C# File Path encoding and decoding

Question

I am looking for a simple method to encode/escape and decode/unescape file paths (illegal characters in file paths "\/?:<>*| )

HttpUtility.UrlEncode does its job, except it does not encode the * character.

All I could find was escaping with regex, or just replacing the illegal chars with _

I want to be able to encode/decode consistently.

I want to know if there's a pre-defined way to do that or I just need to write some code to encode and another piece to decode.

Thanks

Answer 1

I've never tried anything like this before, so I threw this together:

static class PathEscaper
{
    static readonly string invalidChars = @"""\/?:<>*|";
    static readonly string escapeChar = "%";

    static readonly Regex escaper = new Regex(
        "[" + Regex.Escape(escapeChar + invalidChars) + "]",
        RegexOptions.Compiled);
    static readonly Regex unescaper = new Regex(
        Regex.Escape(escapeChar) + "([0-9A-Z]{4})",
        RegexOptions.Compiled);

    public static string Escape(string path)
    {
        return escaper.Replace(path,
            m => escapeChar + ((short)(m.Value[0])).ToString("X4"));
    }

    public static string Unescape(string path)
    {
        return unescaper.Replace(path,
            m => ((char)Convert.ToInt16(m.Groups[1].Value, 16)).ToString());
    }
}

It replaces any forbidden character with a % followed by its 16-bit representation in hex, and back. (You could probably get away with an 8-bit representation for the specific characters you have but I thought I'd err on the safe side.)

Answer 2

Rawling's solution is good. But there is a small problem. The filename generated from Rawling's method may contain "%", which can cause some errors if you use this pathname as url. So, I change the escapeChar from "%" to "__" in order to make sure the generated filename is compatible with url convention.

static class PathEscaper
{
    static readonly string invalidChars = @"""\/?:<>*|";
    static readonly string escapeChar = "__";

    static readonly Regex escaper = new Regex(
        "[" + Regex.Escape(escapeChar + invalidChars) + "]",
        RegexOptions.Compiled);
    static readonly Regex unescaper = new Regex(
        Regex.Escape(escapeChar) + "([0-9A-Z]{4})",
        RegexOptions.Compiled);

    public static string Escape(string path)
    {
        return escaper.Replace(path,
            m => escapeChar + ((short)(m.Value[0])).ToString("X4"));
    }

    public static string Unescape(string path)
    {
        return unescaper.Replace(path,
            m => ((char)Convert.ToInt16(m.Groups[1].Value, 16)).ToString());
    }
}