jwmud/jwmudlib/daemon.py

# This file is part of jwmud, written by Helmut Pozimski in 2014.
#
#       jwmud is free software: you can redistribute it and/or modify
#       it under the terms of the GNU General Public License as published by
#       the Free Software Foundation, version 2 of the License.
#
#       jwmud is distributed in the hope that it will be useful,
#       but WITHOUT ANY WARRANTY; without even the implied warranty of
#       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#       GNU General Public License for more details.
#
#       You should have received a copy of the GNU General Public License
#       along with jwmud.  If not, see <http://www.gnu.org/licenses/>.

# -*- coding: utf8 -*-

import os
import sys

from jwmudlib import jwmu_exceptions


class Daemon(object):
    """ Tries to implement a well behaving unix daemon in a generic way,
    so the code could be used in different projects.

    """

    def __init__(self, pfile_path, pfile_name):
        """ Initializes the object. """
        self.__pfile_path = pfile_path
        self.__pfile_name = pfile_name
        self.__daemon = False
        self.__pid = 0

    def Daemonize(self):
        """ Turns the calling process into a daemon running on it's own """

        try:
            # Fork for the first time
            self.__pid = os.fork()
        except OSError:
            sys.exit(os.EX_OSERR)
        else:
            if self.__pid > 0:
                sys.exit(os.EX_OK)
        # Become session and group leader
        # noinspection PyArgumentList
        os.setsid()
        try:
            #Fork for the second time
            self.__pid = os.fork()
        except OSError:
            sys.exit(os.EX_OSERR)
        else:
            if self.__pid > 0:
                sys.exit(os.EX_OK)
        # Change cwd to / to avoid interfering with other mounted file systems
        os.chdir("/")
        # Reset the umask
        os.umask(0)

        # Close possibly open file descriptors
        os.close(0)
        os.close(1)
        os.close(2)

        # And redirect them to /dev/null
        os.open("/dev/null", 0)
        os.open("/dev/null", 1)
        os.open("/dev/null", 2)

        self.__daemon = True

    def DropPrivileges(self, user, group):
        """ If the daemon is running as root user, drop privileges and continue
        running as the defined unprivileged user.

        """
        pid_file_path = os.path.join(self.__pfile_path, self.__pfile_name)
        try:
            passwd_file = open("/etc/passwd", "r")
            group_file = open("/etc/group", "r")
        except PermissionError:
            raise jwmu_exceptions.PasswdOrGroupAccessFailed()
        else:
            uid = ""
            gid = ""
            for line in passwd_file:
                if user in line:
                    uid = line.split(":")[2]
                    break
            for line in group_file:
                if group in line.split(":")[0]:
                    gid = line.split(":")[2]
                    break
            passwd_file.close()
            group_file.close()
            if os.getuid() == 0:
                os.chown(pid_file_path, int(uid), int(gid))
                os.setgid(int(gid))
                os.setuid(int(uid))

    def Start(self):
        """ Performs the operations needed to "start" the daemon """
        pid_file_path = os.path.join(self.__pfile_path, self.__pfile_name)
        if os.access(pid_file_path, os.F_OK):
            old_pid_file = open(pid_file_path, "r")
            old_pid = old_pid_file.read().strip()
            old_pid_file.close()
            if os.access(os.path.join("/proc/", old_pid), os.F_OK):
                raise jwmu_exceptions.DaemonAlreadyRunning()
        if self.__daemon is True:
            try:
                pid_file = open(pid_file_path, "w")
            except IOError:
                raise jwmu_exceptions.WritingPIDFileFailed()
            else:
                pid_file.write(str(os.getpid()) + "\n")
                pid_file.close()

    def Stop(self):
        """ Performs the operations needed to stop the daemon """
        if self.__daemon is True:
            try:
                os.remove(os.path.join(self.__pfile_path, self.__pfile_name))
            except OSError:
                return False
            else:
                return True
        else:
            return True