Retrieve Terminal Server session information.

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication19
{
    class Program
    {
        static void Main(string[] args)
        {
            var WTS_CURRENT_SERVER_HANDLE = IntPtr.Zero;
            IntPtr ppSessionInfo;
            uint pCount;
            if (!WTSEnumerateSessions(
                WTS_CURRENT_SERVER_HANDLE,
                0,
                1,
                out ppSessionInfo,
                out pCount))
            {
                return;
            }

            Console.WriteLine("===Enumerate Sessions===");
            var iDataSize = Marshal.SizeOf(typeof(WTS_SESSION_INFO));
            var current = new IntPtr(ppSessionInfo.ToInt32());
            for (var i = 0; i < pCount; i++)
            {
                var sessionInfo = (WTS_SESSION_INFO)Marshal.PtrToStructure(current, typeof(WTS_SESSION_INFO));
                //shift pointer value by the size of struct because of array
                current = current + iDataSize;

                Console.WriteLine("Session ID : " + sessionInfo.SessionID);
                Console.WriteLine("Session State : " + sessionInfo.State);
                Console.WriteLine("Workstation Name : " + sessionInfo.WinStationName);
                var sessionId = sessionInfo.SessionID;
                DumpSessionInfo(sessionId);
            }
            WTSFreeMemory(ppSessionInfo);

            Console.WriteLine("===Dump Current Session===");
            DumpSessionInfo();
            Console.ReadLine();
        }

        static void DumpSessionInfo(uint sessionId = uint.MaxValue)
        {
            var WTS_CURRENT_SERVER_HANDLE = IntPtr.Zero;
            IntPtr ppBuffer;
            uint iReturned;

            if (WTSQuerySessionInformation(WTS_CURRENT_SERVER_HANDLE,
                sessionId, 
                WTS_INFO_CLASS.WTSClientAddress,
                out ppBuffer,
                out iReturned))
            {
                var clientAddres = (WTS_CLIENT_ADDRESS)Marshal.PtrToStructure(ppBuffer, typeof(WTS_CLIENT_ADDRESS));
                if (clientAddres.AddressFamily == AddressFamilyType.AF_INET)
                {
                    Console.WriteLine("IPv4Address:" + string.Join(".", clientAddres.Address.Skip(2).Take(4)));
                }
            }

            if (WTSQuerySessionInformation(WTS_CURRENT_SERVER_HANDLE,
                sessionId,
                WTS_INFO_CLASS.WTSClientName,
                out ppBuffer,
                out iReturned))
            {
                Console.WriteLine("ClientName: " + Marshal.PtrToStringAnsi(ppBuffer));
            }
            WTSFreeMemory(ppBuffer);
        }

        [DllImport("wtsapi32.dll")]
        public static extern bool WTSEnumerateSessions(
            IntPtr hServer,
            uint reserved,
            uint version,
            out IntPtr ppSessionInfo,
            out uint pCount);

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

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

        [StructLayout(LayoutKind.Sequential)]
        private struct WTS_CLIENT_ADDRESS
        {
            public AddressFamilyType AddressFamily;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 20)]
            public byte[] Address;
        }

        public enum AddressFamilyType
        {
            AF_INET,
            AF_INET6, 
            AF_IPX, 
            AF_NETBIOS, 
            AF_UNSPEC
        }

        [StructLayout(LayoutKind.Sequential)]
        private struct WTS_SESSION_INFO
        {
            public uint SessionID;
            [MarshalAs(UnmanagedType.LPStr)]
            public string WinStationName;
            public WTS_CONNECTSTATE_CLASS State;
        }

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

        public enum WTS_INFO_CLASS
        {
            WTSInitialProgram,
            WTSApplicationName,
            WTSWorkingDirectory,
            WTSOEMId,
            WTSSessionId,
            WTSUserName,
            WTSWinStationName,
            WTSDomainName,
            WTSConnectState,
            WTSClientBuildNumber,
            WTSClientName,
            WTSClientDirectory,
            WTSClientProductId,
            WTSClientHardwareId,
            WTSClientAddress,
            WTSClientDisplay,
            WTSClientProtocolType,
            WTSIdleTime,
            WTSLogonTime,
            WTSIncomingBytes,
            WTSOutgoingBytes,
            WTSIncomingFrames,
            WTSOutgoingFrames,
            WTSClientInfo,
            WTSSessionInfo,
            WTSConfigInfo,
            WTSValidationInfo,
            WTSSessionAddressV4,
            WTSIsRemoteSession
        }
    }
}