class AuditMiddleware:
    def __init__(self, stats):
        self.stats = stats

    @classmethod
    def from_crawler(cls, crawler):
        return cls(crawler.stats)

    def process_request(self, request):
        request.headers.setdefault(
            "X-Crawl-Source",
            "demo",
        )
        self.stats.inc_value("audit/request")
        return None

    def process_response(self, request, response):
        self.stats.inc_value(
            f"audit/status/{response.status}"
        )
        return response