code: func NewDataReader(r io.Reader) (*Data, error) {
  	d := newData()
  	d.r = r
  	d.cbs.read = C.gpgme_data_read_cb_t(C.gogpgme_readfunc)
  	cbc := callbackAdd(d)
  	d.cbc = cbc
  	return d, handleError(C.gogpgme_data_new_from_cbs(&d.dh, &d.cbs, C.uintptr_t(cbc)))
  }
docs: // NewDataReader returns a new callback based data buffer