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    use crate::io::util::{BufReader, BufWriter};
    use crate::io::{AsyncBufRead, AsyncRead, AsyncWrite, ReadBuf};

    use pin_project_lite::pin_project;
    use std::io;
    use std::pin::Pin;
    use std::task::{Context, Poll};

    pin_project! {
        /// Wraps a type that is [`AsyncWrite`] and [`AsyncRead`], and buffers its input and output.
        ///
        /// It can be excessively inefficient to work directly with something that implements [`AsyncWrite`]
        /// and [`AsyncRead`]. For example, every `write`, however small, has to traverse the syscall
        /// interface, and similarly, every read has to do the same. The [`BufWriter`] and [`BufReader`]
        /// types aid with these problems respectively, but do so in only one direction. `BufStream` wraps
        /// one in the other so that both directions are buffered. See their documentation for details.
        #[derive(Debug)]
        #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
        pub struct BufStream<RW> {
            #[pin]
            inner: BufReader<BufWriter<RW>>,
        }
    }

    impl<RW: AsyncRead + AsyncWrite> BufStream<RW> {
        /// Wraps a type in both [`BufWriter`] and [`BufReader`].
        ///
        /// See the documentation for those types and [`BufStream`] for details.
        pub fn new(stream: RW) -> BufStream<RW> {
            BufStream {
                inner: BufReader::new(BufWriter::new(stream)),
            }
        }

        /// Creates a `BufStream` with the specified [`BufReader`] capacity and [`BufWriter`]
        /// capacity.
        ///
        /// See the documentation for those types and [`BufStream`] for details.
        pub fn with_capacity(
            reader_capacity: usize,
            writer_capacity: usize,
            stream: RW,
        ) -> BufStream<RW> {
            BufStream {
                inner: BufReader::with_capacity(
                    reader_capacity,
                    BufWriter::with_capacity(writer_capacity, stream),
                ),
            }
        }

        /// Gets a reference to the underlying I/O object.
        ///
        /// It is inadvisable to directly read from the underlying I/O object.
        pub fn get_ref(&self) -> &RW {
            self.inner.get_ref().get_ref()
        }

        /// Gets a mutable reference to the underlying I/O object.
        ///
        /// It is inadvisable to directly read from the underlying I/O object.
        pub fn get_mut(&mut self) -> &mut RW {
            self.inner.get_mut().get_mut()
        }

        /// Gets a pinned mutable reference to the underlying I/O object.
        ///
        /// It is inadvisable to directly read from the underlying I/O object.
        pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut RW> {
            self.project().inner.get_pin_mut().get_pin_mut()
        }

        /// Consumes this `BufStream`, returning the underlying I/O object.
        ///
        /// Note that any leftover data in the internal buffer is lost.
        pub fn into_inner(self) -> RW {
            self.inner.into_inner().into_inner()
        }
    }

    impl<RW> From<BufReader<BufWriter<RW>>> for BufStream<RW> {
        fn from(b: BufReader<BufWriter<RW>>) -> Self {
            BufStream { inner: b }
        }
    }

    impl<RW> From<BufWriter<BufReader<RW>>> for BufStream<RW> {
        fn from(b: BufWriter<BufReader<RW>>) -> Self {
            // we need to "invert" the reader and writer
            let BufWriter {
                inner:
                    BufReader {
                        inner,
                        buf: rbuf,
                        pos,
                        cap,
                    },
                buf: wbuf,
                written,
            } = b;

            BufStream {
                inner: BufReader {
                    inner: BufWriter {
                        inner,
                        buf: wbuf,
                        written,
                    },
                    buf: rbuf,
                    pos,
                    cap,
                },
            }
        }
    }

    impl<RW: AsyncRead + AsyncWrite> AsyncWrite for BufStream<RW> {
        fn poll_write(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
            buf: &[u8],
        ) -> Poll<io::Result<usize>> {
            self.project().inner.poll_write(cx, buf)
        }

        fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
            self.project().inner.poll_flush(cx)
        }

        fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
            self.project().inner.poll_shutdown(cx)
        }
    }

    impl<RW: AsyncRead + AsyncWrite> AsyncRead for BufStream<RW> {
        fn poll_read(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
            buf: &mut ReadBuf<'_>,
        ) -> Poll<io::Result<()>> {
            self.project().inner.poll_read(cx, buf)
        }
    }

    impl<RW: AsyncRead + AsyncWrite> AsyncBufRead for BufStream<RW> {
        fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
            self.project().inner.poll_fill_buf(cx)
        }

        fn consume(self: Pin<&mut Self>, amt: usize) {
            self.project().inner.consume(amt)
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;

        #[test]
        fn assert_unpin() {
            crate::is_unpin::<BufStream<()>>();
        }
    }