RemoteSessionNamedPipe.cs

/********************************************************************++
Copyright (c) Microsoft Corporation.  All rights reserved.
--********************************************************************/

using System.Management.Automation.Tracing;
using System.Management.Automation.Internal;
using System.Management.Automation.Remoting.Server;
using System.Globalization;
using System.IO;
using System.IO.Pipes;
using System.Threading;
using System.Security.AccessControl;
using System.Security.Principal;
using System.Runtime.InteropServices;
using Microsoft.Win32.SafeHandles;
using System.Diagnostics.CodeAnalysis;
using Dbg = System.Diagnostics.Debug;

namespace System.Management.Automation.Remoting
{
    /// <summary>
    /// Shared named pipe utilities.
    /// </summary>
    internal static class NamedPipeUtils
    {
        #region Strings

        internal const string DefaultAppDomainName = "DefaultAppDomain";
        internal const string NamedPipeNamePrefix = "PSHost.";
        internal const string NamedPipeNamePrefixSearch = "PSHost*";

        #endregion

        #region Static Methods

        /// <summary>
        /// Create a pipe name based on process information.
        /// E.g., "PSHost.ProcessStartTime.ProcessId.DefaultAppDomain.ProcessName"
        /// </summary>
        /// <param name="procId">Process Id</param>
        /// <returns>Pipe name</returns>
        internal static string CreateProcessPipeName(
            int procId)
        {
            return CreateProcessPipeName(
                System.Diagnostics.Process.GetProcessById(procId));
        }

        /// <summary>
        /// Create a pipe name based on process information.
        /// E.g., "PSHost.ProcessStartTime.ProcessId.DefaultAppDomain.ProcessName"
        /// </summary>
        /// <param name="proc">Process object</param>
        /// <returns>Pipe name</returns>
        internal static string CreateProcessPipeName(
            System.Diagnostics.Process proc)
        {
            return CreateProcessPipeName(proc, DefaultAppDomainName);
        }

        /// <summary>
        /// Create a pipe name based on process Id and appdomain name information.
        /// E.g., "PSHost.ProcessStartTime.ProcessId.DefaultAppDomain.ProcessName"
        /// </summary>
        /// <param name="procId">Process Id</param>
        /// <param name="appDomainName">Name of process app domain to connect to.</param>
        /// <returns>Pipe name</returns>
        internal static string CreateProcessPipeName(
            int procId,
            string appDomainName)
        {
            return CreateProcessPipeName(System.Diagnostics.Process.GetProcessById(procId), appDomainName);
        }

        /// <summary>
        /// Create a pipe name based on process and appdomain name information.
        /// E.g., "PSHost.ProcessStartTime.ProcessId.DefaultAppDomain.ProcessName"
        /// </summary>
        /// <param name="proc">Process object</param>
        /// <param name="appDomainName">Name of process app domain to connect to.</param>
        /// <returns>Pipe name</returns>
        internal static string CreateProcessPipeName(
            System.Diagnostics.Process proc,
            string appDomainName)
        {
            if (proc == null)
            {
                throw new PSArgumentNullException("proc");
            }

            if (string.IsNullOrEmpty(appDomainName))
            {
                appDomainName = DefaultAppDomainName;
            }

            return NamedPipeNamePrefix +
                    proc.StartTime.ToFileTime().ToString(CultureInfo.InvariantCulture) + "." +
                    proc.Id.ToString(CultureInfo.InvariantCulture) + "." +
                    CleanAppDomainNameForPipeName(appDomainName) + "." +
                    proc.ProcessName;
        }

        private static string CleanAppDomainNameForPipeName(string appDomainName)
        {
            // Pipe names cannot contain the ':' character.  Remove unwanted characters.
            return appDomainName.Replace(":", "").Replace(" ", "");
        }

        /// <summary>
        /// Returns the current process AppDomain name.
        /// </summary>
        /// <returns>AppDomain Name string</returns>
        internal static string GetCurrentAppDomainName()
        {
#if CORECLR // There is only one AppDomain per application in CoreCLR, which would be the default
            return DefaultAppDomainName;
#else       // Use the AppDomain in which current powershell is running
            return AppDomain.CurrentDomain.IsDefaultAppDomain() ? DefaultAppDomainName : AppDomain.CurrentDomain.FriendlyName;
#endif
        }

        #endregion
    }

    /// <summary>
    /// Native API for Named Pipes
    /// </summary>
    internal static class NamedPipeNative
    {
        #region Pipe constants

        // Pipe open modes
        internal const uint PIPE_ACCESS_DUPLEX = 0x00000003;
        internal const uint PIPE_ACCESS_OUTBOUND = 0x00000002;
        internal const uint PIPE_ACCESS_INBOUND = 0x00000001;

        // Pipe modes
        internal const uint PIPE_TYPE_BYTE = 0x00000000;
        internal const uint PIPE_TYPE_MESSAGE = 0x00000004;
        internal const uint FILE_FLAG_OVERLAPPED = 0x40000000;
        internal const uint FILE_FLAG_FIRST_PIPE_INSTANCE = 0x00080000;
        internal const uint PIPE_WAIT = 0x00000000;
        internal const uint PIPE_NOWAIT = 0x00000001;
        internal const uint PIPE_READMODE_BYTE = 0x00000000;
        internal const uint PIPE_READMODE_MESSAGE = 0x00000002;
        internal const uint PIPE_ACCEPT_REMOTE_CLIENTS = 0x00000000;
        internal const uint PIPE_REJECT_REMOTE_CLIENTS = 0x00000008;

        // Pipe errors
        internal const uint ERROR_FILE_NOT_FOUND = 2;
        internal const uint ERROR_BROKEN_PIPE = 109;
        internal const uint ERROR_PIPE_BUSY = 231;
        internal const uint ERROR_NO_DATA = 232;
        internal const uint ERROR_MORE_DATA = 234;
        internal const uint ERROR_PIPE_CONNECTED = 535;
        internal const uint ERROR_IO_INCOMPLETE = 996;
        internal const uint ERROR_IO_PENDING = 997;

        // File function constants
        internal const uint GENERIC_READ = 0x80000000;
        internal const uint GENERIC_WRITE = 0x40000000;
        internal const uint GENERIC_EXECUTE = 0x20000000;
        internal const uint GENERIC_ALL = 0x10000000;

        internal const uint CREATE_NEW = 1;
        internal const uint CREATE_ALWAYS = 2;
        internal const uint OPEN_EXISTING = 3;
        internal const uint OPEN_ALWAYS = 4;
        internal const uint TRUNCATE_EXISTING = 5;

        internal const uint SECURITY_IMPERSONATIONLEVEL_ANONYMOUS = 0;
        internal const uint SECURITY_IMPERSONATIONLEVEL_IDENTIFCATION = 1;
        internal const uint SECURITY_IMPERSONATIONLEVEL_IMPERSONATION = 2;
        internal const uint SECURITY_IMPERSONATIONLEVEL_DELEGATION = 3;

        // Infinite timeout
        internal const uint INFINITE = 0xFFFFFFFF;

        #endregion

        #region Data structures

        [StructLayout(LayoutKind.Sequential)]
        internal class SECURITY_ATTRIBUTES
        {
            /// <summary>
            /// The size, in bytes, of this structure. Set this value to the size of the SECURITY_ATTRIBUTES structure.
            /// </summary>
            public int NLength;

            /// <summary>
            /// A pointer to a security descriptor for the object that controls the sharing of it.
            /// </summary>
            public IntPtr LPSecurityDescriptor = IntPtr.Zero;

            /// <summary>
            /// A Boolean value that specifies whether the returned handle is inherited when a new process is created.
            /// </summary>
            public bool InheritHandle;

            /// <summary>
            /// Initializes a new instance of the SECURITY_ATTRIBUTES class
            /// </summary>
            public SECURITY_ATTRIBUTES()
            {
                this.NLength = 12;
            }
        }

        #endregion

        #region Pipe methods

        [DllImport(PinvokeDllNames.CreateNamedPipeDllName, SetLastError = true, CharSet = CharSet.Unicode)]
        internal static extern SafePipeHandle CreateNamedPipe(
           string lpName,
           uint dwOpenMode,
           uint dwPipeMode,
           uint nMaxInstances,
           uint nOutBufferSize,
           uint nInBufferSize,
           uint nDefaultTimeOut,
           SECURITY_ATTRIBUTES securityAttributes);

        internal static SECURITY_ATTRIBUTES GetSecurityAttributes(GCHandle securityDescriptorPinnedHandle, bool inheritHandle = false)
        {
            SECURITY_ATTRIBUTES securityAttributes = new NamedPipeNative.SECURITY_ATTRIBUTES();
            securityAttributes.InheritHandle = inheritHandle;
            securityAttributes.NLength = (int)Marshal.SizeOf(securityAttributes);
            securityAttributes.LPSecurityDescriptor = securityDescriptorPinnedHandle.AddrOfPinnedObject();
            return securityAttributes;
        }

        [DllImport(PinvokeDllNames.CreateFileDllName, SetLastError = true, CharSet = CharSet.Unicode, CallingConvention = CallingConvention.StdCall)]
        internal static extern SafePipeHandle CreateFile(
              string lpFileName,
              uint dwDesiredAccess,
              uint dwShareMode,
              IntPtr SecurityAttributes,
              uint dwCreationDisposition,
              uint dwFlagsAndAttributes,
              IntPtr hTemplateFile);

        [DllImport(PinvokeDllNames.WaitNamedPipeDllName, SetLastError = true, CharSet = CharSet.Unicode)]
        [return: MarshalAs(UnmanagedType.Bool)]
        internal static extern bool WaitNamedPipe(string lpNamedPipeName, uint nTimeOut);

        [DllImport(PinvokeDllNames.ImpersonateNamedPipeClientDllName, SetLastError = true, CharSet = CharSet.Unicode)]
        [return: MarshalAs(UnmanagedType.Bool)]
        internal static extern bool ImpersonateNamedPipeClient(IntPtr hNamedPipe);

        [DllImport(PinvokeDllNames.RevertToSelfDllName, SetLastError = true, CharSet = CharSet.Unicode)]
        [return: MarshalAs(UnmanagedType.Bool)]
        internal static extern bool RevertToSelf();

        #endregion
    }

    /// <summary>
    /// Event arguments for listener thread end event.
    /// </summary>
    internal sealed class ListenerEndedEventArgs : EventArgs
    {
        #region Properties

        /// <summary>
        /// Exception reson for listener end event.  Can be null
        /// which indicates listener thread end is not due to an error.
        /// </summary>
        public Exception Reason
        {
            private set;
            get;
        }

        /// <summary>
        /// True if listener should be restarted after ending.
        /// </summary>
        public bool RestartListener
        {
            private set;
            get;
        }

        #endregion

        #region Constructors

        private ListenerEndedEventArgs() { }

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="reason">Listener end reason</param>
        /// <param name="restartListener">Restart listener</param>
        public ListenerEndedEventArgs(
            Exception reason,
            bool restartListener)
        {
            Reason = reason;
            RestartListener = restartListener;
        }

        #endregion
    }

    /// <summary>
    /// Light wrapper class for BCL NamedPipeServerStream class, that
    /// creates the named pipe server with process named pipe name, 
    /// having correct access restrictions, and provides a listener
    /// thread loop.
    /// </summary>
    internal sealed class RemoteSessionNamedPipeServer : IDisposable
    {
        #region Members

        private readonly object _syncObject;
        private PowerShellTraceSource _tracer = PowerShellTraceSourceFactory.GetTraceSource();

        private const string _threadName = "IPC Listener Thread";
        private const int _namedPipeBufferSizeForRemoting = 32768;

        // Singleton server.
        private static object s_syncObject;
        internal static RemoteSessionNamedPipeServer IPCNamedPipeServer;
        internal static bool IPCNamedPipeServerEnabled;

        // Access mask constant taken from PipeSecurity access rights and is equivalent to
        // PipeAccessRights.FullControl.
        // See: https://msdn.microsoft.com/en-us/library/vstudio/bb348408(v=vs.100).aspx
        //
        private const int _pipeAccessMaskFullControl = 0x1f019f;

        #endregion

        #region Properties

        /// <summary>
        /// Returns the Named Pipe stream object.
        /// </summary>
        public NamedPipeServerStream Stream { get; }

        /// <summary>
        /// Returns the Named Pipe name.
        /// </summary>
        public string PipeName { get; }

        /// <summary>
        /// Returns true if listener is currently running.
        /// </summary>
        public bool IsListenerRunning { get; private set; }

        /// <summary>
        /// Name of session configuration.
        /// </summary>
        public string ConfigurationName { get; set; }

        /// <summary>
        /// Accessor for the named pipe reader.
        /// </summary>
        public StreamReader TextReader { get; private set; }

        /// <summary>
        /// Accessor for the named pipe writer.
        /// </summary>
        public StreamWriter TextWriter { get; private set; }

        /// <summary>
        /// Returns true if object is currently disposed.
        /// </summary>
        public bool IsDisposed { get; private set; }

        /// <summary>
        /// Buffer size for PSRP fragmentor.
        /// </summary>
        internal static int NamedPipeBufferSizeForRemoting
        {
            get { return _namedPipeBufferSizeForRemoting; }
        }

        #endregion

        #region Events

        /// <summary>
        /// Event raised when the named pipe server listening thread
        /// ends.
        /// </summary>
        public event EventHandler<ListenerEndedEventArgs> ListenerEnded;

        #endregion

        #region Constructors

        /// <summary>
        /// Creates a RemoteSessionNamedPipeServer with the current process and AppDomain information.
        /// </summary>
        /// <returns>RemoteSessionNamedPipeServer</returns>
        public static RemoteSessionNamedPipeServer CreateRemoteSessionNamedPipeServer()
        {
            string appDomainName = NamedPipeUtils.GetCurrentAppDomainName();

            return new RemoteSessionNamedPipeServer(NamedPipeUtils.CreateProcessPipeName(
                System.Diagnostics.Process.GetCurrentProcess(), appDomainName));
        }

        /// <summary>
        /// Constructor.  Creates named pipe server with provided pipe name.
        /// </summary>
        /// <param name="pipeName">Named Pipe name</param>
        internal RemoteSessionNamedPipeServer(
            string pipeName)
        {
            if (pipeName == null)
            {
                throw new PSArgumentNullException("pipeName");
            }

            _syncObject = new object();
            PipeName = pipeName;

            Stream = CreateNamedPipe(
                serverName: ".",
                namespaceName: "pipe",
                coreName: pipeName,
                securityDesc: GetServerPipeSecurity());
        }

        /// <summary>
        /// Helper method to create a PowerShell transport named pipe via native API, along
        /// with a returned .Net NamedPipeServerStream object wrapping the named pipe.
        /// </summary>
        /// <param name="serverName">Named pipe server name.</param>
        /// <param name="namespaceName">Named pipe namespace name.</param>
        /// <param name="coreName">Named pipe core name.</param>
        /// <param name="securityDesc"></param>
        /// <returns>NamedPipeServerStream</returns>
        private NamedPipeServerStream CreateNamedPipe(
            string serverName,
            string namespaceName,
            string coreName,
            CommonSecurityDescriptor securityDesc)
        {
            if (serverName == null) { throw new PSArgumentNullException("serverName"); }
            if (namespaceName == null) { throw new PSArgumentNullException("namespaceName"); }
            if (coreName == null) { throw new PSArgumentNullException("coreName"); }

            string fullPipeName = @"\\" + serverName + @"\" + namespaceName + @"\" + coreName;

            // Create optional security attributes based on provided PipeSecurity.
            NamedPipeNative.SECURITY_ATTRIBUTES securityAttributes = null;
            GCHandle? securityDescHandle = null;
            if (securityDesc != null)
            {
                byte[] securityDescBuffer = new byte[securityDesc.BinaryLength];
                securityDesc.GetBinaryForm(securityDescBuffer, 0);
                securityDescHandle = GCHandle.Alloc(securityDescBuffer, GCHandleType.Pinned);
                securityAttributes = NamedPipeNative.GetSecurityAttributes(securityDescHandle.Value);
            }

            // Create named pipe.
            SafePipeHandle pipeHandle = NamedPipeNative.CreateNamedPipe(
                fullPipeName,
                NamedPipeNative.PIPE_ACCESS_DUPLEX | NamedPipeNative.FILE_FLAG_FIRST_PIPE_INSTANCE | NamedPipeNative.FILE_FLAG_OVERLAPPED,
                NamedPipeNative.PIPE_TYPE_MESSAGE | NamedPipeNative.PIPE_READMODE_MESSAGE,
                1,
                _namedPipeBufferSizeForRemoting,
                _namedPipeBufferSizeForRemoting,
                0,
                securityAttributes);

            int lastError = Marshal.GetLastWin32Error();
            if (securityDescHandle != null)
            {
                securityDescHandle.Value.Free();
            }

            if (pipeHandle.IsInvalid)
            {
                throw new PSInvalidOperationException(
                    StringUtil.Format(RemotingErrorIdStrings.CannotCreateNamedPipe, lastError));
            }

            // Create the .Net NamedPipeServerStream wrapper.
            try
            {
                return new NamedPipeServerStream(
                    PipeDirection.InOut,
                    true,                       // IsAsync
                    false,                      // IsConnected
                    pipeHandle);
            }
            catch (Exception e)
            {
                CommandProcessorBase.CheckForSevereException(e);
                pipeHandle.Dispose();
                throw;
            }
        }

        static RemoteSessionNamedPipeServer()
        {
            s_syncObject = new object();

            // All PowerShell instances will start with the named pipe
            // and listner created and running.
            if (Platform.IsWindows)
            {
                IPCNamedPipeServerEnabled = true;
            }

            CreateIPCNamedPipeServerSingleton();
#if !CORECLR // There is only one AppDomain per application in CoreCLR, which would be the default
            CreateAppDomainUnloadHandler();
#endif
        }

        #endregion

        #region IDisposable

        /// <summary>
        /// Dispose
        /// </summary>
        public void Dispose()
        {
            lock (_syncObject)
            {
                if (IsDisposed) { return; }
                IsDisposed = true;
            }

            if (TextReader != null)
            {
                try { TextReader.Dispose(); }
                catch (ObjectDisposedException) { }
                TextReader = null;
            }

            if (TextWriter != null)
            {
                try { TextWriter.Dispose(); }
                catch (ObjectDisposedException) { }
                TextWriter = null;
            }

            if (Stream != null)
            {
                try { Stream.Dispose(); }
                catch (ObjectDisposedException) { }
            }
        }

        #endregion

        #region Public Methods

        /// <summary>
        /// Starts named pipe server listening thread.  When a client connects this thread
        /// makes a callback to implement the client communication.  When the thread ends
        /// this object is disposed and a new RemoteSessionNamedPipeServer must be created
        /// and a new listening thread started to handle subsequent client connections.
        /// </summary>
        /// <param name="clientConnectCallback">Connection callback.</param>
        public void StartListening(
            Action<RemoteSessionNamedPipeServer> clientConnectCallback)
        {
            if (clientConnectCallback == null)
            {
                throw new PSArgumentNullException("clientConnectCallback");
            }

            lock (_syncObject)
            {
                if (IsListenerRunning)
                {
                    throw new InvalidOperationException(RemotingErrorIdStrings.NamedPipeAlreadyListening);
                }
                IsListenerRunning = true;

                // Create listener thread.
                Thread listenterThread = new Thread(ProcessListeningThread);
                listenterThread.Name = _threadName;
                listenterThread.IsBackground = true;
                listenterThread.Start(clientConnectCallback);
            } // Lock _syncObject.
        }

        #endregion

        #region Private Methods

        internal static CommonSecurityDescriptor GetServerPipeSecurity()
        {
            // Built-in Admin SID
            SecurityIdentifier adminSID = new SecurityIdentifier(WellKnownSidType.BuiltinAdministratorsSid, null);
            DiscretionaryAcl dacl = new DiscretionaryAcl(false, false, 1);
            dacl.AddAccess(
                AccessControlType.Allow,
                adminSID,
                _pipeAccessMaskFullControl,
                InheritanceFlags.None,
                PropagationFlags.None);

            CommonSecurityDescriptor securityDesc = new CommonSecurityDescriptor(
                false, false,
                ControlFlags.DiscretionaryAclPresent | ControlFlags.OwnerDefaulted | ControlFlags.GroupDefaulted,
                null, null, null, dacl);

            // Conditionally add User SID
            bool isAdminElevated = new WindowsPrincipal(WindowsIdentity.GetCurrent()).IsInRole(WindowsBuiltInRole.Administrator);
            if (!isAdminElevated)
            {
                securityDesc.DiscretionaryAcl.AddAccess(
                    AccessControlType.Allow,
                    WindowsIdentity.GetCurrent().User,
                    _pipeAccessMaskFullControl,
                    InheritanceFlags.None,
                    PropagationFlags.None);
            }

            return securityDesc;
        }

        /// <summary>
        /// Wait for client connection.
        /// </summary>
        private void WaitForConnection()
        {
            Stream.WaitForConnection();
        }

        /// <summary>
        /// Process listening thread.
        /// </summary>
        /// <param name="state">client callback delegate</param>
        [SuppressMessage("Microsoft.Reliability", "CA2001:AvoidCallingProblematicMethods", MessageId = "System.Runtime.InteropServices.SafeHandle.DangerousGetHandle")]
        private void ProcessListeningThread(object state)
        {
            string processId = System.Diagnostics.Process.GetCurrentProcess().Id.ToString(CultureInfo.InvariantCulture);
            string appDomainName = NamedPipeUtils.GetCurrentAppDomainName();

            // Logging.
            _tracer.WriteMessage("RemoteSessionNamedPipeServer", "StartListening", Guid.Empty,
                "Listener thread started on Process {0} in AppDomainName {1}.", processId, appDomainName);
            PSEtwLog.LogOperationalInformation(
                PSEventId.NamedPipeIPC_ServerListenerStarted, PSOpcode.Open, PSTask.NamedPipe,
                PSKeyword.UseAlwaysOperational,
                processId, appDomainName);

            Exception ex = null;
            string userName = string.Empty;
            bool restartListenerThread = true;

            // Wait for connection.
            try
            {
                // Begin listening for a client connect.
                this.WaitForConnection();

                try
                {
                    userName = WindowsIdentity.GetCurrent().Name;
                }
                catch (System.Security.SecurityException) { }

                // Logging.
                _tracer.WriteMessage("RemoteSessionNamedPipeServer", "StartListening", Guid.Empty,
                    "Client connection started on Process {0} in AppDomainName {1} for User {2}.", processId, appDomainName, userName);
                PSEtwLog.LogOperationalInformation(
                    PSEventId.NamedPipeIPC_ServerConnect, PSOpcode.Connect, PSTask.NamedPipe,
                    PSKeyword.UseAlwaysOperational,
                    processId, appDomainName, userName);

                // Create reader/writer streams.
                TextReader = new StreamReader(Stream);
                TextWriter = new StreamWriter(Stream);
                TextWriter.AutoFlush = true;
            }
            catch (Exception e)
            {
                CommandProcessorBase.CheckForSevereException(e);
                ex = e;
            }
            if (ex != null)
            {
                // Error during connection handling.  Don't try to restart listening thread.
                string errorMessage = !string.IsNullOrEmpty(ex.Message) ? ex.Message : string.Empty;
                _tracer.WriteMessage("RemoteSessionNamedPipeServer", "StartListening", Guid.Empty,
                    "Unexpected error in listener thread on process {0} in AppDomainName {1}.  Error Message: {2}", processId, appDomainName, errorMessage);
                PSEtwLog.LogOperationalError(PSEventId.NamedPipeIPC_ServerListenerError, PSOpcode.Exception, PSTask.NamedPipe,
                    PSKeyword.UseAlwaysOperational,
                    processId, appDomainName, errorMessage);

                Dispose();
                return;
            }

            // Start server session on new connection.
            ex = null;
            try
            {
                Action<RemoteSessionNamedPipeServer> clientConnectCallback = state as Action<RemoteSessionNamedPipeServer>;
                Dbg.Assert(clientConnectCallback != null, "Client callback should never be null.");

                // Handle a new client connect by making the callback.
                // The callback must handle all exceptions except
                // for a named pipe disposed or disconnected exception
                // which propagates up to the thread listener loop.
                clientConnectCallback(this);
            }
            catch (IOException)
            {
                // Expected connection terminated.
            }
            catch (ObjectDisposedException)
            {
                // Expected from PS transport close/dispose.
            }
            catch (Exception e)
            {
                CommandProcessorBase.CheckForSevereException(e);
                ex = e;
                restartListenerThread = false;
            }

            // Logging.
            _tracer.WriteMessage("RemoteSessionNamedPipeServer", "StartListening", Guid.Empty,
                "Client connection ended on process {0} in AppDomainName {1} for User {2}.", processId, appDomainName, userName);
            PSEtwLog.LogOperationalInformation(
                PSEventId.NamedPipeIPC_ServerDisconnect, PSOpcode.Close, PSTask.NamedPipe,
                PSKeyword.UseAlwaysOperational,
                processId, appDomainName, userName);

            if (ex == null)
            {
                // Normal listener exit.
                _tracer.WriteMessage("RemoteSessionNamedPipeServer", "StartListening", Guid.Empty,
                    "Listener thread ended on process {0} in AppDomainName {1}.", processId, appDomainName);
                PSEtwLog.LogOperationalInformation(PSEventId.NamedPipeIPC_ServerListenerEnded, PSOpcode.Close, PSTask.NamedPipe,
                    PSKeyword.UseAlwaysOperational,
                    processId, appDomainName);
            }
            else
            {
                // Unexpected error.
                string errorMessage = !string.IsNullOrEmpty(ex.Message) ? ex.Message : string.Empty;
                _tracer.WriteMessage("RemoteSessionNamedPipeServer", "StartListening", Guid.Empty,
                    "Unexpected error in listener thread on process {0} in AppDomainName {1}.  Error Message: {2}", processId, appDomainName, errorMessage);
                PSEtwLog.LogOperationalError(PSEventId.NamedPipeIPC_ServerListenerError, PSOpcode.Exception, PSTask.NamedPipe,
                    PSKeyword.UseAlwaysOperational,
                    processId, appDomainName, errorMessage);
            }

            lock (_syncObject)
            {
                IsListenerRunning = false;
            }

            // Ensure this named pipe server object is disposed.
            Dispose();

            ListenerEnded.SafeInvoke(
                this,
                new ListenerEndedEventArgs(ex, restartListenerThread));
        }

        #endregion

        #region Static Methods

        /// <summary>
        /// Ensures the namedpipe singleton server is running and waits for a client connection.
        /// This is a blocking call that returns after the client connection ends.
        /// This method supports PowerShell running in "NamedPipeServerMode", which is used for
        /// PowerShell Direct Windows Server Container connection and management.
        /// </summary>
        /// <param name="configurationName">name of the configuration to use</param>
        internal static void RunServerMode(string configurationName)
        {
            IPCNamedPipeServerEnabled = true;
            CreateIPCNamedPipeServerSingleton();

            if (IPCNamedPipeServer == null)
            {
                throw new RuntimeException(RemotingErrorIdStrings.NamedPipeServerCannotStart);
            }

            IPCNamedPipeServer.ConfigurationName = configurationName;

            ManualResetEventSlim clientConnectionEnded = new ManualResetEventSlim(false);
            IPCNamedPipeServer.ListenerEnded -= OnIPCNamedPipeServerEnded;
            IPCNamedPipeServer.ListenerEnded += (sender, e) =>
                {
                    clientConnectionEnded.Set();
                };

            // Wait for server to service a single client connection.
            clientConnectionEnded.Wait();
            clientConnectionEnded.Dispose();
            IPCNamedPipeServerEnabled = false;
        }

        /// <summary>
        /// Creates the process named pipe server object singleton and
        /// starts the client listening thread.
        /// </summary>
        internal static void CreateIPCNamedPipeServerSingleton()
        {
            lock (s_syncObject)
            {
                if (!IPCNamedPipeServerEnabled) { return; }

                if (IPCNamedPipeServer == null || IPCNamedPipeServer.IsDisposed)
                {
                    try
                    {
                        try
                        {
                            IPCNamedPipeServer = CreateRemoteSessionNamedPipeServer();
                        }
                        catch (IOException)
                        {
                            // Expected when named pipe server for this process already exists.
                            // This can happen if process has multiple AppDomains hosting PowerShell (SMA.dll).
                            return;
                        }

                        // Listener ended callback, used to create listening new pipe server.
                        IPCNamedPipeServer.ListenerEnded += OnIPCNamedPipeServerEnded;

                        // Start the pipe server listening thread, and provide client connection callback.
                        IPCNamedPipeServer.StartListening(ClientConnectionCallback);
                    }
                    catch (Exception e)
                    {
                        CommandProcessorBase.CheckForSevereException(e);
                        IPCNamedPipeServer = null;
                    }
                }
            }
        }

#if !CORECLR // There is only one AppDomain per application in CoreCLR, which would be the default
        private static void CreateAppDomainUnloadHandler()
        {
            // Subscribe to the app domain unload event.
            AppDomain.CurrentDomain.DomainUnload += (sender, args) =>
                {
                    IPCNamedPipeServerEnabled = false;
                    RemoteSessionNamedPipeServer namedPipeServer = IPCNamedPipeServer;
                    if (namedPipeServer != null)
                    {
                        try
                        {
                            // Terminate the IPC thread.
                            namedPipeServer.Dispose();
                        }
                        catch (ObjectDisposedException) { }
                        catch (Exception e)
                        {
                            // Don't throw an exception on the app domain unload event thread.
                            CommandProcessorBase.CheckForSevereException(e);
                        }
                    }
                };
        }
#endif
        private static void OnIPCNamedPipeServerEnded(object sender, ListenerEndedEventArgs args)
        {
            if (args.RestartListener)
            {
                CreateIPCNamedPipeServerSingleton();
            }
        }

        private static void ClientConnectionCallback(RemoteSessionNamedPipeServer pipeServer)
        {
            // Create server mediator object and begin remote session with client.
            NamedPipeProcessMediator.Run(
                string.Empty,
                pipeServer);
        }

        #endregion
    }

    /// <summary>
    /// Base class for RemoteSessionNamedPipeClient and ContainerSessionNamedPipeClient.
    /// </summary>
    internal class NamedPipeClientBase : IDisposable
    {
        #region Members

        private NamedPipeClientStream _clientPipeStream;
        private PowerShellTraceSource _tracer = PowerShellTraceSourceFactory.GetTraceSource();

        protected string _pipeName;

        #endregion

        #region Properties

        /// <summary>
        /// Accessor for the named pipe reader.
        /// </summary>
        public StreamReader TextReader { get; private set; }

        /// <summary>
        /// Accessor for the named pipe writer.
        /// </summary>
        public StreamWriter TextWriter { get; private set; }

        /// <summary>
        /// Name of pipe.
        /// </summary>
        public string PipeName
        {
            get { return _pipeName; }
        }

        #endregion

        #region Constructor

        public NamedPipeClientBase()
        { }

        #endregion

        #region IDisposable

        /// <summary>
        /// Dispose
        /// </summary>
        public void Dispose()
        {
            if (TextReader != null)
            {
                try { TextReader.Dispose(); }
                catch (ObjectDisposedException) { }
                TextReader = null;
            }

            if (TextWriter != null)
            {
                try { TextWriter.Dispose(); }
                catch (ObjectDisposedException) { }
                TextWriter = null;
            }

            if (_clientPipeStream != null)
            {
                try { _clientPipeStream.Dispose(); }
                catch (ObjectDisposedException) { }
            }
        }

        #endregion

        #region Methods

        /// <summary>
        /// Connect to named pipe server.  This is a blocking call until a 
        /// connection occurs or the timeout time has ellapsed.
        /// </summary>
        /// <param name="timeout">Connection attempt timeout in milliseconds</param>
        public void Connect(
            int timeout)
        {
            // Uses Native API to connect to pipe and return NamedPipeClientStream object.
            _clientPipeStream = DoConnect(timeout);

            // Create reader/writer streams.
            TextReader = new StreamReader(_clientPipeStream);
            TextWriter = new StreamWriter(_clientPipeStream);
            TextWriter.AutoFlush = true;

            _tracer.WriteMessage("NamedPipeClientBase", "Connect", Guid.Empty,
                "Connection started on pipe: {0}", _pipeName);
        }

        /// <summary>
        /// Closes the named pipe.
        /// </summary>
        public void Close()
        {
            if (_clientPipeStream != null)
            {
                _clientPipeStream.Dispose();
            }
        }

        public virtual void AbortConnect()
        { }

        protected virtual NamedPipeClientStream DoConnect(int timeout)
        {
            return null;
        }