I have the following conf on nginx:

location ~* ^/assets/ {
    add_header Access-Control-Allow-Headers content-type;
    add_header Access-Control-Allow-Origin *;
    add_header Cache-Control "public, max-age=31536000";
    proxy_pass http://nas-mydomain.com;
    proxy_next_upstream http_500 timeout;
    gzip_http_version 1.0;
    gzip_static always;
    gzip_vary on;
    etag on;
}

My goal is to serve the static content in that folder in gzipped form when available.

I of course created files like:

test.js
test.js.gz

I can reach each file and all the headers are correctly set as well as the etags. However, the gzip retrieving is not working. For example, I tested it like this:

curl -H "Accept-Encoding: gzip" http://domain.com/assets/test.js | gunzip
## Cutted useless output
gunzip: unknown compression format

So I guess that is not working. I also tried to listen with:

strace -p pid1 -p pid2 -p pid3.... 2>&1 | grep gz

with no luck.

And, of course, if I do:

curl http://domain.com/assets/test.js.gz | gunzip
## Cutted useless output

everything works perfectly.

Any hints?

nginx -v = nginx version: nginx/1.8.0 
#--with-http_gunzip_module --with-http_gzip_static_module are present