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_responseengine = import_module(settings.SESSION_ENGINE)self.SessionStore = engine.SessionStoredef 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 thesession every time, save the changes and set a session cookie or deletethe session cookie if the session has been emptied."""try:accessed = request.session.accessedmodified = request.session.modifiedempty = request.session.is_empty()except AttributeError:passelse:# First check if we need to delete this cookie.# The session should be deleted only if the session is entirely emptyif 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 = Noneexpires = Noneelse:max_age = request.session.get_expiry_age()expires_time = time.time() + max_ageexpires = 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