if err != nil || len(contentSHA256) == 0 {
			return ErrContentSHA256Mismatch
		}
	}

	// Verify 'Content-Md5' and/or 'X-Amz-Content-Sha256' if present.
	// The verification happens implicit during reading.
	reader, err := hash.NewReader(ctx, r.Body, -1, clientETag.String(), hex.EncodeToString(contentSHA256), -1)
	if err != nil {
		return toAPIErrorCode(ctx, err)
	}
	r.Body = reader
	return ErrNone
}