1 files changed, 99 insertions, 0 deletions
diff --git a/third_party/rust/futures-0.1.31/src/future/flatten_stream.rs b/third_party/rust/futures-0.1.31/src/future/flatten_stream.rs
new file mode 100644
index 0000000000..7bf3b9ca79
--- /dev/null
+++ b/third_party/rust/futures-0.1.31/src/future/flatten_stream.rs
@@ -0,0 +1,99 @@
+use {Async, Future, Poll};
+use core::fmt;
+use stream::Stream;
+
+/// Future for the `flatten_stream` combinator, flattening a
+/// future-of-a-stream to get just the result of the final stream as a stream.
+///
+/// This is created by the `Future::flatten_stream` method.
+#[must_use = "streams do nothing unless polled"]
+pub struct FlattenStream<F>
+    where F: Future,
+          <F as Future>::Item: Stream<Error=F::Error>,
+{
+    state: State<F>
+}
+
+impl<F> fmt::Debug for FlattenStream<F>
+    where F: Future + fmt::Debug,
+          <F as Future>::Item: Stream<Error=F::Error> + fmt::Debug,
+{
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt.debug_struct("FlattenStream")
+            .field("state", &self.state)
+            .finish()
+    }
+}
+
+pub fn new<F>(f: F) -> FlattenStream<F>
+    where F: Future,
+          <F as Future>::Item: Stream<Error=F::Error>,
+{
+    FlattenStream {
+        state: State::Future(f)
+    }
+}
+
+#[derive(Debug)]
+enum State<F>
+    where F: Future,
+          <F as Future>::Item: Stream<Error=F::Error>,
+{
+    // future is not yet called or called and not ready
+    Future(F),
+    // future resolved to Stream
+    Stream(F::Item),
+    // EOF after future resolved to error
+    Eof,
+    // after EOF after future resolved to error
+    Done,
+}
+
+impl<F> Stream for FlattenStream<F>
+    where F: Future,
+          <F as Future>::Item: Stream<Error=F::Error>,
+{
+    type Item = <F::Item as Stream>::Item;
+    type Error = <F::Item as Stream>::Error;
+
+    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
+        loop {
+            let (next_state, ret_opt) = match self.state {
+                State::Future(ref mut f) => {
+                    match f.poll() {
+                        Ok(Async::NotReady) => {
+                            // State is not changed, early return.
+                            return Ok(Async::NotReady)
+                        },
+                        Ok(Async::Ready(stream)) => {
+                            // Future resolved to stream.
+                            // We do not return, but poll that
+                            // stream in the next loop iteration.
+                            (State::Stream(stream), None)
+                        }
+                        Err(e) => {
+                            (State::Eof, Some(Err(e)))
+                        }
+                    }
+                }
+                State::Stream(ref mut s) => {
+                    // Just forward call to the stream,
+                    // do not track its state.
+                    return s.poll();
+                }
+                State::Eof => {
+                    (State::Done, Some(Ok(Async::Ready(None))))
+                }
+                State::Done => {
+                    panic!("poll called after eof");
+                }
+            };
+
+            self.state = next_state;
+            if let Some(ret) = ret_opt {
+                return ret;
+            }
+        }
+    }
+}
+