access the upstream error page (response) while I have defined error_page location?

[Hadi Abbasi]

Hey Guys...

is there any way to access upstream response body which is received through body_flter_by_lua block while the response status code is 5xx and I have defined an error_page location?
just I want to access the upstream error page to show it on some special status codes and also want to show my default error page on some special status codes!

proxy_intercept_errors on;
error_page  401 402 403 500 501 502 503 504 505 506 507 508 509 510 511  /error_page.html;
location /error_page.html {
 root /usr/local/xxx/assets/errors;
 allow all;
 internal;
 
 content_by_lua_block {
 --do something on upstream error response body
 }
}

I don't know why I can access the upstream error response body when there is no any error_page defined! but when  I define error_page location, body_filter_by_lua can't be run and I have no access to upstream error page!