PowerShell: Get active windows login sessions

active_sessions.ps1

# Adopted from: https://www.reddit.com/r/PowerShell/comments/306mcn/wtsenumeratesessions/
# Original Author: u/geostude

$_WTSMyStruct_Def = @'
	namespace mystruct {
		using System;
		using System.Runtime.InteropServices;
			[StructLayout(LayoutKind.Sequential)]
			public struct WTS_SESSION_INFO {
				public Int32 SessionID;

				[MarshalAs(UnmanagedType.LPStr)]
				public String pWinStationName;

				public WTS_CONNECTSTATE_CLASS State;
			}

			public enum WTS_CONNECTSTATE_CLASS { WTSActive, WTSConnected, WTSConnectQuery, WTSShadow, WTSDisconnected, WTSIdle, WTSListen, WTSReset, WTSDown, WTSInit } 
		}
'@

$_WTSEnumerateSessions_Def = @'
	[DllImport("wtsapi32.dll", SetLastError=true)]
	public static extern int WTSEnumerateSessions(System.IntPtr hServer, int Reserved, int Version, ref System.IntPtr ppSessionInfo, ref int pCount);
'@

$_WTSOpenServer_Def = @'
	[DllImport("wtsapi32.dll", SetLastError=true)]
	public static extern IntPtr WTSOpenServer(string pServerName);
'@

Add-Type $_WTSMyStruct_Def
$WTSEnumerateSessions = Add-Type -MemberDefinition $_WTSEnumerateSessions_Def -Name PSWTSEnumerateSessions -Namespace GetLoggedOnUsers -PassThru
$WTSOpenServer = Add-Type -MemberDefinition $_WTSOpenServer_Def -Name PSWTSOpenServer -Namespace GetLoggedOnUsers -PassThru

[long]$count = 0
[long]$ppSessionInfo = 0

# Defaults to current computer; Change $env:computername to target computer
$server = $WTSOpenServer::WTSOpenServer($env:computername)
[long]$sessionCount = $WTSEnumerateSessions::WTSEnumerateSessions($server,0,1,[ref]$ppSessionInfo,[ref]$count)
$dataSize = [system.runtime.interopservices.marshal]::SizeOf([System.Type][mystruct.WTS_SESSION_INFO])

if ($sessionCount -ne 0){
	for ($i = 0; $i -lt $count; $i++){
		$element = [system.runtime.interopservices.marshal]::PtrToStructure($ppSessionInfo + ($dataSize * $i),[System.type][mystruct.WTS_SESSION_INFO])
		$element
	}
}