how nginx deal with gzipped responses when gzip is on

[foxgab]

i configred nginx with gzip directives:
http { 
   gzip            on;
    gzip_types      text/css application/javascript;
    gzip_comp_level 9;
    gzip_http_version 1.0;
    gzip_proxied    any;
}

some upstream servers have already gzipped the response, i see the lengh of
the respense is similar to that send from nginx to client, i'm very curious
to know if nginx just bypassed that response, zipped again or
unzipped&rezipped it.

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,275479,275479#msg-275479