feat: enable BiDi support for connect-existing mode

GeckodriverHttpDriver now requests webSocketUrl: true in the session
capabilities and exposes a getBidi() method that opens a WebSocket to
Firefox's Remote Agent. This allows BiDi-dependent features (console
events, network events) to work when using --connect-existing.

The WebSocket is opened lazily on the first getBidi() call and closed
on quit/kill. The IBiDi interface already defined upstream is satisfied
by wrapping the ws WebSocket instance.

No behavior change for launch mode (continues to use selenium-webdriver
with enableBidi). No behavior change for connect-existing when Firefox
was not started with --remote-debugging-port (getBidi throws a clear
error, same as before but with a better message).

Author: MayCXC

src/firefox/core.ts

@@ -8,6 +8,7 @@ import { spawn, type ChildProcess } from 'node:child_process';
 import { mkdirSync, openSync, closeSync } from 'node:fs';
 import { homedir } from 'node:os';
 import { join } from 'node:path';
+import WebSocket from 'ws';
 import type { FirefoxLaunchOptions } from './types.js';
 import { log, logDebug } from '../utils/logger.js';
 
@@ -129,11 +130,14 @@ class GeckodriverHttpDriver implements IDriver {
   private baseUrl: string;
   private sessionId: string;
   private gdProcess: ChildProcess;
+  private webSocketUrl: string | null;
+  private bidiConnection: IBiDi | null = null;
 
-  constructor(baseUrl: string, sessionId: string, gdProcess: ChildProcess) {
+  constructor(baseUrl: string, sessionId: string, gdProcess: ChildProcess, webSocketUrl: string | null) {
     this.baseUrl = baseUrl;
     this.sessionId = sessionId;
     this.gdProcess = gdProcess;
+    this.webSocketUrl = webSocketUrl;
   }
 
   static async connect(marionettePort: number): Promise<GeckodriverHttpDriver> {
@@ -206,11 +210,11 @@ class GeckodriverHttpDriver implements IDriver {
 
     const baseUrl = `http://127.0.0.1:${port}`;
 
-    // Create a WebDriver session
+    // Create a WebDriver session with BiDi opt-in
     const resp = await fetch(`${baseUrl}/session`, {
       method: 'POST',
       headers: { 'Content-Type': 'application/json' },
-      body: JSON.stringify({ capabilities: { alwaysMatch: {} } }),
+      body: JSON.stringify({ capabilities: { alwaysMatch: { webSocketUrl: true } } }),
     });
     const json = (await resp.json()) as {
       value: { sessionId: string; capabilities: Record<string, unknown> };
@@ -219,7 +223,14 @@ class GeckodriverHttpDriver implements IDriver {
       throw new Error(`Failed to create session: ${JSON.stringify(json)}`);
     }
 
-    return new GeckodriverHttpDriver(baseUrl, json.value.sessionId, gd);
+    const wsUrl = json.value.capabilities.webSocketUrl as string | undefined;
+    if (wsUrl) {
+      logDebug(`BiDi WebSocket URL: ${wsUrl}`);
+    } else {
+      logDebug('BiDi WebSocket URL not available (Firefox may not support it or Remote Agent is not running)');
+    }
+
+    return new GeckodriverHttpDriver(baseUrl, json.value.sessionId, gd, wsUrl ?? null);
   }
 
   private async cmd(method: string, path: string, body?: unknown): Promise<unknown> {
@@ -422,6 +433,10 @@ class GeckodriverHttpDriver implements IDriver {
   }
 
   async quit(): Promise<void> {
+    if (this.bidiConnection) {
+      (this.bidiConnection.socket as unknown as WebSocket).close();
+      this.bidiConnection = null;
+    }
     try {
       await this.cmd('DELETE', '');
     } catch {
@@ -432,11 +447,35 @@ class GeckodriverHttpDriver implements IDriver {
 
   /** Kill the geckodriver process without closing Firefox */
   kill(): void {
+    if (this.bidiConnection) {
+      (this.bidiConnection.socket as unknown as WebSocket).close();
+      this.bidiConnection = null;
+    }
     this.gdProcess.kill();
   }
 
-  getBidi(): Promise<IBiDi> {
-    throw new Error('BiDi not available in connect-existing mode');
+  /**
+   * Return a BiDi handle. Opens a WebSocket to Firefox's Remote Agent on
+   * first call, using the webSocketUrl returned in the session capabilities.
+   */
+  async getBidi(): Promise<IBiDi> {
+    if (this.bidiConnection) return this.bidiConnection;
+    if (!this.webSocketUrl) {
+      throw new Error(
+        'BiDi is not available: no webSocketUrl in session capabilities. ' +
+        'Ensure Firefox was started with --remote-debugging-port.'
+      );
+    }
+
+    const ws = new WebSocket(this.webSocketUrl);
+    await new Promise<void>((resolve, reject) => {
+      ws.on('open', resolve);
+      ws.on('error', reject);
+    });
+    logDebug('BiDi WebSocket connected');
+
+    this.bidiConnection = { socket: ws as unknown as IBiDiSocket };
+    return this.bidiConnection;
   }
 }