Compress a folder using NTFS compression in .NET

Question

I want to compress a folder using NTFS compression in .NET. I found this post, but it does not work. It throws an exception ("Invalid Parameter").

DirectoryInfo directoryInfo = new DirectoryInfo( destinationDir );
if( ( directoryInfo.Attributes & FileAttributes.Compressed ) != FileAttributes.Compressed )
{
   string objPath = "Win32_Directory.Name=" + "\"" + destinationDir + "\"";
   using( ManagementObject dir = new ManagementObject( objPath ) )
   {
      ManagementBaseObject outParams = dir.InvokeMethod( "Compress", null, null );
      uint ret = (uint)( outParams.Properties["ReturnValue"].Value );
   }
}

Anybody knows how to enable NTFS compression on a folder?

Answer 1

I don't believe there is a way to set folder compression in the .NET framework as the docs (remarks section) claim it cannot be done through File.SetAttributes. This seems to be only available in the Win32 API using the DeviceIoControl function. One can still do this through .NET by using PInvoke.

Once familiar with PInvoke in general, check out the reference at pinvoke.net that discusses what the signature needs to look like in order to make this happen.

Answer 2

I have tested the code and it !

• Make sure it works for you with the gui. Maybe the allocation unit size is too big for compression. Or you don't have sufficient permissions.
• For your destination use format like so: "c:/temp/testcomp" with forward slashes.

Full code:

using System.IO;
using System.Management;

class Program
{
    static void Main(string[] args)
    {
        string destinationDir = "c:/temp/testcomp";
        DirectoryInfo directoryInfo = new DirectoryInfo(destinationDir);
        if ((directoryInfo.Attributes & FileAttributes.Compressed) != FileAttributes.Compressed)
        {
            string objPath = "Win32_Directory.Name=" + "\"" + destinationDir + "\"";
            using (ManagementObject dir = new ManagementObject(objPath))
            {
                ManagementBaseObject outParams = dir.InvokeMethod("Compress", null, null);
                uint ret = (uint)(outParams.Properties["ReturnValue"].Value);
            }
        }

    }

}

Answer 3

Using P/Invoke is, in my experience, usually easier than WMI. I believe the following should work:

private const int FSCTL_SET_COMPRESSION = 0x9C040;
private const short COMPRESSION_FORMAT_DEFAULT = 1;

[DllImport("kernel32.dll", SetLastError = true)]
private static extern int DeviceIoControl(
    SafeFileHandle hDevice,
    int dwIoControlCode,
    ref short lpInBuffer,
    int nInBufferSize,
    IntPtr lpOutBuffer,
    int nOutBufferSize,
    ref int lpBytesReturned,
    IntPtr lpOverlapped);

public static void EnableCompression(SafeFileHandle handle)
{
    int lpBytesReturned = 0;
    short lpInBuffer = COMPRESSION_FORMAT_DEFAULT;

    int result = DeviceIoControl(handle, FSCTL_SET_COMPRESSION,
        ref lpInBuffer, sizeof(short), IntPtr.Zero, 0,
        ref lpBytesReturned, IntPtr.Zero);

    if (result != 0)
    {
        Marshal.ThrowExceptionForHR(Marshal.GetLastWin32Error());
    }
}

Since you're trying to set this on a directory, you will probably need to use P/Invoke to call CreateFile using FILE_FLAG_BACKUP_SEMANTICS to get the SafeFileHandle on the directory.

Also, note that setting compression on a directory in NTFS does not compress all the contents, it only makes new files show up as compressed (the same is true for encryption). If you want to compress the entire directory, you'll need to walk the entire directory and call DeviceIoControl on each file/folder.