Body discarding with js_body_filter

[lonerr]

It seems that combination of proxy_cache and sendfile results in an empty first argument of js_body_ filter.

Below is a minimal configuration that reproduces the issue:

load_module modules/ngx_http_js_module.so;

events {
    worker_connections 1024;
}

http {
    js_import lib.js;

    proxy_cache_path /tmp/one levels=1 keys_zone=one:1m;

    server {
        listen 80;

        proxy_cache one;
        proxy_cache_valid any 1s;

        location /origin/ {
            return 200 ok\n;
        }
        location / {
            proxy_pass http://127.0.0.1/origin/;

            js_header_filter lib.headerFilter;
            js_body_filter   lib.bodyFilter buffer_type=buffer;
        }
        location /sf/ {
            proxy_pass http://127.0.0.1/origin/;
            sendfile on;

            js_header_filter lib.headerFilter;
            js_body_filter   lib.bodyFilter  buffer_type=buffer;
        }
    }
}

Where lib.js looks like:

var buffer = '';

function bodyFilter(r, data, flags) {
    buffer += data;

    if (flags.last)
        return r.sendBuffer(buffer, flags);
}

function headerFilter(r) {
    delete r.headersOut['Content-Length'];
}

export default { bodyFilter, headerFilter }

The results (second unexpected):

% curl -s http://127.0.0.1/ | wc -l
       1
% curl -s http://127.0.0.1/sf/ | wc -l
       0

Test was performed on Ubuntu 22.04 with packages from mainline repo at nginx.org

I hope these snippets are enough to catch the bug but don't hesitate to ask me about any additional info you need.
Thank you.