Propagate events from worker stream

[ggrossetie]

We've introduced a bunch of events on pino-socket but as far as I know it's not possible to listen to them as soon as we are using a ThreadStream.

Worker thread can communicate with the parent thread using require('worker_threads').parentPort.on('message'). I think it would be nice to allow transport to publish events through this port:

const parentPort = require('worker_threads').parentPort

const error = new Error('unable to write data to the TCP socket')
outputStream.emit('socketError', error)
if (parentPort) {
  parentPort.postMessage({ code: 'EVENT', name: 'socketError', args: [error] })
}

We will need to add a case in the onWorkerMessage function to propagate the event:

thread-stream/index.js

Lines 152 to 167 in deaedaa

	switch (msg.code) {
	case 'READY':
	// Replace the FakeWeakRef with a
	// proper one.
	this.stream = new WeakRef(stream)
	stream.flush(() => {
	stream[kImpl].ready = true
	stream.emit('ready')
	})
	break
	case 'ERROR':
	destroy(stream, msg.err)
	break
	default:
	destroy(stream, new Error('this should not happen: ' + msg.code))

Something like:

switch (msg.code) { 
  case 'EVENT': 
     stream.emit(msg.name, msg.args)
     break
}

With the above changes it's possible to write:

const socketStream = pino.transport({
  target: "pino-socket",
  options: {
    address: tcpAddress,
    port: tcpPort,
    mode: "tcp",
    reconnect: true,
  }
})
// socketStream is a ThreadStream but events are propagated!
socketStream.on('socketError', (error) => {
  // do something!
})

If we don't want to propagate events but still allow transport to send post message then we should allow the code EVENT. In this case, we could write:

const socketStream = pino.transport({
  target: "pino-socket",
  options: {
    address: tcpAddress,
    port: tcpPort,
    mode: "tcp",
    reconnect: true,
  }
})
// socketStream is a ThreadStream so we can listen to messages on the worker!
socketStream.worker.on('message', (msg) => {
  // do something!
})

[mcollina]

This would be nice to have. Would you like to send a PR?

[ggrossetie]

Sure, I will submit a PR in the next days/weeks 👍🏻