Comparing files between client and server using tcp socket

I am working on a client-server file sharing to update a particular folder. Where the client connects to server using tcp-socket and recieve a particular zip-file then unzip it. I have accomplished doing that so far but I want to compare the files in both folders(client and server) to check for difference in files contents(ie: updated files) and only download the files if the contents are different.

My code:

Client:

import socket
import zipfile
import os

def main():
    host = '192.168.1.8'
    port = 5000
    s = socket.socket()
    s.connect((host, port))
    with open('C:\\file.zip', 'wb') as f:
        while True:
            data = s.recv(1024)
            if not data:
                break
            f.write(data)
    zip_ref = zipfile.ZipFile('C:\\file.zip', 'r')
    zip_ref.extractall('C:\\')
    zip_ref.close()
    os.remove('C:\\file.zip')
    s.close()

if __name__ == '__main__':
    main()

Server:

import socket
from threading import Thread

def send_file(conn, filename):
    with open(filename, 'rb') as f:
        print 'Sending file'
        data = f.read(1024)
        while data:
            conn.send(data)
            data = f.read(1024)
    print 'Finished sending'
    conn.close()


def main():
    host = '192.168.1.8'
    port = 5000
    s = socket.socket()
    s.bind((host, port))
    s.listen(5)
    while True:
        c, addr = s.accept()
        t = Thread(target=send_file, args=(c, 'C:\\file.zip'))
        t.start()

if __name__ == '__main__':
    main()

What I have tried so far:

I tried filecmp.dircmp but It only checks for different files and not different content of files and also I couldn't compare folder from client with folder from server. I also tried to loop through files and use filecmp on each file but I also couldn't compare it with the same file from server.

Is there an efficient way to do this?