Function send 

pub async fn send<T, X, M>(
    conn: &mut Framed<T, Codec>,
    xfer: X,
    mi: M,
) -> Result<String, Error>
where
    T: AsyncRead + AsyncWrite + Unpin,
    X: Borrow<Transport>,
    M: Borrow<MsgInfo>,

Send a message, including (if applicable) its metadata and payload.

On successful completion returns the transfer identifier.