chore(extension): support custom executablePath (microsoft#947)

Fixes microsoft#941

Author: yury-s

extension/tests/extension.spec.ts

@@ -276,3 +276,32 @@ for (const [mode, startClientMethod] of [
   });
 
 }
+
+test(`custom executablePath`, async ({ startClient, server, useShortConnectionTimeout }) => {
+  useShortConnectionTimeout(1000);
+
+  const executablePath = test.info().outputPath('echo.sh');
+  await fs.promises.writeFile(executablePath, '#!/bin/bash\necho "Custom exec args: $@" > "$(dirname "$0")/output.txt"', { mode: 0o755 });
+
+  const { client } = await startClient({
+    args: [`--extension`],
+    config: {
+      browser: {
+        launchOptions: {
+          executablePath,
+        },
+      }
+    },
+  });
+
+  const navigateResponse = await client.callTool({
+    name: 'browser_navigate',
+    arguments: { url: server.HELLO_WORLD },
+    timeout: 1000,
+  });
+  expect(await navigateResponse).toHaveResponse({
+    result: expect.stringContaining('Extension connection timeout.'),
+    isError: true,
+  });
+  expect(await fs.promises.readFile(test.info().outputPath('output.txt'), 'utf8')).toContain('Custom exec args: chrome-extension://jakfalbnbhgkpmoaakfflhflbfpkailf/connect.html?');
+});

src/extension/cdpRelay.ts

@@ -60,6 +60,7 @@ export class CDPRelayServer {
   private _wsHost: string;
   private _browserChannel: string;
   private _userDataDir?: string;
+  private _executablePath?: string;
   private _cdpPath: string;
   private _extensionPath: string;
   private _wss: WebSocketServer;
@@ -73,10 +74,11 @@ export class CDPRelayServer {
   private _nextSessionId: number = 1;
   private _extensionConnectionPromise!: ManualPromise<void>;
 
-  constructor(server: http.Server, browserChannel: string, userDataDir?: string) {
+  constructor(server: http.Server, browserChannel: string, userDataDir?: string, executablePath?: string) {
     this._wsHost = httpAddressToString(server.address()).replace(/^http/, 'ws');
     this._browserChannel = browserChannel;
     this._userDataDir = userDataDir;
+    this._executablePath = executablePath;
 
     const uuid = crypto.randomUUID();
     this._cdpPath = `/cdp/${uuid}`;
@@ -125,12 +127,16 @@ export class CDPRelayServer {
     if (toolName)
       url.searchParams.set('newTab', String(toolName === 'browser_navigate'));
     const href = url.toString();
-    const executableInfo = registry.findExecutable(this._browserChannel);
-    if (!executableInfo)
-      throw new Error(`Unsupported channel: "${this._browserChannel}"`);
-    const executablePath = executableInfo.executablePath();
-    if (!executablePath)
-      throw new Error(`"${this._browserChannel}" executable not found. Make sure it is installed at a standard location.`);
+
+    let executablePath = this._executablePath;
+    if (!executablePath) {
+      const executableInfo = registry.findExecutable(this._browserChannel);
+      if (!executableInfo)
+        throw new Error(`Unsupported channel: "${this._browserChannel}"`);
+      executablePath = executableInfo.executablePath();
+      if (!executablePath)
+        throw new Error(`"${this._browserChannel}" executable not found. Make sure it is installed at a standard location.`);
+    }
 
     const args: string[] = [];
     if (this._userDataDir)

src/extension/extensionContextFactory.ts

@@ -26,10 +26,12 @@ const debugLogger = debug('pw:mcp:relay');
 export class ExtensionContextFactory implements BrowserContextFactory {
   private _browserChannel: string;
   private _userDataDir?: string;
+  private _executablePath?: string;
 
-  constructor(browserChannel: string, userDataDir: string | undefined) {
+  constructor(browserChannel: string, userDataDir: string | undefined, executablePath: string | undefined) {
     this._browserChannel = browserChannel;
     this._userDataDir = userDataDir;
+    this._executablePath = executablePath;
   }
 
   async createContext(clientInfo: ClientInfo, abortSignal: AbortSignal, toolName: string | undefined): Promise<{ browserContext: playwright.BrowserContext, close: () => Promise<void> }> {
@@ -55,7 +57,7 @@ export class ExtensionContextFactory implements BrowserContextFactory {
       httpServer.close();
       throw new Error(abortSignal.reason);
     }
-    const cdpRelayServer = new CDPRelayServer(httpServer, this._browserChannel, this._userDataDir);
+    const cdpRelayServer = new CDPRelayServer(httpServer, this._browserChannel, this._userDataDir, this._executablePath);
     abortSignal.addEventListener('abort', () => cdpRelayServer.stop());
     debugLogger(`CDP relay server started, extension endpoint: ${cdpRelayServer.extensionEndpoint()}.`);
     return cdpRelayServer;

src/program.ts

@@ -72,7 +72,7 @@ program
 
       const config = await resolveCLIConfig(options);
       const browserContextFactory = contextFactory(config);
-      const extensionContextFactory = new ExtensionContextFactory(config.browser.launchOptions.channel || 'chrome', config.browser.userDataDir);
+      const extensionContextFactory = new ExtensionContextFactory(config.browser.launchOptions.channel || 'chrome', config.browser.userDataDir, config.browser.launchOptions.executablePath);
 
       if (options.extension) {
         const serverBackendFactory: mcpServer.ServerBackendFactory = {