A simple single-connection, blocking UDP echo server, which listens on IPv4 and IP6 simultaneously

udpserver.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
#  udpserver.py
#
"""A minimal test UDP (echo) server supporting IPv4 and IPv6."""

import argparse
import logging
import socket
import sys

log = logging.getLogger(__name__)
MAX_DGRAM_SIZE = 1472
DEFAULT_ADDRESS = '::'
DEFAULT_PORT = 9000


def main(args=None):
    ap = argparse.ArgumentParser()
    ap.add_argument('-v', '--verbose', action="store_true",
                    help="Enable debug logging")
    ap.add_argument('-e', '--echo', action="store_true",
                    help="Echo received data back to sender")
    ap.add_argument('-a', '--address', default=DEFAULT_ADDRESS,
                    help="UDP server IP address (default: %(default)s)")
    ap.add_argument('-p', '--port', type=int, default=DEFAULT_PORT,
                    help="UDP server port (default: %(default)s)")

    args = ap.parse_args(args if args is not None else sys.argv[1:])

    logging.basicConfig(level=logging.DEBUG if args.verbose else logging.INFO)

    af = socket.AF_INET6 if '::' in args.address else socket.AF_INET
    sock = socket.socket(af, socket.SOCK_DGRAM)
    if af == socket.AF_INET6:
        sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
    log.debug("Created UDP socket.")
    addr = socket.getaddrinfo(args.address, args.port, af, socket.SOCK_DGRAM)
    sock.bind(addr[0][4])
    log.debug("Bound socket to port %i on '%s'.", args.port, args.address)

    # In each loop iteration, block until one UDP datagram with
    # a maximum size of up to MAX_DGRAM_SIZE is received and
    # print out the received data and the address info of the sender.
    # Optionally, echo back the data to the sender.
    try:
        log.debug("Entering receive loop...")
        while True:
            data, addr = sock.recvfrom(MAX_DGRAM_SIZE)
            log.info("Received data: %r", data)
            log.info("Sender: %r", addr)

            if args.echo:
                sock.sendto(data, addr)
    except KeyboardInterrupt:
        pass
    finally:
        sock.close()
        log.info("Bye!")


if __name__ == '__main__':
    sys.exit(main(sys.argv[1:]) or 0)