diff --git a/src/main/java/ru/redguy/tftpserver/CheckSum.java b/src/main/java/ru/redguy/tftpserver/CheckSum.java
index 5f7dd3d..9870905 100644
--- a/src/main/java/ru/redguy/tftpserver/CheckSum.java
+++ b/src/main/java/ru/redguy/tftpserver/CheckSum.java
@@ -5,31 +5,33 @@ import java.security.MessageDigest;
 
 
 public class CheckSum {
-	static String getChecksum(String fileName) {
-		StringBuffer sb = new StringBuffer("");
-		try {
-			String datafile = fileName;
-			//use SHA1 to calculate checksum
-			MessageDigest md = MessageDigest.getInstance("SHA1");
-			FileInputStream fis = new FileInputStream(datafile);
-			byte[] dataBytes = new byte[1024];
+    static String getChecksum(String fileName) {
+        StringBuffer sb = new StringBuffer("");
+        try {
+            String datafile = fileName;
+            //use SHA1 to calculate checksum
+            MessageDigest md = MessageDigest.getInstance("SHA1");
+            FileInputStream fis = new FileInputStream(datafile);
+            byte[] dataBytes = new byte[1024];
 
-			int nread = 0;
+            int nread = 0;
 
-			while ((nread = fis.read(dataBytes)) != -1) {
-				md.update(dataBytes, 0, nread);
-			}
-			fis.close();
+            while ((nread = fis.read(dataBytes)) != -1) {
+                md.update(dataBytes, 0, nread);
+            }
+            fis.close();
 
-			byte[] mdbytes = md.digest();
+            byte[] mdbytes = md.digest();
 
-			// convert the byte to hex format
-			for (int i = 0; i < mdbytes.length; i++) {
-				sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
-			}
+            // convert the byte to hex format
+            for (int i = 0; i < mdbytes.length; i++) {
+                sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
+            }
 
-		} catch (Exception e){System.out.println("Generate Checksum Failed: "+e.getMessage());}
-		
-		return sb.toString();
-	}
-	}
+        } catch (Exception e) {
+            System.out.println("Generate Checksum Failed: " + e.getMessage());
+        }
+
+        return sb.toString();
+    }
+}
diff --git a/src/main/java/ru/redguy/tftpserver/ErrorEvent.java b/src/main/java/ru/redguy/tftpserver/ErrorEvent.java
index 2db6152..9bc27b1 100644
--- a/src/main/java/ru/redguy/tftpserver/ErrorEvent.java
+++ b/src/main/java/ru/redguy/tftpserver/ErrorEvent.java
@@ -2,8 +2,12 @@ package ru.redguy.tftpserver;
 
 public interface ErrorEvent {
     public void onPacketReceiveException(Exception exception);
+
     public void onPacketReadException(Exception exception);
+
     public void onPacketWriteException(Exception exception);
+
     public void onClientReadException(Exception exception, TFTPread tftPread);
+
     public void onClientWriteException(Exception exception, TFTPwrite tftPwrite);
 }
diff --git a/src/main/java/ru/redguy/tftpserver/TFTPServer.java b/src/main/java/ru/redguy/tftpserver/TFTPServer.java
index 4ea6a2e..9330e02 100644
--- a/src/main/java/ru/redguy/tftpserver/TFTPServer.java
+++ b/src/main/java/ru/redguy/tftpserver/TFTPServer.java
@@ -1,87 +1,88 @@
 package ru.redguy.tftpserver;
 
-import java.net.*;
-import java.io.*;
+import java.io.IOException;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.net.SocketException;
+import java.net.UnknownHostException;
 
 public class TFTPServer {
 
-	private DatagramSocket socket;
-	private Runner runner;
-	private Thread thread;
-	private ErrorEvent errorEvent;
+    private DatagramSocket socket;
+    private Runner runner;
+    private Thread thread;
+    private ErrorEvent errorEvent;
 
-	public void start() throws SocketException {
-		start(69);
-	}
+    public void start() throws SocketException {
+        start(69);
+    }
 
-	public void start(int port) throws SocketException {
-		socket = new DatagramSocket(port);
-		runner = new Runner(socket,this);
-		thread = new Thread(runner);
-		thread.setDaemon(true);
-		thread.start();
-	}
+    public void start(int port) throws SocketException {
+        socket = new DatagramSocket(port);
+        runner = new Runner(socket, this);
+        thread = new Thread(runner);
+        thread.setDaemon(true);
+        thread.start();
+    }
 
-	public void start(String host, int port) throws UnknownHostException, SocketException {
-		socket = new DatagramSocket(port,InetAddress.getByName(host));
-		runner = new Runner(socket,this);
-		thread.setDaemon(true);
-		thread.start();
-	}
+    public void start(String host, int port) throws UnknownHostException, SocketException {
+        socket = new DatagramSocket(port, InetAddress.getByName(host));
+        runner = new Runner(socket, this);
+        thread.setDaemon(true);
+        thread.start();
+    }
 
-	public int getPort() {
-		return socket.getLocalPort();
-	}
+    public int getPort() {
+        return socket.getLocalPort();
+    }
 
-	public void stop() {
-		thread.interrupt();
-	}
+    public void stop() {
+        thread.interrupt();
+    }
 
-	public void onError(ErrorEvent event) {
-		this.errorEvent = event;
-	}
+    public void onError(ErrorEvent event) {
+        this.errorEvent = event;
+    }
 
-	static class Runner implements Runnable {
+    static class Runner implements Runnable {
 
-		DatagramSocket datagramSocket;
-		TFTPServer server;
-		boolean run = true;
+        DatagramSocket datagramSocket;
+        TFTPServer server;
+        boolean run = true;
 
-		public Runner(DatagramSocket socket,TFTPServer server) {
-			this.datagramSocket = socket;
-			this.server = server;
-		}
+        public Runner(DatagramSocket socket, TFTPServer server) {
+            this.datagramSocket = socket;
+            this.server = server;
+        }
 
-		public void stop() {
-			run = false;
-		}
+        public void stop() {
+            run = false;
+        }
 
-		@Override
-		public void run() {
-			while (run) {
-				TFTPpacket in = null;
-				try {
-					in = TFTPpacket.receive(datagramSocket);
-				} catch (IOException e) {
-					server.errorEvent.onPacketReceiveException(e);
-				}
+        @Override
+        public void run() {
+            while (run) {
+                TFTPpacket in = null;
+                try {
+                    in = TFTPpacket.receive(datagramSocket);
+                } catch (IOException e) {
+                    server.errorEvent.onPacketReceiveException(e);
+                }
 
-				if (in instanceof TFTPread) {
-					try {
-						TFTPserverRRQ r = new TFTPserverRRQ((TFTPread) in, server.errorEvent);
-					} catch (TftpException e) {
-						server.errorEvent.onPacketReadException(e);
-					}
-				}
-
-				else if (in instanceof TFTPwrite) {
-					try {
-						TFTPserverWRQ w = new TFTPserverWRQ((TFTPwrite) in, server.errorEvent);
-					} catch (TftpException e) {
-						server.errorEvent.onPacketWriteException(e);
-					}
-				}
-			}
-		}
-	}
+                if (in instanceof TFTPread) {
+                    try {
+                        TFTPserverRRQ r = new TFTPserverRRQ((TFTPread) in, server.errorEvent);
+                    } catch (TftpException e) {
+                        server.errorEvent.onPacketReadException(e);
+                    }
+                } else if (in instanceof TFTPwrite) {
+                    try {
+                        TFTPserverWRQ w = new TFTPserverWRQ((TFTPwrite) in, server.errorEvent);
+                    } catch (TftpException e) {
+                        server.errorEvent.onPacketWriteException(e);
+                    }
+                }
+            }
+        }
+    }
 }
\ No newline at end of file
diff --git a/src/main/java/ru/redguy/tftpserver/TFTPpacket.java b/src/main/java/ru/redguy/tftpserver/TFTPpacket.java
index facd393..54836ad 100644
--- a/src/main/java/ru/redguy/tftpserver/TFTPpacket.java
+++ b/src/main/java/ru/redguy/tftpserver/TFTPpacket.java
@@ -1,132 +1,138 @@
 package ru.redguy.tftpserver;
 
-import java.net.*;
-import java.io.*;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
 
 class TftpException extends Exception {
-	public TftpException() {
-		super();
-	}
-	public TftpException(String s) {
-		super(s);
-	}
+    public TftpException() {
+        super();
+    }
+
+    public TftpException(String s) {
+        super(s);
+    }
 }
+
 //////////////////////////////////////////////////////////////////////////////
 //GENERAL packet: define the packet structure, necessary members and methods// 
 //of TFTP packet. To be extended by other specific packet(read, write, etc) //
 //////////////////////////////////////////////////////////////////////////////
 public class TFTPpacket {
 
-  // TFTP constants
-  public static int tftpPort = 69;
-  public static int maxTftpPakLen=516;
-  public static int maxTftpData=512;
+    // TFTP constants
+    public static int tftpPort = 69;
+    public static int maxTftpPakLen = 516;
+    public static int maxTftpData = 512;
 
-  // Tftp opcodes
-  protected static final short tftpRRQ=1;
-  protected static final short tftpWRQ=2;
-  protected static final short tftpDATA=3;
-  protected static final short tftpACK=4;
-  protected static final short tftpERROR=5;
+    // Tftp opcodes
+    protected static final short tftpRRQ = 1;
+    protected static final short tftpWRQ = 2;
+    protected static final short tftpDATA = 3;
+    protected static final short tftpACK = 4;
+    protected static final short tftpERROR = 5;
 
-  // Packet Offsets
-  protected static final int opOffset=0;
+    // Packet Offsets
+    protected static final int opOffset = 0;
 
-  protected static final int fileOffset=2;
+    protected static final int fileOffset = 2;
 
-  protected static final int blkOffset=2;
-  protected static final int dataOffset=4;
+    protected static final int blkOffset = 2;
+    protected static final int dataOffset = 4;
 
-  protected static final int numOffset=2;
-  protected static final int msgOffset=4;
+    protected static final int numOffset = 2;
+    protected static final int msgOffset = 4;
 
-  // The actual packet for UDP transfer
-  protected byte [] message;
-  protected int length;
+    // The actual packet for UDP transfer
+    protected byte[] message;
+    protected int length;
 
-  // Address info (required for replies)
-  protected InetAddress host;
-  protected int port;
+    // Address info (required for replies)
+    protected InetAddress host;
+    protected int port;
 
-  // Constructor 
-  public TFTPpacket() {
-    message=new byte[maxTftpPakLen]; 
-    length=maxTftpPakLen; 
-  } 
-
-  // Methods to receive packet and convert it to yhe right type(data/ack/read/...)
-  public static TFTPpacket receive(DatagramSocket sock) throws IOException {
-    TFTPpacket in=new TFTPpacket(), retPak=new TFTPpacket();
-    //receive data and put them into in.message
-    DatagramPacket inPak = new DatagramPacket(in.message,in.length);
-    sock.receive(inPak); 
-    
-    //Check the opcode in message, then cast the message into the corresponding type
-    switch (in.get(0)) {
-      case tftpRRQ:
-    	  retPak=new TFTPread();
-        break;
-      case tftpWRQ:
-    	  retPak=new TFTPwrite();
-        break;
-      case tftpDATA:
-    	  retPak=new TFTPdata();
-        break;
-      case tftpACK:
-    	  retPak=new TFTPack();
-        break;
-      case tftpERROR:
-    	  retPak=new TFTPerror();
-        break;
+    // Constructor
+    public TFTPpacket() {
+        message = new byte[maxTftpPakLen];
+        length = maxTftpPakLen;
     }
-    retPak.message=in.message;
-    retPak.length=inPak.getLength();
-    retPak.host=inPak.getAddress();
-    retPak.port=inPak.getPort();
 
-    return retPak;
-  }
-  
-  //Method to send packet
-  public void send(InetAddress ip, int port, DatagramSocket s) throws IOException {
-    s.send(new DatagramPacket(message,length,ip,port));
-  }
+    // Methods to receive packet and convert it to yhe right type(data/ack/read/...)
+    public static TFTPpacket receive(DatagramSocket sock) throws IOException {
+        TFTPpacket in = new TFTPpacket(), retPak = new TFTPpacket();
+        //receive data and put them into in.message
+        DatagramPacket inPak = new DatagramPacket(in.message, in.length);
+        sock.receive(inPak);
 
-  // DatagramPacket like methods
-  public InetAddress getAddress() {
-    return host;
-  }
+        //Check the opcode in message, then cast the message into the corresponding type
+        switch (in.get(0)) {
+            case tftpRRQ:
+                retPak = new TFTPread();
+                break;
+            case tftpWRQ:
+                retPak = new TFTPwrite();
+                break;
+            case tftpDATA:
+                retPak = new TFTPdata();
+                break;
+            case tftpACK:
+                retPak = new TFTPack();
+                break;
+            case tftpERROR:
+                retPak = new TFTPerror();
+                break;
+        }
+        retPak.message = in.message;
+        retPak.length = inPak.getLength();
+        retPak.host = inPak.getAddress();
+        retPak.port = inPak.getPort();
 
-  public int getPort() {
-    return port;
-  }
+        return retPak;
+    }
 
-  public int getLength() {
-    return length;
-  }
+    //Method to send packet
+    public void send(InetAddress ip, int port, DatagramSocket s) throws IOException {
+        s.send(new DatagramPacket(message, length, ip, port));
+    }
 
-  // Methods to put opcode, blkNum, error code into the byte array 'message'. 
-  protected void put(int at, short value) {
-    message[at++] = (byte)(value >>> 8);  // first byte
-    message[at] = (byte)(value % 256);    // last byte
-  }
+    // DatagramPacket like methods
+    public InetAddress getAddress() {
+        return host;
+    }
 
-  @SuppressWarnings("deprecation")
-  //Put the filename and mode into the 'message' at 'at' follow by byte "del"
-  protected void put(int at, String value, byte del) {
-    value.getBytes(0, value.length(), message, at);
-    message[at + value.length()] = del;
-  }
+    public int getPort() {
+        return port;
+    }
 
-  protected int get(int at) {
-    return (message[at] & 0xff) << 8 | message[at+1] & 0xff;
-  }
+    public int getLength() {
+        return length;
+    }
 
-  protected String get (int at, byte del) {
-    StringBuffer result = new StringBuffer();
-    while (message[at] != del) result.append((char)message[at++]);
-    return result.toString();
-  }
+    // Methods to put opcode, blkNum, error code into the byte array 'message'.
+    protected void put(int at, short value) {
+        message[at++] = (byte) (value >>> 8);  // first byte
+        message[at] = (byte) (value % 256);    // last byte
+    }
+
+    @SuppressWarnings("deprecation")
+    //Put the filename and mode into the 'message' at 'at' follow by byte "del"
+    protected void put(int at, String value, byte del) {
+        value.getBytes(0, value.length(), message, at);
+        message[at + value.length()] = del;
+    }
+
+    protected int get(int at) {
+        return (message[at] & 0xff) << 8 | message[at + 1] & 0xff;
+    }
+
+    protected String get(int at, byte del) {
+        StringBuffer result = new StringBuffer();
+        while (message[at] != del) result.append((char) message[at++]);
+        return result.toString();
+    }
 }
 
 ////////////////////////////////////////////////////////
@@ -135,35 +141,37 @@ public class TFTPpacket {
 ////////////////////////////////////////////////////////
 final class TFTPdata extends TFTPpacket {
 
-	// Constructors
-	protected TFTPdata() {}
-	public TFTPdata(int blockNumber, FileInputStream in) throws IOException {
-		this.message = new byte[maxTftpPakLen];
-		// manipulate message
-		this.put(opOffset, tftpDATA);
-		this.put(blkOffset, (short) blockNumber);
-		// read the file into packet and calculate the entire length
-		length = in.read(message, dataOffset, maxTftpData) + 4;
-	}
+    // Constructors
+    protected TFTPdata() {
+    }
 
-	// Accessors
+    public TFTPdata(int blockNumber, FileInputStream in) throws IOException {
+        this.message = new byte[maxTftpPakLen];
+        // manipulate message
+        this.put(opOffset, tftpDATA);
+        this.put(blkOffset, (short) blockNumber);
+        // read the file into packet and calculate the entire length
+        length = in.read(message, dataOffset, maxTftpData) + 4;
+    }
 
-	public int blockNumber() {
-		return this.get(blkOffset);
-	}
+    // Accessors
 
-	/*
-	 * public void data(byte[] buffer) { buffer = new byte[length-4];
-	 * 
-	 * for (int i=0; i<length-4; i++) buffer[i]=message[i+dataOffset]; }
-	 */
-	
-	// File output
-	public int write(FileOutputStream out) throws IOException {
-		out.write(message, dataOffset, length - 4);
+    public int blockNumber() {
+        return this.get(blkOffset);
+    }
 
-		return (length - 4);
-	}
+    /*
+     * public void data(byte[] buffer) { buffer = new byte[length-4];
+     *
+     * for (int i=0; i<length-4; i++) buffer[i]=message[i+dataOffset]; }
+     */
+
+    // File output
+    public int write(FileOutputStream out) throws IOException {
+        out.write(message, dataOffset, length - 4);
+
+        return (length - 4);
+    }
 }
 
 /////////////////////////////////////////////////////////
@@ -172,25 +180,27 @@ final class TFTPdata extends TFTPpacket {
 /////////////////////////////////////////////////////////
 class TFTPerror extends TFTPpacket {
 
-	// Constructors
-	protected TFTPerror() {
-	}
-	//Generate error packet
-	public TFTPerror(int number, String message) {
-		length = 4 + message.length() + 1;
-		this.message = new byte[length];
-		put(opOffset, tftpERROR);
-		put(numOffset, (short) number);
-		put(msgOffset, message, (byte) 0);
-	}
+    // Constructors
+    protected TFTPerror() {
+    }
 
-	// Accessors
-	public int number() {
-		return this.get(numOffset);
-	}
-	public String message() {
-		return this.get(msgOffset, (byte) 0);
-	}
+    //Generate error packet
+    public TFTPerror(int number, String message) {
+        length = 4 + message.length() + 1;
+        this.message = new byte[length];
+        put(opOffset, tftpERROR);
+        put(numOffset, (short) number);
+        put(msgOffset, message, (byte) 0);
+    }
+
+    // Accessors
+    public int number() {
+        return this.get(numOffset);
+    }
+
+    public String message() {
+        return this.get(msgOffset, (byte) 0);
+    }
 }
 
 /////////////////////////////////////////////////////////
@@ -199,21 +209,22 @@ class TFTPerror extends TFTPpacket {
 /////////////////////////////////////////////////////////
 final class TFTPack extends TFTPpacket {
 
-	// Constructors
-	protected TFTPack() {
-	}
-	//Generate ack packet
-	public TFTPack(int blockNumber) {
-		length = 4;
-		this.message = new byte[length];
-		put(opOffset, tftpACK);
-		put(blkOffset, (short) blockNumber);
-	}
+    // Constructors
+    protected TFTPack() {
+    }
 
-	// Accessors
-	public int blockNumber() {
-		return this.get(blkOffset);
-	}
+    //Generate ack packet
+    public TFTPack(int blockNumber) {
+        length = 4;
+        this.message = new byte[length];
+        put(opOffset, tftpACK);
+        put(blkOffset, (short) blockNumber);
+    }
+
+    // Accessors
+    public int blockNumber() {
+        return this.get(blkOffset);
+    }
 }
 
 
diff --git a/src/main/java/ru/redguy/tftpserver/TFTPserverRRQ.java b/src/main/java/ru/redguy/tftpserver/TFTPserverRRQ.java
index 8d6fc90..4d14050 100644
--- a/src/main/java/ru/redguy/tftpserver/TFTPserverRRQ.java
+++ b/src/main/java/ru/redguy/tftpserver/TFTPserverRRQ.java
@@ -1,97 +1,105 @@
 package ru.redguy.tftpserver;
 
-import java.net.*;
-import java.io.*;
+import java.io.File;
+import java.io.FileInputStream;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.net.SocketTimeoutException;
 
 
 class TFTPserverRRQ extends Thread {
 
-	protected DatagramSocket sock;
-	protected InetAddress host;
-	protected int port;
-	protected FileInputStream source;
-	protected TFTPpacket req;
-	protected int timeoutLimit=5;
-	protected String fileName;
+    protected DatagramSocket sock;
+    protected InetAddress host;
+    protected int port;
+    protected FileInputStream source;
+    protected TFTPpacket req;
+    protected int timeoutLimit = 5;
+    protected String fileName;
 
-	// initialize read request
-	public TFTPserverRRQ(TFTPread request, ErrorEvent event) throws TftpException {
-		try {
-			req = request;
-			//open new socket with random port num for tranfer
-			sock = new DatagramSocket();
-			sock.setSoTimeout(1000);
-			fileName = request.fileName();
+    // initialize read request
+    public TFTPserverRRQ(TFTPread request, ErrorEvent event) throws TftpException {
+        try {
+            req = request;
+            //open new socket with random port num for tranfer
+            sock = new DatagramSocket();
+            sock.setSoTimeout(1000);
+            fileName = request.fileName();
 
-			host = request.getAddress();
-			port = request.getPort();
-			
-			//create file object in parent folder
-			File srcFile = new File(fileName);
-			/*System.out.println("procce checking");*/
-			//check file
-			if (srcFile.exists() && srcFile.isFile() && srcFile.canRead()) {
-				source = new FileInputStream(srcFile);
-				this.start(); //open new thread for transfer
-			} else
-				throw new TftpException("access violation");
+            host = request.getAddress();
+            port = request.getPort();
 
-		} catch (Exception e) {
-			TFTPerror ePak = new TFTPerror(1, e.getMessage()); // error code 1
-			try {
-				ePak.send(host, port, sock);
-			} catch (Exception f) {
-			}
+            //create file object in parent folder
+            File srcFile = new File(fileName);
+            /*System.out.println("procce checking");*/
+            //check file
+            if (srcFile.exists() && srcFile.isFile() && srcFile.canRead()) {
+                source = new FileInputStream(srcFile);
+                this.start(); //open new thread for transfer
+            } else
+                throw new TftpException("access violation");
 
-			event.onClientReadException(e,request);
-		}
-	}
-	//everything is fine, open new thread to transfer file
-	public void run() {
-		int bytesRead = TFTPpacket.maxTftpPakLen;
-		// handle read request
-		if (req instanceof TFTPread) {
-			try {
-				for (int blkNum = 1; bytesRead == TFTPpacket.maxTftpPakLen; blkNum++) {
-					TFTPdata outPak = new TFTPdata(blkNum, source);
-					/*System.out.println("send block no. " + outPak.blockNumber()); */
-					bytesRead = outPak.getLength();
-					/*System.out.println("bytes sent:  " + bytesRead);*/
-					outPak.send(host, port, sock);
-					/*System.out.println("current op code  " + outPak.get(0)); */
-					
-					//wait for the correct ack. if incorrect, retry up to 5 times
-					while (timeoutLimit!=0) { 
-						try {
-							TFTPpacket ack = TFTPpacket.receive(sock);
-							if (!(ack instanceof TFTPack)){throw new Exception("Client failed");}
-							TFTPack a = (TFTPack) ack;
-							
-							if(a.blockNumber()!=blkNum){ //check ack
-								throw new SocketTimeoutException("last packet lost, resend packet");}
-							/*System.out.println("confirm blk num " + a.blockNumber()+" from "+a.getPort());*/
-							break;
-						} 
-						catch (SocketTimeoutException t) {//resend last packet
-							System.out.println("Resent blk " + blkNum);
-							timeoutLimit--;
-							outPak.send(host, port, sock);
-						}
-					} // end of while
-					if(timeoutLimit==0){throw new Exception("connection failed");}
-				}
-				System.out.println("Transfer completed.(Client " +host +")" );
-				System.out.println("Filename: "+fileName + "\nSHA1 checksum: "+CheckSum.getChecksum(fileName)+"\n");
-			} catch (Exception e) {
-				TFTPerror ePak = new TFTPerror(1, e.getMessage());
+        } catch (Exception e) {
+            TFTPerror ePak = new TFTPerror(1, e.getMessage()); // error code 1
+            try {
+                ePak.send(host, port, sock);
+            } catch (Exception f) {
+            }
 
-				try {
-					ePak.send(host, port, sock);
-				} catch (Exception f) {
-				}
+            event.onClientReadException(e, request);
+        }
+    }
 
-				System.out.println("Client failed:  " + e.getMessage());
-			}
-		}
-	}
+    //everything is fine, open new thread to transfer file
+    public void run() {
+        int bytesRead = TFTPpacket.maxTftpPakLen;
+        // handle read request
+        if (req instanceof TFTPread) {
+            try {
+                for (int blkNum = 1; bytesRead == TFTPpacket.maxTftpPakLen; blkNum++) {
+                    TFTPdata outPak = new TFTPdata(blkNum, source);
+                    /*System.out.println("send block no. " + outPak.blockNumber()); */
+                    bytesRead = outPak.getLength();
+                    /*System.out.println("bytes sent:  " + bytesRead);*/
+                    outPak.send(host, port, sock);
+                    /*System.out.println("current op code  " + outPak.get(0)); */
+
+                    //wait for the correct ack. if incorrect, retry up to 5 times
+                    while (timeoutLimit != 0) {
+                        try {
+                            TFTPpacket ack = TFTPpacket.receive(sock);
+                            if (!(ack instanceof TFTPack)) {
+                                throw new Exception("Client failed");
+                            }
+                            TFTPack a = (TFTPack) ack;
+
+                            if (a.blockNumber() != blkNum) { //check ack
+                                throw new SocketTimeoutException("last packet lost, resend packet");
+                            }
+                            /*System.out.println("confirm blk num " + a.blockNumber()+" from "+a.getPort());*/
+                            break;
+                        } catch (SocketTimeoutException t) {//resend last packet
+                            System.out.println("Resent blk " + blkNum);
+                            timeoutLimit--;
+                            outPak.send(host, port, sock);
+                        }
+                    } // end of while
+                    if (timeoutLimit == 0) {
+                        throw new Exception("connection failed");
+                    }
+                }
+                System.out.println("Transfer completed.(Client " + host + ")");
+                System.out.println("Filename: " + fileName + "\nSHA1 checksum: " + CheckSum.getChecksum(fileName) + "\n");
+            } catch (Exception e) {
+                TFTPerror ePak = new TFTPerror(1, e.getMessage());
+
+                try {
+                    ePak.send(host, port, sock);
+                } catch (Exception f) {
+                }
+
+                System.out.println("Client failed:  " + e.getMessage());
+            }
+        }
+    }
 }
\ No newline at end of file
diff --git a/src/main/java/ru/redguy/tftpserver/TFTPserverWRQ.java b/src/main/java/ru/redguy/tftpserver/TFTPserverWRQ.java
index ff425f9..52664ed 100644
--- a/src/main/java/ru/redguy/tftpserver/TFTPserverWRQ.java
+++ b/src/main/java/ru/redguy/tftpserver/TFTPserverWRQ.java
@@ -1,106 +1,111 @@
 package ru.redguy.tftpserver;
 
-import java.net.*;
-import java.io.*;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.net.SocketTimeoutException;
 
 
 class TFTPserverWRQ extends Thread {
 
-	protected DatagramSocket sock;
-	protected InetAddress host;
-	protected int port;
-	protected FileOutputStream outFile;
-	protected TFTPpacket req;
-	protected int timeoutLimit = 5;
-	//protected int testloss=0;
-	protected File saveFile;
-	protected String fileName;
+    protected DatagramSocket sock;
+    protected InetAddress host;
+    protected int port;
+    protected FileOutputStream outFile;
+    protected TFTPpacket req;
+    protected int timeoutLimit = 5;
+    //protected int testloss=0;
+    protected File saveFile;
+    protected String fileName;
 
-	// Initialize read request
-	public TFTPserverWRQ(TFTPwrite request, ErrorEvent event) throws TftpException {
-		try {
-			req = request;
-			sock = new DatagramSocket(); // new port for transfer
-			sock.setSoTimeout(1000);
+    // Initialize read request
+    public TFTPserverWRQ(TFTPwrite request, ErrorEvent event) throws TftpException {
+        try {
+            req = request;
+            sock = new DatagramSocket(); // new port for transfer
+            sock.setSoTimeout(1000);
 
-			host = request.getAddress();
-			port = request.getPort();
-			fileName = request.fileName();
-			//create file object in parent folder
-			saveFile = new File(fileName);
+            host = request.getAddress();
+            port = request.getPort();
+            fileName = request.fileName();
+            //create file object in parent folder
+            saveFile = new File(fileName);
 
-			if (!saveFile.exists()) {
-				outFile = new FileOutputStream(saveFile);
-				TFTPack a = new TFTPack(0);
-				a.send(host, port, sock); // send ack 0 at first, ready to
-											// receive
-				this.start();
-			} else
-				throw new TftpException("access violation, file exists");
+            if (!saveFile.exists()) {
+                outFile = new FileOutputStream(saveFile);
+                TFTPack a = new TFTPack(0);
+                a.send(host, port, sock); // send ack 0 at first, ready to
+                // receive
+                this.start();
+            } else
+                throw new TftpException("access violation, file exists");
 
-		} catch (Exception e) {
-			TFTPerror ePak = new TFTPerror(1, e.getMessage()); // error code 1
-			try {
-				ePak.send(host, port, sock);
-			} catch (Exception f) {
-			}
+        } catch (Exception e) {
+            TFTPerror ePak = new TFTPerror(1, e.getMessage()); // error code 1
+            try {
+                ePak.send(host, port, sock);
+            } catch (Exception f) {
+            }
 
-			event.onClientWriteException(e,request);
-		}
-	}
+            event.onClientWriteException(e, request);
+        }
+    }
 
-	public void run() {
-		/*int bytesRead = TFTPpacket.maxTftpPakLen;*/
-		// handle write request
-		if (req instanceof TFTPwrite) {
-			try {
-				for (int blkNum = 1, bytesOut = 512; bytesOut == 512; blkNum++) {
-					while (timeoutLimit != 0) {
-						try {
-							TFTPpacket inPak = TFTPpacket.receive(sock); 
-							//check packet type
-							if (inPak instanceof TFTPerror) {
-								TFTPerror p = (TFTPerror) inPak;
-								throw new TftpException(p.message());
-							} else if (inPak instanceof TFTPdata) {
-								TFTPdata p = (TFTPdata) inPak;
-								/*System.out.println("incoming data " + p.blockNumber());*/
-								// check blk num
-								if (/*testloss==20||*/p.blockNumber() != blkNum) { //expect to be the same
-									//System.out.println("loss. testloss="+testloss+"timeoutLimit="+timeoutLimit);
-									//testloss++;
-									throw new SocketTimeoutException();
-								}
-								//write to the file and send ack
-								bytesOut = p.write(outFile);
-								TFTPack a = new TFTPack(blkNum);
-								a.send(host, port, sock);
-								//testloss++;
-								break;
-							}
-						} catch (SocketTimeoutException t2) {
-							System.out.println("Time out, resend ack");
-							TFTPack a = new TFTPack(blkNum - 1);
-							a.send(host, port, sock);
-							timeoutLimit--;
-						}
-					}
-					if(timeoutLimit==0){throw new Exception("Connection failed");}
-				}
-				outFile.close();
-				System.out.println("Transfer completed.(Client " +host +")" );
-				System.out.println("Filename: "+fileName + "\nSHA1 checksum: "+CheckSum.getChecksum(fileName)+"\n");
-				
-			} catch (Exception e) {
-				TFTPerror ePak = new TFTPerror(1, e.getMessage());
-				try {
-					ePak.send(host, port, sock);
-				} catch (Exception f) {
-				}
+    public void run() {
+        /*int bytesRead = TFTPpacket.maxTftpPakLen;*/
+        // handle write request
+        if (req instanceof TFTPwrite) {
+            try {
+                for (int blkNum = 1, bytesOut = 512; bytesOut == 512; blkNum++) {
+                    while (timeoutLimit != 0) {
+                        try {
+                            TFTPpacket inPak = TFTPpacket.receive(sock);
+                            //check packet type
+                            if (inPak instanceof TFTPerror) {
+                                TFTPerror p = (TFTPerror) inPak;
+                                throw new TftpException(p.message());
+                            } else if (inPak instanceof TFTPdata) {
+                                TFTPdata p = (TFTPdata) inPak;
+                                /*System.out.println("incoming data " + p.blockNumber());*/
+                                // check blk num
+                                if (/*testloss==20||*/p.blockNumber() != blkNum) { //expect to be the same
+                                    //System.out.println("loss. testloss="+testloss+"timeoutLimit="+timeoutLimit);
+                                    //testloss++;
+                                    throw new SocketTimeoutException();
+                                }
+                                //write to the file and send ack
+                                bytesOut = p.write(outFile);
+                                TFTPack a = new TFTPack(blkNum);
+                                a.send(host, port, sock);
+                                //testloss++;
+                                break;
+                            }
+                        } catch (SocketTimeoutException t2) {
+                            System.out.println("Time out, resend ack");
+                            TFTPack a = new TFTPack(blkNum - 1);
+                            a.send(host, port, sock);
+                            timeoutLimit--;
+                        }
+                    }
+                    if (timeoutLimit == 0) {
+                        throw new Exception("Connection failed");
+                    }
+                }
+                outFile.close();
+                System.out.println("Transfer completed.(Client " + host + ")");
+                System.out.println("Filename: " + fileName + "\nSHA1 checksum: " + CheckSum.getChecksum(fileName) + "\n");
 
-				System.out.println("Client failed:  " + e.getMessage());
-				saveFile.delete();
-			}
-		}
-	}
+            } catch (Exception e) {
+                TFTPerror ePak = new TFTPerror(1, e.getMessage());
+                try {
+                    ePak.send(host, port, sock);
+                } catch (Exception f) {
+                }
+
+                System.out.println("Client failed:  " + e.getMessage());
+                saveFile.delete();
+            }
+        }
+    }
 }
\ No newline at end of file
diff --git a/src/main/java/ru/redguy/tftpserver/datasource/FileSystem.java b/src/main/java/ru/redguy/tftpserver/datasource/FileSystem.java
index 04d2d68..65da06b 100644
--- a/src/main/java/ru/redguy/tftpserver/datasource/FileSystem.java
+++ b/src/main/java/ru/redguy/tftpserver/datasource/FileSystem.java
@@ -1,7 +1,5 @@
 package ru.redguy.tftpserver.datasource;
 
-import ru.redguy.tftpserver.IDataSource;
-
 import java.io.File;
 import java.nio.file.Path;
 
diff --git a/src/main/java/ru/redguy/tftpserver/IDataSource.java b/src/main/java/ru/redguy/tftpserver/datasource/IDataSource.java
similarity index 67%
rename from src/main/java/ru/redguy/tftpserver/IDataSource.java
rename to src/main/java/ru/redguy/tftpserver/datasource/IDataSource.java
index e711ac1..9b3c807 100644
--- a/src/main/java/ru/redguy/tftpserver/IDataSource.java
+++ b/src/main/java/ru/redguy/tftpserver/datasource/IDataSource.java
@@ -1,4 +1,4 @@
-package ru.redguy.tftpserver;
+package ru.redguy.tftpserver.datasource;
 
 public interface IDataSource {
     public boolean isFileExists(String localPath);