I'd like to get some feedback/criticism on my attempt to write a simple client/server application that reports back the (client's) global IP address.
It would be nice if you could comment on the UDP socket setup, general security or any other drawbacks you were able to spot. Since this is my first attempt in writing Python network code (or Python in general other than tinkering) please be harsh!
#! /usr/bin/env python
# grip 0.0.1, external IP address lookup utility.
# usage: grip hostname [port]
# grip -l [hostname] [port]
# grip -h
from __future__ import print_function
import sys
from socket import *
MODE_SERVER = 0
MODE_CLIENT = 1
READ_BUFFER = 15
NULL_BUFFER = 1
DEFAULT_HOST = ''
DEFAULT_PORT = 20815
EXIT_SUCCESS = 0
EXIT_FAILURE = 1
EXIT_SYNTAX = 2
USAGE = '''\
grip 0.0.1, external IP address lookup utility.
usage: grip hostname [port]
grip -l [hostname] [port]
grip -h
Options:
-h display this help message and exit
-l run in listen mode, to report back remote hosts' IP addresses
Request mode:
The hostname may be provided in either IP address or DNS format.
The port number - if unspecified - defaults to 20815.
Listen mode:
In listen mode the program will try to serve requests on all
available interfaces unless explicitly told not to.\
'''
def num(n):
try:
return int(n)
except ValueError:
return None
class Server:
"""Reports back the remote host's IP address"""
def __init__(self, socket):
self.socket = socket
def listen(self, host, port):
self.socket.bind((host, port))
try:
while 1:
data, address = self.socket.recvfrom(NULL_BUFFER)
self.socket.sendto(address[0], address)
except KeyboardInterrupt:
pass
return EXIT_SUCCESS
class Client:
"""xyz"""
def __init__(self, socket):
self.socket = socket
def request(self, host, port):
code = EXIT_SUCCESS
self.socket.sendto('', (host,port))
self.socket.settimeout(2)
try:
data, saddr = self.socket.recvfrom(READ_BUFFER)
print(data)
except:
code = EXIT_FAILURE;
print('Error: Request timed out', file=sys.stderr)
self.socket.close()
return code
def main():
args = list(sys.argv[1:])
argsno = len(args)
mode = MODE_CLIENT
hostname = DEFAULT_HOST
port = DEFAULT_PORT
# Mere invocation is NOT supported
if argsno == 0:
print(USAGE, file=sys.stderr)
sys.exit(EXIT_SYNTAX)
# Display a helpfull message when asked
if '-h' in args:
print(USAGE)
sys.exit(EXIT_SUCCESS)
if '-l' in args:
mode = MODE_SERVER
args.remove('-l')
argsno -= 1
if mode == MODE_SERVER:
if argsno > 1:
hostname = args[0]
port = num(args[1])
if argsno == 1:
if num(args[0]) is not None:
port = num(args[0])
else:
hostname = args[0]
try:
serv = Server(socket(AF_INET, SOCK_DGRAM))
retval = serv.listen(hostname, port)
except:
sys.exit(EXIT_FAILURE)
if mode == MODE_CLIENT:
hostname = args[0]
if argsno > 1:
port = num(args[1])
try:
cl = Client(socket(AF_INET, SOCK_DGRAM))
retval = cl.request(hostname, port)
except:
sys.exit(EXIT_FAILURE)
sys.exit(retval)
if __name__ == "__main__":
main()
