diff --git a/src/client.py b/src/client.py
--- a/src/client.py
+++ b/src/client.py
@@ -10,79 +10,85 @@ from networkers import NetworkReader,Net
 filename=sys.argv[1]
 
 
-def connect():
-	s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-	s.connect((conf.hosts[0], conf.port))
-	fr=s.makefile(mode='rb')
-	fw=s.makefile(mode='wb')
+class Connection:
+	def __init__(self):
+		self.socket=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
+		self.socket.connect((conf.hosts[0], conf.port))
+		fr=self.socket.makefile(mode="rb")
+		fw=self.socket.makefile(mode="wb")
 
-	networkReader=NetworkReader(fr)
-	networkReader.start()
-	networkWriter=NetworkWriter(fw)
-	networkWriter.start()
+		networkReader=NetworkReader(fr)
+		networkReader.start()
+		networkWriter=NetworkWriter(fw)
+		networkWriter.start()
 
-	incoming=networkReader.output # synchronized message queue
-	outcoming=networkWriter.input
+		self.incoming=networkReader.output # synchronized message queue
+		self.outcoming=networkWriter.input
 
-	return (s,incoming,outcoming)
+	def __enter__(self):
+		return self.incoming,self.outcoming
+
+	def __exit__(self, exc_type, exc_val, exc_tb):
+		self.socket.close()
 
 
-def negotiate(incoming,outcoming):
+def negotiate():
 	localTree=HashTree.fromFile(open(filename,mode="rb"))
 	blocksToTransfer=[]
 	nodeStack=collections.deque([0]) # root
 
 	# initialize session
-	jsonData={"command":"init", "blockSize":localTree.BLOCK_SIZE, "blockCount":localTree.leafCount, "version":conf.version}
-	outcoming.put((jsonData,b""))
+	with Connection() as (incoming,outcoming):
+		jsonData={"command":"init", "blockSize":localTree.BLOCK_SIZE, "blockCount":localTree.leafCount, "version":conf.version}
+		outcoming.put((jsonData,b""))
 
 	# determine which blocks to send
 	while len(nodeStack)>0:
-		i=nodeStack.pop()
-		jsonData={"command":"req", "index":i}
-		outcoming.put((jsonData,b""))
+		with Connection() as (incoming,outcoming):
+			i=nodeStack.pop()
+			jsonData={"command":"req", "index":i}
+			outcoming.put((jsonData,b""))
 
-		jsonData,binData=incoming.get(timeout=2)
-		assert jsonData["index"]==i
-		assert jsonData["dataType"]=="hash"
+			jsonData,binData=incoming.get(timeout=2)
+			assert jsonData["index"]==i
+			assert jsonData["dataType"]=="hash"
 
-		if localTree.store[i]!=binData:
-			if 2*i+3<len(localTree.store): # inner node
-				nodeStack.append(2*i+2)
-				nodeStack.append(2*i+1)
-			else: blocksToTransfer.append(i-localTree.leafStart) # leaf
+			if localTree.store[i]!=binData:
+				if 2*i+3<len(localTree.store): # inner node
+					nodeStack.append(2*i+2)
+					nodeStack.append(2*i+1)
+				else: blocksToTransfer.append(i-localTree.leafStart) # leaf
 
 	return blocksToTransfer
 
 
-def sendData(outcoming,blocksToTransfer):
+def sendData(blocksToTransfer):
 	print(blocksToTransfer)
 	dataFile=open(filename,mode="rb")
 	i1=-1
 
 	for i2 in blocksToTransfer:
-		jsonData={"command":"send", "index":i2, "dataType":"data"}
-		if i1+1!=i2:
-			dataFile.seek(i2*HashTree.BLOCK_SIZE)
-		binData=dataFile.read(HashTree.BLOCK_SIZE)
+		with Connection() as (incoming,outcoming):
+			jsonData={"command":"send", "index":i2, "dataType":"data"}
+			if i1+1!=i2:
+				dataFile.seek(i2*HashTree.BLOCK_SIZE)
+			binData=dataFile.read(HashTree.BLOCK_SIZE)
 
-		print("block #{0}: {1}...{2}".format(i2,binData[:5],binData[-5:]))
+			print("block #{0}: {1}...{2}".format(i2,binData[:5],binData[-5:]))
 
-		outcoming.put((jsonData,binData),timeout=2)
-		i1=i2
+			outcoming.put((jsonData,binData),timeout=2)
+			i1=i2
 
-	jsonData={"command":"end"}
-	outcoming.put((jsonData,b""),timeout=2)
+	with Connection() as (incoming,outcoming):
+		jsonData={"command":"end"}
+		outcoming.put((jsonData,b""),timeout=2)
 
-	outcoming.put(None)
 	print("closing...")
 	dataFile.close()
 
 
 if __name__=="__main__":
-	sock,incoming,outcoming = connect()
-	blocksToTransfer=negotiate(incoming,outcoming)
-	sendData(outcoming,blocksToTransfer)
+	blocksToTransfer=negotiate()
+	sendData(blocksToTransfer)
 
-	sock.close()
 	sys.exit(0)