前言:作为工作一个3年左右的码农,在各种框架的摸爬滚打中,我也接触了不少前端后端的技术栈,其中 Django REST Framework(DRF)算是我后端日常工作中的用得最多的框架。今天就简单聊聊DRF请求的生命周期。从请求的发起,到数据的处理,再到最终的响应返回,每一步都有着很多的细节和挑战,由于篇幅原因,我在此篇文章中只是稍作解析,点到为止。
drf中请求的生命周期:
1、django接收请求后,先进行中间件的process_request方法,进行路由匹配后再进行中间件的process_view方法;
class MiddlewareMixin:
# 中间件源码,当有请求进来时,会自动执行中间件的call方法;
# 一般我们自定义中间件都是重写process_request和process_view方法
# 从源码中可看出执行顺序:
def __call__(self, request):
# Exit out to async mode, if needed
if asyncio.iscoroutinefunction(self.get_response):
return self.__acall__(request)
response = None
if hasattr(self, 'process_request'):
response = self.process_request(request)
response = response or self.get_response(request)
if hasattr(self, 'process_response'):
response = self.process_response(request, response)
return response
2、再执行APIView类中的as_view方法获取view函数,并同时免除了csrf认证(闭包原理)
class APIView(View):
# 简略版源码:
@classmethod
def as_view(cls, **initkwargs):
view = super().as_view(**initkwargs) # 调用原Django框架的as_view方法获取view函数
view.cls = cls
view.initkwargs = initkwargs
return csrf_exempt(view)
# 原Django框架的as_view方法:
class View:
@classonlymethod
def as_view(cls, **initkwargs):
def view(request, *args, **kwargs):
self = cls(**initkwargs)
self.setup(request, *args, **kwargs)
return self.dispatch(request, *args, **kwargs) # 调用dispatch函数
view.view_class = cls
view.view_initkwargs = initkwargs
return view
3、通过路由匹配执行view函数,并在view中调用dispatch函数。
class APIView(View):
def dispatch(self, request, *args, **kwargs):
self.args = args
self.kwargs = kwargs
# request封装
request = self.initialize_request(request, *args, **kwargs)
self.request = request
self.headers = self.default_response_headers # deprecate?
try: # 捕获异常
self.initial(request, *args, **kwargs) # 版本管理、认证。权限、限流组件执行
if request.method.lower() in self.http_method_names: # 执行视图函数
handler = getattr(self, request.method.lower(),
self.http_method_not_allowed)
else:
handler = self.http_method_not_allowed
response = handler(request, *args, **kwargs)
except Exception as exc:
response = self.handle_exception(exc)
self.response = self.finalize_response(request, response, *args, **kwargs)
return self.response
4、在dispatch中进行版本管理、request封装、认证、权限、限流处理
# 版本管理
def initial(self, request, *args, **kwargs):
self.format_kwarg = self.get_format_suffix(**kwargs)
version, scheme = self.determine_version(request, *args, **kwargs) # 执行versioning_class中的determine_version方法,获取version和scheme
request.version, request.versioning_scheme = version, scheme # 封装参数到request中
# Ensure that the incoming request is permitted
self.perform_authentication(request)
self.check_permissions(request)
self.check_throttles(request)
# request封装
def initialize_request(self, request, *args, **kwargs):
parser_context = self.get_parser_context(request)
return Request(
request,
parsers=self.get_parsers(),
authenticators=self.get_authenticators(),
negotiator=self.get_content_negotiator(),
parser_context=parser_context
)
#认证
def _authenticate(self):
for authenticator in self.authenticators:
try:
user_auth_tuple = authenticator.authenticate(self) # 执行authenticate方法进行具体的认证流程
except exceptions.APIException:
self._not_authenticated()
raise
if user_auth_tuple is not None:
self._authenticator = authenticator
self.user, self.auth = user_auth_tuple # 将返回值进行封装
return
self._not_authenticated()
# 权限
def check_permissions(self, request):
for permission in self.get_permissions():
if not permission.has_permission(request, self): # 多个权限类中有一个方法为False则报错并抛出异常
self.permission_denied(
request,
message=getattr(permission, 'message', None),
code=getattr(permission, 'code', None)
)
# 限流
def check_throttles(self, request):
throttle_durations = []
for throttle in self.get_throttles(): # 循环执行各限流类中的方法
if not throttle.allow_request(request, self):
throttle_durations.append(throttle.wait()) # 限流方法返回False则将等待时间加到列表中
if throttle_durations:
durations = [
duration for duration in throttle_durations
if duration is not None
]
duration = max(durations, default=None) # 取列表中的最大等待时间
self.throttled(request, duration) # 抛出异常
5、执行具体的视图函数并返回数据
6、执行中间件的process_response方法并返回数据到客户端
以上只是简单分析了一下执行流程,涉及到的源码都是为了方便理解而经过简化的,只供参考。每个组件源码的设计思路和执行流程其实都有一定的复杂度,对于各个组件的源码,我在接下来的日子中也会逐一进行详细剖析。
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