publish-cname.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# publish-cname.py - publish CNAMEs pointing to the local host over Avahi/mDNS.
#
# Copyright (c) 2014, SAPO
#


from __future__ import print_function
from __future__ import division
from __future__ import unicode_literals
from __future__ import absolute_import

import sys
import os, os.path
import logging
import logging.handlers
import re
import signal
import functools

from getopt import getopt, GetoptError
from textwrap import TextWrapper
from time import sleep

from daemonize import daemonize
from mpublisher import AvahiPublisher


# Default Time-to-Live for mDNS records, in seconds...
DEFAULT_DNS_TTL = 60


def print_usage():
    """Output the proper usage syntax for this program."""

    print("USAGE: %s [-t <ttl>] [-f] [-v] <hostname.local> [...]" % os.path.basename(sys.argv[0]))

    wrapper = TextWrapper(width=79, initial_indent="\t", subsequent_indent="\t")

    print("\n-t/--ttl <seconds>")
    print(wrapper.fill("Set the TTL for all published records. (Default: %ds)" % DEFAULT_DNS_TTL))

    print("\n-f/--force")
    print(wrapper.fill("Publish all CNAMEs without checking if they are already being published "
                       "elsewhere on the network. This is much faster, but generally unsafe."))

    print("\n-v/--verbose")
    print(wrapper.fill("Produce extra output for debugging purposes."))

    print("\n-d/--daemon")
    print(wrapper.fill("Run the CNAME publishing service in the background."))

    print("\n-l/--log=<filename>")
    print(wrapper.fill("Send log messages into the specified file."))


def parse_args():
    """Parse and enforce command-line arguments."""

    try:
        options, args = getopt(sys.argv[1:], "t:fvdl:h", ["ttl=", "force", "verbose",
                                                          "daemon", "log=", "help"])
    except GetoptError as e:
        print("error: %s." % e, file=sys.stderr)
        print_usage()
        sys.exit(1)

    if len(args) < 1:
        print("error: parameter(s) missing.", file=sys.stderr)
        print_usage()
        sys.exit(1)

    # Minimal checking that the CNAMEs are properly formatted...
    cname_re = re.compile(r"^[a-z0-9-]{1,63}(?:\.[a-z0-9-]{1,63})*\.local$")
    cnames = [arg.strip().lower() for arg in args]

    for cname in cnames:
        if not cname_re.match(cname):
            print("error: malformed hostname: %s" % cname, file=sys.stderr)
            print_usage()
            sys.exit(1)

    ttl = DEFAULT_DNS_TTL
    force = False
    verbose = False
    daemon = False
    logname = None

    for option, value in options:
        if option in ("-h", "--help"):
            print_usage()
            sys.exit(1)
        elif option in ("-t", "--ttl"):
            ttl = int(value)
        elif option in ("-f", "--force"):
            force = True
        elif option in ("-v", "--verbose"):
            verbose = True
        elif option in ("-d", "--daemon"):
            daemon = True
        elif option in ("-l", "--log"):
            logname = value.strip()

    return (ttl, force, verbose, daemon, logname, cnames)


def handle_signals(publisher, signum, frame):
    """Unpublish all mDNS records and exit cleanly."""

    signame = next(v for v, k in signal.__dict__.iteritems() if k == signum)
    logging.debug("Cleaning up on %s...", signame)
    publisher.__del__()

    # Avahi needs time to forget us...
    sleep(1)

    os._exit(0)


def main():
    (ttl, force, verbose, daemon, log, cnames) = parse_args()

    # Since an eventual log file must support external log rotation, we must do this the hard way...
    format = logging.Formatter("%(asctime)s: %(levelname)s [%(process)d]: %(message)s")
    handler = logging.handlers.WatchedFileHandler(log) if log else logging.StreamHandler(sys.stderr)
    handler.setFormatter(format)
    logger = logging.getLogger()
    logger.addHandler(handler)
    logger.setLevel(logging.DEBUG if verbose else logging.INFO)

    # This must be done after initializing the logger, so that an eventual log file gets created in
    # the right place (the user will assume that relative paths start from the current directory)...
    if daemon:
        daemonize()

    logging.info("Avahi/mDNS publisher starting...")

    if force:
        logging.info("Forcing CNAME publishing without collision checks")

    # The publisher needs to be initialized in the loop, to handle disconnects...
    publisher = None

    while True:
        if not publisher or not publisher.available():
            publisher = AvahiPublisher(ttl)

            # To make sure records disappear immediately on exit, clean up properly...
            signal.signal(signal.SIGTERM, functools.partial(handle_signals, publisher))
            signal.signal(signal.SIGINT, functools.partial(handle_signals, publisher))
            signal.signal(signal.SIGQUIT, functools.partial(handle_signals, publisher))

            for cname in cnames:
                status = publisher.publish_cname(cname, force)
                if not status:
                    logging.error("Failed to publish '%s'", cname)
                    continue

            if publisher.count() == len(cnames):
                logging.info("All CNAMEs published")
            else:
                logging.warning("%d out of %d CNAMEs published", publisher.count(), len(cnames))

        # CNAMEs will exist while this service is kept alive,
        # but we don't actually need to do anything useful...
        sleep(1)


if __name__ == "__main__":
    main()


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