// ScalarDecodeFrom provides a generic implementation of Scalar.DecodeFrom,
// based on Scalar.Decode, or Scalar.Pick if r is a Cipher or cipher.Stream.
// The returned byte-count is valid only when decoding from a normal Reader,
// not when picking from a pseudorandom source.
func ScalarUnmarshalFrom(s abstract.Scalar, r io.Reader) (int, error) {
if strm, ok := r.(cipher.Stream); ok {
s.Pick(strm)
return -1, nil // no byte-count when picking randomly
}
buf := make([]byte, s.MarshalSize())
n, err := io.ReadFull(r, buf)
if err != nil {
return n, err
}
return n, s.UnmarshalBinary(buf)
}
