fromBase function
Converts given base encoded string to data bytes
Implementation
List<int> fromBase(String input, String alphabet, {int padding = 61}) {
final ret = input.codeUnits
.map((e) => e == padding ? -2 : alphabet.indexOf(String.fromCharCode(e)))
.where((e) => e != -2)
.toList();
if (ret.contains(-1)) {
throw Exception('invalid input');
}
return fromBaseBytes(ret, alphabet.codeUnits.length);
}