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

执行full_dispatch_request函数
执行所有的before_request函数
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)