ability to ignore client abort when using js_content as content handler

[ivan-u7n]

Is your feature request related to a problem? Please describe

in my js_content handler for a http request:

1. a value is increased in a shared zone
2. a subrequest (via r.subrequest()) is performed (to internal fastcgi-location if that matters)
3. that value is decreased

however, if the client terminates the connection when r.subrequest() is in progress, the VM (I use QuickJS by the way) is just terminated and the value is stuck increased; all I get is [error] pending events while closing request in the error log

Describe the solution you'd like

a directive like js_content_ignore_user_abort (akin to proxy_ignore_user_abort or fastcgi_ignore_user_abort) that when turned on, will make JS VM behave as the counterparts from proxy and fastcgi modules do to proxied requests

Describe alternatives you've considered

I tried try ... finally to no avail, the VM is just terminated

for now as a workaround I use js_periodic to clean such values, but I'd like not to have to

Additional context

the js_content handler in question is used as the image processor

[xeioex]

Hi @ivan-u7n,

I am thinking about njs.on('exit'), this will be called before a VM exits.
You can use it for cleaning up.
It has limitations, but it looks like it will work for your case. This is not implemented for QuickJS engine though.
Let me know anyway whether it will work for you. So I know it is needed for QuickJS.

[ivan-u7n]

@xeioex, yes, I think njs.on("exit") should work for my use case

in general the relevant part of my code looks like

class Controller {
  async getTargetLink() {
    if (!this.acquireWorker()) return "fallback link";
    await this.#httpRequest.subrequest(this.workerLink);
    this.releaseWorker();
    return "subrequest result link or fallback one";
  }
}

as I always return after subrequest completion (the calling party is doing r.internalRedirect(returnedValue)), there wouldn't be a problem to convert the code to

class Controller {
  async getTargetLink() {
    if (!this.acquireWorker()) return "fallback link";
    njs.on("exit", () => { this.releaseWorker(); });
    await this.#httpRequest.subrequest(this.workerLink);
    return "subrequest result link or fallback one";
  }
}

nevertheless, what kind of limitations does this approach have?

[xeioex]

@ivan-u7n

The main limitation is that you cannot invoke any async operation from njs.on('exit') callback, as it is called just right before the VM destruction.

yes, I think njs.on("exit") should work for my use case

Ok. I will add njs.on("exit") support to qjs engine.

[xeioex]

Hi @ivan-u7n,

Please, let me know if you want to try the feature before the release/commit.

[ivan-u7n]

@xeioex

Please, let me know if you want to try the feature before the release/commit.

I'd like to, but I use nginx-provided packages for Debian, thus compiling from sources doesn't sound like a viable option

[xeioex]

@ivan-u7n

Feel free to reopen if it does not work for you.