Upstream: background cache update before cache send (ticket #1782). In case of filter finalization, essential request fields like r->uri, r->args etc could be changed, which affected the cache update subrequest. Also, after filter finalization r->cache could be set to NULL, leading to null pointer dereference in ngx_http_upstream_cache_background_update(). The fix is to create background cache update subrequest before sending the cached response. Since initial introduction in 1aeaae6e9446 (1.11.10) background cache update subrequest was created after sending the cached response because otherwise it blocked the parent request output. In 9552758a786e (1.13.1) background subrequests were introduced to eliminate the delay before sending the final part of the cached response. This also made it possible to create the background cache update subrequest before sending the response. Note that creating the subrequest earlier does not change the fact that in case of filter finalization the background cache update subrequest will likely not have enough time to successfully update the cache entry. Filter finalization leads to the main request termination as soon the current iteration of request processing is complete.

fastcgi_param  QUERY_STRING       $query_string;
fastcgi_param  REQUEST_METHOD     $request_method;
fastcgi_param  CONTENT_TYPE       $content_type;
fastcgi_param  CONTENT_LENGTH     $content_length;

fastcgi_param  SCRIPT_NAME        $fastcgi_script_name;
fastcgi_param  REQUEST_URI        $request_uri;
fastcgi_param  DOCUMENT_URI       $document_uri;
fastcgi_param  DOCUMENT_ROOT      $document_root;
fastcgi_param  SERVER_PROTOCOL    $server_protocol;
fastcgi_param  REQUEST_SCHEME     $scheme;
fastcgi_param  HTTPS              $https if_not_empty;

fastcgi_param  GATEWAY_INTERFACE  CGI/1.1;
fastcgi_param  SERVER_SOFTWARE    nginx/$nginx_version;

fastcgi_param  REMOTE_ADDR        $remote_addr;
fastcgi_param  REMOTE_PORT        $remote_port;
fastcgi_param  SERVER_ADDR        $server_addr;
fastcgi_param  SERVER_PORT        $server_port;
fastcgi_param  SERVER_NAME        $server_name;

# PHP only, required if PHP was built with --enable-force-cgi-redirect
fastcgi_param  REDIRECT_STATUS    200;