# $Id$
#
# Copyright (C) 2012  Internet Systems Consortium ("ISC")
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#
# Some code borrowed from
#   http://www.jejik.com/articles/2007/02/a_simple_unix_linux_daemon_in_python/
#
# (which was explicitly placed in public domain by its author), and from
#
#   /usr/src/lib/libc/gen/daemon.c
#
# (the libc implementation of daemon(3) on FreeBSD), so:
#
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"""
Make a normal program into a "daemon", like the 4.4BSD daemon(3) call.

This doesn't quite follow either the 4.4BSD call or the Python 3.x library,
because it was written to fit into an existing package and I didn't
want to drag in yet another external library just for this.
"""

import os
import sys
import atexit
import signal
import logging

logger = logging.getLogger(__name__)

# Does default_pid_directory need to be autoconf-configurable?

## @var default_pid_directory
# Default directory to which to write process ID files.

default_pid_directory = "/var/run/rpki"

## @var pid_filename
# Configurable filename to which to write process ID file.
# pidfile argument to daemon() overrides this.

pid_filename = None

def daemon(nochdir = False, noclose = False, pidfile = None):
    """
    Make this program become a daemon, like 4.4BSD daemon(3), and
    write its pid out to a file with cleanup on exit.
    """

    if pidfile is None:
        if pid_filename is None:
            prog = os.path.splitext(os.path.basename(sys.argv[0]))[0]
            pidfile = os.path.join(default_pid_directory, "%s.pid" % prog)
        else:
            pidfile = pid_filename

    old_sighup_action = signal.signal(signal.SIGHUP, signal.SIG_IGN)

    try:
        pid = os.fork()
    except OSError, e:
        sys.exit("fork() failed: %d (%s)" % (e.errno, e.strerror))
    else:
        if pid > 0:
            os._exit(0)                 # pylint: disable=W0212

    if not nochdir:
        os.chdir("/")

    os.setsid()

    if not noclose:
        sys.stdout.flush()
        sys.stderr.flush()
        fd = os.open(os.devnull, os.O_RDWR)
        os.dup2(fd, 0)
        os.dup2(fd, 1)
        os.dup2(fd, 2)
        if fd > 2:
            os.close(fd)

    signal.signal(signal.SIGHUP, old_sighup_action)

    def delete_pid_file():
        try:
            os.unlink(pidfile)
        except OSError:
            pass

    atexit.register(delete_pid_file)

    try:
        f = open(pidfile, "w")
        f.write("%d\n" % os.getpid())
        f.close()
    except IOError, e:
        logger.warning("Couldn't write PID file %s: %s", pidfile, e.strerror)