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    use std::collections::VecDeque;

    use {Poll, Async};
    use {StartSend, AsyncSink};
    use sink::Sink;
    use stream::Stream;

    /// Sink for the `Sink::buffer` combinator, which buffers up to some fixed
    /// number of values when the underlying sink is unable to accept them.
    #[derive(Debug)]
    #[must_use = "sinks do nothing unless polled"]
    pub struct Buffer<S: Sink> {
        sink: S,
        buf: VecDeque<S::SinkItem>,

        // Track capacity separately from the `VecDeque`, which may be rounded up
        cap: usize,
    }

    pub fn new<S: Sink>(sink: S, amt: usize) -> Buffer<S> {
        Buffer {
            sink: sink,
            buf: VecDeque::with_capacity(amt),
            cap: amt,
        }
    }

    impl<S: Sink> Buffer<S> {
        /// Get a shared reference to the inner sink.
        pub fn get_ref(&self) -> &S {
            &self.sink
        }

        /// Get a mutable reference to the inner sink.
        pub fn get_mut(&mut self) -> &mut S {
            &mut self.sink
        }

        /// Consumes this combinator, returning the underlying sink.
        ///
        /// Note that this may discard intermediate state of this combinator, so
        /// care should be taken to avoid losing resources when this is called.
        pub fn into_inner(self) -> S {
            self.sink
        }

        fn try_empty_buffer(&mut self) -> Poll<(), S::SinkError> {
            while let Some(item) = self.buf.pop_front() {
                if let AsyncSink::NotReady(item) = self.sink.start_send(item)? {
                    self.buf.push_front(item);

                    return Ok(Async::NotReady);
                }
            }

            Ok(Async::Ready(()))
        }
    }

    // Forwarding impl of Stream from the underlying sink
    impl<S> Stream for Buffer<S> where S: Sink + Stream {
        type Item = S::Item;
        type Error = S::Error;

        fn poll(&mut self) -> Poll<Option<S::Item>, S::Error> {
            self.sink.poll()
        }
    }

    impl<S: Sink> Sink for Buffer<S> {
        type SinkItem = S::SinkItem;
        type SinkError = S::SinkError;

        fn start_send(&mut self, item: Self::SinkItem) -> StartSend<Self::SinkItem, Self::SinkError> {
            if self.cap == 0 {
                return self.sink.start_send(item);
            }

            self.try_empty_buffer()?;
            if self.buf.len() == self.cap {
                return Ok(AsyncSink::NotReady(item));
            }
            self.buf.push_back(item);
            Ok(AsyncSink::Ready)
        }

        fn poll_complete(&mut self) -> Poll<(), Self::SinkError> {
            if self.cap == 0 {
                return self.sink.poll_complete();
            }

            try_ready!(self.try_empty_buffer());
            debug_assert!(self.buf.is_empty());
            self.sink.poll_complete()
        }

        fn close(&mut self) -> Poll<(), Self::SinkError> {
            if self.cap == 0 {
                return self.sink.close();
            }

            if self.buf.len() > 0 {
                try_ready!(self.try_empty_buffer());
            }
            assert_eq!(self.buf.len(), 0);
            self.sink.close()
        }
    }

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