id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
2567	sub_filter and gziped payload should trigger warning	gl-yziquel@…		"Hi.

Reporting an issue that bit me quite some time ago. I don't have the setting to reproduce it because I solved it on my own and moved on. But here is the lesson learned:

I was busy reverse-proxying a website with a path prefix. (The kind of thing you do because you have only one machine, no control over DNS, and want to reuse the same port.) I encountered a Heisenbug because of default headers being passed around by the various tools I was using. But, bottom line:

The reverse proxying didn't work because I had a sub_filter declaration to correct the payloads to account for the prefix in the reverse-proxying. However, the backend gave gziped data. sub_filtering on compressed data is... doomed to failure.

So, for people encountering the same situation, and dealing with the same kind of Heisenbugs: please provide a warning in the logs for people attempting sub_filter on compressed data.

That would have helped me diagnose the problem MUCH MUCH MUCH faster, without having to dissect implicit behaviours related to compression."	enhancement	new	minor		nginx-core	1.18.x				Linux virtucon 6.2.0-1010-nvidia #10-Ubuntu SMP PREEMPT_DYNAMIC Tue Aug 29 17:57:56 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux	"nginx version: nginx/1.18.0 (Ubuntu)
built with OpenSSL 3.0.2 15 Mar 2022
TLS SNI support enabled
configure arguments: --with-cc-opt='-g -O2 -ffile-prefix-map=/build/nginx-zctdR4/nginx-1.18.0=. -flto=auto -ffat-lto-objects -flto=auto -ffat-lto-objects -fstack-protector-strong -Wformat -Werror=format-security -fPIC -Wdate-time -D_FORTIFY_SOURCE=2' --with-ld-opt='-Wl,-Bsymbolic-functions -flto=auto -ffat-lto-objects -flto=auto -Wl,-z,relro -Wl,-z,now -fPIC' --prefix=/usr/share/nginx --conf-path=/etc/nginx/nginx.conf --http-log-path=/var/log/nginx/access.log --error-log-path=/var/log/nginx/error.log --lock-path=/var/lock/nginx.lock --pid-path=/run/nginx.pid --modules-path=/usr/lib/nginx/modules --http-client-body-temp-path=/var/lib/nginx/body --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-proxy-temp-path=/var/lib/nginx/proxy --http-scgi-temp-path=/var/lib/nginx/scgi --http-uwsgi-temp-path=/var/lib/nginx/uwsgi --with-compat --with-debug --with-pcre-jit --with-http_ssl_module --with-http_stub_status_module --with-http_realip_module --with-http_auth_request_module --with-http_v2_module --with-http_dav_module --with-http_slice_module --with-threads --add-dynamic-module=/build/nginx-zctdR4/nginx-1.18.0/debian/modules/http-geoip2 --with-http_addition_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_sub_module"