+        let (mut preferred, mut fallback) =
+            IpAddrs { iter: vec![v6_addr, v4_addr].into_iter() }.split_by_preference();
+        assert!(preferred.next().unwrap().is_ipv6());
+        assert!(fallback.next().unwrap().is_ipv4());
+    }
+}