feat(client): skip dns resolution when host is a valid ip addr (#1372)

src/client/connect.rs

@@ -186,9 +186,18 @@ impl Future for HttpConnecting {
             let state;
             match self.state {
                 State::Lazy(ref executor, ref mut host, port) => {
-                    let host = mem::replace(host, String::new());
-                    let work = dns::Work::new(host, port);
-                    state = State::Resolving(oneshot::spawn(work, executor));
+                    // 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 {
+                            addrs: addrs,
+                            current: None
+                        })
+                    } else {
+                        let host = mem::replace(host, String::new());
+                        let work = dns::Work::new(host, port);
+                        state = State::Resolving(oneshot::spawn(work, executor));
+                    }
                 },
                 State::Resolving(ref mut future) => {
                     match try!(future.poll()) {

src/client/dns.rs

@@ -1,5 +1,9 @@
 use std::io;
-use std::net::{SocketAddr, ToSocketAddrs};
+use std::net::{
+    Ipv4Addr, Ipv6Addr,
+    SocketAddr, ToSocketAddrs,
+    SocketAddrV4, SocketAddrV6,
+};
 use std::vec;
 
 use ::futures::{Async, Future, Poll};
@@ -30,6 +34,20 @@ pub struct IpAddrs {
     iter: vec::IntoIter<SocketAddr>,
 }
 
+impl IpAddrs {
+    pub fn try_parse(host: &str, port: u16) -> Option<IpAddrs> {
+        if let Ok(addr) = host.parse::<Ipv4Addr>() {
+            let addr = SocketAddrV4::new(addr, port);
+            return Some(IpAddrs { iter: vec![SocketAddr::V4(addr)].into_iter() })
+        }
+        if let Ok(addr) = host.parse::<Ipv6Addr>() {
+            let addr = SocketAddrV6::new(addr, port, 0, 0);
+            return Some(IpAddrs { iter: vec![SocketAddr::V6(addr)].into_iter() })
+        }
+        None
+    }
+}
+
 impl Iterator for IpAddrs {
     type Item = SocketAddr;
     #[inline]