flask源码解析_flask app_ctx_stack

flask源码解析

flask源码解析

flask启动时如何收集所有的路由

1.收集静态资源路由

初始化时收集
flask init时

        if self.has_static_folder:
            assert bool(static_host) == host_matching, 'Invalid static_host/host_matching combination'
            self.add_url_rule(
                self.static_url_path + '/<path:filename>',
                endpoint='static',
                host=static_host,
                view_func=self.send_static_file
            )
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2.收集@app.route()路由

初始化时读到@app.route()就添加

    def route(self, rule, **options):
        """A decorator that is used to register a view function for a
        given URL rule.  This does the same thing as :meth:`add_url_rule`
        but is intended for decorator usage::

            @app.route('/')
            def index():
                return 'Hello World'

        For more information refer to :ref:`url-route-registrations`.

        :param rule: the URL rule as string
        :param endpoint: the endpoint for the registered URL rule.  Flask
                         itself assumes the name of the view function as
                         endpoint
        :param options: the options to be forwarded to the underlying
                        :class:`~werkzeug.routing.Rule` object.  A change
                        to Werkzeug is handling of method options.  methods
                        is a list of methods this rule should be limited
                        to (``GET``, ``POST`` etc.).  By default a rule
                        just listens for ``GET`` (and implicitly ``HEAD``).
                        Starting with Flask 0.6, ``OPTIONS`` is implicitly
                        added and handled by the standard request handling.
        """
        def decorator(f):
            endpoint = options.pop('endpoint', None)
            self.add_url_rule(rule, endpoint, f, **options)
            return f
        return decorator
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3.收集蓝图下的路由

读到@index_bp.route(）即添加

self.url_adapter = app.create_url_adapter(self.request)
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实际调用 添加Rule对象

return Map.bind(
            self,
            server_name,
            script_name,
            subdomain,
            environ["wsgi.url_scheme"],
            environ["REQUEST_METHOD"],
            path_info,
            query_args=query_args,
        )
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无论是哪种定义方式 均是由Flask的add_url_rule()
先定义endpoint 若没有则 获取view_func的.name
再获取所有的methods 未设置则给默认值GET
rule = self.url_rule_class(rule, methods=methods, **options)中的rule是一个Rule对象 rule入参是route中的参数
添加到rule_map中 同时去view_functions中根据endpoint去获取值 以此来去重 如为获取到值 就新增

当请求进入flask时 同样 根据请求url来做endpoint从view_functions取值来分发请求

请求在flask中的处理流程

生成request对象把请求的method args 包装起来供在视图函数中使用 同时先生成app上下文 再生成request上下文 并开启session 并把根据正则 match出 请求对应的view_func
在分发请求前 chain()调用请求钩子 再到视图函数
视图函数业务逻辑处理完成之后 经由flask的finalize_request的make_response 包装成一个可返回的Response对象 基本就是补充默认的 headers 和 status
​​

此处的app是一个DispatchingApp 加上()之后触发了他的__call__方法

https://img-blog.csdnimg.cn/3d845ea96788491e9bf9481c03756538.png

1.ctx = self.request_context(environ)

生成request对象

1.flask在wsgi_app中生成一个ctx对象 ctx是一个RequestContext

RequestContext的主要方法 push pop
push方法主要是生成一个request app上下文 并从此开启session

RequestContext对象 init时 生成self.request = app.request_class(environ)
app.request_class就是Request

request因此有了json的相关方法 并带有自身的endpoint blueprint的属性

init时还有一个match_request方法


最终返回值 rule.endpoint, rv rv应是request.view_args
并在match_request方法中给request.url_rule赋值 即endpoint

2.ctx.push()

_app_ctx_stack是一个LocalStack对象
LocalStack 包含push pop方法及top属性 因此 app_ctx =self._local.stack[-1]

此时是未取到stack的值 获取到了None的
当app_ctx是None或者 app_ctx.app != self.app时 调用app_ctx.push()

push 实际就是 self._local.stack在此处被赋值

3.full_dispatch_request()

    def full_dispatch_request(self):
        """Dispatches the request and on top of that performs request
        pre and postprocessing as well as HTTP exception catching and
        error handling.

        .. versionadded:: 0.7
        """
        self.try_trigger_before_first_request_functions()
        try:
            request_started.send(self)
            rv = self.preprocess_request()
            if rv is None:
                rv = self.dispatch_request()
        except Exception as e:
            rv = self.handle_user_exception(e)
        return self.finalize_request(rv)
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1.preprocess_request 中处理了hook

1.self.url_value_preprocessors

处理bp的钩子函数

    def preprocess_request(self):
        """Called before the request is dispatched. Calls
        :attr:`url_value_preprocessors` registered with the app and the
        current blueprint (if any). Then calls :attr:`before_request_funcs`
        registered with the app and the blueprint.

        If any :meth:`before_request` handler returns a non-None value, the
        value is handled as if it was the return value from the view, and
        further request handling is stopped.
        """

        bp = _request_ctx_stack.top.request.blueprint

        funcs = self.url_value_preprocessors.get(None, ())
        if bp is not None and bp in self.url_value_preprocessors:
            funcs = chain(funcs, self.url_value_preprocessors[bp])
        for func in funcs:
            func(request.endpoint, request.view_args)

        funcs = self.before_request_funcs.get(None, ())
        if bp is not None and bp in self.before_request_funcs:
            funcs = chain(funcs, self.before_request_funcs[bp])
        for func in funcs:
            rv = func()
            if rv is not None:
                return rv
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2.self.before_request_funcs

处理请求的钩子函数

2.dispatch_request()

实际请求分发到对应视图过程

    def finalize_request(self, rv, from_error_handler=False):
        """Given the return value from a view function this finalizes
        the request by converting it into a response and invoking the
        postprocessing functions.  This is invoked for both normal
        request dispatching as well as error handlers.

        Because this means that it might be called as a result of a
        failure a special safe mode is available which can be enabled
        with the `from_error_handler` flag.  If enabled, failures in
        response processing will be logged and otherwise ignored.

        :internal:
        """
        response = self.make_response(rv)
        try:
            response = self.process_response(response)
            request_finished.send(self, response=response)
        except Exception:
            if not from_error_handler:
                raise
            self.logger.exception('Request finalizing failed with an '
                                  'error while handling an error')
        return response
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3.finalize_request(rv)

1.make_response

仅返回str时 flask帮我们生成一个可返回的Response对象 并添加默认status headers

# make sure the body is an instance of the response class
        if not isinstance(rv, self.response_class):
            if isinstance(rv, (text_type, bytes, bytearray)):
                # let the response class set the status and headers instead of
                # waiting to do it manually, so that the class can handle any
                # special logic
                rv = self.response_class(rv, status=status, headers=headers)
                status = headers = None
            else:
                # evaluate a WSGI callable, or coerce a different response
                # class to the correct type
                try:
                    rv = self.response_class.force_type(rv, request.environ)
                except TypeError as e:
                    new_error = TypeError(
                        '{e}\nThe view function did not return a valid'
                        ' response. The return type must be a string, tuple,'
                        ' Response instance, or WSGI callable, but it was a'
                        ' {rv.__class__.__name__}.'.format(e=e, rv=rv)
                    )
                    reraise(TypeError, new_error, sys.exc_info()[2])

        # prefer the status if it was provided
        if status is not None:
            if isinstance(status, (text_type, bytes, bytearray)):
                rv.status = status
            else:
                rv.status_code = status

        # extend existing headers with provided headers
        if headers:
            rv.headers.extend(headers)

        return rv
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2.process_response

1.再次调用hook

    def process_response(self, response):
        """Can be overridden in order to modify the response object
        before it's sent to the WSGI server.  By default this will
        call all the :meth:`after_request` decorated functions.

        .. versionchanged:: 0.5
           As of Flask 0.5 the functions registered for after request
           execution are called in reverse order of registration.

        :param response: a :attr:`response_class` object.
        :return: a new response object or the same, has to be an
                 instance of :attr:`response_class`.
        """
        ctx = _request_ctx_stack.top
        bp = ctx.request.blueprint
        funcs = ctx._after_request_functions
        if bp is not None and bp in self.after_request_funcs:
            funcs = chain(funcs, reversed(self.after_request_funcs[bp]))
        if None in self.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):
            self.session_interface.save_session(self, ctx.session, response)
        return response
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2.并设置响应的cookie

    def save_session(self, app, session, response):
        domain = self.get_cookie_domain(app)
        path = self.get_cookie_path(app)

        # If the session is modified to be empty, remove the cookie.
        # If the session is empty, return without setting the cookie.
        if not session:
            if session.modified:
                response.delete_cookie(
                    app.session_cookie_name,
                    domain=domain,
                    path=path
                )

            return

        # Add a "Vary: Cookie" header if the session was accessed at all.
        if session.accessed:
            response.vary.add('Cookie')

        if not self.should_set_cookie(app, session):
            return

        httponly = self.get_cookie_httponly(app)
        secure = self.get_cookie_secure(app)
        samesite = self.get_cookie_samesite(app)
        expires = self.get_expiration_time(app, session)
        val = self.get_signing_serializer(app).dumps(dict(session))
        response.set_cookie(
            app.session_cookie_name,
            val,
            expires=expires,
            httponly=httponly,
            domain=domain,
            path=path,
            secure=secure,
            samesite=samesite
        )
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full_dispatch_request调用完成 如果出现异常就是捕获异常
再调用BaseResponse 包装成get_wsgi_response返回
调用ctx.auto_pop(error)时 do_teardown_request被调用

    def do_teardown_request(self, exc=_sentinel):
        """Called after the request is dispatched and the response is
        returned, right before the request context is popped.

        This calls all functions decorated with
        :meth:`teardown_request`, and :meth:`Blueprint.teardown_request`
        if a blueprint handled the request. Finally, the
        :data:`request_tearing_down` signal is sent.

        This is called by
        :meth:`RequestContext.pop() <flask.ctx.RequestContext.pop>`,
        which may be delayed during testing to maintain access to
        resources.

        :param exc: An unhandled exception raised while dispatching the
            request. Detected from the current exception information if
            not passed. Passed to each teardown function.

        .. versionchanged:: 0.9
            Added the ``exc`` argument.
        """
        if exc is _sentinel:
            exc = sys.exc_info()[1]
        funcs = reversed(self.teardown_request_funcs.get(None, ()))
        bp = _request_ctx_stack.top.request.blueprint
        if bp is not None and bp in self.teardown_request_funcs:
            funcs = chain(funcs, reversed(self.teardown_request_funcs[bp]))
        for func in funcs:
            func(exc)
        request_tearing_down.send(self, exc=exc)
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再调用LocalStack的pop 将request上下文清除 再清除app上下文

    def pop(self):
        """Removes the topmost item from the stack, will return the
        old value or `None` if the stack was already empty.
        """
        stack = getattr(self._local, "stack", None)
        if stack is None:
            return None
        elif len(stack) == 1:
            release_local(self._local)
            return stack[-1]
        else:
            return stack.pop()
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4. ctx.auto_pop(error)

实际调用了RequestContext.pop(exc)

        finally:
            rv = _request_ctx_stack.pop()

            # get rid of circular dependencies at the end of the request
            # so that we don't require the GC to be active.
            if clear_request:
                rv.request.environ['werkzeug.request'] = None

            # Get rid of the app as well if necessary.
            if app_ctx is not None:
                app_ctx.pop(exc)
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该方法又会调用app_ctx.pop(exc) 通过对引用计数 -= 1来回收app_cxt的回收

 def pop(self, exc=_sentinel):
        """Pops the app context."""
        try:
            self._refcnt -= 1
            if self._refcnt <= 0:
                if exc is _sentinel:
                    exc = sys.exc_info()[1]
                self.app.do_teardown_appcontext(exc)
        finally:
            rv = _app_ctx_stack.pop()
        assert rv is self, 'Popped wrong app context.  (%r instead of %r)' \
            % (rv, self)
        appcontext_popped.send(self.app)
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