ContentNotRenderedError：响应内容必须先渲染才能访问（Django 中间件）

Question

我正在创建 Django 中间件，用于在用户被限制超过 5 次时阻止用户，但我得到了ContentNotRenderedError.

完整错误消息：

Traceback (most recent call last):
  File "/home/raptor/Application/utilities/anaconda3/envs/slic4rapi/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/home/raptor/Application/utilities/anaconda3/envs/slic4rapi/lib/python3.8/site-packages/django/utils/deprecation.py", line 119, in __call__
    response = self.process_response(request, response)
  File "/home/raptor/Application/utilities/anaconda3/envs/slic4rapi/lib/python3.8/site-packages/django/middleware/common.py", line 113, in process_response
    response.headers['Content-Length'] = str(len(response.content))
  File "/home/raptor/Application/utilities/anaconda3/envs/slic4rapi/lib/python3.8/site-packages/django/template/response.py", line 126, in content
    raise ContentNotRenderedError(
django.template.response.ContentNotRenderedError: The response content must be rendered before it can be accessed.
[22/Mar/2022 11:55:03] "GET /api/v1/userdetail/ HTTP/1.1" 500 84321

中间件类

class BlockMiddleware:
    
    def __init__(self, get_response):
        self.get_response = get_response
        # some other variables
    
    def __call__(self, request):
        # handle_blocking will return "None" if user can access application else "rest_framework.response.Response" object
        blocking_res = self.handle_blocking(request)
        if blocking_res:
            return blocking_res

        response = self.get_response(request)
        # logic for counting how many throttles have left
        # then
        if throttles_left <= 0:
            return Response(
                    data='User is blocked due to exceeding throttles limit.',
                    status=status.HTTP_403_FORBIDDEN
                )
        else:
            return response

函数返回示例handle_blocking：

return Response(
    data='User is blocked, please contact the support team.',
    status=status.HTTP_403_FORBIDDEN
)

当我删除中间件并且不使用该类Response（而是返回 self.get_response(request) ）时，它会起作用。我无法找出错误。我究竟做错了什么？

Answer 1

如果你确实想返回一个Response实例，则需要在返回之前设置一些属性：

from rest_framework.renderers import JSONRenderer

class BlockMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response
    
    def __call__(self, request):
        blocking_res = self.handle_blocking(request)
        if blocking_res:
            return blocking_res

        response = self.get_response(request)
        if throttles_left <= 0:
            response = Response(
               data='User is blocked due to exceeding throttles limit.',
               status=status.HTTP_403_FORBIDDEN
            )
            response.accepted_renderer = JSONRenderer()
            response.accepted_media_type = "application/json"
            response.renderer_context = {}
            response.render()
            return response
        else:
            return response

您还需要在handle_blocking实现中执行相同的操作，例如：

from rest_framework.renderers import JSONRenderer
response = Response(
    data='User is blocked, please contact the support team.',
    status=status.HTTP_403_FORBIDDEN
)
response.accepted_renderer = JSONRenderer()
response.accepted_media_type = "application/json"
response.renderer_context = {}
response.render()
return response

这些属性通常由api_view装饰器设置，不能与中间件一起使用，因此您必须手动设置它们。