Tries to replicate qwinsta but return structured objects

Get-WTSSessionInfo.ps1

# Copyright: (c) 2022, Jordan Borean (@jborean93) <[email protected]>
# MIT License (see LICENSE or https://opensource.org/licenses/MIT)

Function Get-WTSSessionInfo {
    <#
    .SYNOPSIS
    Enumerates sessions on a Windows host.

    .DESCRIPTION
    Enumerates all the sessions available on a Windows host through the WTSEnumerateSessionsExW API.

    .PARAMETER ComputerName
    A list of hosts to query the sessions for. Omit or set to an empty array to check the local host.

    .EXAMPLE
    Get-WTSSessionInfo
    
    .NOTES
    The output object is modeled after https://docs.microsoft.com/en-us/windows/win32/api/wtsapi32/ns-wtsapi32-wts_session_info_1w.
    #>
    [CmdletBinding()]
    param (
        [Parameter(ValueFromPipeline, ValueFromPipelineByPropertyName)]
        [AllowNull()]
        [AllowEmptyCollection()]
        [string[]]
        $ComputerName
    )

    begin {
        Add-Type -Namespace Wtsapi32 -Name Native -MemberDefinition @'
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
private struct WTS_SESSION_INFO_1W
{
    public int ExecEnvId;
    public WtsConnectState State;
    public int SessionId;
    public string pSessionName;
    public string pHostName;
    public string pUserName;
    public string pDomainName;
    public string pFarmName;
}

public enum WtsConnectState
{
    Active,
    Connected,
    ConnectQuery,
    Shadow,
    Disconnected,
    Idle,
    Listen,
    Reset,
    Down,
    Init
}

public class SessionInfo
{
    public int SessionId { get; set; }
    public WtsConnectState State { get; set; }
    public string SessionName { get; set; }
    public string HostName { get; set; }
    public string UserName { get; set; }
    public string DomainName { get; set; }
    public string FarmName { get; set; }
}

[DllImport("Wtsapi32.dll")]
public static extern void WTSCloseServer(
    IntPtr hServer);

[DllImport("Wtsapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
private static extern bool WTSEnumerateSessionsExW(
    IntPtr hServer,
    ref int pLevel,
    int Filter,
    out IntPtr ppSessionInfo,
    out int pCount);

public static SessionInfo[] WTSEnumerateSessionsEx(IntPtr serverHandle)
{
    int level = 1;
    IntPtr rawInfo;
    int count;
    if (!WTSEnumerateSessionsExW(serverHandle, ref level, 0, out rawInfo, out count))
        throw new System.ComponentModel.Win32Exception();

    try
    {
        var infoCollection = new System.Collections.Generic.List<SessionInfo>();
        IntPtr currentOffset = rawInfo;
        for (int i = 0; i < count; i++)
        {
            WTS_SESSION_INFO_1W info = Marshal.PtrToStructure<WTS_SESSION_INFO_1W>(currentOffset);
            infoCollection.Add(new SessionInfo()
            {
                SessionId = info.SessionId,
                State = info.State,
                SessionName = info.pSessionName,
                HostName = info.pHostName,
                UserName = info.pUserName,
                DomainName = info.pDomainName,
                FarmName = info.pFarmName,
            });
            currentOffset = IntPtr.Add(currentOffset, Marshal.SizeOf(typeof(WTS_SESSION_INFO_1W)));
        }

        return infoCollection.ToArray();
    }
    finally
    {
        WTSFreeMemoryExW(2, rawInfo, count);
    }
}

[DllImport("Wtsapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
private static extern bool WTSFreeMemoryExW(
    int WTSTypeClass,
    IntPtr pMemory,
    int NumberOfEntries);

[DllImport("Wtsapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
private static extern IntPtr WTSOpenServerExW(
    string pServerName);

public static IntPtr WTSOpenServerEx(string serverName)
{
    IntPtr handle = WTSOpenServerExW(serverName);
    if (handle == IntPtr.Zero)
        throw new System.ComponentModel.Win32Exception();

    return handle;
}
'@

        $queried = $false
    }

    process {
        foreach ($name in $ComputerName) {
            $queried = $true
            $serverHandle = [Wtsapi32.Native]::WTSOpenServerEx($name)
            try {
                [Wtsapi32.Native]::WTSEnumerateSessionsEx($serverHandle)
            }
            finally {
                [Wtsapi32.Native]::WTSCloseServer($serverHandle)
            }
        }
    }

    end {
        if (-not $queried) {
            [Wtsapi32.Native]::WTSEnumerateSessionsEx([IntPtr]::Zero)
        }
    }
}