base64 constant
Pattern
const base64
Base64 String Regex Examples: SGVsbG8gd29ybGQ=, U29tZSBzdHJpbmc=
Implementation
static const Pattern base64 =
r'^(?:[A-Za-z0-9+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?$';