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    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()))
                }
            }
        }
    }

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