在C＃中清理文件路径而不影响驱动器号

Question

I need to process some file paths in C# that potentially contain illegal characters, for example:

C:\path\something\output_at_13:26:43.txt

in that path, the : s in the timestamp make the filename invalid, and I want to replace them with another safe character.

I've searched for solutions here on SO, but they seem to be all based around something like:

path = string.Join("_", path.Split(Path.GetInvalidFileNameChars()));

or similar solutions. These solutions however are not good, because they screw up the drive letter, and I obtain an output of:

C_\path\something\output_at_13_26_43.txt

I tried using Path.GetInvalidPathChars() but it still doesn't work, because it doesn't include the : in the illegal characters, so it doesn't replace the ones in the filename.

So, after figuring that out, I tried doing this:

string dir = Path.GetDirectoryName(path);
string file = Path.GetFileName(path);
file = string.Join(replacement, file.Split(Path.GetInvalidFileNameChars()));
dir = string.Join(replacement, dir.Split(Path.GetInvalidPathChars()));

path = Path.Combine(dir, file);

but this is not good either, because the : s in the filename seem to interfere with the Path.GetFilename() logic, and it only returns the last piece after the last : , so I'm losing pieces of the path.

How do I do this "properly" without hacky solutions?

Answer 1

You can write a simple sanitizer that iterates each character and knows when to expect the colon as a drive separator. This one will catch any combination of letter AZ followed directly by a ":". It will also detect path separators and not escape them. It will not detect whitespace at the beginning of the input string, so in case your input data might come with them, you will have to trim it first or modify the sanitizer accordingly:

enum ParserState {
    PossibleDriveLetter,
    PossibleDriveLetterSeparator,
    Path
}

static string SanitizeFileName(string input) {
    StringBuilder output = new StringBuilder(input.Length);
    ParserState state = ParserState.PossibleDriveLetter;
    foreach(char current in input) {
        if (((current >= 'a') && (current <= 'z')) || ((current >= 'A') && (current <= 'Z'))) {
            output.Append(current);
            if (state == ParserState.PossibleDriveLetter) {
                state = ParserState.PossibleDriveLetterSeparator;
            }
            else {
                state = ParserState.Path;
            }
        }
        else if ((current == Path.DirectorySeparatorChar) ||
            (current == Path.AltDirectorySeparatorChar) ||
            ((current == ':') && (state == ParserState.PossibleDriveLetterSeparator)) ||
            !Path.GetInvalidFileNameChars().Contains(current)) {

            output.Append(current);
            state = ParserState.Path;
        }
        else {
            output.Append('_');
            state = ParserState.Path;
        }
    }
    return output.ToString();
}

You can try it out here .

Answer 2

You definitely should make sure that you only receive valid filenames.

If you can't, and you're certain your directory names will be, you could split the path the last backslash (assuming Windows) and reassemble the string:

public static string SanitizePath(string path)
{
    var lastBackslash = path.LastIndexOf('\\');

    var dir = path.Substring(0, lastBackslash);
    var file = path.Substring(lastBackslash, path.Length - lastBackslash);

    foreach (var invalid in Path.GetInvalidFileNameChars())
    {
        file = file.Replace(invalid, '_');
    }

    return dir + file;
}