How do you retrieve a list of logged-in/connected users in .NET?

Question

Here's the scenario:

You have a Windows server that users remotely connect to via RDP. You want your program (which runs as a service) to know who is currently connected. This may or may not include an interactive console session.

Please note that this is the not the same as just retrieving the current interactive user.

I'm guessing that there is some sort of API access to Terminal Services to get this info?

Answer 1

Here's my take on the issue:

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;

namespace EnumerateRDUsers
{
  class Program
  {
    [DllImport("wtsapi32.dll")]
    static extern IntPtr WTSOpenServer([MarshalAs(UnmanagedType.LPStr)] string pServerName);

    [DllImport("wtsapi32.dll")]
    static extern void WTSCloseServer(IntPtr hServer);

    [DllImport("wtsapi32.dll")]
    static extern Int32 WTSEnumerateSessions(
        IntPtr hServer,
        [MarshalAs(UnmanagedType.U4)] Int32 Reserved,
        [MarshalAs(UnmanagedType.U4)] Int32 Version,
        ref IntPtr ppSessionInfo,
        [MarshalAs(UnmanagedType.U4)] ref Int32 pCount);

    [DllImport("wtsapi32.dll")]
    static extern void WTSFreeMemory(IntPtr pMemory);

    [DllImport("wtsapi32.dll")]
    static extern bool WTSQuerySessionInformation(
        IntPtr hServer, int sessionId, WTS_INFO_CLASS wtsInfoClass, out IntPtr ppBuffer, out uint pBytesReturned);

    [StructLayout(LayoutKind.Sequential)]
    private struct WTS_SESSION_INFO
    {
      public Int32 SessionID;

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

      public WTS_CONNECTSTATE_CLASS State;
    }

    public enum WTS_INFO_CLASS
    {
      WTSInitialProgram,
      WTSApplicationName,
      WTSWorkingDirectory,
      WTSOEMId,
      WTSSessionId,
      WTSUserName,
      WTSWinStationName,
      WTSDomainName,
      WTSConnectState,
      WTSClientBuildNumber,
      WTSClientName,
      WTSClientDirectory,
      WTSClientProductId,
      WTSClientHardwareId,
      WTSClientAddress,
      WTSClientDisplay,
      WTSClientProtocolType
    }

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

    static void Main(string[] args)
    {
      ListUsers(Environment.MachineName);
    }

    public static void ListUsers(string serverName)
    {
      IntPtr serverHandle = IntPtr.Zero;
      List<string> resultList = new List<string>();
      serverHandle = WTSOpenServer(serverName);

      try
      {
        IntPtr sessionInfoPtr = IntPtr.Zero;
        IntPtr userPtr = IntPtr.Zero;
        IntPtr domainPtr = IntPtr.Zero;
        Int32 sessionCount = 0;
        Int32 retVal = WTSEnumerateSessions(serverHandle, 0, 1, ref sessionInfoPtr, ref sessionCount);
        Int32 dataSize = Marshal.SizeOf(typeof(WTS_SESSION_INFO));
        IntPtr currentSession = sessionInfoPtr;
        uint bytes = 0;

        if (retVal != 0)
        {
          for (int i = 0; i < sessionCount; i++)
          {
            WTS_SESSION_INFO si = (WTS_SESSION_INFO)Marshal.PtrToStructure((System.IntPtr)currentSession, typeof(WTS_SESSION_INFO));
            currentSession += dataSize;

            WTSQuerySessionInformation(serverHandle, si.SessionID, WTS_INFO_CLASS.WTSUserName, out userPtr, out bytes);
            WTSQuerySessionInformation(serverHandle, si.SessionID, WTS_INFO_CLASS.WTSDomainName, out domainPtr, out bytes);

            Console.WriteLine("Domain and User: " + Marshal.PtrToStringAnsi(domainPtr) + "\\" + Marshal.PtrToStringAnsi(userPtr));

            WTSFreeMemory(userPtr); 
            WTSFreeMemory(domainPtr);
          }

          WTSFreeMemory(sessionInfoPtr);
        }
      }
      finally
      {
        WTSCloseServer(serverHandle);
      }

    }

  }
}