Add support for Flow types

Author: ide

.flowconfig

@@ -0,0 +1,7 @@
+[ignore]
+
+[include]
+
+[libs]
+
+[options]

CONTRIBUTING.md

@@ -2,9 +2,13 @@
 
 This is how the Dash Button code is organized, so you can understand where to make changes and how to test your code.
 
+## Source Code
+
+The source files are under `src` and are written using modern JavaScript and [Flow](https://flowtype.org/).
+
 ## Building
 
-The source files are under `src` and are written using modern JavaScript. They are compiled with [Babel](https://babeljs.io/) to a version of JavaScript that Node.js understands. These compiled files go in a directory called `build`, which is not committed to Git but is published to npm.
+The source files are compiled with [Babel](https://babeljs.io/) to a version of JavaScript that Node.js understands. These compiled files go in a directory called `build`, which is not committed to Git but is published to npm.
 
 We use [Gulp 4](https://github.com/gulpjs/gulp/tree/4.0) to run Babel. The easiest way to run Gulp is to run `npm run build` or `npm run watch`. Both of these compile the JavaScript in `src` and output it in `build`, but the `watch` command will keep watching your filesystem for any changes and compile files when you save them. It's recommended when you are developing.
 

LICENSE

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2015 James Ide
+Copyright (c) 2015-present James Ide
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -19,4 +19,3 @@ 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.
-

circle.yml

@@ -16,6 +16,7 @@ dependencies:
 test:
   pre:
     - yarn run lint
+    - yarn run flow -- check
   override:
     - yarn test -- --coverage
   post:

package.json

@@ -14,6 +14,7 @@
   },
   "scripts": {
     "build": "gulp build",
+    "flow": "flow",
     "lint": "eslint src",
     "prepublish": "gulp clean && gulp build",
     "start": "node build/cli.js",
@@ -48,13 +49,14 @@
   "dependencies": {
     "babel-runtime": "^6.20.0",
     "lodash": "^4.17.0",
+    "nullthrows": "^1.0.0",
     "pcap": "mranney/node_pcap#d920204",
     "yargs": "^6.5.0"
   },
   "devDependencies": {
     "babel-core": "^6.20.0",
     "babel-eslint": "^7.1.1",
-    "babel-jest": "^17.0.0",
+    "babel-jest": "^18.0.0",
     "babel-plugin-add-module-exports": "^0.2.1",
     "babel-plugin-syntax-trailing-function-commas": "^6.20.0",
     "babel-plugin-transform-async-to-generator": "^6.4.6",
@@ -67,6 +69,7 @@
     "eslint-plugin-babel": "^4.0.0",
     "eslint-plugin-flowtype": "^2.26.1",
     "eslint-plugin-import": "^2.2.0",
+    "flow-bin": "^0.37.4",
     "gulp": "gulpjs/gulp#4.0",
     "gulp-babel": "^6.1.1",
     "gulp-changed": "^1.3.2",

src/DashButton.js

@@ -1,14 +1,20 @@
+// @flow
 import assert from 'assert';
+import nullthrows from 'nullthrows';
 import pcap from 'pcap';
 
 import MacAddresses from './MacAddresses';
 import NetworkInterfaces from './NetworkInterfaces';
 import Packets from './Packets';
 
-type Options = {
+export type DashButtonOptions = {
   networkInterface?: string,
 };
 
+export type DashButtonListener = (packet: Object) => void | Promise<void>;
+
+type GuardedListener = (packet: Object) => Promise<?Error>;
+
 let pcapSession;
 
 function getPcapSession(interfaceName: string) {
@@ -24,16 +30,22 @@ function getPcapSession(interfaceName: string) {
 }
 
 export default class DashButton {
-  constructor(macAddress: string, options?: Options = {}) {
+  _macAddress: string;
+  _networkInterface: string;
+  _packetListener: Function;
+  _dashListeners: Set<GuardedListener>;
+  _isResponding: boolean;
+
+  constructor(macAddress: string, options: DashButtonOptions = {}) {
     this._macAddress = macAddress;
     this._networkInterface = options.networkInterface ||
-      NetworkInterfaces.getDefault();
+      nullthrows(NetworkInterfaces.getDefault());
     this._packetListener = this._handlePacket.bind(this);
     this._dashListeners = new Set();
     this._isResponding = false;
   }
 
-  addListener(listener): Subscription {
+  addListener(listener: DashButtonListener): Subscription {
     if (!this._dashListeners.size) {
       let session = getPcapSession(this._networkInterface);
       session.addListener('packet', this._packetListener);
@@ -57,8 +69,10 @@ export default class DashButton {
     });
   }
 
-  _createGuardedListener(listener) {
-    return async(...args) => {
+  _createGuardedListener(
+    listener: (...args: *[]) => void | Promise<void>,
+  ): GuardedListener {
+    return async (...args: *[]): Promise<?Error> => {
       try {
         await listener(...args);
       } catch (error) {
@@ -67,7 +81,7 @@ export default class DashButton {
     };
   }
 
-  async _handlePacket(rawPacket) {
+  async _handlePacket(rawPacket: Object): Promise<void> {
     if (this._isResponding) {
       return;
     }
@@ -83,19 +97,29 @@ export default class DashButton {
       // The listeners are guarded so this should never throw, but wrap it in
       // try-catch to be defensive
       let listeners = Array.from(this._dashListeners);
-      await Promise.all(listeners.map(listener => listener(packet)));
+      let errors = await Promise.all(
+        listeners.map(listener => listener(packet)),
+      );
+      for (let error of errors) {
+        if (error) {
+          // TODO: Figure out how to mock `console` with Jest
+          // console.error(`Listener threw an uncaught error:\n${error.stack}`);
+        }
+      }
     } finally {
       this._isResponding = false;
     }
   }
 }
 
 class Subscription {
-  constructor(onRemove) {
+  _remove: () => void;
+
+  constructor(onRemove: () => void) {
     this._remove = onRemove;
   }
 
-  remove() {
+  remove(): void {
     if (!this._remove) {
       return;
     }

src/MacAddresses.js

@@ -2,12 +2,14 @@
 import padStart from 'lodash/padStart';
 
 const MacAddresses = {
-  getEthernetSource(packet): string {
+  getEthernetSource(packet: *): string {
     return MacAddresses.decimalToHex(packet.payload.shost.addr);
   },
 
   decimalToHex(numbers: Number[]): string {
     let hexStrings = numbers.map(decimal =>
+      // TODO: Use String.prototype.padStart when Node natively supports it, and
+      // increment the major semver version
       padStart(decimal.toString(16), 2, '0'),
     );
     return hexStrings.join(':');

src/NetworkInterfaces.js

@@ -1,7 +1,8 @@
+// @flow
 import os from 'os';
 
 export default {
-  getDefault() {
+  getDefault(): ?string {
     let interfaces = os.networkInterfaces();
     let names = Object.keys(interfaces);
     for (let name of names) {

src/Packets.js

@@ -1,7 +1,7 @@
 // @flow
 import pcap from 'pcap';
 
-// Dash Buttons send DHCPREQUEST messages (new) and ARP probes (old)
+// Dash buttons send DHCPREQUEST messages (new) and ARP probes (old)
 const PACKET_FILTER = '(arp or (udp and src port 68 and dst port 67 and udp[247:4] == 0x63350103)) and src host 0.0.0.0';
 
 export default {

src/__tests__/DashButton-test.js

@@ -1,5 +1,4 @@
 import assert from 'assert';
-import events from 'events';
 
 jest.mock('pcap');
 jest.mock('../NetworkInterfaces');