proxy server

#!/usr/bin/python3
#
#   start proxy server and listen for client connection
#
import socket,sys
import threading
try:
    port=int(input('Enter port to listen:  '))
except KeyboardInterrupt:
    print('Exiting...')
    sys.exit(1)
    #   Max connections
max_con=5
buffer_size=4096
def retry():
    try:
        option=input('Enter Y/n to retry or quit proxy server:')
        if option=='y' or option=="" or option=="Y":
            print("Restarting proxy server...")
            start()
        else:
            sys.exit(1)
    except KeyboardInterrupt:
        print('Stop retrying proxy server initialisation.')
        sys.exit(1)
def start():
    try:
        s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)# IPv4 and tcp socket selected
        print("[+] Socket prepared for IPv4/TCP protocols ")
        s.bind(('0.0.0.0',port))    #bind port for listening
        print("[+] socket binded to listen on port:%d"%(port))
        s.listen(max_con)
        print("[+] Server started \n[+] Waiting for clients to connect...\n")
    except Exception as e:
        #   print the exception object e
        # or just a simple message
        print("Exception error in starting server.\n")
        #print(e,'\n')
        s.close()
        #opt=input('Enter Y/n to retry or quit proxy server:')
        retry()

    while True:
        try:
            connection, addr=s.accept() #Accept connection from client
            #print(connection,'ADDRESS:',addr)
            print('\nGot connection from:', addr)
            data=connection.recv(buffer_size)#recieve client data
            #print(data)
            t=threading.Thread(target=connection_string,args=(connection,data,addr))
            t.start()
            t.join()
            # just started a process thread
        except KeyboardInterrupt:
            s.shutdown(socket.SHUT_RDWR)
            s.close()
            print("Killing server process")
            sys.exit(1)
    s.shutdown(socket.SHUT_RDWR)
    s.close()
##
#   Defining connection_string
#
##
def connection_string(connection,data,addr):
    # Client broser reuest will be seen here
    try:
        data=data.decode('utf-8')
        first_line=data.split('\n')[0]

        url=first_line.split(' ')[1]
        #print("url:",url)
        http_pos=url.find("://")# finding positonn of http tag
        #print(http_pos)#########
        if (http_pos==-1):
            temp=url
        else:
            temp =url[(http_pos+3):]# concating rest url
        #print(temp)

        port_pos=temp.find(':')# find the position of posrt if any

        webserver_pos=temp.find("/")#end of web server
        #print(port_pos,webserver_pos)
        if webserver_pos== -1:
            webserver_pos=len(temp)
        #webserver_pos=""
        port=-1
        if (port ==-1 or webserver_pos<port_pos):
            port=80
            webserver=temp[:webserver_pos]
        else:
        #specific port
            port=int((temp[(port_pos+1):])[:(webserver-port_pos-1)])
            webserver=temp[:port_pos]
        data=bytes(data.encode('utf-8'))
        proxy_server(webserver,port,connection,addr,data)
    except Exception as e:
        print("\nException in connection_string\n")
        print(e,'\n')
        pass
#       connection.shutdown(socket.SHUT_RDWR)
#       connection.close()
        retry=input('Enter Y/n to retry or quit proxy server:')
        if retry=='y' or retry=="" or retry=="Y":
            print("Restarting proxy server...")
            start()
        else:
            sys.exit(1)
def proxy_server(webserver,port,connection,addr,data):
    print("Func-proxy_server")
    #print("\nwebserver->",webserver,"\nport->",port,"\nconnection->",connection,"\naddr->",addr,"\ndata->",data)
    try:
        s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
        #print("\nwebserver->",webserver,"\nport->",port,"\nconnection->",connection,"\naddr->",addr,"\ndata->",data)
        s.connect((webserver,port))
        s.send(data)
        print(data)
        while True:
    # read adata from web server
            reply=s.recv(buffer_size)
            #print("reply from target site to proxy server",reply.decode('utf-8'))
            if len(reply)>0:
                connection.send(reply)
                print(reply)
                #connection.send(bytes(reply.encode('utf-8')))# send rply bak to client

                #Send notification to proxy server#
                data_recieved=float(len(str(reply.decode('utf-8'))))
                data_recieved=float(data_recieved/1024)
                data_recieved="%.3s"%str(data_recieved)
                data_recieved="%s KB "%(data_recieved)
#
#print message on completein each request successfully
#
                print("[+]%s %s "%(str(addr[0]),str(data_recieved)))
            else:
# breaking connection if data not recieved
                break
        s.close()
        connection.close()
    except Exception as e:
        print(e)
        s.shutdown(socket.SHUT_RDWR)
        s.close()
        connection.shutdown(socket.SHUT_RDWR)
        connection.close()
        sys.exit(1)
    #start()
start()