07 flask源码剖析之用户请求过来流程

07 Flask源码之：用户请求过来流程

1.创建ctx = RequestContext对象

• RequestContext对象封装Request对象

• RequestContext对象封装session数据

• 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

• AppContext对象封装App对象

• AppContext对象封装g

• 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

• 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

• 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

• 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

1. 执行full_dispatch_request函数
2. 执行所有的before_request函数
3. 执行视图函数

• 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

• session会加密返回给用户浏览器放到cookie中

• 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 response

  response_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 rv

  def 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

• 如果请求结束不销毁ctx和app_ctx的话，会造成内存泄漏

• 分别调用ctx和app_ctx的pop方法

• 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)

07 flask源码剖析之用户请求过来流程

原文：https://www.cnblogs.com/liubing8/p/11930727.html