import os

import sys

if os.name == 'posix':

    def become_daemon(our_home_dir='.', out_log='/dev/null',

                      err_log='/dev/null', umask=022):

        "Robustly turn into a UNIX daemon, running in our_home_dir."

        # First fork

        try:

            if os.fork() > 0:

                sys.exit(0)     # kill off parent

        except OSError, e:

            sys.stderr.write("fork #1 failed: (%d) %s\n" % (e.errno, e.strerror))

            sys.exit(1)

        os.setsid()

        os.chdir(our_home_dir)

        os.umask(umask)

        # Second fork

        try:

            if os.fork() > 0:

                os._exit(0)

        except OSError, e:

            sys.stderr.write("fork #2 failed: (%d) %s\n" % (e.errno, e.strerror))

            os._exit(1)

        si = open('/dev/null', 'r')

        so = open(out_log, 'a+', 0)

        se = open(err_log, 'a+', 0)

        os.dup2(si.fileno(), sys.stdin.fileno())

        os.dup2(so.fileno(), sys.stdout.fileno())

        os.dup2(se.fileno(), sys.stderr.fileno())

        # Set custom file descriptors so that they get proper buffering.

        sys.stdout, sys.stderr = so, se

else:

    def become_daemon(our_home_dir='.', out_log=None, err_log=None, umask=022):

        """

        If we're not running under a POSIX system, just simulate the daemon

        mode by doing redirections and directory changing.

        """

        os.chdir(our_home_dir)

        os.umask(umask)

        sys.stdin.close()

        sys.stdout.close()

        sys.stderr.close()

        if err_log:

            sys.stderr = open(err_log, 'a', 0)

        else:

            sys.stderr = NullDevice()

        if out_log:

            sys.stdout = open(out_log, 'a', 0)

        else:

            sys.stdout = NullDevice()

    class NullDevice:

        "A writeable object that writes to nowhere -- like /dev/null."

        def write(self, s):

            pass