Converting string to web-safe Base64 format

Question

I am testing how to update user picture using the Admin SDK Directory Service with Google Apps Scripts with the following function:

function updatePhoto(){
  var fileId = 'XXXXXXXXXXXXXXXXXXX';
  var b = DocsList.getFileById(fileId).getBlob();
  var encoded = Utilities.base64Encode(b.getBytes());

  encoded = encoded.replace(/\//g,'_').replace(/\+/g,'-').replace(/\=/g,'*');
  AdminDirectory.Users.Photos.update({
    "photoData": encoded },'harry.potter@abc.edu.hk');
}

However, it doesn't always work. Whenever there is padding in the base64 encoded string, it fails. Referring to Google's document (https://developers.google.com/admin-sdk/directory/v1/reference/users/photos/update), I am a bit confused with the descriptions. It says:

1. The equals sign (=) character is replaced with the asterisk (*).
2. For padding, the period (.) character is used instead of the RFC-4648 baseURL definition which uses the equals sign (=) for padding. This is done to simplify URL-parsing.

What should be actually done? (=) is used for padding in Base64. So, should I use (*) or (.)? I did try to replace (=) with (.) but no luck.

Can anyone help?

---

It is so strange. It works when i do not replace (=).

function updatePhoto(){
  var fileId = 'XXXXXXXXXXXXXXXXXXX';
  var b = DocsList.getFileById(fileId).getBlob();
  var encoded = Utilities.base64Encode(b.getBytes());

  encoded = encoded.replace(/\//g,'_').replace(/\+/g,'-');
  AdminDirectory.Users.Photos.update({
    "photoData": encoded },'harry.potter@abc.edu.hk');

}

Answer 1

The API requires you to use URL-safe base64 encoding. After doing the base64 encoding, try replacing / with _ and + with -. Details at:

https://developers.google.com/admin-sdk/directory/v1/reference/users/photos/update

Answer 2

I know that this is quite old, but I'm working in something similar and I want to share my solution. You can use this function to convert your string to a base64safeurl string:

protected static string Base64ForUrlEncode(string str)
        {

            StringBuilder result = new StringBuilder(Convert.ToBase64String(Encoding.ASCII.GetBytes(str)).TrimEnd('='));
            result.Replace('+', '-');
            result.Replace('/', '_');
            return result.ToString();
        }

More info here: http://www.codeproject.com/Tips/76650/Base-base-url-base-url-and-z-base-encoding

Note: This is C# code, so this solution is for .NET developments.

Answer 3

To add to @Jay lee's and @Daniel Marin's answers:

if you are using Python to encode, you can use:

base64.urlsafe

function, and in Java, you can use:

Base64.encodeBase64URLSafeString(byte[] binaryData)

Answer 4

RFC 4648 specifies "web-safe" base64 and calls it "base64url": https://datatracker.ietf.org/doc/html/rfc4648#section-5