Programmatically check Windows 10's case sensitive directory attribute

Question

Since April 2018, Windows 10 has had the ability to get or set if a directory was marked as case sensitive using fsutil.exe.

Is there a way to programmatically query the case sensitivity of a directory without running fsutil.exe or hackishly creating files with different casing to see if they collide?

I haven't really found any way to test this through research. I've read this is an actual NTFS attribute yet it doesn't show up when getting the file's attributes. I also noticed FindFirstFile will return the casing of the correct file if two different casings exist. Other than this I have no idea where to go as there really isn't a lot of information on this. This stuff is still pretty new.

As others have mentioned, making something case-sensitive is not a good idea in Windows due to comparability issues. I'm aware of that and my goal is to scan and work with existing case sensitive directories in the file system.

Progress:

I've discovered that Windows' FindFirstFile and friends functions respects the case sensitivity of the directory even without using the FIND_FIRST_EX_CASE_SENSITIVE. It will not return a file with invalid casing. Now I'm trying to figure out if there's a good way to make use of this.

Answer 1

Here is my P/Invoke solution thanks to the help of @eryksun's comment.

Edit 2: Added SetDirectoryCaseSensitive()

Edit 3: Added IsDirectoryCaseSensitivitySupported()

I've implemented the the native method NtQueryInformationFile while using the FILE_INFORMATION_CLASS FileCaseSensitiveInformation to read the FILE_CASE_SENSITIVE_INFORMATION structure.

public static partial class NativeMethods {
    public static readonly IntPtr INVALID_HANDLE = new IntPtr(-1);

    public const FileAttributes FILE_FLAG_BACKUP_SEMANTICS = (FileAttributes) 0x02000000;

    public enum NTSTATUS : uint {
        SUCCESS = 0x00000000,
        NOT_IMPLEMENTED = 0xC0000002,
        INVALID_INFO_CLASS = 0xC0000003,
        INVALID_PARAMETER = 0xC000000D,
        NOT_SUPPORTED = 0xC00000BB,
        DIRECTORY_NOT_EMPTY = 0xC0000101,
    }

    public enum FILE_INFORMATION_CLASS {
        None = 0,
        // Note: If you use the actual enum in here, remember to
        // start the first field at 1. There is nothing at zero.
        FileCaseSensitiveInformation = 71,
    }

    // It's called Flags in FileCaseSensitiveInformation so treat it as flags
    [Flags]
    public enum CASE_SENSITIVITY_FLAGS : uint {
        CaseInsensitiveDirectory = 0x00000000,
        CaseSensitiveDirectory = 0x00000001,
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct IO_STATUS_BLOCK {
        [MarshalAs(UnmanagedType.U4)]
        public NTSTATUS Status;
        public ulong Information;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct FILE_CASE_SENSITIVE_INFORMATION {
        [MarshalAs(UnmanagedType.U4)]
        public CASE_SENSITIVITY_FLAGS Flags;
    }

    // An override, specifically made for FileCaseSensitiveInformation, no IntPtr necessary.
    [DllImport("ntdll.dll")]
    [return: MarshalAs(UnmanagedType.U4)]
    public static extern NTSTATUS NtQueryInformationFile(
        IntPtr FileHandle,
        ref IO_STATUS_BLOCK IoStatusBlock,
        ref FILE_CASE_SENSITIVE_INFORMATION FileInformation,
        int Length,
        FILE_INFORMATION_CLASS FileInformationClass);

    [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    public static extern IntPtr CreateFile(
            [MarshalAs(UnmanagedType.LPTStr)] string filename,
            [MarshalAs(UnmanagedType.U4)] FileAccess access,
            [MarshalAs(UnmanagedType.U4)] FileShare share,
            IntPtr securityAttributes, // optional SECURITY_ATTRIBUTES struct or IntPtr.Zero
            [MarshalAs(UnmanagedType.U4)] FileMode creationDisposition,
            [MarshalAs(UnmanagedType.U4)] FileAttributes flagsAndAttributes,
            IntPtr templateFile);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool CloseHandle(
        IntPtr hObject);

    public static bool IsDirectoryCaseSensitive(string directory, bool throwOnError = true) {
        // Read access is NOT required
        IntPtr hFile = CreateFile(directory, 0, FileShare.ReadWrite,
                                    IntPtr.Zero, FileMode.Open,
                                    FILE_FLAG_BACKUP_SEMANTICS, IntPtr.Zero);
        if (hFile == INVALID_HANDLE)
            throw new Win32Exception();
        try {
            IO_STATUS_BLOCK iosb = new IO_STATUS_BLOCK();
            FILE_CASE_SENSITIVE_INFORMATION caseSensitive = new FILE_CASE_SENSITIVE_INFORMATION();
            NTSTATUS status = NtQueryInformationFile(hFile, ref iosb, ref caseSensitive,
                                                        Marshal.SizeOf<FILE_CASE_SENSITIVE_INFORMATION>(),
                                                        FILE_INFORMATION_CLASS.FileCaseSensitiveInformation);
            switch (status) {
            case NTSTATUS.SUCCESS:
                return caseSensitive.Flags.HasFlag(CASE_SENSITIVITY_FLAGS.CaseSensitiveDirectory);

            case NTSTATUS.NOT_IMPLEMENTED:
            case NTSTATUS.NOT_SUPPORTED:
            case NTSTATUS.INVALID_INFO_CLASS:
            case NTSTATUS.INVALID_PARAMETER:
                // Not supported, must be older version of windows.
                // Directory case sensitivity is impossible.
                return false;
            default:
                throw new Exception($"Unknown NTSTATUS: {(uint)status:X8}!");
            }
        }
        finally {
            CloseHandle(hFile);
        }
    }
}

Here is the implementation for setting the case sensitivity of a directory by implementing NTSetInformationFile. (Which has a parameter list that is identical to NTQueryInformationFile. Again, the problem was solved thanks to insight from @eryksun.

FILE_WRITE_ATTRIBUTES is a FileAccess flag that is not implemented in C#, so it needs to be defined and/or casted from the the value 0x100.

partial class NativeMethods {
    public const FileAccess FILE_WRITE_ATTRIBUTES = (FileAccess) 0x00000100;

    // An override, specifically made for FileCaseSensitiveInformation, no IntPtr necessary.
    [DllImport("ntdll.dll")]
    [return: MarshalAs(UnmanagedType.U4)]
    public static extern NTSTATUS NtSetInformationFile(
        IntPtr FileHandle,
        ref IO_STATUS_BLOCK IoStatusBlock,
        ref FILE_CASE_SENSITIVE_INFORMATION FileInformation,
        int Length,
        FILE_INFORMATION_CLASS FileInformationClass);

    // Require's elevated priviledges
    public static void SetDirectoryCaseSensitive(string directory, bool enable) {
        // FILE_WRITE_ATTRIBUTES access is the only requirement
        IntPtr hFile = CreateFile(directory, FILE_WRITE_ATTRIBUTES, FileShare.ReadWrite,
                                    IntPtr.Zero, FileMode.Open,
                                    FILE_FLAG_BACKUP_SEMANTICS, IntPtr.Zero);
        if (hFile == INVALID_HANDLE)
            throw new Win32Exception();
        try {
            IO_STATUS_BLOCK iosb = new IO_STATUS_BLOCK();
            FILE_CASE_SENSITIVE_INFORMATION caseSensitive = new FILE_CASE_SENSITIVE_INFORMATION();
            if (enable)
                caseSensitive.Flags |= CASE_SENSITIVITY_FLAGS.CaseSensitiveDirectory;
            NTSTATUS status = NtSetInformationFile(hFile, ref iosb, ref caseSensitive,
                                                    Marshal.SizeOf<FILE_CASE_SENSITIVE_INFORMATION>(),
                                                    FILE_INFORMATION_CLASS.FileCaseSensitiveInformation);
            switch (status) {
            case NTSTATUS.SUCCESS:
                return;
            case NTSTATUS.DIRECTORY_NOT_EMPTY:
                throw new IOException($"Directory \"{directory}\" contains matching " +
                                      $"case-insensitive files!");

            case NTSTATUS.NOT_IMPLEMENTED:
            case NTSTATUS.NOT_SUPPORTED:
            case NTSTATUS.INVALID_INFO_CLASS:
            case NTSTATUS.INVALID_PARAMETER:
                // Not supported, must be older version of windows.
                // Directory case sensitivity is impossible.
                throw new NotSupportedException("This version of Windows does not support directory case sensitivity!");
            default:
                throw new Exception($"Unknown NTSTATUS: {(uint)status:X8}!");
            }
        }
        finally {
            CloseHandle(hFile);
        }
    }
}

Finally I have added a method to calculate once if the version of Windows supports case sensitive directories. This just creates a folder with a constant GUID name in Temp and checks the NTSTATUS result (so it can check a folder it knows it has access to).

partial class NativeMethods {
    // Use the same directory so it does not need to be recreated when restarting the program
    private static readonly string TempDirectory =
        Path.Combine(Path.GetTempPath(), "88DEB13C-E516-46C3-97CA-46A8D0DDD8B2");

    private static bool? isSupported;
    public static bool IsDirectoryCaseSensitivitySupported() {
        if (isSupported.HasValue)
            return isSupported.Value;

        // Make sure the directory exists
        if (!Directory.Exists(TempDirectory))
            Directory.CreateDirectory(TempDirectory);

        IntPtr hFile = CreateFile(TempDirectory, 0, FileShare.ReadWrite,
                                IntPtr.Zero, FileMode.Open,
                                FILE_FLAG_BACKUP_SEMANTICS, IntPtr.Zero);
        if (hFile == INVALID_HANDLE)
            throw new Exception("Failed to open file while checking case sensitivity support!");
        try {
            IO_STATUS_BLOCK iosb = new IO_STATUS_BLOCK();
            FILE_CASE_SENSITIVE_INFORMATION caseSensitive = new FILE_CASE_SENSITIVE_INFORMATION();
            // Strangely enough, this doesn't fail on files
            NTSTATUS result = NtQueryInformationFile(hFile, ref iosb, ref caseSensitive,
                                                        Marshal.SizeOf<FILE_CASE_SENSITIVE_INFORMATION>(),
                                                        FILE_INFORMATION_CLASS.FileCaseSensitiveInformation);
            switch (result) {
            case NTSTATUS.SUCCESS:
                return (isSupported = true).Value;
            case NTSTATUS.NOT_IMPLEMENTED:
            case NTSTATUS.INVALID_INFO_CLASS:
            case NTSTATUS.INVALID_PARAMETER:
            case NTSTATUS.NOT_SUPPORTED:
                // Not supported, must be older version of windows.
                // Directory case sensitivity is impossible.
                return (isSupported = false).Value;
            default:
                throw new Exception($"Unknown NTSTATUS {(uint)result:X8} while checking case sensitivity support!");
            }
        }
        finally {
            CloseHandle(hFile);
            try {
                // CHOOSE: If you delete the folder, future calls to this will not be any faster
                // Directory.Delete(TempDirectory);
            }
            catch { }
        }
    }
}