net: perform DNS lookup on connect / bind. (#1499)

A sealed `net::ToSocketAddrs` trait is added. This trait is not intended
to be used by users. Instead, it is an argument to `connect` and `bind`
functions.

The operating system's DNS lookup functionality is used. Blocking
operations are performed on a thread pool in order to avoid blocking the
runtime.

tokio/tests/buffered.rs

@@ -13,8 +13,7 @@ use std::thread;
 async fn echo_server() {
     const N: usize = 1024;
 
-    let addr = assert_ok!("127.0.0.1:0".parse());
-    let mut srv = assert_ok!(TcpListener::bind(&addr));
+    let mut srv = assert_ok!(TcpListener::bind("127.0.0.1:0").await);
     let addr = assert_ok!(srv.local_addr());
 
     let msg = "foo bar baz";

tokio/tests/reactor.rs

@@ -50,9 +50,8 @@ fn test_drop_on_notify() {
 
     // Define a task that just drains the listener
     let task = Arc::new(Task::new(async move {
-        let addr = assert_ok!("127.0.0.1:0".parse());
         // Create a listener
-        let mut listener = assert_ok!(TcpListener::bind(&addr));
+        let mut listener = assert_ok!(TcpListener::bind("127.0.0.1:0").await);
 
         // Send the address
         let addr = listener.local_addr().unwrap();

tokio/tests/runtime_current_thread.rs

@@ -13,8 +13,7 @@ use std::time::{Duration, Instant};
 use tokio::timer::delay;
 
 async fn client_server(tx: mpsc::Sender<()>) {
-    let addr = assert_ok!("127.0.0.1:0".parse());
-    let mut server = assert_ok!(TcpListener::bind(&addr));
+    let mut server = assert_ok!(TcpListener::bind("127.0.0.1:0").await);
 
     // Get the assigned address
     let addr = assert_ok!(server.local_addr());

tokio/tests/runtime_threaded.rs

@@ -15,8 +15,7 @@ use std::thread;
 use std::time::{Duration, Instant};
 
 async fn client_server(tx: mpsc::Sender<()>) {
-    let addr = assert_ok!("127.0.0.1:0".parse());
-    let mut server = assert_ok!(TcpListener::bind(&addr));
+    let mut server = assert_ok!(TcpListener::bind("127.0.0.1:0").await);
 
     // Get the assigned address
     let addr = assert_ok!(server.local_addr());
@@ -78,11 +77,9 @@ fn block_on_socket() {
     let rt = Runtime::new().unwrap();
 
     rt.block_on(async move {
-        let addr = "127.0.0.1:0".parse().unwrap();
-
         let (tx, rx) = oneshot::channel();
 
-        let mut listener = TcpListener::bind(&addr).unwrap();
+        let mut listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
         let addr = listener.local_addr().unwrap();
 
         tokio::spawn(async move {