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    use crate::io::{AsyncRead, ReadBuf};

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

    cfg_io_util! {
        /// An async reader which yields one byte over and over and over and over and
        /// over and...
        ///
        /// This struct is generally created by calling [`repeat`][repeat]. Please
        /// see the documentation of `repeat()` for more details.
        ///
        /// This is an asynchronous version of [`std::io::Repeat`][std].
        ///
        /// [repeat]: fn@repeat
        /// [std]: std::io::Repeat
        #[derive(Debug)]
        pub struct Repeat {
            byte: u8,
        }

        /// Creates an instance of an async reader that infinitely repeats one byte.
        ///
        /// All reads from this reader will succeed by filling the specified buffer with
        /// the given byte.
        ///
        /// This is an asynchronous version of [`std::io::repeat`][std].
        ///
        /// [std]: std::io::repeat
        ///
        /// # Examples
        ///
        /// ```
        /// use tokio::io::{self, AsyncReadExt};
        ///
        /// #[tokio::main]
        /// async fn main() {
        ///     let mut buffer = [0; 3];
        ///     io::repeat(0b101).read_exact(&mut buffer).await.unwrap();
        ///     assert_eq!(buffer, [0b101, 0b101, 0b101]);
        /// }
        /// ```
        pub fn repeat(byte: u8) -> Repeat {
            Repeat { byte }
        }
    }

    impl AsyncRead for Repeat {
        #[inline]
        fn poll_read(
            self: Pin<&mut Self>,
            _: &mut Context<'_>,
            buf: &mut ReadBuf<'_>,
        ) -> Poll<io::Result<()>> {
            // TODO: could be faster, but should we unsafe it?
            while buf.remaining() != 0 {
                buf.put_slice(&[self.byte]);
            }
            Poll::Ready(Ok(()))
        }
    }

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

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