text: #!/usr/bin/python
  # -*- coding: utf-8 -*-
  
  # Copyright (c) 2014 clowwindy
  #
  # 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 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.
  
  from __future__ import absolute_import, division, print_function, \
      with_statement
  
  import os
  import sys
  import logging
  import signal
  import time
  from shadowsocks import common
  
  # this module is ported from ShadowVPN daemon.c
  
  
  def daemon_exec(config):
      if 'daemon' in config:
          if os.name != 'posix':
              raise Exception('daemon mode is only supported in unix')
          command = config['daemon']
          if not command:
              command = 'start'
          pid_file = config['pid-file']
          log_file = config['log-file']
          command = common.to_str(command)
          pid_file = common.to_str(pid_file)
          log_file = common.to_str(log_file)
          if command == 'start':
              daemon_start(pid_file, log_file)
          elif command == 'stop':
              daemon_stop(pid_file)
              # always exit after daemon_stop
              sys.exit(0)
          elif command == 'restart':
              daemon_stop(pid_file)
              daemon_start(pid_file, log_file)
          else:
              raise Exception('unsupported daemon command %s' % command)
  
  
  def write_pid_file(pid_file, pid):
      import fcntl
      import stat
  
      try:
          fd = os.open(pid_file, os.O_RDWR | os.O_CREAT,
                       stat.S_IRUSR | stat.S_IWUSR)
      except OSError as e:
          logging.error(e)
          return -1
      flags = fcntl.fcntl(fd, fcntl.F_GETFD)
      assert flags != -1
      flags |= fcntl.FD_CLOEXEC
      r = fcntl.fcntl(fd, fcntl.F_SETFD, flags)
      assert r != -1
      # There is no platform independent way to implement fcntl(fd, F_SETLK, &fl)
      # via fcntl.fcntl. So use lockf instead
      try:
          fcntl.lockf(fd, fcntl.LOCK_EX | fcntl.LOCK_NB, 0, 0, os.SEEK_SET)
      except IOError:
          r = os.read(fd, 32)
          if r:
              logging.error('already started at pid %s' % common.to_str(r))
          else:
              logging.error('already started')
          os.close(fd)
          return -1
      os.ftruncate(fd, 0)
      os.write(fd, common.to_bytes(str(pid)))
      return 0
  
  
  def freopen(f, mode, stream):
      oldf = open(f, mode)
      oldfd = oldf.fileno()
      newfd = stream.fileno()
      os.close(newfd)
      os.dup2(oldfd, newfd)
  
  
  def daemon_start(pid_file, log_file):
      # fork only once because we are sure parent will exit
      pid = os.fork()
      assert pid != -1
  
      def handle_exit(signum, _):
          if signum == signal.SIGTERM:
              sys.exit(0)
          sys.exit(1)
  
      if pid > 0:
          # parent waits for its child
          signal.signal(signal.SIGINT, handle_exit)
          signal.signal(signal.SIGTERM, handle_exit)
          time.sleep(5)
          sys.exit(0)
  
      # child signals its parent to exit
      ppid = os.getppid()
      pid = os.getpid()
      if write_pid_file(pid_file, pid) != 0:
          os.kill(ppid, signal.SIGINT)
          sys.exit(1)
  
      print('started')
      os.kill(ppid, signal.SIGTERM)
  
      sys.stdin.close()
      try:
          freopen(log_file, 'a', sys.stdout)
          freopen(log_file, 'a', sys.stderr)
      except IOError as e:
          logging.error(e)
          os.kill(ppid, signal.SIGINT)
          sys.exit(1)
  
  
  def daemon_stop(pid_file):
      import errno
      try:
          with open(pid_file) as f:
              buf = f.read()
              pid = common.to_str(buf)
              if not buf:
                  logging.error('not running')
      except IOError as e:
          logging.error(e)
          if e.errno == errno.ENOENT:
              # always exit 0 if we are sure daemon is not running
              logging.error('not running')
              return
          sys.exit(1)
      pid = int(pid)
      if pid > 0:
          try:
              os.kill(pid, signal.SIGTERM)
          except OSError as e:
              if e.errno == errno.ESRCH:
                  logging.error('not running')
                  # always exit 0 if we are sure daemon is not running
                  return
              logging.error(e)
              sys.exit(1)
      else:
          logging.error('pid is not positive: %d', pid)
  
      # sleep for maximum 10s
      for i in range(0, 200):
          try:
              # query for the pid
              os.kill(pid, 0)
          except OSError as e:
              if e.errno == errno.ESRCH:
                  break
          time.sleep(0.05)
      else:
          logging.error('timed out when stopping pid %d', pid)
          sys.exit(1)
      print('stopped')
      os.unlink(pid_file)
  