base64 function
Implementation
bool base64(String str, {bool? urlSafe}) {
final notBase64 = RegExp(r'/[^A-Z0-9+\/=]/i');
final urlSafeBase64 = RegExp(r'/^[A-Z0-9_\-]*$/i');
final len = str.length;
if (urlSafe!) {
return urlSafeBase64.hasMatch(str);
}
if (len % 4 != 0 || notBase64.hasMatch(str)) {
return false;
}
final firstPaddingChar = str.indexOf('=');
return firstPaddingChar == -1 ||
firstPaddingChar == len - 1 ||
(firstPaddingChar == len - 2 && str[len - 1] == '=');
}