Help for use WinStationShadow Win32 function

[szolnokit]

I would like to use the WinStationShadow function in my small project. I would like to write a console RDP shadow switch utility. I found the Process Hacker use this function. See: https://github.com/processhacker/processhacker/blob/master/ProcessHacker/sessshad.c (at line 215)

My POC code:

using System;
using System.Runtime.InteropServices;

namespace ShadowSwitch
{
    class Program
    {
        public const short KBDSHIFT = 0x1;
        public const short KBDCTRL = 0x2;
        public const short KBDALT = 0x4;

        [DllImport(@"winsta.dll")]
        internal static extern Boolean WinStationShadow(IntPtr hServer, String TargetServerName, ulong TargetSessionId, byte HotKeyVk, ushort HotkeyModifiers);

        static void Main(string[] args)
        {
            Console.WriteLine(WinStationShadow(IntPtr.Zero, Environment.MachineName, uint.Parse(args[0]), (byte)'*', KBDCTRL | KBDALT));
            Console.WriteLine(Marshal.GetLastWin32Error());
        }
    }
}

But I get True as WinStationShadow result, and Win32 last error: 120 (This function is not supported on this system.)

I tested on same machine and with same (source/target) session and with same user account as like tested with Process Hacker. My shadow switching drop the error above, until Process Explorer shadow switch working as expected.

What I wrong? Thank you for suggestion...

[dmex]

True as WinStationShadow result

C# boolean is 4 bytes, C boolean is 1 byte. Your dllimport is missing MarshalAs(UnmanagedType.I1) so that result is incorrect.

Win32 last error: 120

Your dllimport is missing SetLastError = true. C# interop won't return the error code for the dllimport without it.

(byte)'*'

Don't cast C# chars (UTF16) to C chars (ANSI).

What I wrong?

Fix the type mashaling:

[DllImport("winsta.dll", CharSet = CharSet.Unicode, SetLastError = true)]
[return: MarshalAs(UnmanagedType.I1)]
public static extern Boolean WinStationShadow(IntPtr hServer, string serverName, uint targetSessionId, uint hotkeyVk, uint hotkeyModifier);

Use the correct types:

const uint KBDCTRL = 0x2;
const uint KBDALT = 0x4;
const uint VK_MULTIPLY = 0x6A;

Console.WriteLine(WinStationShadow(IntPtr.Zero, Environment.MachineName, 1, VK_MULTIPLY, KBDCTRL | KBDALT));
Console.WriteLine(Marshal.GetLastWin32Error());

[szolnokit]

Thank you for fast answer :) This was good at first try 👍