base64.decode: Invalid encoding before padding

user_10325698 0
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I'm working on a flutter project and I'm currently getting an error with some of the strings I try do decode using the base64.decode() method. I've created a short dart code which can reproduce the problem I'm facing with a specific string:

import 'dart:convert';

void main() {
  final message = 'RU5UUkVHQUdSQVRJU1==';
  print(utf8.decode(base64.decode(message)));
}

I'm getting the following error message:

Uncaught Error: FormatException: Invalid encoding before padding (at character 19)
RU5UUkVHQUdSQVRJU1==

I've tried decoding the same string with JavaScript and it works fine. Would be glad if someone could explain why am I getting this error, and possibly show me a solution. Thanks.

dart flutter decode base64 string
1 Answers

Base64 encoding breaks binary data into 6-bit segments of 3 full bytes and represents those as printable characters in ASCII standard. It does that in essentially two steps.

The first step is to break the binary string down into 6-bit blocks. Base64 only uses 6 bits (corresponding to 2^6 = 64 characters) to ensure encoded data is printable and humanly readable. None of the special characters available in ASCII are used.

The 64 characters (hence the name Base64) are 10 digits, 26 lowercase characters, 26 uppercase characters as well as the Plus sign (+) and the Forward Slash (/). There is also a 65th character known as a pad, which is the Equal sign (=). This character is used when the last segment of binary data doesn't contain a full 6 bits

So RU5UUkVHQUdSQVRJU1== doesn't follow the encoding pattern.

user_101054870
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