response对象
原理
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实现full_dispatch_request方法
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回到wsgi_app方法
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回顾一下wsgi协议
你要被wsgi server调用，那么你的返回值，应该是可以被迭代的，例如下面的list
def application(environ, start_response): start_response(‘200 OK’, [(‘Content-Type’, ‘text/html’)]) return [b'<h1>Hello, web!</h1>’]也就是在flask里面，这个Response对象，执行 __call__方法之后返回的是一个类似 list的可迭代对象
我们知道既然Response对象是被finalize_request方法返回的，那他的实例化过程应该就在这个方法中
我们找到 finalize_request方法
def finalize_request(self, rv, from_error_handler=False): 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再看 make_response，代码有点多
这个函数的大概逻辑就是，你的rv是视图函数的返回值
如果返回值本身就是 Response 实例，就直接使用它；如果返回值是字符串类型，就把它作为响应的 body，并自动设置状态码和头部信息；如果返回值是 tuple，会尝试用 (response, status, headers) 或者 (response, headers) 去解析。
def make_response(self, rv):
# make sure the body is an instance of the response class # 看这里就好了， 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 elif isinstance(rv, dict): rv = jsonify(rv) elif isinstance(rv, BaseResponse) or callable(rv): # 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, dict, 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]) else: raise TypeError( “The view function did not return a valid” ” response. The return type must be a string, dict, tuple,” ” Response instance, or WSGI callable, but it was a” ” {rv.__class__.__name__}.”.format(rv=rv) )
# 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我们还可以看出来，Response对象就是 response_class的实例，点进去就可以看到定义了
Response定义class Response(ResponseBase, JSONMixin): default_mimetype = “text/html”
def _get_data_for_json(self, cache): return self.get_data()
@property def max_cookie_size(self): “””Read-only view of the :data:`MAX_COOKIE_SIZE` config key.
See :attr:`~werkzeug.wrappers.BaseResponse.max_cookie_size` in Werkzeug’s docs. “”” if current_app: return current_app.config[“MAX_COOKIE_SIZE”]
# return Werkzeug’s default when not in an app context return super(Response, self).max_cookie_size又是mixin实现多继承
别忘了，我们的目的是看他的 __call__方法返回的是否是迭代对象
不用大海捞针去父类找，pycharm已经帮我们找好了，在左侧structure中找
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def __call__(self, environ, start_response): “””Process this response as WSGI application.
:param environ: the WSGI environment. :param start_response: the response callable provided by the WSGI server. :return: an application iterator “”” app_iter, status, headers = self.get_wsgi_response(environ) start_response(status, headers) return app_iter看名字也知道，app_iter是可迭代对象，可以被wsgi server迭代调用
start_response是 wsgi server提供的回调函数，我们调用就好了，wsgi server会帮我们返回http response
再看一眼 wsgi协议的demo
def application(environ, start_response): start_response(‘200 OK’, [(‘Content-Type’, ‘text/html’)]) return [b'<h1>Hello, web!</h1>’]可以发现 header的格式要是list套 tuple这种
werkzeug实现了Headers数据结构
定义在
fro werkzeug.datastructures import Headers他是一个类似字典的数据结构，只不过支持多个相同的key以及key的有序
参考Headers对象[1]
自定义Response对象我们知道Reseponse对象是在 make_response 这样被实例化的
rv = self.response_class(rv, status=status, headers=headers)因此我们只需要
from flask import Flask, Response
class MyResponse(Response): pass
app = Flask(__name__)app.response_class = MyResponse
便可以定义我们自己的Response对象
References[1] Headers对象: https://cizixs.com/2017/01/22/flask-insight-response/
