diff --git a/src/server.py b/src/server.py
--- a/src/server.py
+++ b/src/server.py
@@ -1,20 +1,11 @@
 import socket
 from hashtree import HashTree
 from networkers import NetworkReader,NetworkWriter
-import collections
-import sys
 import logging as log
 
 import config as conf
 
 
-# debug copy default file
-import shutil
-origFilename=sys.argv[1]
-filename=origFilename+"_"
-shutil.copyfile(origFilename,filename)
-
-
 class Connection:
 	def __init__(self,server_socket):
 		self.socket, address = server_socket.accept()
@@ -32,53 +23,63 @@ class Connection:
 		self.socket.close()
 
 
-localTree=HashTree.fromFile(filename)
+class Server:
+	def __init__(self,filename):
+		self.filename=filename
+		self.tree=HashTree.fromFile(filename)
+		self.BLOCK_SIZE=self.tree.BLOCK_SIZE
 
-ss = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-ss.bind(("",conf.port))
-ss.listen(1)
+		self.ss = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+		self.ss.bind(("",conf.port))
+		self.ss.listen(1)
 
-blocksToTransfer=[]
-nodeStack=collections.deque([0])
+		self._lastWrite=-1
 
-i1=-1
+	def serve(self):
+		while self._serveOne():
+			pass
 
+	def _serveOne(self):
+		with Connection(self.ss) as (incoming,outcoming):
+			jsonData,binData=incoming.readMsg()
 
-while True:
-	with Connection(ss) as (incoming,outcoming):
-		jsonData,binData=incoming.readMsg()
-		dataFile=open(filename,mode="rb+")
+			if jsonData["command"]=="init":
+				assert jsonData["blockSize"]==self.BLOCK_SIZE
+				assert jsonData["blockCount"]==self.tree.leafCount
 
-		if jsonData["command"]=="init":
-			assert jsonData["blockSize"]==localTree.BLOCK_SIZE
-			assert jsonData["blockCount"]==localTree.leafCount
+			elif jsonData["command"]=="req":
+				outcoming.writeMsg(*self._requestHash(jsonData))
+
+			elif jsonData["command"]=="send" and jsonData["dataType"]=="data":
+				self._receiveData(jsonData,binData)
 
-		elif jsonData["command"]=="req":
-			log.info("received request for node #{0}".format(jsonData["index"]))
-			assert jsonData["index"]<len(localTree.store)
-			nodeHash=localTree.store[jsonData["index"]]
+			elif jsonData["command"]=="end":
+				log.info("closing session...")
+				return False
+
+			else:
+				assert False, jsonData["command"]
 
-			jsonResponse={"command":"send", "index":jsonData["index"], "dataType":"hash"}
-			binResponse=nodeHash
+			return True
 
-			outcoming.writeMsg(jsonResponse,binResponse)
-
-		elif jsonData["command"]=="send" and jsonData["dataType"]=="data":
-			log.info("received data block #{0}: {1}...{2}".format(jsonData["index"],binData[:5],binData[-5:]))
+	def _requestHash(self,jsonData):
+		log.info("received request for node #{0}".format(jsonData["index"]))
+		assert jsonData["index"]<len(self.tree.store)
+		nodeHash=self.tree.store[jsonData["index"]]
 
-			i2=jsonData["index"]
-			if i1+1!=i2:
-				dataFile.seek(i2*localTree.BLOCK_SIZE)
-			dataFile.write(binData)
-			i1=i2
+		jsonResponse={"command":"send", "index":jsonData["index"], "dataType":"hash"}
+		binResponse=nodeHash
 
-			# never update the hash tree
+		return (jsonResponse,binResponse)
+
+	def _receiveData(self,jsonData,binData):
+		log.info("received data block #{0}: {1}...{2}".format(jsonData["index"],binData[:5],binData[-5:]))
 
-		elif jsonData["command"]=="end":
-			log.info("closing session...")
-			break
-	
-		else:
-			assert False, jsonData["command"]
+		i=jsonData["index"]
+		with open(self.filename,mode="rb+") as dataFile:
+			if self._lastWrite+1!=i:
+				dataFile.seek(i*self.BLOCK_SIZE)
+			dataFile.write(binData)
+		self._lastWrite=i
 
-dataFile.close()
+		# never update the hash tree