Add package metadata files and get tests running

.eslintignore

@@ -0,0 +1,3 @@
+build/
+dist/
+**/*.js

.eslintrc

@@ -0,0 +1,14 @@
+{
+  "extends": "./node_modules/gts/",
+  "rules": {
+    "@typescript-eslint/explicit-function-return-type": [
+      "error",
+      {"allowExpressions": true}
+    ],
+    "func-style": ["error", "declaration"],
+    "prefer-const": ["error", {"destructuring": "all"}],
+    // It would be nice to sort import declaration order as well, but that's not
+    // autofixable and it's not worth the effort of handling manually.
+    "sort-imports": ["error", {"ignoreDeclarationSort": true}],
+  }
+}

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/ci.yml

@@ -0,0 +1,94 @@
+name: CI
+
+defaults:
+  run: {shell: bash}
+
+env:
+  PROTOC_VERSION: 3.x
+
+on:
+  push:
+    branches: [main, feature.*]
+    tags: ['**']
+  pull_request:
+
+jobs:
+  static_analysis:
+    name: Static analysis
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 'lts/*'
+          check-latest: true
+      - run: npm install
+      - run: npm run check
+
+  tests:
+    name: 'Tests | Node ${{ matrix.node-version }} | ${{ matrix.os }}'
+    runs-on: ${{ matrix.os }}-latest
+
+    strategy:
+      matrix:
+        os: [ubuntu, macos, windows]
+        node-version: ['lts/*', 'lts/-1', 'lts/-2']
+      fail-fast: false
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          check-latest: true
+      - run: npm install
+      - run: npm run test
+
+  deploy:
+    name: Deploy
+    runs-on: ubuntu-latest
+    if: "startsWith(github.ref, 'refs/tags/') && github.repository == 'sass/sync-message-channel'"
+    needs: [static_analysis, tests, sass_spec]
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 'lts/*'
+          check-latest: true
+          registry-url: 'https://registry.npmjs.org'
+      - run: npm install
+      - run: npm publish
+        env:
+          NODE_AUTH_TOKEN: '${{ secrets.NPM_TOKEN }}'
+
+  typedoc:
+    runs-on: ubuntu-latest
+    if: "startsWith(github.ref, 'refs/tags/') && github.repository == 'sass/sync-message-channel'"
+    needs: [deploy]
+
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+
+    permissions:
+      pages: write
+      id-token: write
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 'lts/*'
+          check-latest: true
+          registry-url: 'https://registry.npmjs.org'
+      - run: npm install
+      - run: npm run doc
+
+      - name: Upload static files as artifact
+        uses: actions/upload-pages-artifact@v3
+        with: {path: docs}
+
+      - id: deployment
+        uses: actions/deploy-pages@v4

.gitignore

@@ -0,0 +1,15 @@
+.DS_Store
+build
+dist
+node_modules
+npm-debug.log*
+package-lock.json
+
+# Editors
+.idea
+.vscode
+*.njsproj
+*.ntvs*
+*.sln
+*.suo
+*.sw?

.prettierrc.js

@@ -0,0 +1,3 @@
+module.exports = {
+  ...require('gts/.prettierrc.json'),
+};

CODE_OF_CONDUCT.md

@@ -0,0 +1,10 @@
+Sass is more than a technology; Sass is driven by the community of individuals
+that power its development and use every day. As a community, we want to embrace
+the very differences that have made our collaboration so powerful, and work
+together to provide the best environment for learning, growing, and sharing of
+ideas. It is imperative that we keep Sass a fun, welcoming, challenging, and
+fair place to play.
+
+[The full community guidelines can be found on the Sass website.][link]
+
+[link]: http://sass-lang.com/community-guidelines

CONTRIBUTING.md

@@ -0,0 +1,38 @@
+# How to Contribute
+
+We'd love to accept your patches and contributions to this project. There are
+just a few small guidelines you need to follow.
+
+* [Contributor License Agreement](#contributor-license-agreement)
+* [Code Reviews](#code-reviews)
+* [Large Language Models](#large-language-models)
+
+## Contributor License Agreement
+
+Contributions to this project must be accompanied by a Contributor License
+Agreement. You (or your employer) retain the copyright to your contribution;
+this simply gives us permission to use and redistribute your contributions as
+part of the project. Head over to <https://cla.developers.google.com/> to see
+your current agreements on file or to sign a new one.
+
+You generally only need to submit a CLA once, so if you've already submitted one
+(even if it was for a different project), you probably don't need to do it
+again.
+
+## Code Reviews
+
+All submissions, including submissions by project members, require review. We
+use GitHub pull requests for this purpose. Consult
+[GitHub Help](https://help.github.com/articles/about-pull-requests/) for more
+information on using pull requests.
+
+## Large Language Models
+
+Do not submit any code or prose written or modified by large language models or
+"artificial intelligence" such as GitHub Copilot or ChatGPT to this project.
+These tools produce code that looks plausible, which means that not only is it
+likely to contain bugs those bugs are likely to be difficult to notice on
+review. In addition, because these models were trained indiscriminately and
+non-consensually on open-source code with a variety of licenses, it's not
+obvious that we have the moral or legal right to redistribute code they
+generate.

LICENSE

@@ -0,0 +1,20 @@
+Copyright (c) 2024, Google LLC
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

@@ -0,0 +1,124 @@
+# `sync-message-port`
+
+This package exposes a utility class that encapsulates the ability to send and
+receive messages with arbitrary structure across Node.js worker boundaries. It
+can be used as the building block for synchronous versions of APIs that are
+traditionally only available asynchronously in the Node.js ecosystem by running
+the asynchronous APIs in a worker and accessing their results synchronously from
+the main thread.
+
+See [the `sync-process` package] for an example of `sync-message-channel` in
+action.
+
+[the `sync-process` package]: https://github.com/sass/sync-process
+
+## Usage
+
+1. Use `SyncMessagePort.createChanenl()` to create a message channel that's set
+   up to be compatible iwth `SyncMessagePort`s. A normal `MessageChannel` won't
+   work!
+
+2. You can send this `MessageChannel`'s ports across worker boundaries just like
+   any other `MessagePort`. Send one to the worker you want to communicate with
+   synchronously.
+
+3. Once you're ready to start sending and receiving messages, wrap *both* ports
+   in `new SyncMessagePort()`, even if one is only ever going to be sending
+   messages and not receiving them.
+
+4. Use `SyncMessagePort.postMessage()` to send messages and
+   `SyncMessagePort.receiveMessage()` to receive them synchronously.
+
+```js
+import {Worker} from 'node:worker_threads';
+import {SyncMessagePort} from 'sync-message-channel';
+// or
+// const {SyncMessagePort} = require('sync-message-port');
+
+// Channels must be created using this function. A MessageChannel created by
+// hand won't work.
+const channel = SyncMessagePort.createChannel();
+const localPort = new SyncMessagePort(channel.port1);
+
+const worker = new Worker(`
+  import {workerData} = require('node:worker_threads');
+  import {SyncMessagePort} from 'sync-message-channel';
+
+  const remotePort = new SyncMessagePort(workerData.port);
+
+  setTimeout(() => {
+    remotePort.postMessage("hello from worker!");
+  }, 2000);
+`, {
+  workerData: {port: channel.port2},
+  transferList: [channel.port2],
+  eval: true,
+});
+
+// Note that because workers report errors asynchronously, this won't report an
+// error if the worker fails to load because the main thread will be
+// synchronously waiting for its first message.
+worker.on('error', console.error);
+
+console.log(localPort.receiveMessage());
+```
+
+## Why synchrony?
+
+Although JavaScript in general and Node.js in particular are typically designed
+to embrace asynchrony, there are a number of reasons why a synchronous API may
+be preferable or even necessary.
+
+### No a/synchronous polymorphism
+
+Although `async`/`await` and the `Promise` API has substantially improved the
+usability of writing asynchronous code in JavaScript, it doesn't address one
+core issue: there's no way to write code that's *polymorphic* over asynchrony.
+Put in simpler terms, there's no language-level way to write a complex function
+that takes a callback and to run that functions synchronously if the callback is
+synchronous and asynchronously otherwise. The only option is to write the
+function twice.
+
+This poses a real, practical problem when interacting with libraries. Suppose
+you have a library that takes a callback option—for example, an HTML
+sanitization library that takes a callback to determine how to handle a given
+`<a href="...">`. The library doesn't need to do any IO itself, so it's written
+synchronously. But what if your callback wants to make an HTTP request to
+determine how to handle a tag? You're stuck unless you can make that request
+synchronous. This library makes that possible.
+
+### Performance considerations
+
+Asynchrony is generally more performant in situations where there's a large
+amount of concurrent IO happening. But when performance is CPU-bound, it's often
+substantially worse due to the overhead of bouncing back and forth between the
+event loop and user code.
+
+As a real-world example, the Sass compiler API supports both synchronous and
+asynchronous code paths to work around the polymorphism problem described above.
+The logic of these paths is exactly the same—the only difference is that the
+asynchronous path's functions all return `Promise`s instead of synchronous
+values. Compiling with the asynchronous path often takes 2-3x longer than with
+the synchronous path. This means that being able to run plugins synchronously
+can provide a substantial overall performance gain, even if the plugins
+themselves lose the benefit of concurrency.
+
+## How does it work?
+
+This uses [`Atomics`] and [`SharedArrayBuffer`] under the covers to signal
+across threads when messages are available, and
+[`worker_threads.receiveMessageOnPort()`] to actually retrieve messages.
+
+[`Atomics`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics
+[`SharedArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer
+[`Worker.receiveMessageOnPort()`]: https://nodejs.org/api/worker_threads.html#workerreceivemessageonportport
+
+### Can I use this in a browser?
+
+Unfortunately, no. Browsers don't support any equivalent of
+`worker_threads.receiveMessageOnPort()`, even within worker threads. You could
+make a similar package that can transmit only binary data (or data that can be
+encoded as binary) using only `SharedArrayBuffer`, but that's outside the scope
+of this package.
+
+Disclaimer: this is not an official Google product.

jest.config.ts

@@ -0,0 +1,7 @@
+const config = {
+  roots: ['<rootDir>/lib/'],
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+};
+
+export default config;

lib/index.test.ts

@@ -6,7 +6,7 @@ import * as fs from 'fs';
 import * as p from 'path';
 import {MessagePort, Worker} from 'worker_threads';
 
-import {SyncMessagePort} from './sync-message-port';
+import {SyncMessagePort} from './index';
 
 describe('SyncMessagePort', () => {
   describe('sends a message', () => {
@@ -152,7 +152,7 @@ function spawnWorker(source: string, port: MessagePort): Worker {
     file,
     `
     const {SyncMessagePort} = require(${JSON.stringify(
-      p.join(p.dirname(__filename), 'sync-message-port')
+      p.join(p.dirname(__filename), 'index')
     )});
     const {workerData} = require('worker_threads');
 

lib/index.ts

@@ -11,8 +11,6 @@ import {
   receiveMessageOnPort,
 } from 'worker_threads';
 
-// TODO(nex3): Make this its own package.
-
 /**
  * An enum of possible states for the shared buffer that two `SyncMessagePort`s
  * use to communicate.