'error_page' directive does not work under 'ngx.location.capture()'

'error_page' directive does not work under 'ngx.location.capture()'

Summary:

If the requested location has the 'error_page' configured and should be triggered (including default error_page), instead, the original code is returned with the truncated flag set to true

Environment Info:

• OpenResty version: not installed
• Nginx version: nginx/1.12.2
• Nginx Lua Module version: 0.10.11rc2
• OS: Linux 4.4.0-130-generic #156-Ubuntu SMP Thu Jun 14 08:53:28 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
• Nginx Build Flags:
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   --prefix=/etc/ringcentral/nginx-test --sbin-path=/usr/sbin/nginx-test --modules-path=/usr/lib64/ringcentral/nginx-test/modules --conf-path=/etc/ringcentral/nginx-test/nginx-test.conf --error-log-path=/var/log/ringcentral/nginx-test/nginx-test-nginx_error.log --http-log-path=/var/log/ringcentral/nginx-test/nginx-test-nginx_access.log --pid-path=/var/run/ringcentral/nginx-test/nginx-test.pid --lock-path=/var/run/ringcentral/nginx-test/nginx-test.lock --http-client-body-temp-path=/var/cache/ringcentral/nginx-test/nginx-test/client_temp --http-proxy-temp-path=/var/cache/ringcentral/nginx-test/nginx-test/proxy_temp --http-fastcgi-temp-path=/var/cache/ringcentral/nginx-test/nginx-test/fastcgi_temp --http-uwsgi-temp-path=/var/cache/ringcentral/nginx-test/nginx-test/uwsgi_temp --http-scgi-temp-path=/var/cache/ringcentral/nginx-test/nginx-test/scgi_temp --user=peter --group=root --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_stub_status_module --with-http_sub_module --with-http_v2_module --with-mail --with-stream --add-module=/home/peter/git/rcv-nginx/build/rpmbuild/BUILD/nginx-test/ngx_devel_kit-0.3.0 --with-http_ssl_module --with-mail_ssl_module --with-stream_ssl_module --add-module=/home/peter/git/rcv-nginx/build/rpmbuild/BUILD/nginx-test/lua-nginx-module-0.10.11rc2 --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' --with-debug

How to Reproduce:

1. Configure Nginx:

location /sub
{
    error_page 502 @intercept_502;
    set $remote_host "http://invalid_host";
    proxy_pass $remote_host;
}
location /lua
{
    content_by_lua_block
    {
        res = ngx.location.capture("/sub")
        ngx.say(("Status: '%s';"):format(res.status));
        ngx.say(("Body: '%s';"):format(res.body));
        ngx.say(("Truncated: '%s';"):format(res.truncated));
    }
}
location @intercept_502
{
    default_type application/json;
    return 500 '{ "error": "cannot proxy request (502: Bad Gateway)" }';
}

2. Request /sub
3. Request /lua

Expected:

{
    "error": "cannot proxy request (502: Bad Gateway)"
}

Status: '500';
Body: '{ "error": "cannot proxy request (502: Bad Gateway)" }';
Truncated: 'false';

Actual:

{
    "error": "cannot proxy request (502: Bad Gateway)"
}

Status: '502';
Body: '';
Truncated: 'true';

Nginx Debug Logs:

nginx-location-capture.log

Start with the ngx.location.capture() reproduction and the linked nginx-location-capture.log, using the provided /sub, /lua, and @intercept_502 configuration. Trace how the configured error_page response is handled during capture. Done means the capture returns status 500 with the expected response body and truncated set to false.