C# Sanitize File Name

Jason_Sundram_2683 0
Viewed 108587

I recently have been moving a bunch of MP3s from various locations into a repository. I had been constructing the new file names using the ID3 tags (thanks, TagLib-Sharp!), and I noticed that I was getting a System.NotSupportedException:

"The given path's format is not supported."

This was generated by either File.Copy() or Directory.CreateDirectory().

It didn't take long to realize that my file names needed to be sanitized. So I did the obvious thing:

public static string SanitizePath_(string path, char replaceChar)
{
    string dir = Path.GetDirectoryName(path);
    foreach (char c in Path.GetInvalidPathChars())
        dir = dir.Replace(c, replaceChar);

    string name = Path.GetFileName(path);
    foreach (char c in Path.GetInvalidFileNameChars())
        name = name.Replace(c, replaceChar);

    return dir + name;
}

To my surprise, I continued to get exceptions. It turned out that ':' is not in the set of Path.GetInvalidPathChars(), because it is valid in a path root. I suppose that makes sense - but this has to be a pretty common problem. Does anyone have some short code that sanitizes a path? The most thorough I've come up with this, but it feels like it is probably overkill.

    // replaces invalid characters with replaceChar
    public static string SanitizePath(string path, char replaceChar)
    {
        // construct a list of characters that can't show up in filenames.
        // need to do this because ":" is not in InvalidPathChars
        if (_BadChars == null)
        {
            _BadChars = new List<char>(Path.GetInvalidFileNameChars());
            _BadChars.AddRange(Path.GetInvalidPathChars());
            _BadChars = Utility.GetUnique<char>(_BadChars);
        }

        // remove root
        string root = Path.GetPathRoot(path);
        path = path.Remove(0, root.Length);

        // split on the directory separator character. Need to do this
        // because the separator is not valid in a filename.
        List<string> parts = new List<string>(path.Split(new char[]{Path.DirectorySeparatorChar}));

        // check each part to make sure it is valid.
        for (int i = 0; i < parts.Count; i++)
        {
            string part = parts[i];
            foreach (char c in _BadChars)
            {
                part = part.Replace(c, replaceChar);
            }
            parts[i] = part;
        }

        return root + Utility.Join(parts, Path.DirectorySeparatorChar.ToString());
    }

Any improvements to make this function faster and less baroque would be much appreciated.

invalid-characters sanitize validation path c#
13 Answers

To clean up a file name you could do this

private static string MakeValidFileName( string name )
{
   string invalidChars = System.Text.RegularExpressions.Regex.Escape( new string( System.IO.Path.GetInvalidFileNameChars() ) );
   string invalidRegStr = string.Format( @"([{0}]*\.+$)|([{0}]+)", invalidChars );

   return System.Text.RegularExpressions.Regex.Replace( name, invalidRegStr, "_" );
}
user_1046720

there are a lot of working solutions here. just for the sake of completeness, here's an approach that doesn't use regex, but uses LINQ:

var invalids = Path.GetInvalidFileNameChars();
filename = invalids.Aggregate(filename, (current, c) => current.Replace(c, '_'));

Also, it's a very short solution ;)

user_43107100

I think the problem is that you first call Path.GetDirectoryName on the bad string. If this has non-filename characters in it, .Net can't tell which parts of the string are directories and throws. You have to do string comparisons.

Assuming it's only the filename that is bad, not the entire path, try this:

public static string SanitizePath(string path, char replaceChar)
{
    int filenamePos = path.LastIndexOf(Path.DirectorySeparatorChar) + 1;
    var sb = new System.Text.StringBuilder();
    sb.Append(path.Substring(0, filenamePos));
    for (int i = filenamePos; i < path.Length; i++)
    {
        char filenameChar = path[i];
        foreach (char c in Path.GetInvalidFileNameChars())
            if (filenameChar.Equals(c))
            {
                filenameChar = replaceChar;
                break;
            }

        sb.Append(filenameChar);
    }

    return sb.ToString();
}
Dour_High_Arch_224370

Your code would be cleaner if you appended the directory and filename together and sanitized that rather than sanitizing them independently. As for sanitizing away the :, just take the 2nd character in the string. If it is equal to "replacechar", replace it with a colon. Since this app is for your own use, such a solution should be perfectly sufficient.

Brian_181920

Based @fiat's and @Andre's approach, I'd like to share my solution too. Main difference:

  • its an extension method
  • regex is compiled at first use to save some time with a lot executions
  • reserved words are preserved
public static class StringPathExtensions
{
    private static Regex _invalidPathPartsRegex;
    
    static StringPathExtensions()
    {
        var invalidReg = System.Text.RegularExpressions.Regex.Escape(new string(Path.GetInvalidFileNameChars()));
        _invalidPathPartsRegex = new Regex($"(?<reserved>^(CON|PRN|AUX|CLOCK\\$|NUL|COM0|COM1|COM2|COM3|COM4|COM5|COM6|COM7|COM8|COM9|LPT0|LPT1|LPT2|LPT3|LPT4|LPT5|LPT6|LPT7|LPT8|LPT9))|(?<invalid>[{invalidReg}:]+|\\.$)", RegexOptions.Compiled);
    }

    public static string SanitizeFileName(this string path)
    {
        return _invalidPathPartsRegex.Replace(path, m =>
        {
            if (!string.IsNullOrWhiteSpace(m.Groups["reserved"].Value))
                return string.Concat("_", m.Groups["reserved"].Value);
            return "_";
        });
    }
}
user_25916670
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