feat(client): add resolve timeout to HttpConnector (#1994)

The recently-added connect timeout does not cover resolving hostnames, which
could also stall on an OS-level timeout if there are issues reaching the DNS
server.

src/client/connect/http.rs

@@ -29,6 +29,7 @@ use super::dns::{self, GaiResolver, Resolve, TokioThreadpoolGaiResolver};
 pub struct HttpConnector<R = GaiResolver> {
     enforce_http: bool,
     handle: Option<Handle>,
+    resolve_timeout: Option<Duration>,
     connect_timeout: Option<Duration>,
     happy_eyeballs_timeout: Option<Duration>,
     keep_alive_timeout: Option<Duration>,
@@ -121,6 +122,7 @@ impl<R> HttpConnector<R> {
         HttpConnector {
             enforce_http: true,
             handle: None,
+            resolve_timeout: None,
             connect_timeout: None,
             happy_eyeballs_timeout: Some(Duration::from_millis(300)),
             keep_alive_timeout: None,
@@ -189,6 +191,17 @@ impl<R> HttpConnector<R> {
         self.local_address = addr;
     }
 
+    /// Set timeout for hostname resolution.
+    ///
+    /// If `None`, then no timeout is applied by the connector, making it
+    /// subject to the timeout imposed by the operating system.
+    ///
+    /// Default is `None`.
+    #[inline]
+    pub fn set_resolve_timeout(&mut self, dur: Option<Duration>) {
+        self.resolve_timeout = dur;
+    }
+
     /// Set the connect timeout.
     ///
     /// If a domain resolves to multiple IP addresses, the timeout will be
@@ -272,6 +285,7 @@ where
         HttpConnecting {
             state: State::Lazy(self.resolver.clone(), host.into(), self.local_address),
             handle: self.handle.clone(),
+            resolve_timeout: self.resolve_timeout,
             connect_timeout: self.connect_timeout,
             happy_eyeballs_timeout: self.happy_eyeballs_timeout,
             keep_alive_timeout: self.keep_alive_timeout,
@@ -299,6 +313,7 @@ fn invalid_url<R: Resolve>(err: InvalidUrl, handle: &Option<Handle>) -> HttpConn
         keep_alive_timeout: None,
         nodelay: false,
         port: 0,
+        resolve_timeout: None,
         connect_timeout: None,
         happy_eyeballs_timeout: None,
         reuse_address: false,
@@ -334,6 +349,7 @@ impl StdError for InvalidUrl {
 pub struct HttpConnecting<R: Resolve = GaiResolver> {
     state: State<R>,
     handle: Option<Handle>,
+    resolve_timeout: Option<Duration>,
     connect_timeout: Option<Duration>,
     happy_eyeballs_timeout: Option<Duration>,
     keep_alive_timeout: Option<Duration>,
@@ -346,11 +362,16 @@ pub struct HttpConnecting<R: Resolve = GaiResolver> {
 
 enum State<R: Resolve> {
     Lazy(R, String, Option<IpAddr>),
-    Resolving(R::Future, Option<IpAddr>),
+    Resolving(ResolvingFuture<R>, Option<IpAddr>),
     Connecting(ConnectingTcp),
     Error(Option<io::Error>),
 }
 
+enum ResolvingFuture<R: Resolve> {
+    Timed(Timeout<R::Future>),
+    Untimed(R::Future),
+}
+
 impl<R: Resolve> Future for HttpConnecting<R> {
     type Item = (TcpStream, Connected);
     type Error = io::Error;
@@ -367,11 +388,27 @@ impl<R: Resolve> Future for HttpConnecting<R> {
                             local_addr, addrs, self.connect_timeout, self.happy_eyeballs_timeout, self.reuse_address));
                     } else {
                         let name = dns::Name::new(mem::replace(host, String::new()));
-                        state = State::Resolving(resolver.resolve(name), local_addr);
+                        let future = resolver.resolve(name);
+                        state = if let Some(timeout) = self.resolve_timeout {
+                            State::Resolving(ResolvingFuture::Timed(Timeout::new(future, timeout)), local_addr)
+                        } else {
+                            State::Resolving(ResolvingFuture::Untimed(future), local_addr)
+                        }
                     }
                 },
-                State::Resolving(ref mut future, local_addr) => {
-                    match future.poll()? {
+                State::Resolving(ref mut rfuture, local_addr) => {
+                    let res: Async<R::Addrs> = match rfuture {
+                        ResolvingFuture::Timed(future) => match future.poll() {
+                            Ok(res) => res,
+                            Err(err) => if err.is_inner() {
+                                return Err(err.into_inner().unwrap())
+                            } else {
+                                return Err(io::Error::new(io::ErrorKind::TimedOut, err.description()))
+                            },
+                        },
+                        ResolvingFuture::Untimed(future) => future.poll()?,
+                    };
+                    match res {
                         Async::NotReady => return Ok(Async::NotReady),
                         Async::Ready(addrs) => {
                             let port = self.port;