# thread-stream
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A streaming way to send data to a Node.js Worker Thread.

## install

```sh
npm i thread-stream
```

## Usage

```js
'use strict'

const ThreadStream = require('thread-stream')
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()
})
```

`flush(cb)` waits for the worker destination flush when supported (`flush`, `flushSync`, or pending `drain`).

In `worker.js`:

```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`](https://nodejs.org/api/stream.html#stream_new_stream_writable_options)
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.

```js
const ThreadStream = require('thread-stream')

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()`](https://nodejs.org/api/worker_threads.html#workerparentport).
Messages that do not carry a thread-stream protocol `code` are ignored.
For custom events, 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
})
```

### Post Messages

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

```js
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)`](https://nodejs.org/api/worker_threads.html#event-message).

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

## License

MIT
