ngx.location.capture subrequest freeze in combination with NJS

Hi,

I have following situation.

I have a nginx plus ingress controller running inside Kubernetes. Nginx exposes a service with a location:

server {
      listen 80;
      listen [::]:80;

      server_name luatest.com;
      error_log stderr debug;

      location /init {
        rewrite_by_lua_file /etc/nginx/lua/rewrite.lua;
      }
      include /etc/nginx/custom-conf/*.conf;
    }

The rewrite.lua script looks like this:

    ngx.log(ngx.INFO, "start lua process")
    local res_cookie = ngx.location.capture("/testlocation")
    ngx.say("I am ok") ngx.exit(200)
    ngx.log(ngx.INFO, "did subrequest")

The script sends a subrequest to following location:

    location /testlocation {
        internal;
        js_content request_handling.request_handling;
    } 

Further, the njs script does following:

    async function request_handling(r) {
      r.log("here in njs script");
      let test= await r.subrequest('/njs_target');
      r.log("did subrequest from njs to location");
      r.return(200, test);
      return;
    }
    export default {request_handling}

As soons as i do a curl request to the location /init the request stucks until i terminate the connection, or some timeout kicks in.
Inside the Nginx debug logs, i can see the last log lines from njs and the nginx line "http finalize request: 0, "/njs_target?" a:0, c:3" which should close everything and return back to LUA, but its not the case.
These are the last debug logs:

[info] 25#25: *3 js: here in njs script
[debug] 25#25: *3 posix_memalign: 00006166EFF0A4A0:4096 @16
[debug] 25#25: *3 http subrequest "/njs_target?"
[debug] 25#25: *3 http finalize request: -4, "/testlocation?" a:0, c:4
[debug] 25#25: *3 http request count:4 blk:0
[debug] 25#25: *3 http posted request: "/njs_target?"
[debug] 25#25: *3 rewrite phase: 1
[debug] 25#25: *3 test location: "/njs_target"
[debug] 25#25: *3 using configuration "/njs_target"
[debug] 25#25: *3 http cl:-1 max:1048576
[debug] 25#25: *3 rewrite phase: 3
[debug] 25#25: *3 http output filter "/njs_target?"
[debug] 25#25: *3 http copy filter: "/njs_target?"
[debug] 25#25: *3 http postpone filter "/njs_target?" 00007FFCA7882B40
[debug] 25#25: *3 http postpone filter in memory
[debug] 25#25: *3 http postpone filter in memory 7 bytes
[debug] 25#25: *3 http copy filter: 0 "/njs_target?"
[debug] 25#25: *3 http finalize request: 0, "/njs_target?" a:0, c:3
[info] 25#25: *3 js: did subrequest from njs to location
[debug] 25#25: *3 http output filter "/testlocation?"
[debug] 25#25: *3 http copy filter: "/testlocation?"
[debug] 25#25: *3 http copy filter: 0 "/testlocation?"
[debug] 25#25: *3 http request count:3 blk:0
[debug] 25#25: *3 delete posted event 00006166F0044560
[debug] 25#25: *3 http run request: "/init?"
[debug] 25#25: *3 rewrite phase: 4

If i terminate the curl command on the client side, these two lines show up in the nginx logs:

[debug] 26#26: *4 http run request: "/init?"
[debug] 26#26: *4 http reading blocked

If i remove the njs subrequest, it is working again, but from my side it seems LUA is waiting for something if i enable the NJS subrequest, but i cant figure out what it is.

Version overview of the test environment:

NJS: 0.8.5
LUA: 0.10.26
Nginx: nginx/1.25.5 (nginx-plus-r32-p1)

I also had the same behavior with the latest NJS Version 0.8.8 and NGINX plus r33.

One more thing to mention, everything is working with following version:

NJS: 0.7.11
LUA: 10.22
Nginx: nginx/1.23.2 (nginx-plus-r28)

Many thanks in advance.

Cheers

Start with rewrite.lua, the request_handling njs entry point, and the /njs_target location, then reproduce the nested subrequest using the provided NGINX debug logs and version combinations. Done means a request to /init returns instead of hanging when the njs subrequest is enabled, while preserving the working behavior without it.