Remove Headless from user agent

common/browser.go

@@ -691,6 +691,19 @@ func (b *Browser) fetchVersion() (browserVersion, error) {
 		return browserVersion{}, fmt.Errorf("getting browser version information: %w", err)
 	}
 
+	// Adjust the user agent to remove the headless part.
+	//
+	// Including Headless might cause issues with some websites that treat headless
+	// browsers differently. Later on, [BrowserContext] will set the user agent to
+	// this user agent if not set by the user. This will force [FrameSession] to
+	// set the user agent to the browser's user agent.
+	//
+	// Doing this here provides a consistent user agent across all browser contexts.
+	// Also, it makes it consistent to query the user agent from the browser.
+	if b.browserOpts.Headless {
+		bv.userAgent = strings.ReplaceAll(bv.userAgent, "Headless", "")
+	}
+
 	return bv, nil
 }
 

common/browser_context.go

@@ -118,6 +118,11 @@ func NewBrowserContext(
 	if opts == nil {
 		opts = DefaultBrowserContextOptions()
 	}
+	// Always use the [Browser]'s user agent if it's not set by the user.
+	// Setting this forces [FrameSession] to set Chromium's user agent.
+	if strings.TrimSpace(opts.UserAgent) == "" {
+		opts.UserAgent = browser.UserAgent()
+	}
 
 	b := BrowserContext{
 		BaseEventEmitter: NewBaseEventEmitter(ctx),

examples/useragent.js

@@ -0,0 +1,49 @@
+import { browser } from 'k6/x/browser/async';
+import { check } from 'https://jslib.k6.io/k6-utils/1.5.0/index.js';
+
+export const options = {
+  scenarios: {
+    ui: {
+      executor: 'shared-iterations',
+      options: {
+        browser: {
+            type: 'chromium',
+        },
+      },
+    },
+  },
+  thresholds: {
+    checks: ["rate==1.0"]
+  }
+}
+
+export default async function() {
+  let context = await browser.newContext({
+    userAgent: 'k6 test user agent',
+  })
+  let page = await context.newPage();
+  await check(page, {
+    'user agent is set': async p => {
+        const userAgent = await p.evaluate(() => navigator.userAgent);
+        return userAgent.includes('k6 test user agent');
+    }
+  });
+  await page.close();
+  await context.close();
+
+  context = await browser.newContext();
+  check(context.browser(), {
+    'user agent does not contain headless': b => {
+        return b.userAgent().includes('Headless') === false;
+    }
+  });
+
+  page = await context.newPage();
+  await check(page, {
+    'chromium user agent does not contain headless': async p => {
+        const userAgent = await p.evaluate(() => navigator.userAgent);
+        return userAgent.includes('Headless') === false;
+    }
+  });
+  await page.close();
+}