use tokio::prelude::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};

const BUFF_SIZE: usize = 2048;

pub async fn copy<R, W>(mut reader: R, mut writer: W) -> usize
where
    R: AsyncRead,
    W: AsyncWrite,
{
    let mut buff: Box<[u8]> = vec![0; BUFF_SIZE].into_boxed_slice();
    let mut totall: usize = 0;

    while let Ok(n) = await!(reader.read_async(&mut buff)) {
        // Nothing more to read
        if n == 0 { break }

        match await!(writer.write_async(&mut buff[..n])) {

            // empty write
            Ok(0) => return totall,

            // normal write
            Ok(n) => continue,

            // error
            Err(e) => return totall
        }
    }

    await!(writer.flush_async());

    totall
}