深入探究Django中的Session与Cookie

import time
from importlib import import_module
from django.conf import settings
from django.contrib.sessions.backends.base import UpdateError
from django.core.exceptions import SuspiciousOperation
from django.utils.cache import patch_vary_headers
from django.utils.deprecation import MiddlewareMixin
from django.utils.http import cookie_date
class SessionMiddleware(MiddlewareMixin):
 def __init__(self, get_response=None):
  self.get_response = get_response
  engine = import_module(settings.SESSION_ENGINE)
  self.SessionStore = engine.SessionStore
 def process_request(self, request):
  session_key = request.COOKIES.get(settings.SESSION_COOKIE_NAME)
  request.session = self.SessionStore(session_key)
 def process_response(self, request, response):
  """
  If request.session was modified, or if the configuration is to save the
  session every time, save the changes and set a session cookie or delete
  the session cookie if the session has been emptied.
  """
  try:
   accessed = request.session.accessed
   modified = request.session.modified
   empty = request.session.is_empty()
  except AttributeError:
   pass
  else:
   # First check if we need to delete this cookie.
   # The session should be deleted only if the session is entirely empty
   if settings.SESSION_COOKIE_NAME in request.COOKIES and empty:
    response.delete_cookie(
     settings.SESSION_COOKIE_NAME,
     path=settings.SESSION_COOKIE_PATH,
     domain=settings.SESSION_COOKIE_DOMAIN,
    )
   else:
    if accessed:
     patch_vary_headers(response, ('Cookie',))
    if (modified or settings.SESSION_SAVE_EVERY_REQUEST) and not empty:
     if request.session.get_expire_at_browser_close():
      max_age = None
      expires = None
     else:
      max_age = request.session.get_expiry_age()
      expires_time = time.time() + max_age
      expires = cookie_date(expires_time)
     # Save the session data and refresh the client cookie.
     # Skip session save for 500 responses, refs #3881.
     if response.status_code != 500:
      try:
       request.session.save()
      except UpdateError:
       raise SuspiciousOperation(
        "The request's session was deleted before the "
        "request completed. The user may have logged "
        "out in a concurrent request, for example."
       )
      response.set_cookie(
       settings.SESSION_COOKIE_NAME,
       request.session.session_key, max_age=max_age,
       expires=expires, domain=settings.SESSION_COOKIE_DOMAIN,
       path=settings.SESSION_COOKIE_PATH,
       secure=settings.SESSION_COOKIE_SECURE or None,
       httponly=settings.SESSION_COOKIE_HTTPONLY or None,
      )
  return response