Read bound address from server.address() and handle IPv6 formatting

apps/playwright-browser-tunnel/src/HttpServer.ts

@@ -2,12 +2,24 @@
 // See LICENSE in the project root for license information.
 
 import http from 'node:http';
+import type { AddressInfo } from 'node:net';
 
-import { WebSocketServer, type WebSocket, type AddressInfo } from 'ws';
+import { WebSocketServer, type WebSocket } from 'ws';
 
 import type { ITerminal } from '@rushstack/terminal';
 
-const LOCALHOST_IP: string = '127.0.0.1';
+const LOCALHOST: string = 'localhost';
+
+/**
+ * Formats an address info object into a WebSocket-compatible address string.
+ * IPv6 addresses are formatted with brackets: [address]:port
+ * IPv4 addresses are formatted as: address:port
+ */
+function formatAddress(addressInfo: AddressInfo): string {
+  return addressInfo.family === 'IPv6'
+    ? `[${addressInfo.address}]:${addressInfo.port}`
+    : `${addressInfo.address}:${addressInfo.port}`;
+}
 
 /**
  * This HttpServer is used for the localProxyWs WebSocketServer.
@@ -17,7 +29,7 @@ const LOCALHOST_IP: string = '127.0.0.1';
 export class HttpServer {
   private readonly _server: http.Server;
   private readonly _wsServer: WebSocketServer; // local proxy websocket server accepting browser clients
-  private _listeningPort: number | undefined;
+  private _listeningAddress: string | undefined;
   private _logger: ITerminal;
 
   public constructor(logger: ITerminal) {
@@ -37,22 +49,32 @@ export class HttpServer {
 
   public listen(): Promise<void> {
     return new Promise((resolve) => {
-      this._server.listen(0, LOCALHOST_IP, () => {
-        this._listeningPort = (this._server.address() as AddressInfo).port;
+      // Bind to 'localhost' which resolves to IPv4 (127.0.0.1) or IPv6 (::1)
+      // depending on system configuration and DNS resolution
+      this._server.listen(0, LOCALHOST, () => {
+        const addressInfo = this._server.address();
+        if (!addressInfo) {
+          throw new Error('Server address is null - server may not be bound properly');
+        }
+        if (typeof addressInfo === 'string') {
+          throw new Error(
+            `Server address is a pipe/socket path (${addressInfo}), expected an IP address`
+          );
+        }
+        const formattedAddress: string = formatAddress(addressInfo);
+        this._listeningAddress = formattedAddress;
         // This MUST be printed to terminal so VS Code can auto-port forward
-        this._logger.writeLine(
-          `Local proxy HttpServer listening at ws://${LOCALHOST_IP}:${this._listeningPort}`
-        );
+        this._logger.writeLine(`Local proxy HttpServer listening at ws://${formattedAddress}`);
         resolve();
       });
     });
   }
 
   public get endpoint(): string {
-    if (this._listeningPort === undefined) {
+    if (this._listeningAddress === undefined) {
       throw new Error('HttpServer not listening yet');
     }
-    return `ws://${LOCALHOST_IP}:${this._listeningPort}`;
+    return `ws://${this._listeningAddress}`;
   }
 
   public get wsServer(): WebSocketServer {