# Django 3.2.12 documentation

# Source code for django.contrib.sessions.middleware

    import time
    from importlib import import_module

    from django.conf import settings
    from django.contrib.sessions.backends.base import UpdateError
    from django.contrib.sessions.exceptions import SessionInterrupted
    from django.utils.cache import patch_vary_headers
    from django.utils.deprecation import MiddlewareMixin
    from django.utils.http import http_date

    class SessionMiddleware(MiddlewareMixin):
        # RemovedInDjango40Warning: when the deprecation ends, replace with:
        #   def __init__(self, get_response):
        def __init__(self, get_response=None):
            super().__init__(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:
                return response
            # 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,
                    samesite=settings.SESSION_COOKIE_SAMESITE,
                )
                need_vary_cookie = True
            else:
                # If the session was accessed, it must be varied on, regardless of
                # whether it was modified or will be saved.
                need_vary_cookie = accessed
                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 = http_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 SessionInterrupted(
                                "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,
                            samesite=settings.SESSION_COOKIE_SAMESITE,
                        )
                        # With a session cookie set, it must be varied on.
                        need_vary_cookie = True
            if need_vary_cookie:
                patch_vary_headers(response, ("Cookie",))
            return response