Function drive_async_stream 

pub async fn drive_async_stream<S, D>(
    policy: StreamPolicy,
    source: &mut S,
    sink: &mut D,
    scratch: &mut [u8],
    outcome: &mut StreamOutcome,
) -> Result<StreamCompletion, StreamExecutionError<S::Error, D::Error>>
where
    S: AsyncStreamSource + Send,
    D: AsyncStreamSink + Send,

Drives one cross-thread asynchronous transfer without owning an executor.