# Django 2.1.8.dev20190330215650 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.core.exceptions import SuspiciousOperation
    from django.utils.cache import patch_vary_headers
    from django.utils.deprecation import MiddlewareMixin
    from django.utils.http import http_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 = 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 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,
                                samesite=settings.SESSION_COOKIE_SAMESITE,
                            )
            return response