SessionMiddleware
浏览器会发送包含SESSION_COOKIE_NAME的的Cookie中间件从django_session中按照SESSION_COOKIE_NAME取出存入的session，
设置request中的session属性(SessionStore)，包括_auth_user_id,_auth_user_backend,_auth_user_hash等
返回response时同步session和返回给浏览器的cookie状态源码：
class SessionMiddleware(MiddlewareMixin):
def __init__(self, get_response=None):
#初始化session，django启动时执行一次
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) #从cookie中读取sessionkey
request.session = self.SessionStore(session_key) #根据sessionkey从django_session中读取session 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
# 如果cookie有sessionid并且请求中session是空的，将cookie中的session置空
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',))
# 如果更改过session并且请求中的session非空，保存session数据，并且更新返回的cookie（返回状态500除外）
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
AuthenticationMiddleware
比较简单，根据request请求设置request中的user和cache user，返回的为惰性加载对象
源码：
如果此时传入的request中有_cached_user，则会跳过从request中获取登录对象的操作
def get_user(request):
if not hasattr(request, '_cached_user'):
request._cached_user = auth.get_user(request)
return request._cached_user
class AuthenticationMiddleware(MiddlewareMixin):
def process_request(self, request):
#必选先执行session middleware，不然报错
assert hasattr(request, 'session'), (
"The Django authentication middleware requires session middleware "
"to be installed. Edit your MIDDLEWARE%s setting to insert "
"'django.contrib.sessions.middleware.SessionMiddleware' before "
"'django.contrib.auth.middleware.AuthenticationMiddleware'."
) % ("_CLASSES" if settings.MIDDLEWARE is None else "")
#request.user为从request中得到的用户
request.user = SimpleLazyObject(lambda: get_user(request))
