@skylernpm/impedit-modi-unde

A streaming way to send data to a Node.js Worker Thread.

install

npm i @skylernpm/impedit-modi-unde

Usage

'use strict'

const ThreadStream = require('@skylernpm/impedit-modi-unde')
const { join } = require('path')

const stream = new ThreadStream({
  filename: join(__dirname, 'worker.js'),
  workerData: { dest },
  workerOpts: {}, // Other options to be passed to Worker
  sync: false, // default
})

stream.write('hello')

// Asynchronous flushing
stream.flush(function () {
  stream.write(' ')
  stream.write('world')

  // Synchronous flushing
  stream.flushSync()
  stream.end()
})

In worker.js:

'use strict'

const fs = require('fs')
const { once } = require('events')

async function run (opts) {
  const stream = fs.createWriteStream(opts.dest)
  await once(stream, 'open')
  return stream
}

module.exports = run

Make sure that the stream emits 'close' when the stream completes. This can usually be achieved by passing the autoDestroy: true flag your stream classes.

The underlining worker is automatically closed if the stream is garbage collected.

External modules

You may use this module within compatible external modules, that exports the worker.js interface.

const ThreadStream = require('@skylernpm/impedit-modi-unde')

const modulePath = require.resolve('pino-elasticsearch')

const stream = new ThreadStream({
  filename: modulePath,
  workerData: { node: 'http://localhost:9200' }
})

stream.write('log to elasticsearch!')
stream.flushSync()
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(). The message (JSON object) must have the following data structure:

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:

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
})

Post Messages

You can post messages to the worker by emitting a message event on the ThreadStream.

const stream = new ThreadStream({
  filename: join(__dirname, 'worker.js'),
  workerData: {},
})
stream.emit('message', message)

On your worker, you can listen for this message using worker.parentPort.on('message', cb).

const { parentPort } = require('worker_threads')
parentPort.on('message', function (message) {
  console.log('received:', message)
})

License

MIT