Preventing backslash in path building on .NET for cross platform deploy

Question

I have a legacy .NET application that I have ported to .NET 6.0 and am executing cross platform (Windows & Linux).

Much of the legacy code was developed with hard coded path creation, using backslash in strings, like

new StreamWriter(FeuxBarreFolderName + @"\\JazzSchmazz.txt");

that I have converted to something like

new StreamWriter(Path.Combine(FeuxBarreFolderName, "JazzSchmazz.txt"));

I want to prevent any developer from accidentally or purposefully adding \ in a hard coded path again. Other than handling this at code review, is there a way that I can do this automatically, either by code analysis or spectacular failure at testing time? My searches have been unhelpful.

Ideas that I've had

• Modify the ext4 filesystem on my Docker integration tests to prevent filenames with a \. I have no idea if this is possible / reasonable.
• Get creative with permissions on my Docker integration tests to prevent creating files in a root directory (take away w from the parent dir), but allow it on the child dir (add w again to a specific child dir). This feels super brittle.
• Find or write an analyzer to look at strings and complain about any strings that contain a \ character.

Is there a better way here?

Answer 1

As there's not a built in way to protect against this at development or execution time, I'm going to add this code to run after my integration tests. It will sweep the filesystem and throw an exception if it finds any files or directories created with an inappropriate character (backslash).

I wanted to add a check for colon as well, in case folks were creating paths like "c:\feux\barre.txt", but it looks like at least NuGet creates directories with colon (ex. ~/.local/share/NuGet/v3-cache/670c1461c29885f9aa22c281d8b7da90845b38e4$ps:_api.nuget.org_v3_index.json)

void walkTree(System.IO.DirectoryInfo dirInfo, Action<System.IO.FileSystemInfo> action)
{
    try
    {
        foreach (var file in dirInfo.GetFiles())
            action(file);
    }
    catch (System.IO.DirectoryNotFoundException)
    { }

    try
    {
        foreach (var subdir in dirInfo.GetDirectories())
        {
            action(subdir);
            walkTree(subdir, action);
        }
    }
    catch (System.UnauthorizedAccessException)
    { }
    catch (System.IO.DirectoryNotFoundException)
    { }
    catch (System.Security.SecurityException)
    { }
}

foreach (var drive in System.Environment.GetLogicalDrives())
{
    var driveInfo = new System.IO.DriveInfo(drive);

    if (!driveInfo.IsReady)
        continue;
    walkTree(driveInfo.RootDirectory,
        (FileSystemInfo fi) =>
        {
            if (fi.Name.Contains('\\'))
                throw new InvalidOperationException($"'{fi.FullName}' was created with an inappropriate character");
        });
}