【Django源码阅读】Django 自定义异常处理页面源码解读

# 参考：https://github.com/the5fire/typeidea/blob/deploy-to-cloud/typeidea/typeidea/urls.py#L24
handler404 = Handler404.as_view()
handler500 = Handler50x.as_view()

class Handler404(CommonViewMixin, TemplateView):
    template_name = '404.html'

    def get(self, request, *args, **kwargs):
        context = self.get_context_data(**kwargs)
        return self.render_to_response(context, status=404)


class Handler50x(CommonViewMixin, TemplateView):
    template_name = '50x.html'

    def get(self, request, *args, **kwargs):
        context = self.get_context_data(**kwargs)
        return self.render_to_response(context, status=500)

# 代码：https://github.com/the5fire/django-inside/blob/84f272e1206554b43c86c0f7a50f37d1f3efbc28/django/core/handlers/wsgi.py#L135
class WSGIHandler(base.BaseHandler):
    request_class = WSGIRequest

    def __init__(self, *args, **kwargs):
        super(WSGIHandler, self).__init__(*args, **kwargs)
        self.load_middleware()

    def __call__(self, environ, start_response):
        set_script_prefix(get_script_name(environ))
        signals.request_started.send(sender=self.__class__, environ=environ)
        request = self.request_class(environ)
        response = self.get_response(request)  # the5fire: 注意这儿
        # ... the5fire:省略其他

    # ref: https://github.com/the5fire/django-inside/blob/84f272e1206554b43c86c0f7a50f37d1f3efbc28/django/core/handlers/base.py#L94
    def get_response(self, request):
        """Return an HttpResponse object for the given HttpRequest."""
        # Setup default url resolver for this thread
        set_urlconf(settings.ROOT_URLCONF)

        response = self._middleware_chain(request)  # the5fire: 这里进去

        response._closable_objects.append(request)

        # If the exception handler returns a TemplateResponse that has not
        # been rendered, force it to be rendered.
        if not getattr(response, 'is_rendered', True) and callable(getattr(response, 'render', None)):
            response = response.render()

        if response.status_code == 404:
            logger.warning(
                'Not Found: %s', request.path,
                extra={'status_code': 404, 'request': request},
            )

        return response

    # https://github.com/the5fire/django-inside/blob/84f272e1206554b43c86c0f7a50f37d1f3efbc28/django/core/handlers/base.py#L76
    def load_middleware(self):
        """
        Populate middleware lists from settings.MIDDLEWARE.

        Must be called after the environment is fixed (see __call__ in subclasses).
        """
        self._request_middleware = []
        self._view_middleware = []
        self._template_response_middleware = []
        self._response_middleware = []
        self._exception_middleware = []

        handler = convert_exception_to_response(self._get_response)
        for middleware_path in reversed(settings.MIDDLEWARE):
            middleware = import_string(middleware_path)
            # ...  the5fire：忽略中间这些代码
            handler = convert_exception_to_response(mw_instance)

        # We only assign to this when initialization is complete as it is used
        # as a flag for initialization being complete.
        self._middleware_chain = handler

    def convert_exception_to_response(get_response):
        """
        Wrap the given get_response callable in exception-to-response conversion.

        All exceptions will be converted. All known 4xx exceptions (Http404,
        PermissionDenied, MultiPartParserError, SuspiciousOperation) will be
        converted to the appropriate response, and all other exceptions will be
        converted to 500 responses.

        This decorator is automatically applied to all middleware to ensure that
        no middleware leaks an exception and that the next middleware in the stack
        can rely on getting a response instead of an exception.
        """
        @wraps(get_response)
        def inner(request):
            try:
                response = get_response(request)
            except Exception as exc:
                response = response_for_exception(request, exc)  # the5fire: 这里进去
            return response
        return inner


    def response_for_exception(request, exc):
        if isinstance(exc, Http404):
            if settings.DEBUG:
                response = debug.technical_404_response(request, exc)
            else:
                response = get_exception_response(request, get_resolver(get_urlconf()), 404, exc)

        # ... the5fire: 省略掉一大坨类似的代码

        else:
            signals.got_request_exception.send(sender=None, request=request)
            # the5fire: 下面这一行，具体的处理逻辑。
            response = handle_uncaught_exception(request, get_resolver(get_urlconf()), sys.exc_info())

        # Force a TemplateResponse to be rendered.
        if not getattr(response, 'is_rendered', True) and callable(getattr(response, 'render', None)):
            response = response.render()

        return response

    # https://github.com/the5fire/django-inside/blob/84f272e1206554b43c86c0f7a50f37d1f3efbc28/django/core/handlers/exception.py#L107
    def handle_uncaught_exception(request, resolver, exc_info):
        """
        Processing for any otherwise uncaught exceptions (those that will
        generate HTTP 500 responses).
        """
        if settings.DEBUG_PROPAGATE_EXCEPTIONS:
            raise

        logger.error(
            'Internal Server Error: %s', request.path,
            exc_info=exc_info,
            extra={'status_code': 500, 'request': request},
        )

        if settings.DEBUG:
            return debug.technical_500_response(request, *exc_info)

        # Return an HttpResponse that displays a friendly error message.
        # the5fire: 这里会解析到对应的handler ，比如我们定义的那个
        callback, param_dict = resolver.resolve_error_handler(500)
        return callback(request, **param_dict)

    # 完整代码: https://github.com/the5fire/django-inside/blob/84f272e1206554b43c86c0f7a50f37d1f3efbc28/django/urls/resolvers.py#L555
    def resolve_error_handler(self, view_type):
        callback = getattr(self.urlconf_module, 'handler%s' % view_type, None)  # the5fire: 这里就是去获取 urls.py 中对应的配置
        if not callback:
            # No handler specified in file; use lazy import, since
            # django.conf.urls imports this file.
            from django.conf import urls
            callback = getattr(urls, 'handler%s' % view_type)
        return get_callable(callback), {}