public static string UrlEncode(this string input)
{
    const int maxLength = 32766;

    if (input == null)
        throw new ArgumentNullException("input");

    if (input.Length <= maxLength)
        return Uri.EscapeDataString(input);

    var sb = new StringBuilder(input.Length * 2);
    var index = 0;

    while (index < input.Length)
    {
        var length = Math.Min(input.Length - index, maxLength);
        var subString = input.Substring(index, length);

        sb.Append(Uri.EscapeDataString(subString));
        index += subString.Length;
    }

    return sb.ToString();
}