SSH.NET/Renci.SshClient/Renci.SshNet/Session.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using Renci.SshNet.Channels;
using Renci.SshNet.Common;
using Renci.SshNet.Compression;
using Renci.SshNet.Messages;
using Renci.SshNet.Messages.Authentication;
using Renci.SshNet.Messages.Connection;
using Renci.SshNet.Messages.Transport;
using Renci.SshNet.Security;
using System.Globalization;

namespace Renci.SshNet
{
    /// <summary>
    /// Provides functionality to connect and interact with SSH server.
    /// </summary>
    public class Session : IDisposable
    {
        /// <summary>
        /// Specifies maximum packet size defined by the protocol.
        /// </summary>
        protected const int MAXIMUM_PACKET_SIZE = 35000;

        /// <summary>
        /// Specifies maximum payload size defined by the protocol.
        /// </summary>
        protected const int MAXIMUM_PAYLOAD_SIZE = 1024 * 32;

        private static RNGCryptoServiceProvider _randomizer = new System.Security.Cryptography.RNGCryptoServiceProvider();

        private static Regex _serverVersionRe = new Regex("^SSH-(?<protoversion>[^-]+)-(?<softwareversion>.+)( SP.+)?$", RegexOptions.Compiled);

        /// <summary>
        /// Controls how many authentication attempts can take place at the same time.
        /// </summary>
        /// <remarks>
        /// Some server may restrict number to prevent authentication attacks
        /// </remarks>
        private static SemaphoreSlim _authenticationConnection = new SemaphoreSlim(3);

        /// <summary>
        /// Holds metada about session messages
        /// </summary>
        private IEnumerable<MessageMetadata> _messagesMetadata;

        /// <summary>
        /// Holds connection socket.
        /// </summary>
        private Socket _socket;

        /// <summary>
        /// Holds reference to task that listens for incoming messages
        /// </summary>
        private Task _messageListener;

        /// <summary>
        /// Specifies outbound packet number
        /// </summary>
        private volatile UInt32 _outboundPacketSequence = 0;

        /// <summary>
        /// Specifies incoming packet number
        /// </summary>
        private UInt32 _inboundPacketSequence = 0;

        /// <summary>
        /// WaitHandle to signal that last service request was accepted
        /// </summary>
        private EventWaitHandle _serviceAccepted = new AutoResetEvent(false);

        /// <summary>
        /// WaitHandle to signal that exception was thrown by another thread.
        /// </summary>
        private EventWaitHandle _exceptionWaitHandle = new AutoResetEvent(false);

        /// <summary>
        /// WaitHandle to signal that key exchange was completed.
        /// </summary>
        private EventWaitHandle _keyExchangeCompletedWaitHandle = new ManualResetEvent(false);

        /// <summary>
        /// Exception that need to be thrown by waiting thread
        /// </summary>
        private Exception _exception;

        /// <summary>
        /// Specifies whether connection is authenticated
        /// </summary>
        private bool _isAuthenticated;

        /// <summary>
        /// Specifies whether user issued Disconnect command or not
        /// </summary>
        private bool _isDisconnecting;

        private KeyExchange _keyExchange;

        private HMac _serverMac;

        private HMac _clientMac;

        private Cipher _clientCipher;

        private Cipher _serverCipher;

        private Compressor _serverDecompression;

        private Compressor _clientCompression;

        private SemaphoreSlim _sessionSemaphore;
        /// <summary>
        /// Gets the session semaphore that controls session channels.
        /// </summary>
        /// <value>The session semaphore.</value>
        public SemaphoreSlim SessionSemaphore
        {
            get
            {
                if (this._sessionSemaphore == null)
                {
                    lock (this)
                    {
                        if (this._sessionSemaphore == null)
                        {
                            this._sessionSemaphore = new SemaphoreSlim(this.ConnectionInfo.MaxSessions);
                        }
                    }
                }

                return this._sessionSemaphore;
            }
        }

        private bool _isDisconnectMessageSent;

        private uint _nextChannelNumber;
        /// <summary>
        /// Gets the next channel number.
        /// </summary>
        /// <value>The next channel number.</value>
        internal uint NextChannelNumber
        {
            get
            {
                uint result;

                lock (this)
                {
                    result = this._nextChannelNumber++;
                }

                return result;
            }
        }

        /// <summary>
        /// Gets a value indicating whether socket connected.
        /// </summary>
        /// <value>
        /// 	<c>true</c> if socket connected; otherwise, <c>false</c>.
        /// </value>
        public bool IsConnected
        {
            get
            {
                return this._socket != null && this._socket.Connected && this._isAuthenticated && this._messageListener.Status == TaskStatus.Running;
            }
        }

        /// <summary>
        /// Gets or sets the session id.
        /// </summary>
        /// <value>The session id.</value>
        public byte[] SessionId { get; private set; }

        private Message _clientInitMessage;
        /// <summary>
        /// Gets the client init message.
        /// </summary>
        /// <value>The client init message.</value>
        public Message ClientInitMessage
        {
            get
            {
                if (this._clientInitMessage == null)
                {
                    this._clientInitMessage = new KeyExchangeInitMessage()
                    {
                        KeyExchangeAlgorithms = this.ConnectionInfo.KeyExchangeAlgorithms.Keys,
                        ServerHostKeyAlgorithms = this.ConnectionInfo.HostKeyAlgorithms.Keys,
                        EncryptionAlgorithmsClientToServer = this.ConnectionInfo.Encryptions.Keys,
                        EncryptionAlgorithmsServerToClient = this.ConnectionInfo.Encryptions.Keys,
                        MacAlgorithmsClientToServer = this.ConnectionInfo.HmacAlgorithms.Keys,
                        MacAlgorithmsServerToClient = this.ConnectionInfo.HmacAlgorithms.Keys,
                        CompressionAlgorithmsClientToServer = this.ConnectionInfo.CompressionAlgorithms.Keys,
                        CompressionAlgorithmsServerToClient = this.ConnectionInfo.CompressionAlgorithms.Keys,
                        LanguagesClientToServer = new string[] { string.Empty },
                        LanguagesServerToClient = new string[] { string.Empty },
                        FirstKexPacketFollows = false,
                        Reserved = 0,
                    };
                }
                return this._clientInitMessage;
            }
        }

        /// <summary>
        /// Gets or sets the server version string.
        /// </summary>
        /// <value>The server version.</value>
        public string ServerVersion { get; private set; }

        /// <summary>
        /// Gets or sets the client version string.
        /// </summary>
        /// <value>The client version.</value>
        public string ClientVersion { get; private set; }

        /// <summary>
        /// Gets or sets the connection info.
        /// </summary>
        /// <value>The connection info.</value>
        public ConnectionInfo ConnectionInfo { get; private set; }

        /// <summary>
        /// Occurs when an error occurred.
        /// </summary>
        public event EventHandler<ExceptionEventArgs> ErrorOccured;

        /// <summary>
        /// Occurs when session has been disconnected form the server.
        /// </summary>
        public event EventHandler<EventArgs> Disconnected;

        #region Message events

        /// <summary>
        /// Occurs when <see cref="DisconnectMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<DisconnectMessage>> DisconnectReceived;

        /// <summary>
        /// Occurs when <see cref="IgnoreMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<IgnoreMessage>> IgnoreReceived;

        /// <summary>
        /// Occurs when <see cref="UnimplementedMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<UnimplementedMessage>> UnimplementedReceived;

        /// <summary>
        /// Occurs when <see cref="DebugMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<DebugMessage>> DebugReceived;

        /// <summary>
        /// Occurs when <see cref="ServiceRequestMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ServiceRequestMessage>> ServiceRequestReceived;

        /// <summary>
        /// Occurs when <see cref="ServiceAcceptMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ServiceAcceptMessage>> ServiceAcceptReceived;

        /// <summary>
        /// Occurs when <see cref="KeyExchangeInitMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<KeyExchangeInitMessage>> KeyExchangeInitReceived;

        /// <summary>
        /// Occurs when <see cref="NewKeysMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<NewKeysMessage>> NewKeysReceived;

        /// <summary>
        /// Occurs when <see cref="RequestMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<RequestMessage>> UserAuthenticationRequestReceived;

        /// <summary>
        /// Occurs when <see cref="FailureMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<FailureMessage>> UserAuthenticationFailureReceived;

        /// <summary>
        /// Occurs when <see cref="SuccessMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<SuccessMessage>> UserAuthenticationSuccessReceived;

        /// <summary>
        /// Occurs when <see cref="BannerMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<BannerMessage>> UserAuthenticationBannerReceived;

        /// <summary>
        /// Occurs when <see cref="GlobalRequestMessage"/> message received
        /// </summary>        
        internal event EventHandler<MessageEventArgs<GlobalRequestMessage>> GlobalRequestReceived;

        /// <summary>
        /// Occurs when <see cref="RequestSuccessMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<RequestSuccessMessage>> RequestSuccessReceived;

        /// <summary>
        /// Occurs when <see cref="RequestFailureMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<RequestFailureMessage>> RequestFailureReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelOpenMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelOpenMessage>> ChannelOpenReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelOpenConfirmationMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelOpenConfirmationMessage>> ChannelOpenConfirmationReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelOpenFailureMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelOpenFailureMessage>> ChannelOpenFailureReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelWindowAdjustMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelWindowAdjustMessage>> ChannelWindowAdjustReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelDataMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelDataMessage>> ChannelDataReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelExtendedDataMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelExtendedDataMessage>> ChannelExtendedDataReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelEofMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelEofMessage>> ChannelEofReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelCloseMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelCloseMessage>> ChannelCloseReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelRequestMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelRequestMessage>> ChannelRequestReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelSuccessMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelSuccessMessage>> ChannelSuccessReceived;

        /// <summary>
        /// Occurs when <see cref="ChannelFailureMessage"/> message received
        /// </summary>
        internal event EventHandler<MessageEventArgs<ChannelFailureMessage>> ChannelFailureReceived;

        /// <summary>
        /// Occurs when message received and is not handled by any of the event handlers
        /// </summary>
        internal event EventHandler<MessageEventArgs<Message>> MessageReceived;

        #endregion

        /// <summary>
        /// Initializes a new instance of the <see cref="Session"/> class.
        /// </summary>
        /// <param name="connectionInfo">The connection info.</param>
        internal Session(ConnectionInfo connectionInfo)
        {
            this.ConnectionInfo = connectionInfo;
            this.ClientVersion = string.Format(CultureInfo.CurrentCulture, "SSH-2.0-Renci.SshNet.SshClient.{0}", this.GetType().Assembly.GetName().Version);
        }

        /// <summary>
        /// Connects to the server.
        /// </summary>
        public void Connect()
        {
            if (this.ConnectionInfo == null)
            {
                throw new ArgumentNullException("connectionInfo");
            }

            if (this.IsConnected)
                return;

            try
            {
                _authenticationConnection.Wait();

                if (this.IsConnected)
                    return;

                lock (this)
                {
                    //  If connected don't connect again
                    if (this.IsConnected)
                        return;

                    var ep = new IPEndPoint(Dns.GetHostAddresses(this.ConnectionInfo.Host)[0], this.ConnectionInfo.Port);
                    this._socket = new Socket(ep.AddressFamily, SocketType.Stream, ProtocolType.Tcp);

                    var socketBufferSize = 2 * MAXIMUM_PACKET_SIZE;
                    this._socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay, true);
                    this._socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.SendBuffer, socketBufferSize);
                    this._socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveBuffer, socketBufferSize);

                    //  Connect socket with 5 seconds timeout
                    var connectResult = this._socket.BeginConnect(ep, null, null);

                    connectResult.AsyncWaitHandle.WaitOne(this.ConnectionInfo.Timeout);

                    //  Build list of available messages while connecting
                    this._messagesMetadata = (from type in this.GetType().Assembly.GetTypes()
                                              from messageAttribute in type.GetCustomAttributes(false).OfType<MessageAttribute>()
                                              select new MessageMetadata
                                              {
                                                  Name = messageAttribute.Name,
                                                  Number = messageAttribute.Number,
                                                  Enabled = false,
                                                  Activated = false,
                                                  Type = type,
                                              }).ToList();

                    this._socket.EndConnect(connectResult);

                    Match versionMatch = null;
                    //  Get server version from the server,
                    //  ignore text lines which are sent before if any
                    using (var ns = new NetworkStream(this._socket))
                    {
                        using (var sr = new StreamReader(ns))
                        {
                            while (true)
                            {
                                this.ServerVersion = sr.ReadLine();
                                if (string.IsNullOrEmpty(this.ServerVersion))
                                {
                                    throw new InvalidOperationException("Server string is null or empty.");
                                }

                                versionMatch = _serverVersionRe.Match(this.ServerVersion);

                                if (versionMatch.Success)
                                {
                                    break;
                                }
                            }
                        }
                    }

                    //  Get server SSH version
                    var version = versionMatch.Result("${protoversion}");

                    if (!(version.Equals("2.0") || version.Equals("1.99")))
                    {
                        throw new SshConnectionException(string.Format(CultureInfo.CurrentCulture, "Server version '{0}' is not supported.", version), DisconnectReason.ProtocolVersionNotSupported);
                    }

                    this.Write(Encoding.ASCII.GetBytes(string.Format(CultureInfo.InvariantCulture, "{0}\x0D\x0A", this.ClientVersion)));

                    //  Register Transport response messages
                    this.RegisterMessage("SSH_MSG_DISCONNECT");
                    this.RegisterMessage("SSH_MSG_IGNORE");
                    this.RegisterMessage("SSH_MSG_UNIMPLEMENTED");
                    this.RegisterMessage("SSH_MSG_DEBUG");
                    this.RegisterMessage("SSH_MSG_SERVICE_ACCEPT");
                    this.RegisterMessage("SSH_MSG_KEXINIT");
                    this.RegisterMessage("SSH_MSG_NEWKEYS");

                    //  Some server implementations might sent this message first, prior establishing encryption algorithm
                    this.RegisterMessage("SSH_MSG_USERAUTH_BANNER");

                    //  Start incoming request listener
                    this._messageListener = Task.Factory.StartNew(() => { this.MessageListener(); }, TaskCreationOptions.LongRunning);

                    //  Wait for key exchange to be completed
                    this.WaitHandle(this._keyExchangeCompletedWaitHandle);

                    //  If sessionId is not set then its not connected
                    if (this.SessionId == null)
                    {
                        this.Disconnect();
                        return;
                    }

                    //  Request user authorization service
                    this.SendMessage(new ServiceRequestMessage(ServiceName.UserAuthentication));

                    //  Wait for service to be accepted
                    this.WaitHandle(this._serviceAccepted);

                    if (string.IsNullOrEmpty(this.ConnectionInfo.Username))
                    {
                        throw new SshException("Username is not specified.");
                    }

                    //  Try authenticate using none method
                    using (var noneConnectionInfo = new NoneConnectionInfo(this.ConnectionInfo.Host, this.ConnectionInfo.Port, this.ConnectionInfo.Username))
                    {
                        noneConnectionInfo.Authenticate(this);

                        this._isAuthenticated = noneConnectionInfo.IsAuthenticated;

                        if (!this._isAuthenticated)
                        {
                            //  Ensure that authentication method is allowed
                            if (!noneConnectionInfo.AllowedAuthentications.Contains(this.ConnectionInfo.Name))
                            {
                                throw new SshAuthenticationException("User authentication method is not supported.");
                            }

                            //  In future, if more then one authentication methods are supported perform the check here.
                            //  Authenticate using provided connection info object
                            this.ConnectionInfo.Authenticate(this);

                            this._isAuthenticated = this.ConnectionInfo.IsAuthenticated;
                        }
                    }

                    if (!this._isAuthenticated)
                    {
                        throw new SshAuthenticationException("User cannot be authenticated.");
                    }

                    //  Register Connection messages
                    this.RegisterMessage("SSH_MSG_GLOBAL_REQUEST");
                    this.RegisterMessage("SSH_MSG_REQUEST_SUCCESS");
                    this.RegisterMessage("SSH_MSG_REQUEST_FAILURE");
                    this.RegisterMessage("SSH_MSG_CHANNEL_OPEN_CONFIRMATION");
                    this.RegisterMessage("SSH_MSG_CHANNEL_OPEN_FAILURE");
                    this.RegisterMessage("SSH_MSG_CHANNEL_WINDOW_ADJUST");
                    this.RegisterMessage("SSH_MSG_CHANNEL_EXTENDED_DATA");
                    this.RegisterMessage("SSH_MSG_CHANNEL_REQUEST");
                    this.RegisterMessage("SSH_MSG_CHANNEL_SUCCESS");
                    this.RegisterMessage("SSH_MSG_CHANNEL_FAILURE");
                    this.RegisterMessage("SSH_MSG_CHANNEL_DATA");
                    this.RegisterMessage("SSH_MSG_CHANNEL_EOF");
                    this.RegisterMessage("SSH_MSG_CHANNEL_CLOSE");

                    Monitor.Pulse(this);
                }
            }
            finally
            {
                _authenticationConnection.Release();
            }
        }

        /// <summary>
        /// Disconnects from the server
        /// </summary>
        public void Disconnect()
        {
            this.Dispose();
        }

        internal T CreateChannel<T>() where T : Channel, new()
        {
            return CreateChannel<T>(0, 0x100000, 0x8000);
        }

        internal T CreateChannel<T>(uint serverChannelNumber, uint windowSize, uint packetSize) where T : Channel, new()
        {
            T channel = new T();
            lock (this)
            {
                channel.Initialize(this, serverChannelNumber, windowSize, packetSize);
            }
            return channel;
        }

        /// <summary>
        /// Sends "keep alive" message to keep connection alive.
        /// </summary>
        internal void SendKeepAlive()
        {
            this.SendMessage(new IgnoreMessage());
        }

        /// <summary>
        /// Waits for handle to signal while checking other handles as well including timeout check to prevent waiting for ever
        /// </summary>
        /// <param name="waitHandle">The wait handle.</param>
        internal void WaitHandle(WaitHandle waitHandle)
        {
            var waitHandles = new WaitHandle[]
                {
                    this._exceptionWaitHandle,
                    waitHandle,
                };

            var index = EventWaitHandle.WaitAny(waitHandles, this.ConnectionInfo.Timeout);

            if (index < 1)
            {
                throw this._exception;
            }
            else if (index > 1)
            {
                this.SendDisconnect(DisconnectReason.ByApplication, "Operation timeout");

                throw new SshOperationTimeoutException("Session operation has timed out");
            }
        }

        /// <summary>
        /// Sends packet message to the server.
        /// </summary>
        /// <param name="message">The message.</param>
        internal void SendMessage(Message message)
        {
            if (this._socket == null || !this._socket.Connected)
                return;

            //  Messages can be sent by different thread so we need to synchronize it            
            var paddingMultiplier = this._clientCipher == null ? (byte)8 : (byte)this._clientCipher.BlockSize;    //    Should be recalculate base on cipher min length if cipher specified

            var messageData = message.GetBytes();

            if (messageData.Length > Session.MAXIMUM_PAYLOAD_SIZE)
            {
                throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, "Payload cannot be more then {0} bytes.", Session.MAXIMUM_PAYLOAD_SIZE));
            }

            if (this._clientCompression != null)
            {
                messageData = this._clientCompression.Compress(messageData);
            }

            var packetLength = messageData.Length + 4 + 1; //  add length bytes and padding byte
            byte paddingLength = (byte)((-packetLength) & (paddingMultiplier - 1));
            if (paddingLength < paddingMultiplier)
            {
                paddingLength += paddingMultiplier;
            }

            //  Build Packet data
            var packetData = new byte[4 + 1 + messageData.Length + paddingLength];

            //  Add packet length
            ((uint)packetData.Length - 4).GetBytes().CopyTo(packetData, 0);

            //  Add packet padding length
            packetData[4] = paddingLength;

            //  Add packet payload
            messageData.CopyTo(packetData, 4 + 1);

            //  Add random padding
            var paddingBytes = new byte[paddingLength];
            _randomizer.GetBytes(paddingBytes);
            paddingBytes.CopyTo(packetData, 4 + 1 + messageData.Length);

            //  Lock handling of _outboundPacketSequence since it must be sent sequently to server
            lock (this._socket)
            {
                //  Calculate packet hash
                var hashData = new byte[4 + packetData.Length];
                this._outboundPacketSequence.GetBytes().CopyTo(hashData, 0);
                packetData.CopyTo(hashData, 4);

                //  Encrypt packet data
                if (this._clientCipher != null)
                {
                    packetData = this._clientCipher.Encrypt(packetData);
                }

                if (packetData.Length > Session.MAXIMUM_PACKET_SIZE)
                {
                    throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, "Packet is too big. Maximum packet size is {0} bytes.", Session.MAXIMUM_PACKET_SIZE));
                }

                if (this._clientMac == null)
                {
                    this.Write(packetData);
                }
                else
                {
                    var hash = this._clientMac.ComputeHash(hashData.ToArray());

                    var data = new byte[packetData.Length + this._clientMac.HashSize / 8];
                    packetData.CopyTo(data, 0);
                    hash.CopyTo(data, packetData.Length);

                    this.Write(data);
                }

                this._outboundPacketSequence++;

                Monitor.Pulse(this._socket);
            }
        }

        /// <summary>
        /// Receives the message from the server.
        /// </summary>
        /// <returns></returns>
        private Message ReceiveMessage()
        {
            if (!this._socket.Connected)
                return null;

            //  No lock needed since all messages read by only one thread
            var blockSize = this._serverCipher == null ? (byte)8 : (byte)this._serverCipher.BlockSize;

            //  Read packet length first
            var firstBlock = this.Read(blockSize);

            if (this._serverCipher != null)
            {
                firstBlock = this._serverCipher.Decrypt(firstBlock);
            }

            var packetLength = (uint)(firstBlock[0] << 24 | firstBlock[1] << 16 | firstBlock[2] << 8 | firstBlock[3]);

            //  Test packet minimum and maximum boundaries
            if (packetLength < Math.Max((byte)16, blockSize) - 4 || packetLength > Session.MAXIMUM_PACKET_SIZE - 4)
                throw new SshConnectionException(string.Format(CultureInfo.CurrentCulture, "Bad packet length {0}", packetLength), DisconnectReason.ProtocolError);

            //  Read rest of the packet data
            int bytesToRead = (int)(packetLength - (blockSize - 4));

            var data = new byte[bytesToRead + blockSize];

            firstBlock.CopyTo(data, 0);

            byte[] serverHash = null;
            if (this._serverMac != null)
            {
                serverHash = new byte[this._serverMac.HashSize / 8];
                bytesToRead += serverHash.Length;
            }

            if (bytesToRead > 0)
            {
                var nextBlocks = this.Read(bytesToRead);

                if (serverHash != null)
                {
                    Array.Copy(nextBlocks, nextBlocks.Length - serverHash.Length, serverHash, 0, serverHash.Length);
                    nextBlocks = nextBlocks.Take(nextBlocks.Length - serverHash.Length).ToArray();
                }

                if (nextBlocks.Length > 0)
                {
                    if (this._serverCipher != null)
                    {
                        nextBlocks = this._serverCipher.Decrypt(nextBlocks);
                    }
                    nextBlocks.CopyTo(data, blockSize);
                }
            }

            var paddingLength = data[4];

            var messagePayload = new byte[packetLength - paddingLength - 1];
            Array.Copy(data, 5, messagePayload, 0, messagePayload.Length);

            if (this._serverDecompression != null)
            {
                messagePayload = this._serverDecompression.Decompress(messagePayload);
            }

            //  Validate message against MAC            
            if (this._serverMac != null)
            {
                var clientHashData = new byte[4 + data.Length];
                var lengthBytes = this._inboundPacketSequence.GetBytes();

                lengthBytes.CopyTo(clientHashData, 0);
                data.CopyTo(clientHashData, 4);

                //  Calculate packet hash
                var clientHash = this._serverMac.ComputeHash(clientHashData);

                if (!serverHash.SequenceEqual(clientHash))
                {
                    throw new SshConnectionException("MAC error", DisconnectReason.MacError);
                }
            }

            this._inboundPacketSequence++;

            return this.LoadMessage(messagePayload);
        }

        private void SendDisconnect(DisconnectReason reasonCode, string message)
        {
            //  If disconnect message was sent already dont send it again
            if (this._isDisconnectMessageSent)
                return;

            var disconnectMessage = new DisconnectMessage(reasonCode, message);

            this.SendMessage(disconnectMessage);

            this._isDisconnectMessageSent = true;
        }

        /// <summary>
        /// Handles the message.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="message">The message.</param>
        private void HandleMessage<T>(T message) where T : Message
        {
            this.OnMessageReceived(message);
        }

        #region Handle transport messages

        private void HandleMessage(DisconnectMessage message)
        {
            this.OnDisconnectReceived(message);

            //  Shutdown and disconnect from the socket
            if (this._socket != null)
            {
                lock (this._socket)
                {
                    if (this._socket != null)
                    {
                        this._socket.Disconnect(true);

                        //  When socket is disconnected wait for listener to finish
                        if (this._messageListener != null)
                        {
                            //  Wait for listener task to finish
                            this._messageListener.Wait();
                            this._messageListener = null;
                        }

                        this._socket.Dispose();
                        this._socket = null;
                    }
                }
            }
        }

        private void HandleMessage(IgnoreMessage message)
        {
            this.OnIgnoreReceived(message);
        }

        private void HandleMessage(UnimplementedMessage message)
        {
            this.OnUnimplementedReceived(message);
        }

        private void HandleMessage(DebugMessage message)
        {
            this.OnDebugReceived(message);
        }

        private void HandleMessage(ServiceRequestMessage message)
        {
            this.OnServiceRequestReceived(message);
        }

        private void HandleMessage(ServiceAcceptMessage message)
        {
            //  TODO:   Refactor to avoid this method here
            this.OnServiceAcceptReceived(message);

            this._serviceAccepted.Set();
        }

        private void HandleMessage(KeyExchangeInitMessage message)
        {
            this.OnKeyExchangeInitReceived(message);
        }

        private void HandleMessage(NewKeysMessage message)
        {
            this.OnNewKeysReceived(message);
        }

        #endregion

        #region Handle User Authentication messages

        private void HandleMessage(RequestMessage message)
        {
            this.OnUserAuthenticationRequestReceived(message);
        }

        private void HandleMessage(FailureMessage message)
        {
            this.OnUserAuthenticationFailureReceived(message);
        }

        private void HandleMessage(SuccessMessage message)
        {
            this.OnUserAuthenticationSuccessReceived(message);
        }

        private void HandleMessage(BannerMessage message)
        {
            this.OnUserAuthenticationBannerReceived(message);
        }

        #endregion

        #region Handle connection messages

        private void HandleMessage(GlobalRequestMessage message)
        {
            this.OnGlobalRequestReceived(message);
        }

        private void HandleMessage(RequestSuccessMessage message)
        {
            this.OnRequestSuccessReceived(message);
        }

        private void HandleMessage(RequestFailureMessage message)
        {
            this.OnRequestFailureReceived(message);
        }

        private void HandleMessage(ChannelOpenMessage message)
        {
            this.OnChannelOpenReceived(message);
        }

        private void HandleMessage(ChannelOpenConfirmationMessage message)
        {
            this.OnChannelOpenConfirmationReceived(message);
        }

        private void HandleMessage(ChannelOpenFailureMessage message)
        {
            this.OnChannelOpenFailureReceived(message);
        }

        private void HandleMessage(ChannelWindowAdjustMessage message)
        {
            this.OnChannelWindowAdjustReceived(message);
        }

        private void HandleMessage(ChannelDataMessage message)
        {
            this.OnChannelDataReceived(message);
        }

        private void HandleMessage(ChannelExtendedDataMessage message)
        {
            this.OnChannelExtendedDataReceived(message);
        }

        private void HandleMessage(ChannelEofMessage message)
        {
            this.OnChannelEofReceived(message);
        }

        private void HandleMessage(ChannelCloseMessage message)
        {
            this.OnChannelCloseReceived(message);
        }

        private void HandleMessage(ChannelRequestMessage message)
        {
            this.OnChannelRequestReceived(message);
        }

        private void HandleMessage(ChannelSuccessMessage message)
        {
            this.OnChannelSuccessReceived(message);
        }

        private void HandleMessage(ChannelFailureMessage message)
        {
            this.OnChannelFailureReceived(message);
        }

        #endregion

        #region Handle received message events

        /// <summary>
        /// Called when <see cref="DisconnectMessage"/> received.
        /// </summary>
        /// <param name="message"><see cref="DisconnectMessage"/> message.</param>
        protected virtual void OnDisconnectReceived(DisconnectMessage message)
        {
            if (this.DisconnectReceived != null)
            {
                this.DisconnectReceived(this, new MessageEventArgs<DisconnectMessage>(message));
            }

            if (this.Disconnected != null)
            {
                this.Disconnected(this, new EventArgs());
            }
        }

        /// <summary>
        /// Called when <see cref="IgnoreMessage"/> received.
        /// </summary>
        /// <param name="message"><see cref="IgnoreMessage"/> message.</param>
        protected virtual void OnIgnoreReceived(IgnoreMessage message)
        {
            if (this.IgnoreReceived != null)
            {
                this.IgnoreReceived(this, new MessageEventArgs<IgnoreMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="UnimplementedMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="UnimplementedMessage"/> message.</param>
        protected virtual void OnUnimplementedReceived(UnimplementedMessage message)
        {
            if (this.UnimplementedReceived != null)
            {
                this.UnimplementedReceived(this, new MessageEventArgs<UnimplementedMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="DebugMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="DebugMessage"/> message.</param>
        protected virtual void OnDebugReceived(DebugMessage message)
        {
            if (this.DebugReceived != null)
            {
                this.DebugReceived(this, new MessageEventArgs<DebugMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ServiceRequestMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ServiceRequestMessage"/> message.</param>
        protected virtual void OnServiceRequestReceived(ServiceRequestMessage message)
        {
            if (this.ServiceRequestReceived != null)
            {
                this.ServiceRequestReceived(this, new MessageEventArgs<ServiceRequestMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ServiceAcceptMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ServiceAcceptMessage"/> message.</param>
        protected virtual void OnServiceAcceptReceived(ServiceAcceptMessage message)
        {
            if (this.ServiceAcceptReceived != null)
            {
                this.ServiceAcceptReceived(this, new MessageEventArgs<ServiceAcceptMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="KeyExchangeInitMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="KeyExchangeInitMessage"/> message.</param>
        protected virtual void OnKeyExchangeInitReceived(KeyExchangeInitMessage message)
        {
            this._keyExchangeCompletedWaitHandle.Reset();

            //  Disable all registered messages except key exchange related
            foreach (var messageMetadata in this._messagesMetadata)
            {
                if (messageMetadata.Activated == true && messageMetadata.Number > 2 && (messageMetadata.Number < 20 || messageMetadata.Number > 30))
                    messageMetadata.Enabled = false;
            }

            var keyExchangeAlgorithmName = (from c in this.ConnectionInfo.KeyExchangeAlgorithms.Keys
                                            from s in message.KeyExchangeAlgorithms
                                            where s == c
                                            select c).FirstOrDefault();

            if (keyExchangeAlgorithmName == null)
            {
                throw new SshConnectionException("Failed to negotiate key exchange algorithm.", DisconnectReason.KeyExchangeFailed);
            }

            //  Create instance of key exchange algorithm that will be used
            this._keyExchange = this.ConnectionInfo.KeyExchangeAlgorithms[keyExchangeAlgorithmName].CreateInstance<KeyExchange>();

            //  Start the algorithm implementation
            this._keyExchange.Start(this, message);

            if (this.KeyExchangeInitReceived != null)
            {
                this.KeyExchangeInitReceived(this, new MessageEventArgs<KeyExchangeInitMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="NewKeysMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="NewKeysMessage"/> message.</param>
        protected virtual void OnNewKeysReceived(NewKeysMessage message)
        {
            //  Update sessionId
            if (this.SessionId == null)
            {
                this.SessionId = this._keyExchange.ExchangeHash;
            }

            //  Dispose of old ciphers and hash algorithms
            if (this._serverCipher != null)
            {
                this._serverCipher.Dispose();
                this._serverCipher = null;
            }

            if (this._clientCipher != null)
            {
                this._clientCipher.Dispose();
                this._clientCipher = null;
            }

            if (this._serverMac != null)
            {
                this._serverMac.Dispose();
                this._serverMac = null;
            }

            if (this._clientMac != null)
            {
                this._clientMac.Dispose();
                this._clientMac = null;
            }

            //  Update negotiated algorithms
            this._serverCipher = this._keyExchange.CreateServerCipher();
            this._clientCipher = this._keyExchange.CreateClientCipher();
            this._serverMac = this._keyExchange.CreateServerHash();
            this._clientMac = this._keyExchange.CreateClientHash();
            this._clientCompression = this._keyExchange.CreateCompressor();
            this._serverDecompression = this._keyExchange.CreateDecompressor();

            //  Dispose of old KeyExchange object as it is no longer needed.
            if (this._keyExchange != null)
            {
                this._keyExchange.Dispose();
                this._keyExchange = null;
            }

            //  Enable all active registered messages
            foreach (var messageMetadata in this._messagesMetadata)
            {
                if (messageMetadata.Activated == true)
                    messageMetadata.Enabled = true;
            }

            if (this.NewKeysReceived != null)
            {
                this.NewKeysReceived(this, new MessageEventArgs<NewKeysMessage>(message));
            }

            //  Signal that key exchange completed
            this._keyExchangeCompletedWaitHandle.Set();
        }

        /// <summary>
        /// Called when <see cref="RequestMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="RequestMessage"/> message.</param>
        protected virtual void OnUserAuthenticationRequestReceived(RequestMessage message)
        {
            if (this.UserAuthenticationRequestReceived != null)
            {
                this.UserAuthenticationRequestReceived(this, new MessageEventArgs<RequestMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="FailureMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="FailureMessage"/> message.</param>
        protected virtual void OnUserAuthenticationFailureReceived(FailureMessage message)
        {
            if (this.UserAuthenticationFailureReceived != null)
            {
                this.UserAuthenticationFailureReceived(this, new MessageEventArgs<FailureMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="SuccessMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="SuccessMessage"/> message.</param>
        protected virtual void OnUserAuthenticationSuccessReceived(SuccessMessage message)
        {
            if (this.UserAuthenticationSuccessReceived != null)
            {
                this.UserAuthenticationSuccessReceived(this, new MessageEventArgs<SuccessMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="BannerMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="BannerMessage"/> message.</param>
        protected virtual void OnUserAuthenticationBannerReceived(BannerMessage message)
        {
            if (this.UserAuthenticationBannerReceived != null)
            {
                this.UserAuthenticationBannerReceived(this, new MessageEventArgs<BannerMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="GlobalRequestMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="GlobalRequestMessage"/> message.</param>
        protected virtual void OnGlobalRequestReceived(GlobalRequestMessage message)
        {
            if (this.GlobalRequestReceived != null)
            {
                this.GlobalRequestReceived(this, new MessageEventArgs<GlobalRequestMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="RequestSuccessMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="RequestSuccessMessage"/> message.</param>
        protected virtual void OnRequestSuccessReceived(RequestSuccessMessage message)
        {
            if (this.RequestSuccessReceived != null)
            {
                this.RequestSuccessReceived(this, new MessageEventArgs<RequestSuccessMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="RequestFailureMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="RequestFailureMessage"/> message.</param>
        protected virtual void OnRequestFailureReceived(RequestFailureMessage message)
        {
            if (this.RequestFailureReceived != null)
            {
                this.RequestFailureReceived(this, new MessageEventArgs<RequestFailureMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelOpenMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelOpenMessage"/> message.</param>
        protected virtual void OnChannelOpenReceived(ChannelOpenMessage message)
        {
            if (this.ChannelOpenReceived != null)
            {
                this.ChannelOpenReceived(this, new MessageEventArgs<ChannelOpenMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelOpenConfirmationMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelOpenConfirmationMessage"/> message.</param>
        protected virtual void OnChannelOpenConfirmationReceived(ChannelOpenConfirmationMessage message)
        {
            if (this.ChannelOpenConfirmationReceived != null)
            {
                this.ChannelOpenConfirmationReceived(this, new MessageEventArgs<ChannelOpenConfirmationMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelOpenFailureMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelOpenFailureMessage"/> message.</param>
        protected virtual void OnChannelOpenFailureReceived(ChannelOpenFailureMessage message)
        {
            if (this.ChannelOpenFailureReceived != null)
            {
                this.ChannelOpenFailureReceived(this, new MessageEventArgs<ChannelOpenFailureMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelWindowAdjustMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelWindowAdjustMessage"/> message.</param>
        protected virtual void OnChannelWindowAdjustReceived(ChannelWindowAdjustMessage message)
        {
            if (this.ChannelWindowAdjustReceived != null)
            {
                this.ChannelWindowAdjustReceived(this, new MessageEventArgs<ChannelWindowAdjustMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelDataMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelDataMessage"/> message.</param>
        protected virtual void OnChannelDataReceived(ChannelDataMessage message)
        {
            if (this.ChannelDataReceived != null)
            {
                this.ChannelDataReceived(this, new MessageEventArgs<ChannelDataMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelExtendedDataMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelExtendedDataMessage"/> message.</param>
        protected virtual void OnChannelExtendedDataReceived(ChannelExtendedDataMessage message)
        {
            if (this.ChannelExtendedDataReceived != null)
            {
                this.ChannelExtendedDataReceived(this, new MessageEventArgs<ChannelExtendedDataMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelCloseMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelCloseMessage"/> message.</param>
        protected virtual void OnChannelEofReceived(ChannelEofMessage message)
        {
            if (this.ChannelEofReceived != null)
            {
                this.ChannelEofReceived(this, new MessageEventArgs<ChannelEofMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelCloseMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelCloseMessage"/> message.</param>
        protected virtual void OnChannelCloseReceived(ChannelCloseMessage message)
        {
            if (this.ChannelCloseReceived != null)
            {
                this.ChannelCloseReceived(this, new MessageEventArgs<ChannelCloseMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelRequestMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelRequestMessage"/> message.</param>
        protected virtual void OnChannelRequestReceived(ChannelRequestMessage message)
        {
            if (this.ChannelRequestReceived != null)
            {
                this.ChannelRequestReceived(this, new MessageEventArgs<ChannelRequestMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelSuccessMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelSuccessMessage"/> message.</param>
        protected virtual void OnChannelSuccessReceived(ChannelSuccessMessage message)
        {
            if (this.ChannelSuccessReceived != null)
            {
                this.ChannelSuccessReceived(this, new MessageEventArgs<ChannelSuccessMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="ChannelFailureMessage"/> message received.
        /// </summary>
        /// <param name="message"><see cref="ChannelFailureMessage"/> message.</param>
        protected virtual void OnChannelFailureReceived(ChannelFailureMessage message)
        {
            if (this.ChannelFailureReceived != null)
            {
                this.ChannelFailureReceived(this, new MessageEventArgs<ChannelFailureMessage>(message));
            }
        }

        /// <summary>
        /// Called when <see cref="Message"/> message received.
        /// </summary>
        /// <param name="message"><see cref="Message"/> message.</param>
        protected virtual void OnMessageReceived(Message message)
        {
            if (this.MessageReceived != null)
            {
                this.MessageReceived(this, new MessageEventArgs<Message>(message));
            }
        }

        #endregion

        #region Read & Write operations

        /// <summary>
        /// Reads the specified length of bytes from the server
        /// </summary>
        /// <param name="length">The length.</param>
        /// <returns></returns>
        private byte[] Read(int length)
        {
            var buffer = new byte[length];
            var offset = 0;
            int receivedTotal = 0;  // how many bytes is already received

            do
            {
                try
                {
                    var receivedBytes = this._socket.Receive(buffer, offset + receivedTotal, length - receivedTotal, SocketFlags.None);
                    if (receivedBytes > 0)
                    {
                        receivedTotal += receivedBytes;
                        continue;
                    }
                    else
                    {
                        throw new SshConnectionException("An established connection was aborted by the software in your host machine.", DisconnectReason.ConnectionLost);
                    }
                }
                catch (SocketException exp)
                {
                    if (exp.SocketErrorCode == SocketError.WouldBlock ||
                        exp.SocketErrorCode == SocketError.IOPending ||
                        exp.SocketErrorCode == SocketError.NoBufferSpaceAvailable)
                    {
                        // socket buffer is probably empty, wait and try again
                        Thread.Sleep(30);
                    }
                    else
                        throw;  // any serious error occurred
                }
            } while (receivedTotal < length);

            return buffer;
        }

        /// <summary>
        /// Writes the specified data to the server.
        /// </summary>
        /// <param name="data">The data.</param>
        private void Write(byte[] data)
        {
            int sent = 0;  // how many bytes is already sent
            int length = data.Length;

            do
            {
                try
                {
                    sent += this._socket.Send(data, sent, length - sent, SocketFlags.None);
                }
                catch (SocketException ex)
                {
                    if (ex.SocketErrorCode == SocketError.WouldBlock ||
                        ex.SocketErrorCode == SocketError.IOPending ||
                        ex.SocketErrorCode == SocketError.NoBufferSpaceAvailable)
                    {
                        // socket buffer is probably full, wait and try again
                        Thread.Sleep(30);
                    }
                    else
                        throw;  // any serious error occurr
                }
            } while (sent < length);
        }

        #endregion

        #region Message loading functions

        /// <summary>
        /// Registers SSH Message with the session.
        /// </summary>
        /// <param name="messageName">Name of the message.</param>
        public void RegisterMessage(string messageName)
        {
            lock (this._messagesMetadata)
            {
                Parallel.ForEach(
                    from m in this._messagesMetadata where m.Name == messageName select m,
                    (item) => { item.Enabled = true; item.Activated = true; });
            }
        }

        /// <summary>
        /// Removes SSH message from the session
        /// </summary>
        /// <param name="messageName">Name of the message.</param>
        public void UnRegisterMessage(string messageName)
        {
            lock (this._messagesMetadata)
            {
                Parallel.ForEach(
                    from m in this._messagesMetadata where m.Name == messageName select m,
                    (item) => { item.Enabled = false; item.Activated = false; });
            }
        }

        /// <summary>
        /// Loads the message.
        /// </summary>
        /// <param name="data">Message data.</param>
        /// <returns>New message</returns>
        private Message LoadMessage(byte[] data)
        {
            var messageType = data[0];
            var messageMetadata = (from m in this._messagesMetadata where m.Number == messageType && m.Enabled && m.Activated select m).SingleOrDefault();

            if (messageMetadata == null)
                throw new SshException(string.Format(CultureInfo.CurrentCulture, "Message type {0} is not valid.", messageType));

            var message = messageMetadata.Type.CreateInstance<Message>();

            message.Load(data);

            return message;
        }

        #endregion

        /// <summary>
        /// Listens for incoming message from the server and handles them. This method run as a task on separate thread.
        /// </summary>
        private void MessageListener()
        {
            try
            {
                while (this._socket.Connected)
                {
                    var message = this.ReceiveMessage();

                    if (message == null)
                    {
                        throw new NullReferenceException("The 'message' variable cannot be null");
                    }
                    else
                    {
                        this.HandleMessage((dynamic)message);
                    }
                }
            }
            catch (Exception exp)
            {
                this.RaiseError(exp);
            }
        }

        /// <summary>
        /// Raises the <see cref="ErrorOccured"/> event.
        /// </summary>
        /// <param name="exp">The exp.</param>
        private void RaiseError(Exception exp)
        {
            var connectionException = exp as SshConnectionException;

            //  If connection exception was raised while isDisconnecting is true then this is expected
            //  case and should be ignore
            if (connectionException != null && this._isDisconnecting)
                return;

            this._exception = exp;

            this._exceptionWaitHandle.Set();

            if (this.ErrorOccured != null)
            {
                this.ErrorOccured(this, new ExceptionEventArgs(exp));
            }

            if (connectionException != null && connectionException.DisconnectReason != DisconnectReason.ConnectionLost)
            {
                this.SendDisconnect(connectionException.DisconnectReason, exp.ToString());
            }
        }

        #region IDisposable Members

        private bool _disposed = false;

        /// <summary>
        /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged ResourceMessages.
        /// </summary>
        public void Dispose()
        {
            Dispose(true);

            GC.SuppressFinalize(this);
        }

        /// <summary>
        /// Releases unmanaged and - optionally - managed resources
        /// </summary>
        /// <param name="disposing"><c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged ResourceMessages.</param>
        protected virtual void Dispose(bool disposing)
        {
            // Check to see if Dispose has already been called.
            if (!this._disposed)
            {
                // If disposing equals true, dispose all managed
                // and unmanaged ResourceMessages.
                if (disposing)
                {
                    this._isDisconnecting = true;

                    if (this._socket != null)
                    {
                        //  If socket still open try to send disconnect message to the server
                        this.SendDisconnect(DisconnectReason.ByApplication, "Connection terminated by the client.");

                        this._socket.Dispose();
                        this._socket = null;
                    }

                    if (this._messageListener != null)
                    {
                        //  Wait for socket to be closed and for task to complete before disposing a task
                        this._messageListener.Wait();
                        this._messageListener.Dispose();
                        this._messageListener = null;
                    }

                    if (this._serviceAccepted != null)
                    {
                        this._serviceAccepted.Dispose();
                        this._serviceAccepted = null;
                    }

                    if (this._exceptionWaitHandle != null)
                    {
                        this._exceptionWaitHandle.Dispose();
                        this._exceptionWaitHandle = null;
                    }

                    if (this._sessionSemaphore != null)
                    {
                        this._sessionSemaphore.Dispose();
                        this._sessionSemaphore = null;
                    }

                    if (this._keyExchangeCompletedWaitHandle != null)
                    {
                        this._keyExchangeCompletedWaitHandle.Dispose();
                        this._keyExchangeCompletedWaitHandle = null;
                    }

                    if (this._serverCipher != null)
                    {
                        this._serverCipher.Dispose();
                        this._serverCipher = null;
                    }

                    if (this._clientCipher != null)
                    {
                        this._clientCipher.Dispose();
                        this._clientCipher = null;
                    }

                    if (this._serverMac != null)
                    {
                        this._serverMac.Dispose();
                        this._serverMac = null;
                    }

                    if (this._clientMac != null)
                    {
                        this._clientMac.Dispose();
                        this._clientMac = null;
                    }

                    if (this._keyExchange != null)
                    {
                        this._keyExchange.Dispose();
                        this._keyExchange = null;
                    }
                }

                // Note disposing has been done.
                this._disposed = true;
            }
        }

        /// <summary>
        /// Releases unmanaged resources and performs other cleanup operations before the
        /// <see cref="Session"/> is reclaimed by garbage collection.
        /// </summary>
        ~Session()
        {
            // Do not re-create Dispose clean-up code here.
            // Calling Dispose(false) is optimal in terms of
            // readability and maintainability.
            Dispose(false);
        }

        #endregion

        private class MessageMetadata
        {
            public string Name { get; set; }

            public byte Number { get; set; }

            public bool Enabled { get; set; }

            public bool Activated { get; set; }

            public Type Type { get; set; }
        }
    }
}