Inline TryFutureExt logic for src/io/timeout.rs (#317)

src/io/timeout.rs

@@ -1,6 +1,9 @@
+use std::pin::Pin;
+use std::task::{Context, Poll};
 use std::time::Duration;
 
-use futures_timer::TryFutureExt;
+use futures_core::future::TryFuture;
+use futures_timer::Delay;
 
 use crate::future::Future;
 use crate::io;
@@ -33,5 +36,48 @@ pub async fn timeout<F, T>(dur: Duration, f: F) -> io::Result<T>
 where
     F: Future<Output = io::Result<T>>,
 {
-    f.timeout(dur).await
+    let f = TimeoutFuture {
+        timeout: Delay::new(dur),
+        future: f,
+    };
+    f.await
+}
+
+// Future returned by the [`io::timeout`](./fn.timeout.html) function.
+#[derive(Debug)]
+pub struct TimeoutFuture<F, T>
+where
+    F: Future<Output = io::Result<T>>,
+{
+    future: F,
+    timeout: Delay,
+}
+
+impl<F, T> TimeoutFuture<F, T>
+where
+    F: Future<Output = io::Result<T>>,
+{
+    pin_utils::unsafe_pinned!(future: F);
+    pin_utils::unsafe_pinned!(timeout: Delay);
+}
+
+impl<F, T> Future for TimeoutFuture<F, T>
+where
+    F: Future<Output = io::Result<T>>,
+{
+    type Output = io::Result<T>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.as_mut().future().try_poll(cx) {
+            Poll::Pending => {}
+            other => return other,
+        }
+
+        if self.timeout().poll(cx).is_ready() {
+            let err = Err(io::Error::new(io::ErrorKind::TimedOut, "future timed out").into());
+            Poll::Ready(err)
+        } else {
+            Poll::Pending
+        }
+    }
 }