#!/usr/bin/env python
# $Id: unix_daemon.py 977 2012-01-22 23:05:09Z g.rodola $

#  pyftpdlib is released under the MIT license, reproduced below:
#  ======================================================================
#  Copyright (C) 2007-2012 Giampaolo Rodola' <g.rodola@gmail.com>
#
#                         All Rights Reserved
#
# 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
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#  ======================================================================

"""A basic unix daemon using the python-daemon library:
http://pypi.python.org/pypi/python-daemon

Example usages:

 $ python unix_daemon.py start
 $ python unix_daemon.py stop
 $ python unix_daemon.py status
 $ python unix_daemon.py  # foreground (no daemon)
 $ python unix_daemon.py --logfile /var/log/ftpd.log start
 $ python unix_daemon.py --pidfile /var/run/ftpd.pid start

This is just a proof of concept which demonstrates how to daemonize
the FTP server.
You might want to use this as an example and provide the necessary
customizations.

Parts you might want to customize are:
 - UMASK, WORKDIR, HOST, PORT constants
 - get_server() function (to define users and customize FTP handler)

Authors:
 - Ben Timby - btimby <at> gmail.com
 - Giampaolo Rodola' - g.rodola <at> gmail.com
"""

from __future__ import with_statement

import os
import errno
import sys
import time
import optparse
import signal

from pyftpdlib import ftpserver
from pyftpdlib.contrib.authorizers import UnixAuthorizer

# http://pypi.python.org/pypi/python-daemon
import daemon
import daemon.pidfile


# overridable options
HOST = ""
PORT = 21
PID_FILE = "/var/run/pyftpdlib.pid"
LOG_FILE = "/var/log/pyftpdlib.log"
WORKDIR = os.getcwd()
UMASK = 0


def pid_exists(pid):
    """Return True if a process with the given PID is currently running."""
    try:
        os.kill(pid, 0)
    except OSError, e:
        return e.errno == errno.EPERM
    else:
        return True

def get_pid():
    """Return the PID saved in the pid file if possible, else None."""
    try:
        with open(PID_FILE) as f:
            return int(f.read().strip())
    except IOError, err:
        if err.errno != errno.ENOENT:
            raise

def stop():
    """Keep attempting to stop the daemon for 5 seconds, first using
    SIGTERM, then using SIGKILL.
    """
    pid = get_pid()
    if not pid or not pid_exists(pid):
        print "daemon not running"
        return
    sig = signal.SIGTERM
    i = 0
    while True:
        sys.stdout.write('.')
        sys.stdout.flush()
        try:
            os.kill(pid, sig)
        except OSError, e:
            if e.errno == errno.ESRCH:
                print "\nstopped (pid %s)" % pid
                return
            else:
                raise
        i += 1
        if i == 25:
            sig = signal.SIGKILL
        elif i == 50:
            sys.exit("\ncould not kill daemon (pid %s)" % pid)
        time.sleep(0.1)

def status():
    """Print daemon status and exit."""
    pid = get_pid()
    if not pid or not pid_exists(pid):
        print "daemon not running"
    else:
        print "daemon running with pid %s" % pid
    sys.exit(0)

def get_server():
    """Return a pre-configured FTP server instance."""
    # when daemonized, it seems we need to flush() stdout explicitly
    # in order to get the log file written in real time
    def log(s):
        sys.stdout.write(s + "\n")
        sys.stdout.flush()
    ftpserver.log = ftpserver.logline = log
    ftp_handler = ftpserver.FTPHandler
    ftp_handler.authorizer = UnixAuthorizer()
    server = ftpserver.FTPServer((HOST, PORT), ftp_handler)
    return server

def daemonize():
    """A wrapper around python-daemonize context manager."""
    pid = get_pid()
    if pid and pid_exists(pid):
        sys.exit('daemon already running (pid %s)' % pid)
    # instance FTPd before daemonizing, so that in case of problems we
    # get an exception here and exit immediately
    server = get_server()
    logfile = open(LOG_FILE, 'a+')
    ctx = daemon.DaemonContext(
        stdout=logfile,
        stderr=logfile,
        working_directory=WORKDIR,
        umask=UMASK,
        pidfile=daemon.pidfile.TimeoutPIDLockFile(PID_FILE),
        files_preserve=[server],
    )
    with ctx:
        server.serve_forever()

def main():
    global PID_FILE, LOG_FILE
    USAGE = "python [-p PIDFILE] [-l LOGFILE]\n\n" \
            "Commands:\n  - start\n  - stop\n  - status"
    parser = optparse.OptionParser(usage=USAGE)
    parser.add_option('-l', '--logfile', dest='logfile',
                      help='the log file location')
    parser.add_option('-p', '--pidfile', dest='pidfile', default=PID_FILE,
                      help='file to store/retreive daemon pid')
    options, args = parser.parse_args()

    if options.pidfile:
        PID_FILE = options.pidfile
    if options.logfile:
        LOG_FILE = options.logfile

    if not args:
        server = get_server()
        server.serve_forever()
    else:
        if len(args) != 1:
            sys.exit('too many commands')
        elif args[0] == 'start':
            daemonize()
        elif args[0] == 'stop':
            stop()
        elif args[0] == 'status':
            status()
        else:
            sys.exit('invalid command')

if __name__ == '__main__':
    sys.exit(main())