test: link preload interception (#16908)

tests/assets/preload.html

@@ -0,0 +1,5 @@
+<script>
+let preloadedStyles = false;
+</script>
+<link rel="preload" href="./one-style.css" as="style" onload="window.preloadedStyles=true;this.onload=null;this.rel='stylesheet'" />
+<div>hello, world!</div>

tests/page/page-request-continue.spec.ts

@@ -349,3 +349,27 @@ it('should delete the origin header', async ({ page, server, isAndroid, browserN
   expect(interceptedRequest.headers()['origin']).toEqual(undefined);
   expect(serverRequest.headers.origin).toBeFalsy();
 });
+
+it('should continue preload link requests', async ({ page, server, browserName }) => {
+  it.info().annotations.push({ type: 'issue', description: 'https://github.com/microsoft/playwright/issues/16745' });
+  it.fixme(browserName === 'webkit', 'Preload requests are aborted in WebKit when interception is enabled');
+  let intercepted = false;
+  await page.route('**/one-style.css', route => {
+    intercepted = true;
+    route.continue({
+      headers: {
+        ...route.request().headers(),
+        'custom': 'value'
+      }
+    });
+  });
+  const [serverRequest] = await Promise.all([
+    server.waitForRequest('/one-style.css'),
+    page.goto(server.PREFIX + '/preload.html')
+  ]);
+  expect(serverRequest.headers['custom']).toBe('value');
+  await page.waitForFunction(() => (window as any).preloadedStyles);
+  expect(intercepted).toBe(true);
+  const color = await page.evaluate(() => window.getComputedStyle(document.body).backgroundColor);
+  expect(color).toBe('rgb(255, 192, 203)');
+});

tests/page/page-request-fulfill.spec.ts

@@ -353,3 +353,31 @@ function findResponse(har: har.HARFile, url: string): har.Response {
   expect(entry, originalUrl).toBeTruthy();
   return entry?.response;
 }
+
+it('should fulfill preload link requests', async ({ page, server, browserName }) => {
+  it.info().annotations.push({ type: 'issue', description: 'https://github.com/microsoft/playwright/issues/16745' });
+  it.fixme(browserName === 'webkit', 'Preload requests are aborted in WebKit when interception is enabled');
+  let intercepted = false;
+  await page.route('**/one-style.css', route => {
+    intercepted = true;
+    route.fulfill({
+      status: 200,
+      headers: {
+        'content-type': 'text/css; charset=utf-8',
+        'cache-control': 'no-cache, no-store',
+        'custom': 'value'
+      },
+      body: 'body { background-color: green; }'
+    });
+  });
+  const [response] = await Promise.all([
+    page.waitForResponse('**/one-style.css'),
+    page.goto(server.PREFIX + '/preload.html')
+  ]);
+  expect(await response.headerValue('custom')).toBe('value');
+  await page.waitForFunction(() => (window as any).preloadedStyles);
+  expect(intercepted).toBe(true);
+  const color = await page.evaluate(() => window.getComputedStyle(document.body).backgroundColor);
+  expect(color).toBe('rgb(0, 128, 0)');
+});
+