Pino-pretty as a transport target causes `--require` modules to be loaded multiple times

[rowanmanning]

Hiya, we're currently using pino-pretty as part of our logging in local development. Today we found that, if you import modules via the node --require flag, pino-pretty causes them to load twice.

Node.js: v20
Pino: v8.16.2
Pino-pretty: v10.2.3

Reproducing

Given the following:

package.json

{
  "dependencies": {
    "pino": "^8.16.2",
    "pino-pretty": "^10.2.3"
  }
}

main.js

const pino = require('pino');

const logger = pino({
    transport: {
        target: 'pino-pretty'
    }
});

required.js

console.log('required file loaded', new Date());

Running

Run the following:

node --require ./required.js ./main.js

You will see the console.log statement from required.js appear twice with different dates:

required file loaded 2023-11-21T15:50:18.651Z
required file loaded 2023-11-21T15:50:19.137Z

Workaround

This doesn't happen if you pass pino-pretty as a stream to the pino logger:

const pino = require('pino');
const pretty = require('pino-pretty');

const logger = pino({}, pretty());

Because of this I wasn't sure whether this was an issue in pino or pino-pretty. I tried digging into both codebases but was unable to work out how you might be loading the --require multiple times.

[jsumners]

Transports of this type are run in a worker thread. My guess is that the required module gets propagated to the child thread and invoked again.

[mcollina]

Moved it to pino, might even be one for thread-stream

[mcollina]

I researched this problem and this is not a bug, but a feature of workers to enable setting up APMs, etc.

If you want to remove the --require, you can do:

const pino = require('pino');

const logger = pino({
    transport: {
        target: 'pino-pretty',
        worker: { execArgv: [] } // drops all Node specific CLI options
    }
});

[rowanmanning]

Amazing, yep this works! Thanks so much for looking into it 🙂

[github-actions]

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