Add watch option (#77)

index.d.ts

@@ -201,6 +201,15 @@ declare namespace Conf {
 
 		*/
 		readonly accessPropertiesByDotNotation?: boolean;
+
+		/**
+		Watch for any changes in the config file and call the callback for `onDidChange` if set. This is useful if there are multiple processes changing the same config file.
+
+		__Currently this option doesn't work on Node.js 8 on macOS.__
+
+		@default false
+		*/
+		readonly watch?: boolean;
 	}
 }
 

index.js

@@ -11,6 +11,7 @@ const pkgUp = require('pkg-up');
 const envPaths = require('env-paths');
 const writeFileAtomic = require('write-file-atomic');
 const Ajv = require('ajv');
+const debounceFn = require('debounce-fn');
 const semver = require('semver');
 const onetime = require('onetime');
 
@@ -109,6 +110,10 @@ class Conf {
 			this.store = store;
 		}
 
+		if (options.watch) {
+			this._watch();
+		}
+
 		if (options.migrations) {
 			if (!options.projectVersion) {
 				options.projectVersion = getPackageData().version;
@@ -135,6 +140,44 @@ class Conf {
 		}
 	}
 
+	_ensureDirectory() {
+		// TODO: Use `fs.mkdirSync` `recursive` option when targeting Node.js 12.
+		// Ensure the directory exists as it could have been deleted in the meantime.
+		makeDir.sync(path.dirname(this.path));
+	}
+
+	_write(value) {
+		let data = this.serialize(value);
+
+		if (this.encryptionKey) {
+			const initializationVector = crypto.randomBytes(16);
+			const password = crypto.pbkdf2Sync(this.encryptionKey, initializationVector.toString(), 10000, 32, 'sha512');
+			const cipher = crypto.createCipheriv(encryptionAlgorithm, password, initializationVector);
+			data = Buffer.concat([initializationVector, Buffer.from(':'), cipher.update(Buffer.from(data)), cipher.final()]);
+		}
+
+		// Temporary workaround for Conf being packaged in a Ubuntu Snap app.
+		// See https://github.com/sindresorhus/conf/pull/82
+		if (process.env.SNAP) {
+			fs.writeFileSync(this.path, data);
+		} else {
+			writeFileAtomic.sync(this.path, data);
+		}
+	}
+
+	_watch() {
+		this._ensureDirectory();
+
+		if (!fs.existsSync(this.path)) {
+			this._write({});
+		}
+
+		fs.watch(this.path, {persistent: false}, debounceFn(() => {
+			// On Linux and Windows, writing to the config file emits a `rename` event, so we skip checking the event type.
+			this.events.emit('change');
+		}, {wait: 100}));
+	}
+
 	_migrate(migrations, versionToMigrate) {
 		let previousMigratedVersion = this._get(MIGRATION_KEY, '0.0.0');
 
@@ -353,8 +396,7 @@ class Conf {
 			return Object.assign(plainObject(), data);
 		} catch (error) {
 			if (error.code === 'ENOENT') {
-				// TODO: Use `fs.mkdirSync` `recursive` option when targeting Node.js 12
-				makeDir.sync(path.dirname(this.path));
+				this._ensureDirectory();
 				return plainObject();
 			}
 
@@ -367,26 +409,10 @@ class Conf {
 	}
 
 	set store(value) {
-		// Ensure the directory exists as it could have been deleted in the meantime
-		makeDir.sync(path.dirname(this.path));
+		this._ensureDirectory();
 
 		this._validate(value);
-		let data = this.serialize(value);
-
-		if (this.encryptionKey) {
-			const initializationVector = crypto.randomBytes(16);
-			const password = crypto.pbkdf2Sync(this.encryptionKey, initializationVector.toString(), 10000, 32, 'sha512');
-			const cipher = crypto.createCipheriv(encryptionAlgorithm, password, initializationVector);
-			data = Buffer.concat([initializationVector, Buffer.from(':'), cipher.update(Buffer.from(data)), cipher.final()]);
-		}
-
-		// Temporary workaround for Conf being packaged in a Ubuntu Snap app.
-		// See https://github.com/sindresorhus/conf/pull/82
-		if (process.env.SNAP) {
-			fs.writeFileSync(this.path, data);
-		} else {
-			writeFileAtomic.sync(this.path, data);
-		}
+		this._write(value);
 
 		this.events.emit('change');
 	}

index.test-d.ts

@@ -26,6 +26,7 @@ new Conf<UnicornFoo>({clearInvalidConfig: false});
 new Conf<UnicornFoo>({serialize: value => 'foo'});
 new Conf<UnicornFoo>({deserialize: string => ({foo: 'foo', unicorn: true})});
 new Conf<UnicornFoo>({projectSuffix: 'foo'});
+new Conf<UnicornFoo>({watch: true});
 
 new Conf<UnicornFoo>({
 	schema: {
@@ -40,6 +41,7 @@ new Conf<UnicornFoo>({
 		}
 	}
 });
+
 expectError(
 	new Conf<UnicornFoo>({
 		schema: {

package.json

@@ -40,6 +40,7 @@
 	],
 	"dependencies": {
 		"ajv": "^6.10.2",
+		"debounce-fn": "^3.0.1",
 		"dot-prop": "^5.0.0",
 		"env-paths": "^2.2.0",
 		"json-schema-typed": "^7.0.1",
@@ -54,6 +55,8 @@
 		"ava": "^2.3.0",
 		"clear-module": "^4.0.0",
 		"del": "^5.1.0",
+		"delay": "^4.3.0",
+		"p-event": "^4.1.0",
 		"tempy": "^0.3.0",
 		"tsd": "^0.7.4",
 		"xo": "^0.24.0"

readme.md

@@ -259,6 +259,15 @@ console.log(config.get('foo.bar.foobar'));
 //=> '🦄'
 ```
 
+#### watch
+
+type: `boolean`<br>
+Default: `false`
+
+Watch for any changes in the config file and call the callback for `onDidChange` if set. This is useful if there are multiple processes changing the same config file.
+
+**Currently this option doesn't work on Node.js 8 on macOS.**
+
 ### Instance
 
 You can use [dot-notation](https://github.com/sindresorhus/dot-prop) in a `key` to access nested properties.

test.js

@@ -5,6 +5,8 @@ import tempy from 'tempy';
 import del from 'del';
 import pkgUp from 'pkg-up';
 import clearModule from 'clear-module';
+import pEvent from 'p-event';
+import delay from 'delay';
 import Conf from '.';
 
 const fixture = '🦄';
@@ -717,6 +719,64 @@ test('.delete() - without dot notation', t => {
 	t.deepEqual(configWithoutDotNotation.get('foo.bar.zoo'), {awesome: 'redpanda'});
 });
 
+test('`watch` option watches for config file changes by another process', async t => {
+	if (process.platform === 'darwin' && process.version.split('.')[0] === 'v8') {
+		t.plan(0);
+		return;
+	}
+
+	const cwd = tempy.directory();
+	const conf1 = new Conf({cwd, watch: true});
+	const conf2 = new Conf({cwd});
+	conf1.set('foo', '👾');
+
+	t.plan(4);
+
+	const checkFoo = (newValue, oldValue) => {
+		t.is(newValue, '🐴');
+		t.is(oldValue, '👾');
+	};
+
+	t.is(conf2.get('foo'), '👾');
+	t.is(conf1.path, conf2.path);
+	conf1.onDidChange('foo', checkFoo);
+
+	(async () => {
+		await delay(50);
+		conf2.set('foo', '🐴');
+	})();
+
+	await pEvent(conf1.events, 'change');
+});
+
+test('`watch` option watches for config file changes by file write', async t => {
+	// TODO: Remove this when targeting Node.js 10.
+	if (process.platform === 'darwin' && process.version.split('.')[0] === 'v8') {
+		t.plan(0);
+		return;
+	}
+
+	const cwd = tempy.directory();
+	const conf = new Conf({cwd, watch: true});
+	conf.set('foo', '🐴');
+
+	t.plan(2);
+
+	const checkFoo = (newValue, oldValue) => {
+		t.is(newValue, '🦄');
+		t.is(oldValue, '🐴');
+	};
+
+	conf.onDidChange('foo', checkFoo);
+
+	(async () => {
+		await delay(50);
+		fs.writeFileSync(path.join(cwd, 'config.json'), JSON.stringify({foo: '🦄'}));
+	})();
+
+	await pEvent(conf.events, 'change');
+});
+
 test('migrations - should save the project version as the initial migrated version', t => {
 	const cwd = tempy.directory();