1 files changed, 64 insertions, 0 deletions
diff --git a/third_party/rust/futures-0.1.31/src/stream/select.rs b/third_party/rust/futures-0.1.31/src/stream/select.rs
new file mode 100644
index 0000000000..ae6b66cf14
--- /dev/null
+++ b/third_party/rust/futures-0.1.31/src/stream/select.rs
@@ -0,0 +1,64 @@
+use {Poll, Async};
+use stream::{Stream, Fuse};
+
+/// An adapter for merging the output of two streams.
+///
+/// The merged stream produces items from either of the underlying streams as
+/// they become available, and the streams are polled in a round-robin fashion.
+/// Errors, however, are not merged: you get at most one error at a time.
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Select<S1, S2> {
+    stream1: Fuse<S1>,
+    stream2: Fuse<S2>,
+    flag: bool,
+}
+
+pub fn new<S1, S2>(stream1: S1, stream2: S2) -> Select<S1, S2>
+    where S1: Stream,
+          S2: Stream<Item = S1::Item, Error = S1::Error>
+{
+    Select {
+        stream1: stream1.fuse(),
+        stream2: stream2.fuse(),
+        flag: false,
+    }
+}
+
+impl<S1, S2> Stream for Select<S1, S2>
+    where S1: Stream,
+          S2: Stream<Item = S1::Item, Error = S1::Error>
+{
+    type Item = S1::Item;
+    type Error = S1::Error;
+
+    fn poll(&mut self) -> Poll<Option<S1::Item>, S1::Error> {
+        let (a, b) = if self.flag {
+            (&mut self.stream2 as &mut Stream<Item=_, Error=_>,
+             &mut self.stream1 as &mut Stream<Item=_, Error=_>)
+        } else {
+            (&mut self.stream1 as &mut Stream<Item=_, Error=_>,
+             &mut self.stream2 as &mut Stream<Item=_, Error=_>)
+        };
+        self.flag = !self.flag;
+
+        let a_done = match a.poll()? {
+            Async::Ready(Some(item)) => return Ok(Some(item).into()),
+            Async::Ready(None) => true,
+            Async::NotReady => false,
+        };
+
+        match b.poll()? {
+            Async::Ready(Some(item)) => {
+                // If the other stream isn't finished yet, give them a chance to
+                // go first next time as we pulled something off `b`.
+                if !a_done {
+                    self.flag = !self.flag;
+                }
+                Ok(Some(item).into())
+            }
+            Async::Ready(None) if a_done => Ok(None.into()),
+            Async::Ready(None) | Async::NotReady => Ok(Async::NotReady),
+        }
+    }
+}