1 files changed, 49 insertions, 0 deletions
diff --git a/third_party/rust/futures-0.1.29/src/future/fuse.rs b/third_party/rust/futures-0.1.29/src/future/fuse.rs
new file mode 100644
index 0000000000..05ad3d5afa
--- /dev/null
+++ b/third_party/rust/futures-0.1.29/src/future/fuse.rs
@@ -0,0 +1,49 @@
+use {Future, Poll, Async};
+
+/// A future which "fuses" a future once it's been resolved.
+///
+/// Normally futures can behave unpredictable once they're used after a future
+/// has been resolved, but `Fuse` is always defined to return `Async::NotReady`
+/// from `poll` after it has resolved successfully or returned an error.
+///
+/// This is created by the `Future::fuse` method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless polled"]
+pub struct Fuse<A: Future> {
+    future: Option<A>,
+}
+
+pub fn new<A: Future>(f: A) -> Fuse<A> {
+    Fuse {
+        future: Some(f),
+    }
+}
+
+impl<A: Future> Fuse<A> {
+    /// Returns whether the underlying future has finished or not.
+    /// 
+    /// If this method returns `true`, then all future calls to `poll`
+    /// are guaranteed to return `Ok(Async::NotReady)`. If this returns
+    /// false, then the underlying future has not been driven to
+    /// completion.
+    pub fn is_done(&self) -> bool {
+        self.future.is_none()
+    }
+}
+
+impl<A: Future> Future for Fuse<A> {
+    type Item = A::Item;
+    type Error = A::Error;
+
+    fn poll(&mut self) -> Poll<A::Item, A::Error> {
+        let res = self.future.as_mut().map(|f| f.poll());
+        match res.unwrap_or(Ok(Async::NotReady)) {
+            res @ Ok(Async::Ready(_)) |
+            res @ Err(_) => {
+                self.future = None;
+                res
+            }
+            Ok(Async::NotReady) => Ok(Async::NotReady)
+        }
+    }
+}