1 files changed, 74 insertions, 0 deletions
diff --git a/third_party/rust/futures-0.1.31/src/stream/peek.rs b/third_party/rust/futures-0.1.31/src/stream/peek.rs
new file mode 100644
index 0000000000..96e657663b
--- /dev/null
+++ b/third_party/rust/futures-0.1.31/src/stream/peek.rs
@@ -0,0 +1,74 @@
+use {Async, Poll};
+use stream::{Stream, Fuse};
+
+/// A `Stream` that implements a `peek` method.
+///
+/// The `peek` method can be used to retrieve a reference
+/// to the next `Stream::Item` if available. A subsequent
+/// call to `poll` will return the owned item.
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Peekable<S: Stream> {
+    stream: Fuse<S>,
+    peeked: Option<S::Item>,
+}
+
+
+pub fn new<S: Stream>(stream: S) -> Peekable<S> {
+    Peekable {
+        stream: stream.fuse(),
+        peeked: None
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+impl<S> ::sink::Sink for Peekable<S>
+    where S: ::sink::Sink + Stream
+{
+    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: Stream> Stream for Peekable<S> {
+    type Item = S::Item;
+    type Error = S::Error;
+
+    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
+        if let Some(item) = self.peeked.take() {
+            return Ok(Async::Ready(Some(item)))
+        }
+        self.stream.poll()
+    }
+}
+
+
+impl<S: Stream> Peekable<S> {
+    /// Peek retrieves a reference to the next item in the stream.
+    ///
+    /// This method polls the underlying stream and return either a reference
+    /// to the next item if the stream is ready or passes through any errors.
+    pub fn peek(&mut self) -> Poll<Option<&S::Item>, S::Error> {
+        if self.peeked.is_some() {
+            return Ok(Async::Ready(self.peeked.as_ref()))
+        }
+        match try_ready!(self.poll()) {
+            None => Ok(Async::Ready(None)),
+            Some(item) => {
+                self.peeked = Some(item);
+                Ok(Async::Ready(self.peeked.as_ref()))
+            }
+        }
+    }
+}