Support asynchronous connect function

Author: szmarczak

README.md

@@ -5,7 +5,7 @@
 
 ## API
 
-### resolveALPN(options)
+### resolveALPN(options, connect = tls.connect)
 
 Returns an object with an `alpnProtocol` property. The `socket` property may be also present.
 
@@ -48,6 +48,11 @@ console.log(result); // {alpnProtocol: 'h2', socket: tls.TLSSocket}
 result.socket.destroy();
 ```
 
+#### connect
+
+Type: `Function<TLSSocket> | AsyncFunction<TLSSocket>`\
+Default: [`tls.connect`](https://nodejs.org/dist/latest-v16.x/docs/api/tls.html#tls_tls_connect_options_callback)
+
 ## License
 
 MIT

index.js

@@ -1,9 +1,11 @@
 'use strict';
 const tls = require('tls');
 
-module.exports = (options = {}) => new Promise((resolve, reject) => {
+module.exports = (options = {}, connect = tls.connect) => new Promise((resolve, reject) => {
 	let timeout = false;
 
+	let socket;
+
 	const callback = async () => {
 		socket.off('timeout', onTimeout);
 		socket.off('error', reject);
@@ -26,8 +28,14 @@ module.exports = (options = {}) => new Promise((resolve, reject) => {
 		callback();
 	};
 
-	const socket = tls.connect(options, callback);
+	(async () => {
+		try {
+			socket = await connect(options, callback);
 
-	socket.on('error', reject);
-	socket.once('timeout', onTimeout);
+			socket.on('error', reject);
+			socket.once('timeout', onTimeout);
+		} catch (error) {
+			reject(error);
+		}
+	})();
 });

test.js

@@ -112,3 +112,49 @@ test('works with timeout', async t => {
 
 	t.true(timeout);
 });
+
+test('accept custom createConnection function', async t => {
+	const custom = Symbol('custom');
+
+	const result = await resolveALPN({
+		...s.options,
+		resolveSocket: true
+	}, (options, callback) => {
+		const socket = tls.connect(options, callback);
+		socket[custom] = true;
+
+		return socket;
+	});
+
+	t.is(result.alpnProtocol, 'h2');
+	t.true(result.socket instanceof tls.TLSSocket);
+	t.true(result.socket[custom]);
+
+	result.socket.destroy();
+});
+
+test('async createConnection function', async t => {
+	const custom = Symbol('custom');
+
+	const result = await resolveALPN({
+		...s.options,
+		resolveSocket: true
+	}, async (options, callback) => {
+		return new Promise((resolve, reject) => {
+			const socket = tls.connect(options, callback);
+			socket[custom] = true;
+
+			socket.once('error', reject);
+			socket.once('connect', () => {
+				socket.off('error', reject);
+				resolve(socket);
+			});
+		});
+	});
+
+	t.is(result.alpnProtocol, 'h2');
+	t.true(result.socket instanceof tls.TLSSocket);
+	t.true(result.socket[custom]);
+
+	result.socket.destroy();
+});