text: # -*- coding: utf-8 -*-
  r"""
      werkzeug.contrib.sessions
      ~~~~~~~~~~~~~~~~~~~~~~~~~
  
      This module contains some helper classes that help one to add session
      support to a python WSGI application.  For full client-side session
      storage see :mod:`~werkzeug.contrib.securecookie` which implements a
      secure, client-side session storage.
  
  
      Application Integration
      =======================
  
      ::
  
          from werkzeug.contrib.sessions import SessionMiddleware, \
               FilesystemSessionStore
  
          app = SessionMiddleware(app, FilesystemSessionStore())
  
      The current session will then appear in the WSGI environment as
      `werkzeug.session`.  However it's recommended to not use the middleware
      but the stores directly in the application.  However for very simple
      scripts a middleware for sessions could be sufficient.
  
      This module does not implement methods or ways to check if a session is
      expired.  That should be done by a cronjob and storage specific.  For
      example to prune unused filesystem sessions one could check the modified
      time of the files.  It sessions are stored in the database the new()
      method should add an expiration timestamp for the session.
  
      For better flexibility it's recommended to not use the middleware but the
      store and session object directly in the application dispatching::
  
          session_store = FilesystemSessionStore()
  
          def application(environ, start_response):
              request = Request(environ)
              sid = request.cookies.get('cookie_name')
              if sid is None:
                  request.session = session_store.new()
              else:
                  request.session = session_store.get(sid)
              response = get_the_response_object(request)
              if request.session.should_save:
                  session_store.save(request.session)
                  response.set_cookie('cookie_name', request.session.sid)
              return response(environ, start_response)
  
      :copyright: (c) 2014 by the Werkzeug Team, see AUTHORS for more details.
      :license: BSD, see LICENSE for more details.
  """
  import re
  import os
  import sys
  import tempfile
  from os import path
  from time import time
  from random import random
  from hashlib import sha1
  from pickle import dump, load, HIGHEST_PROTOCOL
  
  from werkzeug.datastructures import CallbackDict
  from werkzeug.utils import dump_cookie, parse_cookie
  from werkzeug.wsgi import ClosingIterator
  from werkzeug.posixemulation import rename
  from werkzeug._compat import PY2, text_type
  
  
  _sha1_re = re.compile(r'^[a-f0-9]{40}$')
  
  
  def _urandom():
      if hasattr(os, 'urandom'):
          return os.urandom(30)
      return text_type(random()).encode('ascii')
  
  
  def generate_key(salt=None):
      if salt is None:
          salt = repr(salt).encode('ascii')
      return sha1(b''.join([
          salt,
          str(time()).encode('ascii'),
          _urandom()
      ])).hexdigest()
  
  
  class ModificationTrackingDict(CallbackDict):
      __slots__ = ('modified',)
  
      def __init__(self, *args, **kwargs):
          def on_update(self):
              self.modified = True
          self.modified = False
          CallbackDict.__init__(self, on_update=on_update)
          dict.update(self, *args, **kwargs)
  
      def copy(self):
          """Create a flat copy of the dict."""
          missing = object()
          result = object.__new__(self.__class__)
          for name in self.__slots__:
              val = getattr(self, name, missing)
              if val is not missing:
                  setattr(result, name, val)
          return result
  
      def __copy__(self):
          return self.copy()
  
  
  class Session(ModificationTrackingDict):
      """Subclass of a dict that keeps track of direct object changes.  Changes
      in mutable structures are not tracked, for those you have to set
      `modified` to `True` by hand.
      """
      __slots__ = ModificationTrackingDict.__slots__ + ('sid', 'new')
  
      def __init__(self, data, sid, new=False):
          ModificationTrackingDict.__init__(self, data)
          self.sid = sid
          self.new = new
  
      def __repr__(self):
          return '<%s %s%s>' % (
              self.__class__.__name__,
              dict.__repr__(self),
              self.should_save and '*' or ''
          )
  
      @property
      def should_save(self):
          """True if the session should be saved.
  
          .. versionchanged:: 0.6
             By default the session is now only saved if the session is
             modified, not if it is new like it was before.
          """
          return self.modified
  
  
  class SessionStore(object):
      """Baseclass for all session stores.  The Werkzeug contrib module does not
      implement any useful stores besides the filesystem store, application
      developers are encouraged to create their own stores.
  
      :param session_class: The session class to use.  Defaults to
                            :class:`Session`.
      """
  
      def __init__(self, session_class=None):
          if session_class is None:
              session_class = Session
          self.session_class = session_class
  
      def is_valid_key(self, key):
          """Check if a key has the correct format."""
          return _sha1_re.match(key) is not None
  
      def generate_key(self, salt=None):
          """Simple function that generates a new session key."""
          return generate_key(salt)
  
      def new(self):
          """Generate a new session."""
          return self.session_class({}, self.generate_key(), True)
  
      def save(self, session):
          """Save a session."""
  
      def save_if_modified(self, session):
          """Save if a session class wants an update."""
          if session.should_save:
              self.save(session)
  
      def delete(self, session):
          """Delete a session."""
  
      def get(self, sid):
          """Get a session for this sid or a new session object.  This method
          has to check if the session key is valid and create a new session if
          that wasn't the case.
          """
          return self.session_class({}, sid, True)
  
  
  #: used for temporary files by the filesystem session store
  _fs_transaction_suffix = '.__wz_sess'
  
  
  class FilesystemSessionStore(SessionStore):
      """Simple example session store that saves sessions on the filesystem.
      This store works best on POSIX systems and Windows Vista / Windows
      Server 2008 and newer.
  
      .. versionchanged:: 0.6
         `renew_missing` was added.  Previously this was considered `True`,
         now the default changed to `False` and it can be explicitly
         deactivated.
  
      :param path: the path to the folder used for storing the sessions.
                   If not provided the default temporary directory is used.
      :param filename_template: a string template used to give the session
                                a filename.  ``%s`` is replaced with the
                                session id.
      :param session_class: The session class to use.  Defaults to
                            :class:`Session`.
      :param renew_missing: set to `True` if you want the store to
                            give the user a new sid if the session was
                            not yet saved.
      """
  
      def __init__(self, path=None, filename_template='werkzeug_%s.sess',
                   session_class=None, renew_missing=False, mode=0o644):
          SessionStore.__init__(self, session_class)
          if path is None:
              path = tempfile.gettempdir()
          self.path = path
          if isinstance(filename_template, text_type) and PY2:
              filename_template = filename_template.encode(
                  sys.getfilesystemencoding() or 'utf-8')
          assert not filename_template.endswith(_fs_transaction_suffix), \
              'filename templates may not end with %s' % _fs_transaction_suffix
          self.filename_template = filename_template
          self.renew_missing = renew_missing
          self.mode = mode
  
      def get_session_filename(self, sid):
          # out of the box, this should be a strict ASCII subset but
          # you might reconfigure the session object to have a more
          # arbitrary string.
          if isinstance(sid, text_type) and PY2:
              sid = sid.encode(sys.getfilesystemencoding() or 'utf-8')
          return path.join(self.path, self.filename_template % sid)
  
      def save(self, session):
          fn = self.get_session_filename(session.sid)
          fd, tmp = tempfile.mkstemp(suffix=_fs_transaction_suffix,
                                     dir=self.path)
          f = os.fdopen(fd, 'wb')
          try:
              dump(dict(session), f, HIGHEST_PROTOCOL)
          finally:
              f.close()
          try:
              rename(tmp, fn)
              os.chmod(fn, self.mode)
          except (IOError, OSError):
              pass
  
      def delete(self, session):
          fn = self.get_session_filename(session.sid)
          try:
              os.unlink(fn)
          except OSError:
              pass
  
      def get(self, sid):
          if not self.is_valid_key(sid):
              return self.new()
          try:
              f = open(self.get_session_filename(sid), 'rb')
          except IOError:
              if self.renew_missing:
                  return self.new()
              data = {}
          else:
              try:
                  try:
                      data = load(f)
                  except Exception:
                      data = {}
              finally:
                  f.close()
          return self.session_class(data, sid, False)
  
      def list(self):
          """Lists all sessions in the store.
  
          .. versionadded:: 0.6
          """
          before, after = self.filename_template.split('%s', 1)
          filename_re = re.compile(r'%s(.{5,})%s$' % (re.escape(before),
                                                      re.escape(after)))
          result = []
          for filename in os.listdir(self.path):
              #: this is a session that is still being saved.
              if filename.endswith(_fs_transaction_suffix):
                  continue
              match = filename_re.match(filename)
              if match is not None:
                  result.append(match.group(1))
          return result
  
  
  class SessionMiddleware(object):
      """A simple middleware that puts the session object of a store provided
      into the WSGI environ.  It automatically sets cookies and restores
      sessions.
  
      However a middleware is not the preferred solution because it won't be as
      fast as sessions managed by the application itself and will put a key into
      the WSGI environment only relevant for the application which is against
      the concept of WSGI.
  
      The cookie parameters are the same as for the :func:`~dump_cookie`
      function just prefixed with ``cookie_``.  Additionally `max_age` is
      called `cookie_age` and not `cookie_max_age` because of backwards
      compatibility.
      """
  
      def __init__(self, app, store, cookie_name='session_id',
                   cookie_age=None, cookie_expires=None, cookie_path='/',
                   cookie_domain=None, cookie_secure=None,
                   cookie_httponly=False, environ_key='werkzeug.session'):
          self.app = app
          self.store = store
          self.cookie_name = cookie_name
          self.cookie_age = cookie_age
          self.cookie_expires = cookie_expires
          self.cookie_path = cookie_path
          self.cookie_domain = cookie_domain
          self.cookie_secure = cookie_secure
          self.cookie_httponly = cookie_httponly
          self.environ_key = environ_key
  
      def __call__(self, environ, start_response):
          cookie = parse_cookie(environ.get('HTTP_COOKIE', ''))
          sid = cookie.get(self.cookie_name, None)
          if sid is None:
              session = self.store.new()
          else:
              session = self.store.get(sid)
          environ[self.environ_key] = session
  
          def injecting_start_response(status, headers, exc_info=None):
              if session.should_save:
                  self.store.save(session)
                  headers.append(('Set-Cookie', dump_cookie(self.cookie_name,
                                  session.sid, self.cookie_age,
                                  self.cookie_expires, self.cookie_path,
                                  self.cookie_domain, self.cookie_secure,
                                  self.cookie_httponly)))
              return start_response(status, headers, exc_info)
          return ClosingIterator(self.app(environ, injecting_start_response),
                                 lambda: self.store.save_if_modified(session))
  