You must write a client and server to support file transfer. The client should s

Question

You must write a client and server to support file transfer. The client should send to the server a request to initiate a transfer of a specific file. Upon recieving the request, if the file exists, it should be sent to the client. Be sure your program works with all file types, not just text files. UDP (datagram) sockets must be used. The data in each packet (not including any header information you add) must be 1024 bytes or less. You must implement a sliding window of 5 packets for your file transfer.

Explanation / Answer

Local file transfer

# server.py

import socket # Import socket module

port = 60000 # Reserve a port for your service.
s = socket.socket() # Create a socket object
host = socket.gethostname() # Get local machine name
s.bind((host, port)) # Bind to the port
s.listen(5) # Now wait for client connection.

print 'Server listening....'

while True:
conn, addr = s.accept() # Establish connection with client.
print 'Got connection from', addr
data = conn.recv(1024)
print('Server received', repr(data))

filename='mytext.txt'
f = open(filename,'rb')
l = f.read(1024)
while (l):
conn.send(l)
print('Sent ',repr(l))
l = f.read(1024)
f.close()

print('Done sending')
conn.send('Thank you for connecting')
conn.close()

# client.py

import socket # Import socket module

s = socket.socket() # Create a socket object
host = socket.gethostname() # Get local machine name
port = 60000 # Reserve a port for your service.

s.connect((host, port))
s.send("Hello server!")

with open('received_file', 'wb') as f:
print 'file opened'
while True:
print('receiving data...')
data = s.recv(1024)
print('data=%s', (data))
if not data:
break
# write data to a file
f.write(data)

f.close()
print('Successfully get the file')
s.close()
print('connection closed')

Output on a local server:

Server listening....
Got connection from ('192.168.56.10', 62854)
('Server received', "'Hello server!'")
('Sent ', "'1 1234567890
...
('Sent ', "'4567890 105
...
('Sent ', "'300 1234567890 '")
Done sending

Output on a local client:

file opened
receiving data...
data=1 1234567890
2 1234567890
...
103 1234567890
104 123
receiving data...
data=4567890
105 1234567890
106 1234567890
...
299 1234567890

receiving data...
data=300 1234567890
Thank you for connecting
receiving data...
data=
Successfully get the file
connection closed

multithread tcp file transfer on localhost

Our server code above can only interact with one client. If we try to connect with a second client, however, it simply won't reply to the new client. To let the server interact with multiple clients, we need to use multi-threading. Here is the new server script to accept multiple client connections:

# server2.py
import socket
from threading import Thread
from SocketServer import ThreadingMixIn

TCP_IP = 'localhost'
TCP_PORT = 9001
BUFFER_SIZE = 1024

class ClientThread(Thread):

def __init__(self,ip,port,sock):
Thread.__init__(self)
self.ip = ip
self.port = port
self.sock = sock
print " New thread started for "+ip+":"+str(port)

def run(self):
filename='mytext.txt'
f = open(filename,'rb')
while True:
l = f.read(BUFFER_SIZE)
while (l):
self.sock.send(l)
#print('Sent ',repr(l))
l = f.read(BUFFER_SIZE)
if not l:
f.close()
self.sock.close()
break

tcpsock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
tcpsock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
tcpsock.bind((TCP_IP, TCP_PORT))
threads = []

while True:
tcpsock.listen(5)
print "Waiting for incoming connections..."
(conn, (ip,port)) = tcpsock.accept()
print 'Got connection from ', (ip,port)
newthread = ClientThread(ip,port,conn)
newthread.start()
threads.append(newthread)

for t in threads:
t.join()

# client2.py
#!/usr/bin/env python

import socket

TCP_IP = 'localhost'
TCP_PORT = 9001
BUFFER_SIZE = 1024

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TCP_IP, TCP_PORT))
with open('received_file', 'wb') as f:
print 'file opened'
while True:
#print('receiving data...')
data = s.recv(BUFFER_SIZE)
print('data=%s', (data))
if not data:
f.close()
print 'file close()'
break
# write data to a file
f.write(data)

print('Successfully get the file')
s.close()
print('connection closed')

Below is the output from the server console when we run two clients simultaneously:

$ python server2.py
Waiting for incoming connections...
Got connection from ('127.0.0.1', 55184)
New thread started for 127.0.0.1:55184
Waiting for incoming connections...
Got connection from ('127.0.0.1', 55185)
New thread started for 127.0.0.1:55185
Waiting for incoming connections...

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