def abort_if_not_modified(self, last_modified, private=True,
                              max_age=timedelta(0),
                              must_revalidate=True):
        """Check If-Modified-Since and abort(304) if appropriate."""

        if c.user_is_loggedin and not c.allow_loggedin_cache:
            return

        # HTTP timestamps round to nearest second. truncate this value for
        # comparisons.
        last_modified = last_modified.replace(microsecond=0)

        date_str = http_utils.http_date_str(last_modified)
        response.headers['last-modified'] = date_str

        cache_control = []
        if private:
            cache_control.append('private')
        cache_control.append('max-age=%d' % max_age.total_seconds())
        if must_revalidate:
            cache_control.append('must-revalidate')
        response.headers['cache-control'] = ', '.join(cache_control)

        modified_since = request.if_modified_since
        if modified_since and modified_since >= last_modified:
            abort(304, 'not modified')

    def check_modified(self, thing, action):
        if c.user_is_loggedin:
            return

        date = utils.is_modified_since(thing, action, request.if_modified_since)
        if date is True:
            abort(304, 'not modified')
        else:
            c.response.headers['Last-Modified'] = http_utils.http_date_str(date)

    def check_modified(self, thing, action):
        if c.user_is_loggedin:
            return

        last_modified = utils.last_modified_date(thing, action)
        date_str = http_utils.http_date_str(last_modified)
        c.response.headers['last-modified'] = date_str
        c.response.headers['cache-control'] = "private, max-age=0, must-revalidate"

        modified_since = request.if_modified_since
        if modified_since and modified_since >= last_modified:
            abort(304, 'not modified')

    def check_modified(self, thing, action, private=True, max_age=0, must_revalidate=True):
        if c.user_is_loggedin and not c.allow_loggedin_cache:
            return

        last_modified = utils.last_modified_date(thing, action)
        date_str = http_utils.http_date_str(last_modified)
        c.response.headers["last-modified"] = date_str

        cache_control = []
        if private:
            cache_control.append("private")
        cache_control.append("max-age=%d" % max_age)
        if must_revalidate:
            cache_control.append("must-revalidate")
        c.response.headers["cache-control"] = ", ".join(cache_control)

        modified_since = request.if_modified_since
        if modified_since and modified_since >= last_modified:
            abort(304, "not modified")