UrlEncode –The correct encoding

While developing the OAuth C# Lubrary I discovered that the HttpUtility class that’s available in the System.Web assembly in .NET (in particular the HttpUtility.UrlEncode() method) doesn’t quite do it correctly. So I had to develop my own method that did the encoding correctly. I used this wiki page as a reference.

Notice the UrlEncode() method in the code listing below, that’s the method I present in this post. The outputs of the HttpUtility.UrlEncode() method any my UrlEncode() method are listed below such that you can compare the two outputs.

UrlEncoding a string in C# the correct way

  class Program
  {
    private readonly static string unreservedCharacters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.~";

    static void Main(string[] args)
    {
      var url = "!*'();:@&=+$,/?#[] <>~.\"{}|\\-`_^%";

      Console.WriteLine("Using HttpUtility: " + HttpUtility.UrlEncode(url));
      Console.WriteLine("Using UrlEncode:   " + UrlEncode(url));
      Console.WriteLine(HttpUtility.UrlDecode(UrlEncode(url)));

      Console.ReadLine();
    }

    /// <summary>
    /// This method is the correct implementation of UrlEncode.
    /// Given a string, it returns a UrlEncoded version on the string.
    /// </summary>
    /// <param name="value">the string/url to be UrlEncoded</param>
    /// <returns>The UrlEncoded string</returns>
    public static string UrlEncode(string value)
    {
      if (String.IsNullOrEmpty(value))
        return String.Empty;

      var sb = new StringBuilder();

      foreach (char @char in value)
      {
        if (unreservedCharacters.IndexOf(@char) != -1)
          sb.Append(@char);
        else
          sb.AppendFormat("%{0:x2}", (int)@char);
      }
      return sb.ToString();
    }
  }