text: # Copyright (c) 2012 OpenStack Foundation.
  # Administrator of the National Aeronautics and Space Administration.
  # All Rights Reserved.
  #
  #    Licensed under the Apache License, Version 2.0 (the "License"); you may
  #    not use this file except in compliance with the License. You may obtain
  #    a copy of the License at
  #
  #         http://www.apache.org/licenses/LICENSE-2.0
  #
  #    Unless required by applicable law or agreed to in writing, software
  #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  #    License for the specific language governing permissions and limitations
  #    under the License.
  
  from __future__ import print_function
  
  import errno
  import gc
  import os
  import pprint
  import socket
  import sys
  import traceback
  
  import eventlet
  import eventlet.backdoor
  import greenlet
  
  from essential.config import cfg
  from essential.gettextutils import _LI
  from essential import log as logging
  
  help_for_backdoor_port = (
      "Acceptable values are 0, <port>, and <start>:<end>, where 0 results "
      "in listening on a random tcp port number; <port> results in listening "
      "on the specified port number (and not enabling backdoor if that port "
      "is in use); and <start>:<end> results in listening on the smallest "
      "unused port number within the specified range of port numbers.  The "
      "chosen port is displayed in the service's log file.")
  eventlet_backdoor_opts = [
      cfg.StrOpt('backdoor_port',
                 default=None,
                 help="Enable eventlet backdoor.  %s" % help_for_backdoor_port)
  ]
  
  CONF = cfg.CONF
  CONF.register_opts(eventlet_backdoor_opts)
  LOG = logging.getLogger(__name__)
  
  
  class EventletBackdoorConfigValueError(Exception):
      def __init__(self, port_range, help_msg, ex):
          msg = ('Invalid backdoor_port configuration %(range)s: %(ex)s. '
                 '%(help)s' %
                 {'range': port_range, 'ex': ex, 'help': help_msg})
          super(EventletBackdoorConfigValueError, self).__init__(msg)
          self.port_range = port_range
  
  
  def _dont_use_this():
      print("Don't use this, just disconnect instead")
  
  
  def _find_objects(t):
      return [o for o in gc.get_objects() if isinstance(o, t)]
  
  
  def _print_greenthreads():
      for i, gt in enumerate(_find_objects(greenlet.greenlet)):
          print(i, gt)
          traceback.print_stack(gt.gr_frame)
          print()
  
  
  def _print_nativethreads():
      for threadId, stack in sys._current_frames().items():
          print(threadId)
          traceback.print_stack(stack)
          print()
  
  
  def _parse_port_range(port_range):
      if ':' not in port_range:
          start, end = port_range, port_range
      else:
          start, end = port_range.split(':', 1)
      try:
          start, end = int(start), int(end)
          if end < start:
              raise ValueError
          return start, end
      except ValueError as ex:
          raise EventletBackdoorConfigValueError(port_range, ex,
                                                 help_for_backdoor_port)
  
  
  def _listen(host, start_port, end_port, listen_func):
      try_port = start_port
      while True:
          try:
              return listen_func((host, try_port))
          except socket.error as exc:
              if (exc.errno != errno.EADDRINUSE or
                 try_port >= end_port):
                  raise
              try_port += 1
  
  
  def initialize_if_enabled():
      backdoor_locals = {
          'exit': _dont_use_this,      # So we don't exit the entire process
          'quit': _dont_use_this,      # So we don't exit the entire process
          'fo': _find_objects,
          'pgt': _print_greenthreads,
          'pnt': _print_nativethreads,
      }
  
      if CONF.backdoor_port is None:
          return None
  
      start_port, end_port = _parse_port_range(str(CONF.backdoor_port))
  
      # NOTE(johannes): The standard sys.displayhook will print the value of
      # the last expression and set it to __builtin__._, which overwrites
      # the __builtin__._ that gettext sets. Let's switch to using pprint
      # since it won't interact poorly with gettext, and it's easier to
      # read the output too.
      def displayhook(val):
          if val is not None:
              pprint.pprint(val)
      sys.displayhook = displayhook
  
      sock = _listen('localhost', start_port, end_port, eventlet.listen)
  
      # In the case of backdoor port being zero, a port number is assigned by
      # listen().  In any case, pull the port number out here.
      port = sock.getsockname()[1]
      LOG.info(
          _LI('Eventlet backdoor listening on %(port)s for process %(pid)d') %
          {'port': port, 'pid': os.getpid()}
      )
      eventlet.spawn_n(eventlet.backdoor.backdoor_server, sock,
                       locals=backdoor_locals)
      return port
  