Avoid caching FPM response by content-length

[Andrei ZeeGiant]

Hello!

I have an odd upstream application (out of my control) which intermittently responds with incomplete pages, and a 200.. This causes blank pages to appear in cache. Is there a way to avoid caching a fastcgi/fpm backend response if the content-length is lower than 5kb for example?

I'm guessing this can be done using Lua somewhere along these lines.. but I'm not entirely certain how

location ~ .php$ {

[..]

body_filter_by_lua_block {

 if ngx.var.request_uri == "/" then

  if ngx.var.http_content_length < 5120 then

    ngx.status = 503

    return ngx.exit(503)

  fi

 fi

}

}

Thanks!