System.FormatException: 'Invalid length for a Base-64 char array or string.'

Question

I'm beating my head against a wall here, with this simple code that just doesn't work:

string middle = "eyJzdWIiOiJtYXR0d2ViZXIiLCJqdGkiOiJlMWVmNjc5Mi02YTBjLTQ4YWUtYmQzNi0wZDlmMTVlMDFiY2UiLCJpYXQiOjE0OTMwOTI0OTQsIm5iZiI6MTQ5MzA5MjQ5NCwiZXhwIjoxNDkzMjY1Mjk0LCJpc3MiOiJFQ29tbVdlYkFQSTIiLCJhdWQiOiJFQ29tbVdlYkNsaWVudDIifQ"

byte[] newBytes = Convert.FromBase64String(middle);
middle = Encoding.UTF8.GetString(newBytes);

It's that simple! And yet I get the error in the Title.

Also, I ran this on https://www.base64decode.org/ and it decodes perfectly.

Answer 1

Since your provided string does not completely fit criteria of FromBase64String method accepted values you need to add end symbol to follow the convention. It does not automatically add end symbols to your string.

The valueless character, "=", is used for trailing padding. The end of s can consist of zero, one, or two padding characters.

Source.

To fix issue you are having add "==" to the end of your string.

For example: string middle = "SomeString=="