Function co_copy 

pub async fn co_copy<'a, R, W>(
    reader: &'a mut R,
    writer: &'a mut W,
) -> Result<u64>
where
    R: AsyncRead + Unpin + ?Sized,
    W: AsyncWrite + Unpin + ?Sized,

Available on crate feature coroutine only.

Copy an async reader to an async writer.

This is wrapper for tokio::io::copy with error context