preview method
Implementation
String preview({int maxTextChars = 160, int maxBytes = 12}) {
final failure = error;
if (failure != null) return failure;
final textValue = textPreview(maxChars: maxTextChars);
if (textValue != null) return textValue;
final signature = byteSignature(maxBytes: maxBytes);
if (signature != null) {
return 'bytes=$sizeBytes; signature=$signature';
}
return 'empty export payload';
}