07 Flask源码之：用户请求过来流程
目录
1.创建ctx = RequestContext对象
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RequestContext对象封装Request对象
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RequestContext对象封装session数据
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源码实现：
def wsgi_app(self, environ, start_response): """ ctx = RequestContext(self, environ) """ # 2.1 创建RequestContext对象 ctx = self.request_context(environ)def request_context(self, environ): return RequestContext(self, environ)request_class = Request class RequestContext(object): def __init__(self, app, environ, request=None, session=None): self.app = app if request is None: """ request_class = Request """ request = app.request_class(environ) self.request = request self.session = session
2. 创建app_ctx = AppContext对象
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AppContext对象封装App对象
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AppContext对象封装g
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源码实现：
def wsgi_app(self, environ, start_response): """ ctx = RequestContext(self, environ) """ # 2.1 创建RequestContext对象 ctx = self.request_context(environ) error = None try: try: """ 2.2 执行ctx.push - app_ctx = 创建AppContext对象（app,g） - 将app_ctx放入local中 - 将ctx放入到local中 - session赋值 - 路由匹配 """ ctx.push()def push(self): top = _request_ctx_stack.top if top is not None and top.preserved: top.pop(top._preserved_exc) app_ctx = _app_ctx_stack.top if app_ctx is None or app_ctx.app != self.app: """ app_ctx = AppContext(app) """ # 创建appcontext对象 app_ctx = self.app.app_context()def app_context(self): return AppContext(self)class AppContext(object): def __init__(self, app): self.app = app self.g = app.app_ctx_globals_class()
3. 将ctx对象、app_ctx对象放到local中
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然后ctx.push触发将 ctx对象，通过自己的LocalStack对象将其放入到Local中
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然后app_ctx.push触发将 app_ctx对象，通过自己的LocalStack对象将其放入到Local中
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Local的本质是以线程ID为key，以{“stack”:[]}为value的字典
存储结构：{
1111:{“stack”:[ctx,]}
}； {
1111:{“stack”:[app_ctx,]}
} -
源码示例：
def push(self): top = _request_ctx_stack.top if top is not None and top.preserved: top.pop(top._preserved_exc) app_ctx = _app_ctx_stack.top if app_ctx is None or app_ctx.app != self.app: """ app_ctx = AppContext(app) """ # 创建appcontext对象 app_ctx = self.app.app_context() # push将app_ctx放入到local中 app_ctx.push() self._implicit_app_ctx_stack.append(app_ctx) else: self._implicit_app_ctx_stack.append(None) if hasattr(sys, "exc_clear"): sys.exc_clear() """ self = ctx = RequestContext(self, environ) """ # push将ctx放入到local中 _request_ctx_stack.push(self) if self.session is None: session_interface = self.app.session_interface self.session = session_interface.open_session(self.app, self.request) if self.session is None: self.session = session_interface.make_null_session(self.app) if self.url_adapter is not None: # 路由匹配，将匹配到的endpoint放到request.url_rule中 self.match_request()
4. 执行所有before_request函数以及所有的视图函数
- 执行full_dispatch_request函数
- 执行所有的before_request函数
- 执行视图函数
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源码示例：
def wsgi_app(self, environ, start_response): """ ctx = RequestContext(self, environ) """ #2.1 创建RequestContext对象 ctx = self.request_context(environ) error = None try: try: # 做了很多事 """ 2.2 执行ctx.push - app_ctx = 创建AppContext对象（app,g） - 将app_ctx放入local中 - 将ctx放入到local中 - session赋值 - 路由匹配 """ ctx.push() # 2.3 执行before_request/视图/after_request (处理session) response = self.full_dispatch_request()def full_dispatch_request(self): # 触发所有的before_first_request_funcs函数 # 只在启动程序后，第一个请求到来时执行 self.try_trigger_before_first_request_functions() try: # 信号，暂留 request_started.send(self) # 执行before_request_funcs函数，如果有返回值就不执行视图函数了 rv = self.preprocess_request() if rv is None: # 执行视图函数 rv = self.dispatch_request() except Exception as e: rv = self.handle_user_exception(e) # 视图函数执行之后 # 1.执行所有的after_request # 2.保存session return self.finalize_request(rv)
5. 执行所有after_request函数
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session会加密返回给用户浏览器放到cookie中
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源码示例：
def finalize_request(self, rv, from_error_handler=False): # 将rv视图函数返回值，封装到Reponse对象中 response = self.make_response(rv) response = self.process_response(response) return responseresponse_class = Response def make_response(self, rv): if not isinstance(rv, self.response_class): if isinstance(rv, (text_type, bytes, bytearray)): rv = self.response_class(rv, status=status, headers=headers) return rvdef process_response(self, response): ctx = _request_ctx_stack.top funcs = ctx._after_request_functions # 执行所有的after_request_funcs funcs = chain(funcs, reversed(self.after_request_funcs[None])) for handler in funcs: response = handler(response) if not self.session_interface.is_null_session(ctx.session): # 保存session self.session_interface.save_session(self, ctx.session, response) return response
6. 销毁ctx和app_ctx
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如果请求结束不销毁ctx和app_ctx的话，会造成内存泄漏
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分别调用ctx和app_ctx的pop方法
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源码示例:
def wsgi_app(self, environ, start_response): """ ctx = RequestContext(self, environ) """ #2.1 创建RequestContext对象 ctx = self.request_context(environ) error = None try: try: """ 2.2 执行ctx.push - app_ctx = 创建AppContext对象（app,g） - 将app_ctx放入local中 - 将ctx放入到local中 - session赋值 - 路由匹配 """ ctx.push() # 2.3 执行before_request/视图/after_request (处理session) response = self.full_dispatch_request() except Exception as e: error = e response = self.handle_exception(e) except: # noqa: B001 error = sys.exc_info()[1] raise return response(environ, start_response) finally: if self.should_ignore_error(error): error = None # 2.4 销毁ctx/app_ctx ctx.auto_pop(error)def auto_pop(self, exc): self.pop(exc)def pop(self, exc=_sentinel): app_ctx = self._implicit_app_ctx_stack.pop() finally: rv = _request_ctx_stack.pop() if app_ctx is not None: app_ctx.pop(exc)