fix(body): fetch body explicitly for prefetched scripts (#14941)

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

@@ -271,8 +271,25 @@ export class CRNetworkManager {
 
   _createResponse(request: InterceptableRequest, responsePayload: Protocol.Network.Response): network.Response {
     const getResponseBody = async () => {
+      const contentLengthHeader = Object.entries(responsePayload.headers).find(header => header[0].toLowerCase() === 'content-length');
+      const expectedLength = contentLengthHeader ? +contentLengthHeader[1] : undefined;
+
       const response = await this._client.send('Network.getResponseBody', { requestId: request._requestId });
-      return Buffer.from(response.body, response.base64Encoded ? 'base64' : 'utf8');
+      if (response.body || !expectedLength)
+        return Buffer.from(response.body, response.base64Encoded ? 'base64' : 'utf8');
+
+      // For <link prefetch we are going to receive empty body with non-emtpy content-length expectation. Reach out for the actual content.
+      const resource = await this._client.send('Network.loadNetworkResource', { url: request.request.url(), frameId: request.request.frame()._id, options: { disableCache: false, includeCredentials: true } });
+      const chunks: Buffer[] = [];
+      while (resource.resource.stream) {
+        const chunk = await this._client.send('IO.read', { handle: resource.resource.stream });
+        chunks.push(Buffer.from(chunk.data, chunk.base64Encoded ? 'base64' : 'utf-8'));
+        if (chunk.eof) {
+          await this._client.send('IO.close', { handle: resource.resource.stream });
+          break;
+        }
+      }
+      return Buffer.concat(chunks);
     };
     const timingPayload = responsePayload.timing!;
     let timing: network.ResourceTiming;

tests/assets/prefetch.html

@@ -0,0 +1 @@
+<link rel="prefetch" href="prefetch.js">

tests/assets/prefetch.js

@@ -0,0 +1 @@
+// Scripts will be pre-fetched

tests/page/page-network-response.spec.ts

@@ -334,3 +334,13 @@ it('should report if request was fromServiceWorker', async ({ page, server, isAn
     expect(res.fromServiceWorker()).toBe(true);
   }
 });
+
+it('should return body for prefetch script', async ({ page, server, browserName }) => {
+  it.skip(browserName === 'webkit', 'No prefetch in WebKit: https://caniuse.com/link-rel-prefetch');
+  const [response] = await Promise.all([
+    page.waitForResponse('**/prefetch.js'),
+    page.goto(server.PREFIX + '/prefetch.html')
+  ]);
+  const body = await response.body();
+  expect(body.toString()).toBe('// Scripts will be pre-fetched');
+});

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

@@ -64,6 +64,7 @@ it('should fulfill response with empty body', async ({ page, server, isAndroid,
     const response = await page.request.fetch(route.request());
     await route.fulfill({
       response,
+      headers: { 'content-length': '0' },
       status: 201,
       body: ''
     });