public class FTPClient
    {
        private string remoteHost;
        private string remoteUser;
        private string remotePass;
        private string remotePath;

        private int remotePort = 21;
        private int bytes;
        private Socket clientSocket;

        private int retValue;
        private Boolean logined;
        private string reply;
        private string mes = "";

        private static int BLOCK_SIZE = 512;

        Byte[] buffer = new Byte[BLOCK_SIZE];
        Encoding ASCII = Encoding.ASCII;

        public FTPClient(string host, string user, string password)
        {
            remoteHost = host;
            remoteUser = user;
            remotePass = password;
            Login();
        }

        public void Login()
        {
            clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            IPEndPoint ep = new IPEndPoint(Dns.Resolve(remoteHost).AddressList[0], remotePort);

            try
            {
                clientSocket.Connect(ep);
            }
            catch (Exception)
            {
                throw new IOException("Couldn't connect to remote server");
            }

            ReadReply();
            if (retValue != 220)
            {
                Close();
                throw new IOException(reply.Substring(4));
            }

            SendCommand("USER " + remoteUser);
            if (!(retValue == 331 || retValue == 230))
            {
                CleanUp();
                throw new IOException(reply.Substring(4));
            }

            if (retValue != 230)
            {
                SendCommand("PASS " + remotePass);
                if (!(retValue == 230 || retValue == 202))
                {
                    CleanUp();
                    throw new IOException(reply.Substring(4));
                }
            }

            logined = true;
        }

        private void ChangeDir(string dirName)
        {
            if (dirName.Equals("."))
            {
                return;
            }

            SendCommand("CWD " + dirName);

            if (retValue != 250)
            {
                throw new IOException(reply.Substring(4));
            }

            this.remotePath = dirName;
        }

        private void ReadReply()
        {
            mes = "";
            reply = ReadLine();
            retValue = Int32.Parse(reply.Substring(0, 3));
        }

        private string ReadLine()
        {
            while (true)
            {
                bytes = clientSocket.Receive(buffer, buffer.Length, 0);
                mes += ASCII.GetString(buffer, 0, bytes);
                if (bytes < buffer.Length)
                {
                    break;
                }
            }

            string[] messages = mes.Split('\n');

            if (mes.Length > 2)
            {
                mes = messages[messages.Length - 2];
            }
            else
            {
                mes = messages[0];
            }

            if (!mes.Substring(3, 1).Equals(" "))
            {
                return ReadLine();
            }

            return mes;
        }

        private void SendCommand(string command)
        {
            Byte[] cmdBytes = Encoding.ASCII.GetBytes((command + "\r\n").ToCharArray());
            clientSocket.Send(cmdBytes, cmdBytes.Length, 0);
            ReadReply();
        }

        public void Close()
        {
            if (clientSocket != null)
            {
                SendCommand("QUIT");
            }

            CleanUp();
        }

        public void CleanUp()
        {
            if (clientSocket != null)
            {
                clientSocket.Close();
                clientSocket = null;
            }
            logined = false;
        }

        public void UploadFile(string fileName, Stream filePosted)
        {
            Socket cSocket = CreateDataSocket();
            //long offset = 0;

            //if (resume)
            //{
            //    try
            //    {
            //        SetBinaryMode(true);
            //        offset = getFileSize(fileName);
            //    }
            //    catch (Exception)
            //    {
            //        offset = 0;
            //    }
            //}

            //if (offset > 0)
            //{
            //    SendCommand("REST " + offset);
            //    if (retValue != 350)
            //    {
            //        offset = 0;
            //    }
            //}

            SendCommand("STOR " + fileName);

            if (!(retValue == 125 || retValue == 150))
            {
                throw new IOException(reply.Substring(4));
            }

            while ((bytes = filePosted.Read(buffer, 0, buffer.Length)) > 0)
            {
                cSocket.Send(buffer, bytes, 0);
            }

            filePosted.Close();
            if (cSocket.Connected)
            {
                cSocket.Close();
            }

            ReadReply();
            if (!(retValue == 226 || retValue == 250))
            {
                throw new IOException(reply.Substring(4));
            }
        }

        private Socket CreateDataSocket()
        {
            SendCommand("PASV");

            if (retValue != 227)
            {
                throw new IOException(reply.Substring(4));
            }

            int index1 = reply.IndexOf('(');
            int index2 = reply.IndexOf(')');
            string ipData = reply.Substring(index1 + 1, index2 - index1 - 1);
            int[] parts = new int[6];

            int len = ipData.Length;
            int partCount = 0;
            string buf = "";

            for (int i = 0; i < len && partCount <= 6; i++)
            {

                char ch = Char.Parse(ipData.Substring(i, 1));
                if (Char.IsDigit(ch))
                    buf += ch;
                else if (ch != ',')
                {
                    throw new IOException("Malformed PASV reply: " + reply);
                }

                if (ch == ',' || i + 1 == len)
                {

                    try
                    {
                        parts[partCount++] = Int32.Parse(buf);
                        buf = "";
                    }
                    catch (Exception)
                    {
                        throw new IOException("Malformed PASV reply: " + reply);
                    }
                }
            }

            string ipAddress = parts[0] + "." + parts[1] + "." +
              parts[2] + "." + parts[3];

            int port = (parts[4] << 8) + parts[5];

            Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            IPEndPoint ep = new IPEndPoint(Dns.Resolve(ipAddress).AddressList[0], port);

            try
            {
                s.Connect(ep);
            }
            catch (Exception)
            {
                throw new IOException("Can't connect to remote server");
            }

            return s;
        }

        private void SetBinaryMode(bool mode)
        {
            if (mode)
            {
                SendCommand("TYPE I");
            }
            else
            {
                SendCommand("TYPE A");
            }

            if (retValue != 200)
            {
                throw new IOException(reply.Substring(4));
            }
        }
    }