heuristics.py 文件源码

def update_headers(self, resp):
        headers = resp.headers

        if 'expires' in headers:
            return {}

        if 'cache-control' in headers and headers['cache-control'] != 'public':
            return {}

        if resp.status not in self.cacheable_by_default_statuses:
            return {}

        if 'date' not in headers or 'last-modified' not in headers:
            return {}

        date = calendar.timegm(parsedate_tz(headers['date']))
        last_modified = parsedate(headers['last-modified'])
        if date is None or last_modified is None:
            return {}

        now = time.time()
        current_age = max(0, now - date)
        delta = date - calendar.timegm(last_modified)
        freshness_lifetime = max(0, min(delta / 10, 24 * 3600))
        if freshness_lifetime <= current_age:
            return {}

        expires = date + freshness_lifetime
        return {'expires': time.strftime(TIME_FMT, time.gmtime(expires))}