uplink/daemon.py

# Copyright (c) 2022 Johannes Findeisen <you@hanez.org>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is furnished
# to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice (including the next
# paragraph) shall be included in all copies or substantial portions of the
# Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
# FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
# OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
# WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
# OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

import atexit
import os
import signal
import sys
import time

from logging import getLogger

logger = getLogger(__name__)


class Daemon:
    """
    Usage: subclass the daemon class and override the run() method.
    """

    def __init__(self, pid_file):
        self.pid_file = pid_file

    def daemonize(self):
        """
        Daemonize the class using the UNIX double fork mechanism.
        """

        # Do first fork
        try:
            pid = os.fork()
            if pid > 0:
                # Exit first parent
                sys.exit(0)
        except OSError as err:
            logger.error(str("fork #1 failed: {0}".format(err)))
            sys.exit(1)

        # Decouple from parent environment
        os.chdir('/')
        os.setsid()
        os.umask(0)

        # Do second fork
        try:
            pid = os.fork()
            if pid > 0:
                # Exit from second parent
                sys.exit(0)
        except OSError as err:
            logger.error(str("fork #2 failed: {0}".format(err)))
            sys.exit(1)

        # Redirect standard file descriptors
        sys.stdout.flush()
        sys.stderr.flush()
        si = open(os.devnull, 'r')
        so = open(os.devnull, 'a+')
        se = open(os.devnull, 'a+')

        os.dup2(si.fileno(), sys.stdin.fileno())
        os.dup2(so.fileno(), sys.stdout.fileno())
        os.dup2(se.fileno(), sys.stderr.fileno())

        # Write pidfile
        atexit.register(self.del_pid)

        pid = str(os.getpid())
        with open(self.pid_file, 'w+') as f:
            f.write(pid + '\n')

    def del_pid(self):
        os.remove(self.pid_file)

    def start(self):
        """
        Start the daemon.
        """

        # Check for a pidfile to see if the daemon already runs
        try:
            with open(self.pid_file, 'r') as pf:
                pid = int(pf.read().strip())
        except IOError:
            pid = None

        if pid:
            message = "pid_file {0} already exist. daemon already running?"
            logger.error(str(message.format(self.pid_file)))
            sys.exit(1)

        # Start the daemon
        self.daemonize()
        self.run()

    def stop(self):
        """
        Stop the daemon.
        """

        # Get the pid from the pid_file
        try:
            with open(self.pid_file, 'r') as pf:
                pid = int(pf.read().strip())
        except IOError:
            pid = None

        if not pid:
            message = "pid_file {0} does not exist. daemon not running?"
            logger.error(str(message.format(self.pid_file)))
            return  # not an error in a restart

        # Try killing the daemon process
        try:
            while 1:
                os.kill(pid, signal.SIGTERM)
                time.sleep(0.1)
        except OSError as err:
            e = str(err.args)
            if e.find("No such process") > 0:
                if os.path.exists(self.pid_file):
                    os.remove(self.pid_file)
            else:
                logger.error(str(err.args))
                sys.exit(1)

    def restart(self):
        """
        Restart the daemon.
        """
        self.stop()
        self.start()

    def run(self):
        """
        You should override this method when you subclass Daemon.

        It will be called after the process has been daemonized by
        start() or restart().
        """