id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
2058	nginx returns code 500 on zero-size request body when filter module returns 40x	meelisroos@…		"When nginx HTTP filter module processes the request body and filter returns 40x (400 and 403 tested), nginx returns this response code to client if request body has non-zero size and fail with error 500 when request body size is 0 (and the filter module returns answer 40x).

I am debugging my own request body filter module for nginx proxy. I found a problem so I reduced it to minimal reproducer code fragment.

I took http://mdounin.ru/hg/ngx_http_catch_body_filter_module as a base and applied byte counter patch to it, to return 40x on zero or 1 byte body size. For 1-byte body, the 40x response is returned to the client, and for 0-byte body, 500 is returned.

Found on nginx 1.18.0 and tested on 1.19.3.

Patch for my reproducer. In configuration, I have the module turned on for /test:

    location = /test {
        set_real_ip_from 192.168.0.1;
        real_ip_header X-Forwarded-For;

        # Check content.
        catch_body on;
        proxy_request_buffering on;

        # Proxied server.
        proxy_pass http://localhost:808/blobserver;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_redirect off;

    }

The test:
curl -s -S -H 'Content-Type: application/octet-stream' --data-binary '' http://localhost/test

debug log results in this:
2020/10/08 22:07:49 [debug] 23777#23777: *1 generic phase: 13
2020/10/08 22:07:49 [debug] 23777#23777: *1 http request body content length filter
2020/10/08 22:07:49 [debug] 23777#23777: *1 catch request body filter
2020/10/08 22:07:49 [debug] 23777#23777: *1 catch body: wrong length
2020/10/08 22:07:49 [debug] 23777#23777: *1 http finalize request: 500, ""/test?"" a:1, c:1
2020/10/08 22:07:49 [debug] 23777#23777: *1 http special response: 500, ""/test?""
2020/10/08 22:07:49 [debug] 23777#23777: *1 HTTP/1.1 500 Internal Server Error
"	defect	closed	minor		nginx-core	1.19.x	fixed	filter module 500	meelisroos@…	Linux test-nginx 3.10.0-957.10.1.el7.x86_64 #1 SMP Mon Mar 18 15:06:45 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux	"nginx version: nginx/1.19.3
built by gcc 4.8.5 20150623 (Red Hat 4.8.5-39) (GCC) 
built with OpenSSL 1.0.2k-fips  26 Jan 2017
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib64/nginx/modules --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-log-path=/var/log/nginx/access.log --pid-path=/var/run/nginx.pid --lock-path=/var/run/nginx.lock --http-client-body-temp-path=/var/cache/nginx/client_temp --http-proxy-temp-path=/var/cache/nginx/proxy_temp --http-fastcgi-temp-path=/var/cache/nginx/fastcgi_temp --http-uwsgi-temp-path=/var/cache/nginx/uwsgi_temp --http-scgi-temp-path=/var/cache/nginx/scgi_temp --user=nginx --group=nginx --with-compat --with-file-aio --with-threads --with-http_addition_module --with-http_auth_request_module --with-http_dav_module --with-http_flv_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_mp4_module --with-http_random_index_module --with-http_realip_module --with-http_secure_link_module --with-http_slice_module --with-http_ssl_module --with-http_stub_status_module --with-http_sub_module --with-http_v2_module --with-mail --with-mail_ssl_module --with-stream --with-stream_realip_module --with-stream_ssl_module --with-stream_ssl_preread_module --with-cc-opt='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC' --with-ld-opt='-Wl,-z,relro -Wl,-z,now -pie' --add-module=/home/builder/rpmbuild/BUILD/nginx-1.19.3/ngx_http_catch_body_filter_module"