Function copy_interactive

async fn copy_interactive<R, W>(reader: R, writer: W) -> Result<()>
where
    R: AsyncRead + Unpin,
    W: AsyncWrite + Unpin,

Copy all the data from reader into writer until we encounter an EOF or an error.

Unlike as futures::io::copy(), this function is meant for use with interactive readers and writers, where the reader might pause for a while, but where we want to send data on the writer as soon as it is available.

This function assumes that the writer might need to be flushed for any buffered data to be sent. It tries to minimize the number of flushes, however, by only flushing the writer when the reader has no data.