fix: detect X server display on Linux (ChromeDevTools#1027)

in headful mode on Linux we should try detecting X server if DISPLAY is
not set.

Author: OrKoN

src/browser.ts

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {execSync} from 'node:child_process';
 import fs from 'node:fs';
 import os from 'node:os';
 import path from 'node:path';
@@ -148,6 +149,24 @@ interface McpLaunchOptions {
   enableExtensions?: boolean;
 }
 
+export function detectDisplay(): void {
+  // Only detect display on Linux/UNIX.
+  if (os.platform() === 'win32' || os.platform() === 'darwin') {
+    return;
+  }
+  if (!process.env['DISPLAY']) {
+    try {
+      const result = execSync(
+        `ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\\0' '\\n' | grep -m1 '^DISPLAY=' | cut -d= -f2`,
+      );
+      const display = result.toString('utf8').trim();
+      process.env['DISPLAY'] = display;
+    } catch {
+      // no-op
+    }
+  }
+}
+
 export async function launch(options: McpLaunchOptions): Promise<Browser> {
   const {channel, executablePath, headless, isolated} = options;
   const profileDirName =
@@ -189,6 +208,10 @@ export async function launch(options: McpLaunchOptions): Promise<Browser> {
         : 'chrome';
   }
 
+  if (!headless) {
+    detectDisplay();
+  }
+
   try {
     const browser = await puppeteer.launch({
       channel: puppeteerChannel,

tests/browser.test.ts

@@ -11,9 +11,13 @@ import {describe, it} from 'node:test';
 
 import {executablePath} from 'puppeteer';
 
-import {ensureBrowserConnected, launch} from '../src/browser.js';
+import {detectDisplay, ensureBrowserConnected, launch} from '../src/browser.js';
 
 describe('browser', () => {
+  it('detects display does not crash', () => {
+    detectDisplay();
+  });
+
   it('cannot launch multiple times with the same profile', async () => {
     const tmpDir = os.tmpdir();
     const folderPath = path.join(tmpDir, `temp-folder-${crypto.randomUUID()}`);