//
// NewReader may try merge the given size, MD5 and SHA256 values
// into src - if src is a Reader - to avoid computing the same
// checksums multiple times.
// NewReader enforces S3 compatibility strictly by ensuring caller
// does not send more content than specified size.
func NewReader(ctx context.Context, src io.Reader, size int64, md5Hex, sha256Hex string, actualSize int64) (*Reader, error) {

	sum := r.md5.Sum(nil)
	return ETag(sum)
}

// VerifyError is an error signaling that a
// computed ETag does not match an expected
// ETag.
type VerifyError struct {
	Expected ETag
	Computed ETag
}

func (v VerifyError) Error() string {
	return fmt.Sprintf("etag: expected ETag %q does not match computed ETag %q", v.Expected, v.Computed)
}

// UUIDHash - use uuid to make md5sum
type UUIDHash struct {