"""
Make a normal program into a "daemon", like the 4.4BSD daemon(3) call.

This 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.

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).

$Id$

Copyright (C) 2012  Internet Systems Consortium ("ISC")

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       The Regents of the University of California.  All rights reserved.

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  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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"""

import sys
import os
import atexit
import signal
import rpki.log

# 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)
	
  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:
    rpki.log.warn("Couldn't write PID file %s: %s" % (pidfile, e.strerror))