之前以为PHP的ob函数无法在gzip的时候获得内容长度，简单地改了Twip的代码，使之不报告Content-Length。今天偶然搜索Gravity的相关内容，看到@empyreaner君提供的获取Content-Length方法：
Ob_Start();
Ob_Start(‘ob_gzhandler’);
echo $content;
Ob_End_Flush();
header(“Content-Length: “.ob_get_length());
Ob_End_Flush();
Ob_Start(‘ob_gzhandler’);
echo $content;
Ob_End_Flush();
header(“Content-Length: “.ob_get_length());
Ob_End_Flush();
此法甚为巧妙，PHP手册也有一句：Output buffers are stackable, that is, you may call ob_start() while another ob_start() is active.只恨自己阅读太不仔细，遂写此文以志之。