resolves #97 propagate events (#98)

README.md

@@ -84,6 +84,31 @@ stream.end()
 
 This module works with `yarn` in PnP (plug'n play) mode too!
 
+### Emit events
+
+You can emit events on the ThreadStream from your worker using [`worker.parentPort.postMessage()`](https://nodejs.org/api/worker_threads.html#workerparentport).
+The message (JSON object) must have the following data structure:
+
+```js
+parentPort.postMessage({
+  code: 'EVENT',
+  name: 'eventName',
+  args: ['list', 'of', 'args', 123, new Error('Boom')]
+})
+```
+
+On your ThreadStream, you can add a listener function for this event name:
+
+```js
+const stream = new ThreadStream({
+  filename: join(__dirname, 'worker.js'),
+  workerData: {},
+})
+stream.on('eventName', function (a, b, c, n, err) {
+  console.log('received:', a, b, c, n, err) // received: list of args 123 Error: Boom
+})
+```
+
 ## License
 
 MIT

index.js

@@ -163,6 +163,13 @@ function onWorkerMessage (msg) {
     case 'ERROR':
       destroy(stream, msg.err)
       break
+    case 'EVENT':
+      if (Array.isArray(msg.args)) {
+        stream.emit(msg.name, ...msg.args)
+      } else {
+        stream.emit(msg.name, msg.args)
+      }
+      break
     default:
       destroy(stream, new Error('this should not happen: ' + msg.code))
   }

test/emit-event.js

@@ -0,0 +1,22 @@
+'use strict'
+
+const { Writable } = require('stream')
+const parentPort = require('worker_threads').parentPort
+
+async function run () {
+  return new Writable({
+    autoDestroy: true,
+    write (chunk, enc, cb) {
+      if (parentPort) {
+        parentPort.postMessage({
+          code: 'EVENT',
+          name: 'socketError',
+          args: ['list', 'of', 'args', 123, new Error('unable to write data to the TCP socket')]
+        })
+      }
+      cb()
+    }
+  })
+}
+
+module.exports = run

test/event.test.js

@@ -0,0 +1,23 @@
+'use strict'
+
+const { test } = require('tap')
+const { join } = require('path')
+const ThreadStream = require('..')
+
+test('event propagate', function (t) {
+  const stream = new ThreadStream({
+    filename: join(__dirname, 'emit-event.js'),
+    workerData: {},
+    sync: true
+  })
+  stream.on('socketError', function (a, b, c, n, error) {
+    t.same(a, 'list')
+    t.same(b, 'of')
+    t.same(c, 'args')
+    t.same(n, 123)
+    t.same(error, new Error('unable to write data to the TCP socket'))
+    t.end()
+  })
+  stream.write('hello')
+  stream.end()
+})