ngx_http_error_404_page  108 http/ngx_http_special_response.c static char ngx_http_error_404_page[] =
ngx_http_error_404_page  311 http/ngx_http_special_response.c     ngx_string(ngx_http_error_404_page),
ngx_http_error_404_page  332 http/ngx_http_special_response.c     ngx_string(ngx_http_error_404_page), /* 498, canceled */