(define (u8vectors->base64 . vecs)
  (if (= 1 (length vecs))
    (base64-encode (blob->string (u8vector->blob/shared (car vecs))))
    (u8vectors->base64 (list->u8vector (flatten (map u8vector->list vecs))))))

(define (base64->u8vectors str . subu8ranges)
  (let ((vec (blob->u8vector (string->blob (base64-decode str)))))
    (if (> (length subu8ranges) 0)
      (apply values (map (lambda (x) (subu8vector vec (car x) (cadr x))) subu8ranges))
      vec)))