fix(chromium): sync navigator.platform with userAgentData when custom UA is set

packages/playwright-core/src/server/browserContext.ts

@@ -821,6 +821,27 @@ export function normalizeProxySettings(proxy: types.ProxySettings): types.ProxyS
   return { ...proxy, server, bypass };
 }
 
+// Maps a user agent string to the corresponding navigator.platform value.
+// Used by Firefox and WebKit; Chromium uses its own navigatorPlatform()
+// in crPage.ts which operates on already-parsed UserAgentMetadata.
+export function navigatorPlatformFromUA(ua: string): string | undefined {
+  if (!ua)
+    return undefined;
+  if (ua.includes('Android'))
+    return ua.includes('x86') ? 'Linux x86_64' : 'Linux armv8l';
+  if (ua.includes('iPhone OS'))
+    return 'iPhone';
+  if (ua.includes('iPad'))
+    return 'iPad';
+  if (ua.includes('Mac OS X'))
+    return 'MacIntel';
+  if (ua.includes('Windows'))
+    return 'Win32';
+  if (ua.toLowerCase().includes('linux'))
+    return ua.includes('aarch64') ? 'Linux aarch64' : 'Linux x86_64';
+  return undefined;
+}
+
 const paramsThatAllowContextReuse: (keyof channels.BrowserNewContextForReuseParams)[] = [
   'colorScheme',
   'forcedColors',

packages/playwright-core/src/server/chromium/crPage.ts

@@ -988,10 +988,13 @@ class FrameSession {
 
   async _updateUserAgent(): Promise<void> {
     const options = this._crPage._browserContext._options;
+    const userAgentMetadata = calculateUserAgentMetadata(options);
+    const emulateUAPlatform = !process.env.PLAYWRIGHT_NO_UA_PLATFORM;
     await this._client.send('Emulation.setUserAgentOverride', {
       userAgent: options.userAgent || '',
       acceptLanguage: options.locale,
-      userAgentMetadata: calculateUserAgentMetadata(options),
+      platform: emulateUAPlatform && userAgentMetadata ? navigatorPlatform(userAgentMetadata, options.userAgent || '') : undefined,
+      userAgentMetadata,
     });
   }
 
@@ -1199,7 +1202,18 @@ function calculateUserAgentMetadata(options: types.BrowserContextOptions) {
   } else if (ua.toLowerCase().includes('linux')) {
     metadata.platform = 'Linux';
   }
-  if (ua.includes('ARM'))
+  if (ua.includes('ARM') || ua.includes('aarch64'))
     metadata.architecture = 'arm';
   return metadata;
 }
+
+function navigatorPlatform(metadata: Protocol.Emulation.UserAgentMetadata, ua: string): string {
+  switch (metadata.platform) {
+    case 'Android': return metadata.architecture === 'arm' ? 'Linux armv8l' : 'Linux x86_64';
+    case 'iOS': return ua.includes('iPad') ? 'iPad' : 'iPhone';
+    case 'macOS': return 'MacIntel';
+    case 'Linux': return metadata.architecture === 'arm' ? 'Linux aarch64' : 'Linux x86_64';
+    case 'Windows': return 'Win32';
+    default: return metadata.platform;
+  }
+}

packages/playwright-core/src/server/firefox/ffBrowser.ts

@@ -17,7 +17,7 @@
 
 import { assert } from '../../utils';
 import { Browser } from '../browser';
-import { BrowserContext, verifyGeolocation } from '../browserContext';
+import { BrowserContext, navigatorPlatformFromUA, verifyGeolocation } from '../browserContext';
 import * as network from '../network';
 import { ConnectionEvents, FFConnection  } from './ffConnection';
 import { FFPage } from './ffPage';
@@ -191,6 +191,10 @@ export class FFBrowserContext extends BrowserContext {
       promises.push(this._browser.session.send('Browser.setTouchOverride', { browserContextId, hasTouch: true }));
     if (this._options.userAgent)
       promises.push(this._browser.session.send('Browser.setUserAgentOverride', { browserContextId, userAgent: this._options.userAgent }));
+    if (this._options.userAgent && !process.env.PLAYWRIGHT_NO_UA_PLATFORM) {
+      const platform = navigatorPlatformFromUA(this._options.userAgent);
+      promises.push(this._browser.session.send('Browser.setPlatformOverride', { browserContextId, platform: platform || null }));
+    }
     if (this._options.bypassCSP)
       promises.push(this._browser.session.send('Browser.setBypassCSP', { browserContextId, bypassCSP: true }));
     if (this._options.ignoreHTTPSErrors || this._options.internalIgnoreHTTPSErrors)
@@ -325,6 +329,8 @@ export class FFBrowserContext extends BrowserContext {
 
   async setUserAgent(userAgent: string | undefined): Promise<void> {
     await this._browser.session.send('Browser.setUserAgentOverride', { browserContextId: this._browserContextId, userAgent: userAgent || null });
+    const platform = userAgent && !process.env.PLAYWRIGHT_NO_UA_PLATFORM ? navigatorPlatformFromUA(userAgent) : null;
+    await this._browser.session.send('Browser.setPlatformOverride', { browserContextId: this._browserContextId, platform: platform || null });
   }
 
   async doUpdateOffline(): Promise<void> {

packages/playwright-core/src/server/webkit/wkPage.ts

@@ -21,6 +21,7 @@ import { eventsHelper } from '../utils/eventsHelper';
 import { hostPlatform } from '../utils/hostPlatform';
 import { splitErrorMessage } from '../../utils/isomorphic/stackTrace';
 import { PNG, jpegjs } from '../../utilsBundle';
+import { navigatorPlatformFromUA } from '../browserContext';
 import * as dialog from '../dialog';
 import * as dom from '../dom';
 import { TargetClosedError } from '../errors';
@@ -691,6 +692,12 @@ export class WKPage implements PageDelegate {
   async updateUserAgent(): Promise<void> {
     const contextOptions = this._browserContext._options;
     this._updateState('Page.overrideUserAgent', { value: contextOptions.userAgent });
+    if (contextOptions.userAgent && !process.env.PLAYWRIGHT_NO_UA_PLATFORM) {
+      const platform = navigatorPlatformFromUA(contextOptions.userAgent);
+      this._updateState('Page.overridePlatform', platform ? { value: platform } : { });
+    } else {
+      this._updateState('Page.overridePlatform', { });
+    }
   }
 
   async bringToFront(): Promise<void> {

tests/library/browsercontext-user-agent.spec.ts

@@ -107,6 +107,38 @@ it('custom user agent for download', async ({ server, contextFactory, browserVer
   expect(req.headers['user-agent']).toBe('MyCustomUA');
 });
 
+it('should override navigator.platform to match custom user agent', async ({ browser, server }) => {
+  {
+    const context = await browser.newContext({
+      userAgent: 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36',
+    });
+    const page = await context.newPage();
+    await page.goto(server.EMPTY_PAGE);
+    expect.soft(await page.evaluate(() => navigator.platform)).toBe('Win32');
+    await context.close();
+  }
+
+  {
+    const context = await browser.newContext({
+      userAgent: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36',
+    });
+    const page = await context.newPage();
+    await page.goto(server.EMPTY_PAGE);
+    expect.soft(await page.evaluate(() => navigator.platform)).toBe('MacIntel');
+    await context.close();
+  }
+
+  {
+    const context = await browser.newContext({
+      userAgent: 'Mozilla/5.0 (Linux; Android 13; Pixel 7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Mobile Safari/537.36',
+    });
+    const page = await context.newPage();
+    await page.goto(server.EMPTY_PAGE);
+    expect.soft(await page.evaluate(() => navigator.platform)).toBe('Linux armv8l');
+    await context.close();
+  }
+});
+
 it('should work for navigator.userAgentData and sec-ch-ua headers', async ({ playwright, browserName, browser, server }) => {
   it.skip(browserName !== 'chromium', 'This API is Chromium-only');
 
@@ -139,6 +171,35 @@ it('should work for navigator.userAgentData and sec-ch-ua headers', async ({ pla
     expect.soft(await page.evaluate(() => (window.navigator as any).userAgentData.toJSON())).toEqual(
         expect.objectContaining({ mobile: true, platform: 'Android' })
     );
+    expect.soft(await page.evaluate(() => navigator.platform)).toBe('Linux armv8l');
+    await context.close();
+  }
+
+  {
+    const context = await browser.newContext(playwright.devices['Desktop Chrome']);
+    const page = await context.newPage();
+    const [request] = await Promise.all([
+      server.waitForRequest('/empty.html'),
+      page.goto(server.EMPTY_PAGE),
+    ]);
+    expect.soft(request.headers['sec-ch-ua-platform']).toBe(`"Windows"`);
+    expect.soft(await page.evaluate(() => (window.navigator as any).userAgentData.toJSON())).toEqual(
+        expect.objectContaining({ mobile: false, platform: 'Windows' })
+    );
+    expect.soft(await page.evaluate(() => navigator.platform)).toBe('Win32');
+    await context.close();
+  }
+
+  {
+    const context = await browser.newContext({
+      userAgent: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36',
+    });
+    const page = await context.newPage();
+    await page.goto(server.EMPTY_PAGE);
+    expect.soft(await page.evaluate(() => (window.navigator as any).userAgentData.toJSON())).toEqual(
+        expect.objectContaining({ platform: 'macOS' })
+    );
+    expect.soft(await page.evaluate(() => navigator.platform)).toBe('MacIntel');
     await context.close();
   }
 });