Add io::timeout()

src/io/mod.rs

@@ -32,6 +32,7 @@ pub use seek::Seek;
 pub use stderr::{stderr, Stderr};
 pub use stdin::{stdin, Stdin};
 pub use stdout::{stdout, Stdout};
+pub use timeout::timeout;
 pub use write::Write;
 
 mod buf_read;
@@ -42,4 +43,5 @@ mod seek;
 mod stderr;
 mod stdin;
 mod stdout;
+mod timeout;
 mod write;

src/io/timeout.rs

@@ -0,0 +1,70 @@
+use std::pin::Pin;
+use std::time::Duration;
+
+use futures_timer::Delay;
+use pin_utils::unsafe_pinned;
+
+use crate::future::Future;
+use crate::io;
+use crate::task::{Context, Poll};
+
+/// Awaits an I/O future or times out after a duration of time.
+///
+/// # Examples
+///
+/// ```no_run
+/// # #![feature(async_await)]
+/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
+/// #
+/// use std::time::Duration;
+///
+/// use async_std::io;
+///
+/// let stdin = io::stdin();
+/// let mut line = String::new();
+///
+/// let dur = Duration::from_secs(5);
+/// let n = io::timeout(dur, stdin.read_line(&mut line)).await?;
+/// #
+/// # Ok(()) }) }
+/// ```
+pub async fn timeout<F, T>(dur: Duration, f: F) -> io::Result<T>
+where
+    F: Future<Output = io::Result<T>>,
+{
+    let f = TimeoutFuture {
+        future: f,
+        delay: Delay::new(dur),
+    };
+    f.await
+}
+
+struct TimeoutFuture<F> {
+    future: F,
+    delay: Delay,
+}
+
+impl<F> TimeoutFuture<F> {
+    unsafe_pinned!(future: F);
+    unsafe_pinned!(delay: Delay);
+}
+
+impl<F, T> Future for TimeoutFuture<F>
+where
+    F: Future<Output = io::Result<T>>,
+{
+    type Output = F::Output;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.as_mut().future().poll(cx) {
+            Poll::Ready(v) => Poll::Ready(v),
+            Poll::Pending => match self.delay().poll(cx) {
+                Poll::Ready(_) => Poll::Ready(Err(io::Error::new(
+                    io::ErrorKind::TimedOut,
+                    "future has timed out",
+                ))),
+                Poll::Pending => Poll::Pending,
+            },
+        }
+    }
+}