1 files changed, 81 insertions, 0 deletions
diff --git a/third_party/rust/futures-0.1.31/src/stream/then.rs b/third_party/rust/futures-0.1.31/src/stream/then.rs
new file mode 100644
index 0000000000..cab338e922
--- /dev/null
+++ b/third_party/rust/futures-0.1.31/src/stream/then.rs
@@ -0,0 +1,81 @@
+use {Async, IntoFuture, Future, Poll};
+use stream::Stream;
+
+/// A stream combinator which chains a computation onto each item produced by a
+/// stream.
+///
+/// This structure is produced by the `Stream::then` method.
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Then<S, F, U>
+    where U: IntoFuture,
+{
+    stream: S,
+    future: Option<U::Future>,
+    f: F,
+}
+
+pub fn new<S, F, U>(s: S, f: F) -> Then<S, F, U>
+    where S: Stream,
+          F: FnMut(Result<S::Item, S::Error>) -> U,
+          U: IntoFuture,
+{
+    Then {
+        stream: s,
+        future: None,
+        f: f,
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+impl<S, F, U> ::sink::Sink for Then<S, F, U>
+    where S: ::sink::Sink, U: IntoFuture,
+{
+    type SinkItem = S::SinkItem;
+    type SinkError = S::SinkError;
+
+    fn start_send(&mut self, item: S::SinkItem) -> ::StartSend<S::SinkItem, S::SinkError> {
+        self.stream.start_send(item)
+    }
+
+    fn poll_complete(&mut self) -> Poll<(), S::SinkError> {
+        self.stream.poll_complete()
+    }
+
+    fn close(&mut self) -> Poll<(), S::SinkError> {
+        self.stream.close()
+    }
+}
+
+impl<S, F, U> Stream for Then<S, F, U>
+    where S: Stream,
+          F: FnMut(Result<S::Item, S::Error>) -> U,
+          U: IntoFuture,
+{
+    type Item = U::Item;
+    type Error = U::Error;
+
+    fn poll(&mut self) -> Poll<Option<U::Item>, U::Error> {
+        if self.future.is_none() {
+            let item = match self.stream.poll() {
+                Ok(Async::NotReady) => return Ok(Async::NotReady),
+                Ok(Async::Ready(None)) => return Ok(Async::Ready(None)),
+                Ok(Async::Ready(Some(e))) => Ok(e),
+                Err(e) => Err(e),
+            };
+            self.future = Some((self.f)(item).into_future());
+        }
+        assert!(self.future.is_some());
+        match self.future.as_mut().unwrap().poll() {
+            Ok(Async::Ready(e)) => {
+                self.future = None;
+                Ok(Async::Ready(Some(e)))
+            }
+            Err(e) => {
+                self.future = None;
+                Err(e)
+            }
+            Ok(Async::NotReady) => Ok(Async::NotReady)
+        }
+    }
+}