Connect inspector.Session to inspector in another process or thread.

[everett1992]

Is your feature request related to a problem? Please describe.
I want to use the inspector module in a worker thread to control the inspector in another thread.

const { isMainThread, Worker } = require('worker_threads');
const inspector = require('inspector');

if (isMainThread) {
  new Worker(__filename)
} else {
  // session connects to the worker thread inspector, not the main thread.
  const session = new inspector.Session();
  session.connect();
}

inspector.Session doesn't support connecting to the inspector of a different thread or process.

Describe the solution you'd like

• add a url parameter to inspector.Session

if (isMainThread) {
  inspector.open(0);
  const url = inspector.url();
  new Worker(__filename, { workerData: { url }})
} else {
  const session = new inspector.Session(workerData.url);
  // ...
}

• or allow inspector to be transfered

if (isMainThread) {
  new Worker(__filename, { workerData: { inspector }})
} else {
  const session = new new workerData.inspector.Session();
  // ...
}

Describe alternatives you've considered
The v8 inspector API is not complicated and I have written a client using the ws npm module instead of using inspector.Session.

---

I'm open to writing a CR to implement this, but I would like feedback from a maintainer before I start, especially because both worker_threads and inspector are experimental.

[eugeneo]

You should be able to connect to main Inspector service from a worker over the WS 😀

I tried implementing passing inspector session from main thread to a worker, but currently it is bit involved... I plan to revisit it at some point. This would resolve many issues with the current inspector session JS API - e.g. could be implemented with promises, could do IO, etc. It may even allow us to reimplement WS server in JS instead of current C++ code.

[rochdev]

You should be able to connect to main Inspector service from a worker over the WS

@eugeneo Could you explain how since this is not documented in the inspector session API and there appears to be no way to configure it to connect to a different process?

[eugeneo]

Please take a look at a inspector.Session.connectToMainThread available since 12.11.

[rochdev]

@eugeneo This only works for the very specific use case of using the main thread inspector from a worker thread. It doesn't allow connecting to other threads or a different process. Are there any plans for these to be supported? Having to use raw websockets is not very intuitive.

[eugeneo]

You can connect to other worker threads by using the target domain. You can only debug other processes by using the WebSocket interface.

[sliftist]

@eugeneo , I am running into the same issue as @rochdev , but as this ticket is closed I'm assuming I am just misunderstanding the solution.

I wish the use the inspector on other worker threads (not only the main thread). It seems like session.connectToMainThread() should be session.connectToThread(threadId: number). Alternatively, inspector.openOnThread(threadId: number, port, host, wait) would accomplish the same result for me.

Presently my approach is to change all of my entry points to call inspector.open and then send the result to a dedicated debugger thread. This is problematic as it requires me to be able to change all of the entry points of worker threads I wish to debug.

As worker threads become more common it is more and more likely to encounter libraries which use worker threads, in which case I will not reasonably be able to change their entry points.

[richterdennis]

5 years later nothing changed I guess. I am looking for a solution to use the inspector console of the main thread and I cant get it working.

I tried multiple versions of this code inside a worker:

import inspector from 'node:inspector';

const session = new inspector.Session();
session.connectToMainThread();

inspector.console.log('Test1');
process.stdout.write('Test2');
console.log('Test3');

I can't get a single line to log out in the debugger console of chrome.

[eugeneo]

I do not have access to Node atm, but this (bit contrived) test case showcases how connectToMainThread is supposed to work: test-inspector-connect-main-thread.js. Specifically, focus on childMain function. It verifies that only one session can be connected (ignore that in your code) and then sets a breakpoint and makes the main thread hit it.