Async/await polish (#1058)

A general refresh of Tokio's experimental async / await support.

async-await/src/echo_client.rs

@@ -0,0 +1,50 @@
+#![feature(await_macro, async_await)]
+
+use tokio::await;
+use tokio::net::TcpStream;
+use tokio::prelude::*;
+
+use std::io;
+use std::net::SocketAddr;
+
+const MESSAGES: &[&str] = &[
+    "hello",
+    "world",
+    "one two three",
+];
+
+async fn run_client(addr: &SocketAddr) -> io::Result<()> {
+    let mut stream = await!(TcpStream::connect(addr))?;
+
+    // Buffer to read into
+    let mut buf = [0; 128];
+
+    for msg in MESSAGES {
+        println!(" > write = {:?}", msg);
+
+        // Write the message to the server
+        await!(stream.write_all_async(msg.as_bytes()))?;
+
+        // Read the message back from the server
+        await!(stream.read_exact_async(&mut buf[..msg.len()]))?;
+
+        assert_eq!(&buf[..msg.len()], msg.as_bytes());
+    }
+
+    Ok(())
+}
+
+#[tokio::main]
+async fn main() {
+    use std::env;
+
+    let addr = env::args().nth(1).unwrap_or("127.0.0.1:8080".to_string());
+    let addr = addr.parse::<SocketAddr>().unwrap();
+
+    // Connect to the echo serveer
+
+    match await!(run_client(&addr)) {
+        Ok(_) => println!("done."),
+        Err(e) => eprintln!("echo client failed; error = {:?}", e),
+    }
+}