How to decode Feedburner result containing \x3c and so on

Question

Feed burner changed their blog service return results that it returns blocks of javascript similar to:

document.write("\x3cdiv class\x3d\x22feedburnerFeedBlock\x22 id\x3d\x22RitterInsuranceMarketingRSSv3iugf6igask14fl8ok645b6l0\x22\x3e"); document.write("\x3cul\x3e"); document.write("\x3cli\x3e\x3cspan class\x3d\x22headline\x22\x3e\x3ca href\x3d\x22

I want the raw html out of this. Previously I was able to easily just use .Replace to cleave out the document.write syntax but I can't figure out what kind of encoding this is or atleast how to decode it with C#.

Edit: Well this was a semi-nightmare to finally solve, here's what I came up with incase anyone has any improvements to offer

public static  char ConvertHexToASCII(this string hex)
{
    if (hex == null) throw new ArgumentNullException(hex);
    return (char)Convert.ToByte(hex, 16);
}

.

private string DecodeFeedburnerHtml(string html)
{
    var builder = new StringBuilder(html.Length);
    var stack = new Stack<char>(4);
    foreach (var chr in html)
    {
        switch (chr)
        {
            case '\\':
                if (stack.Count == 0)
                {
                    stack.Push(chr);
                }
                else
                {
                    stack.Clear();
                    builder.Append(chr);
                }
                break;
            case 'x':
                if (stack.Count == 1)
                {
                    stack.Push(chr);
                }
                else
                {
                    stack.Clear();
                    builder.Append(chr);
                }
                break;
            default:
                if (stack.Count >= 2)
                {
                    stack.Push(chr);

                    if (stack.Count == 4)
                    {
                        //get stack[3]stack[4]
                        string hexString = string.Format("{1}{0}", stack.Pop(),
                                                     stack.Pop());

                        builder.Append(hexString.ConvertHexToASCII());
                        stack.Clear();
                    }
                }
                else
                {
                    builder.Append(chr);
                }
                break;
        }
    }

    html = builder.ToString();
    return html;
}

Not sure what else I could do better. For some reason code like this always feels really dirty to me even though it's a linear time algorithm I guess this is related to how long it has to be.

Answer 1

Those look like ASCII values, encoded in hex. You could traverse the string, and whenever you find a \x followed by two hexadecimal digits (0-9,a-f), replace it with the corresponding ASCII character. If the string is long, it would be faster to save the result incrementally to a StringBuilder instead of using String.Replace().

I don't know the encoding specification, but there might be more rules to follow (for example, if \\ is an escape character for a literal \).