1 files changed, 57 insertions, 0 deletions
diff --git a/third_party/rust/futures-0.1.29/src/stream/chain.rs b/third_party/rust/futures-0.1.29/src/stream/chain.rs
new file mode 100644
index 0000000000..0ff0e5ce6f
--- /dev/null
+++ b/third_party/rust/futures-0.1.29/src/stream/chain.rs
@@ -0,0 +1,57 @@
+use core::mem;
+
+use stream::Stream;
+use {Async, Poll};
+
+
+/// State of chain stream.
+#[derive(Debug)]
+enum State<S1, S2> {
+    /// Emitting elements of first stream
+    First(S1, S2),
+    /// Emitting elements of second stream
+    Second(S2),
+    /// Temporary value to replace first with second
+    Temp,
+}
+
+/// An adapter for chaining the output of two streams.
+///
+/// The resulting stream produces items from first stream and then
+/// from second stream.
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Chain<S1, S2> {
+    state: State<S1, S2>
+}
+
+pub fn new<S1, S2>(s1: S1, s2: S2) -> Chain<S1, S2>
+    where S1: Stream, S2: Stream<Item=S1::Item, Error=S1::Error>,
+{
+    Chain { state: State::First(s1, s2) }
+}
+
+impl<S1, S2> Stream for Chain<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<Self::Item>, Self::Error> {
+        loop {
+            match self.state {
+                State::First(ref mut s1, ref _s2) => match s1.poll() {
+                    Ok(Async::Ready(None)) => (), // roll
+                    x => return x,
+                },
+                State::Second(ref mut s2) => return s2.poll(),
+                State::Temp => unreachable!(),
+            }
+
+            self.state = match mem::replace(&mut self.state, State::Temp) {
+                State::First(_s1, s2) => State::Second(s2),
+                _ => unreachable!(),
+            };
+        }
+    }
+}