Getting a handle for a directory in .NET

On Windows, you can get a handle on a directory. This can be useful to prevent other applications from accessing or deleting the folder while your application is accessing it. You can use the win32 method CreateFile to open a folder. This method is not available in .NET, but it is possible to use it using the Microsoft.Windows.CsWin32 package.

dotnet new console
dotnet add package Microsoft.Windows.CsWin32 --prerelease

Create a new file named NativeMethods.txt with the following content:

CreateFileW
GENERIC_ACCESS_RIGHTS

Add the following section to the .csproj file. This allows the Microsoft.Windows.CsWin32 to generate the code to access the methods declared in NativeMethods.txt.

<Project Sdk="Microsoft.NET.Sdk">

  <ItemGroup>
    <AdditionalFiles Include="NativeMethods.txt" />
  </ItemGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Windows.CsWin32" Version="0.3.18-beta">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
  </ItemGroup>
</Project>

Finally you can use the following code to get a handle for a directory:

var path = @"C:\folder";
using var handle = Windows.Win32.PInvoke.CreateFile(
    path,
    (uint)Windows.Win32.Foundation.GENERIC_ACCESS_RIGHTS.GENERIC_READ,
    Windows.Win32.Storage.FileSystem.FILE_SHARE_MODE.FILE_SHARE_NONE, // Choose the share mode you want
    null,
    Windows.Win32.Storage.FileSystem.FILE_CREATION_DISPOSITION.OPEN_EXISTING,

    // FILE_FLAG_BACKUP_SEMANTICS is required to open a directory, see
    // https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew?WT.mc_id=DT-MVP-5003978#directories
    Windows.Win32.Storage.FileSystem.FILE_FLAGS_AND_ATTRIBUTES.FILE_FLAG_BACKUP_SEMANTICS,
    null);

if (handle.IsInvalid)
    throw new Exception("Cannot open folder");

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