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.

18 files changed, 34 insertions, 60 deletions

diff --git a/tokio/examples/chat.rs b/tokio/examples/chat.rs
index 8ace878c..719a2530 100644
--- a/tokio/examples/chat.rs
+++ b/tokio/examples/chat.rs
@@ -45,12 +45,11 @@ async fn main() -> Result<(), Box<dyn Error>> {
     let state = Lock::new(Shared::new());
 
     let addr = env::args().nth(1).unwrap_or("127.0.0.1:6142".to_string());
-    let addr = addr.parse::<SocketAddr>()?;
 
     // Bind a TCP listener to the socket address.
     //
     // Note that this is the Tokio TcpListener, which is fully async.
-    let mut listener = TcpListener::bind(&addr)?;
+    let mut listener = TcpListener::bind(&addr).await?;
 
     println!("server running on {}", addr);
 
diff --git a/tokio/examples/connect.rs b/tokio/examples/connect.rs
index 6036eec3..0ba8a6f2 100644
--- a/tokio/examples/connect.rs
+++ b/tokio/examples/connect.rs
@@ -126,13 +126,13 @@ mod udp {
         // We'll bind our UDP socket to a local IP/port, but for now we
         // basically let the OS pick both of those.
         let bind_addr = if addr.ip().is_ipv4() {
-            "0.0.0.0:0".parse()?
+            "0.0.0.0:0"
         } else {
-            "[::]:0".parse()?
+            "[::]:0"
         };
 
-        let socket = UdpSocket::bind(&bind_addr)?;
-        socket.connect(addr)?;
+        let socket = UdpSocket::bind(&bind_addr).await?;
+        socket.connect(addr).await?;
         let (mut r, mut w) = socket.split();
 
         future::try_join(send(stdin, &mut w), recv(stdout, &mut r)).await?;
diff --git a/tokio/examples/echo-udp.rs b/tokio/examples/echo-udp.rs
index 330a3cd8..f1e8134d 100644
--- a/tokio/examples/echo-udp.rs
+++ b/tokio/examples/echo-udp.rs
@@ -52,9 +52,8 @@ impl Server {
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn Error>> {
     let addr = env::args().nth(1).unwrap_or("127.0.0.1:8080".to_string());
-    let addr = addr.parse::<SocketAddr>()?;
 
-    let socket = UdpSocket::bind(&addr)?;
+    let socket = UdpSocket::bind(&addr).await?;
     println!("Listening on: {}", socket.local_addr()?);
 
     let server = Server {
diff --git a/tokio/examples/echo.rs b/tokio/examples/echo.rs
index c8842b73..455aebde 100644
--- a/tokio/examples/echo.rs
+++ b/tokio/examples/echo.rs
@@ -27,7 +27,6 @@ use tokio::net::TcpListener;
 
 use std::env;
 use std::error::Error;
-use std::net::SocketAddr;
 
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn Error>> {
@@ -35,12 +34,11 @@ async fn main() -> Result<(), Box<dyn Error>> {
     // program, but otherwise we'll just set up our TCP listener on
     // 127.0.0.1:8080 for connections.
     let addr = env::args().nth(1).unwrap_or("127.0.0.1:8080".to_string());
-    let addr = addr.parse::<SocketAddr>()?;
 
     // Next up we create a TCP listener which will listen for incoming
     // connections. This TCP listener is bound to the address we determined
     // above and must be associated with an event loop.
-    let mut listener = TcpListener::bind(&addr)?;
+    let mut listener = TcpListener::bind(&addr).await?;
     println!("Listening on: {}", addr);
 
     loop {
diff --git a/tokio/examples/hello_world.rs b/tokio/examples/hello_world.rs
index 69c3b3f6..8ff40902 100644
--- a/tokio/examples/hello_world.rs
+++ b/tokio/examples/hello_world.rs
@@ -13,7 +13,6 @@
 
 #![warn(rust_2018_idioms)]
 
-use tokio;
 use tokio::io::AsyncWriteExt;
 use tokio::net::TcpStream;
 
@@ -21,12 +20,10 @@ use std::error::Error;
 
 #[tokio::main]
 pub async fn main() -> Result<(), Box<dyn Error>> {
-    let addr = "127.0.0.1:6142".parse()?;
-
     // Open a TCP stream to the socket address.
     //
     // Note that this is the Tokio TcpStream, which is fully async.
-    let mut stream = TcpStream::connect(&addr).await?;
+    let mut stream = TcpStream::connect("127.0.0.1:6142").await?;
     println!("created stream");
 
     let result = stream.write(b"hello world\n").await;
diff --git a/tokio/examples/print_each_packet.rs b/tokio/examples/print_each_packet.rs
index b801ac8b..3729c3e9 100644
--- a/tokio/examples/print_each_packet.rs
+++ b/tokio/examples/print_each_packet.rs
@@ -54,28 +54,26 @@
 
 #![warn(rust_2018_idioms)]
 
-use std::env;
-use std::net::SocketAddr;
-
 use tokio;
 use tokio::codec::{BytesCodec, Decoder};
 use tokio::net::TcpListener;
 use tokio::prelude::*;
 
+use std::env;
+
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
     // Allow passing an address to listen on as the first argument of this
     // program, but otherwise we'll just set up our TCP listener on
     // 127.0.0.1:8080 for connections.
     let addr = env::args().nth(1).unwrap_or("127.0.0.1:8080".to_string());
-    let addr = addr.parse::<SocketAddr>()?;
 
     // Next up we create a TCP listener which will listen for incoming
     // connections. This TCP listener is bound to the address we determined
     // above and must be associated with an event loop, so we pass in a handle
     // to our event loop. After the socket's created we inform that we're ready
     // to go and start accepting connections.
-    let mut listener = TcpListener::bind(&addr)?;
+    let mut listener = TcpListener::bind(&addr).await?;
     println!("Listening on: {}", addr);
 
     loop {
diff --git a/tokio/examples/proxy.rs b/tokio/examples/proxy.rs
index 848c0a40..7946be8a 100644
--- a/tokio/examples/proxy.rs
+++ b/tokio/examples/proxy.rs
@@ -23,7 +23,7 @@
 #![warn(rust_2018_idioms)]
 
 use futures::{future::try_join, FutureExt, StreamExt};
-use std::{env, error::Error, net::SocketAddr};
+use std::{env, error::Error};
 use tokio::{
     io::AsyncReadExt,
     net::{TcpListener, TcpStream},
@@ -32,18 +32,15 @@ use tokio::{
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn Error>> {
     let listen_addr = env::args().nth(1).unwrap_or("127.0.0.1:8081".to_string());
-    let listen_addr = listen_addr.parse::<SocketAddr>()?;
-
     let server_addr = env::args().nth(2).unwrap_or("127.0.0.1:8080".to_string());
-    let server_addr = server_addr.parse::<SocketAddr>()?;
 
     println!("Listening on: {}", listen_addr);
     println!("Proxying to: {}", server_addr);
 
-    let mut incoming = TcpListener::bind(&listen_addr)?.incoming();
+    let mut incoming = TcpListener::bind(listen_addr).await?.incoming();
 
     while let Some(Ok(inbound)) = incoming.next().await {
-        let transfer = transfer(inbound, server_addr).map(|r| {
+        let transfer = transfer(inbound, server_addr.clone()).map(|r| {
             if let Err(e) = r {
                 println!("Failed to transfer; error={}", e);
             }
@@ -55,8 +52,8 @@ async fn main() -> Result<(), Box<dyn Error>> {
     Ok(())
 }
 
-async fn transfer(inbound: TcpStream, proxy_addr: SocketAddr) -> Result<(), Box<dyn Error>> {
-    let outbound = TcpStream::connect(&proxy_addr).await?;
+async fn transfer(inbound: TcpStream, proxy_addr: String) -> Result<(), Box<dyn Error>> {
+    let outbound = TcpStream::connect(proxy_addr).await?;
 
     let (mut ri, mut wi) = inbound.split();
     let (mut ro, mut wo) = outbound.split();
diff --git a/tokio/examples/tinydb.rs b/tokio/examples/tinydb.rs
index fa3cefee..be4951dc 100644
--- a/tokio/examples/tinydb.rs
+++ b/tokio/examples/tinydb.rs
@@ -44,7 +44,6 @@
 use std::collections::HashMap;
 use std::env;
 use std::error::Error;
-use std::net::SocketAddr;
 use std::sync::{Arc, Mutex};
 
 use tokio;
@@ -88,8 +87,8 @@ async fn main() -> Result<(), Box<dyn Error>> {
     // Parse the address we're going to run this server on
     // and set up our TCP listener to accept connections.
     let addr = env::args().nth(1).unwrap_or("127.0.0.1:8080".to_string());
-    let addr = addr.parse::<SocketAddr>()?;
-    let mut listener = TcpListener::bind(&addr)?;
+
+    let mut listener = TcpListener::bind(&addr).await?;
     println!("Listening on: {}", addr);
 
     // Create the shared state of this server that will be shared amongst all
diff --git a/tokio/examples/tinyhttp.rs b/tokio/examples/tinyhttp.rs
index 6aa5a183..65074018 100644
--- a/tokio/examples/tinyhttp.rs
+++ b/tokio/examples/tinyhttp.rs
@@ -17,7 +17,7 @@ use bytes::BytesMut;
 use futures::{SinkExt, StreamExt};
 use http::{header::HeaderValue, Request, Response, StatusCode};
 use serde::Serialize;
-use std::{env, error::Error, fmt, io, net::SocketAddr};
+use std::{env, error::Error, fmt, io};
 use tokio::{
     codec::{Decoder, Encoder, Framed},
     net::{TcpListener, TcpStream},
@@ -28,9 +28,8 @@ async fn main() -> Result<(), Box<dyn Error>> {
     // Parse the arguments, bind the TCP socket we'll be listening to, spin up
     // our worker threads, and start shipping sockets to those worker threads.
     let addr = env::args().nth(1).unwrap_or("127.0.0.1:8080".to_string());
-    let addr = addr.parse::<SocketAddr>()?;
 
-    let mut incoming = TcpListener::bind(&addr)?.incoming();
+    let mut incoming = TcpListener::bind(&addr).await?.incoming();
     println!("Listening on: {}", addr);
 
     while let Some(Ok(stream)) = incoming.next().await {
diff --git a/tokio/examples/udp-client.rs b/tokio/examples/udp-client.rs
index 915c06d9..5437daf6 100644
--- a/tokio/examples/udp-client.rs
+++ b/tokio/examples/udp-client.rs
@@ -55,9 +55,9 @@ async fn main() -> Result<(), Box<dyn Error>> {
     }
     .parse()?;
 
-    let mut socket = UdpSocket::bind(&local_addr)?;
+    let mut socket = UdpSocket::bind(local_addr).await?;
     const MAX_DATAGRAM_SIZE: usize = 65_507;
-    socket.connect(&remote_addr)?;
+    socket.connect(&remote_addr).await?;
     let data = get_stdin_data()?;
     socket.send(&data).await?;
     let mut data = vec![0u8; MAX_DATAGRAM_SIZE];
diff --git a/tokio/examples/udp-codec.rs b/tokio/examples/udp-codec.rs
index c055eaa4..7d0aaf69 100644
--- a/tokio/examples/udp-codec.rs
+++ b/tokio/examples/udp-codec.rs
@@ -27,11 +27,10 @@ async fn main() -> Result<(), Box<dyn Error>> {
     let _ = env_logger::init();
 
     let addr = env::args().nth(1).unwrap_or("127.0.0.1:0".to_string());
-    let addr = addr.parse::<SocketAddr>()?;
 
     // Bind both our sockets and then figure out what ports we got.
-    let a = UdpSocket::bind(&addr)?;
-    let b = UdpSocket::bind(&addr)?;
+    let a = UdpSocket::bind(&addr).await?;
+    let b = UdpSocket::bind(&addr).await?;
 
     let b_addr = b.local_addr()?;
 
diff --git a/tokio/src/executor.rs b/tokio/src/executor.rs
index 7026cd63..75f0f9d4 100644
--- a/tokio/src/executor.rs
+++ b/tokio/src/executor.rs
@@ -73,8 +73,7 @@ pub struct Spawn(());
 ///
 /// # async fn process<T>(t: T) {}
 /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
-/// let addr = "127.0.0.1:8080".parse()?;
-/// let mut listener = TcpListener::bind(&addr).unwrap();
+/// let mut listener = TcpListener::bind("127.0.0.1:8080").await?;
 ///
 /// loop {
 ///     let (socket, _) = listener.accept().await?;
@@ -84,7 +83,6 @@ pub struct Spawn(());
 ///         process(socket).await
 ///     });
 /// }
-/// # Ok(())
 /// # }
 /// ```
 ///
diff --git a/tokio/src/lib.rs b/tokio/src/lib.rs
index 2c804c77..7ddcefdf 100644
--- a/tokio/src/lib.rs
+++ b/tokio/src/lib.rs
@@ -35,8 +35,7 @@
 //!
 //! #[tokio::main]
 //! async fn main() -> Result<(), Box<dyn std::error::Error>> {
-//!     let addr = "127.0.0.1:8080".parse()?;
-//!     let mut listener = TcpListener::bind(&addr).unwrap();
+//!     let mut listener = TcpListener::bind("127.0.0.1:8080").await?;
 //!
 //!     loop {
 //!         let (mut socket, _) = listener.accept().await?;
diff --git a/tokio/src/runtime/mod.rs b/tokio/src/runtime/mod.rs
index 9b630d87..4ba6663a 100644
--- a/tokio/src/runtime/mod.rs
+++ b/tokio/src/runtime/mod.rs
@@ -39,8 +39,7 @@
 //!
 //! #[tokio::main]
 //! async fn main() -> Result<(), Box<dyn std::error::Error>> {
-//!     let addr = "127.0.0.1:8080".parse()?;
-//!     let mut listener = TcpListener::bind(&addr).unwrap();
+//!     let mut listener = TcpListener::bind("127.0.0.1:8080").await?;
 //!
 //!     loop {
 //!         let (mut socket, _) = listener.accept().await?;
@@ -87,12 +86,11 @@
 //!
 //! fn main() -> Result<(), Box<dyn std::error::Error>> {
 //!     // Create the runtime
-//!     let mut rt = Runtime::new().unwrap();
+//!     let mut rt = Runtime::new()?;
 //!
 //!     // Spawn the root task
 //!     rt.block_on(async {
-//!         let addr = "127.0.0.1:8080".parse()?;
-//!         let mut listener = TcpListener::bind(&addr).unwrap();
+//!         let mut listener = TcpListener::bind("127.0.0.1:8080").await?;
 //!
 //!         loop {
 //!             let (mut socket, _) = listener.accept().await?;
diff --git a/tokio/tests/buffered.rs b/tokio/tests/buffered.rs
index 351cb30a..fe419099 100644
--- a/tokio/tests/buffered.rs
+++ b/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";
diff --git a/tokio/tests/reactor.rs b/tokio/tests/reactor.rs
index 59ff8128..f1ed8703 100644
--- a/tokio/tests/reactor.rs
+++ b/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();
diff --git a/tokio/tests/runtime_current_thread.rs b/tokio/tests/runtime_current_thread.rs
index 9f77ac7c..ff742707 100644
--- a/tokio/tests/runtime_current_thread.rs
+++ b/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());
diff --git a/tokio/tests/runtime_threaded.rs b/tokio/tests/runtime_threaded.rs
index bd8ce6a0..36f652dd 100644
--- a/tokio/tests/runtime_threaded.rs
+++ b/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 {