How to Implement URL-Safe Base64 Encoding and Decoding in C#?

The URL security base64 encoding

Base64 encoding is a common encoding method, but when URL security coding is performed, some characters (,/, and =) may cause problems. Although Java's CodeC library provides a direct solution, C# requires a little different ways.

Implement URL security coding

To implement the URL security base64 encoding in C#, you can simply replace the problematic characters to URL-friendly characters (-replacement, _ replacement /), and delete any filling character (=).

Among them, padding is defined as:

string returnValue = System.Convert.ToBase64String(toEncodeAsBytes)
        .TrimEnd(padding).Replace('+', '-').Replace('/', '_');

To reverse this process:

static readonly char[] padding = { '=' };

Comparison with the CODEC library

string incoming = returnValue
    .Replace('_', '/').Replace('-', '+');
switch(returnValue.Length % 4) {
    case 2: incoming += "=="; break;
    case 3: incoming += "="; break;
}
byte[] bytes = Convert.FromBase64String(incoming);
string originalText = Encoding.ASCII.GetString(bytes);

It is worth noting that this method is similar to the method of using the CODEC library of Java. However, it is recommended to test this assumption to ensure that it is compatible with specific libraries in use.

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