feat(browser): Add http.response_delivery_type attribute to resource spans

dev-packages/browser-integration-tests/suites/public-api/startSpan/attributes/subject.js

@@ -0,0 +1,11 @@
+async function run() {
+  Sentry.startSpan({ name: 'parent_span' }, () => {
+    Sentry.startSpan({ name: 'child_span', attributes: { someAttribute: '' } }, () => {
+      // whatever a user would do here
+    });
+  });
+}
+
+(async () => {
+  await run();
+})();

dev-packages/browser-integration-tests/suites/public-api/startSpan/attributes/test.ts

@@ -0,0 +1,21 @@
+import { expect } from '@playwright/test';
+
+import { sentryTest } from '../../../../utils/fixtures';
+import {
+  envelopeRequestParser,
+  shouldSkipTracingTest,
+  waitForTransactionRequestOnUrl,
+} from '../../../../utils/helpers';
+
+sentryTest('sends an empty string attribute', async ({ getLocalTestPath, page }) => {
+  if (shouldSkipTracingTest()) {
+    sentryTest.skip();
+  }
+
+  const url = await getLocalTestPath({ testDir: __dirname });
+  const req = await waitForTransactionRequestOnUrl(page, url);
+  const transaction = envelopeRequestParser(req);
+
+  const childSpan = transaction.spans?.[0];
+  expect(childSpan?.data?.someAttribute).toBe('');
+});

packages/browser-utils/src/metrics/browserMetrics.ts

@@ -513,6 +513,7 @@ export interface ResourceEntry extends Record<string, unknown> {
   encodedBodySize?: number;
   decodedBodySize?: number;
   renderBlockingStatus?: string;
+  deliveryType?: string;
 }
 
 /** Create resource-related spans */
@@ -539,6 +540,10 @@ export function _addResourceSpans(
   setResourceEntrySizeData(attributes, entry, 'encodedBodySize', 'http.response_content_length');
   setResourceEntrySizeData(attributes, entry, 'decodedBodySize', 'http.decoded_response_content_length');
 
+  if (entry.deliveryType != null) {
+    attributes['http.response_delivery_type'] = entry.deliveryType;
+  }
+
   if ('renderBlockingStatus' in entry) {
     attributes['resource.render_blocking_status'] = entry.renderBlockingStatus;
   }

packages/browser-utils/test/browser/browserMetrics.test.ts

@@ -338,6 +338,32 @@ describe('_addResourceSpans', () => {
       }),
     );
   });
+
+  // resource delivery types: https://developer.mozilla.org/en-US/docs/Web/API/PerformanceResourceTiming/deliveryType
+  // i.e. better but not yet widely supported way to check for browser cache hit
+  it.each(['cache', 'navigational-prefetch', ''])(
+    'attaches delivery type ("%s") to resource spans if available',
+    deliveryType => {
+      const spans: Span[] = [];
+
+      getClient()?.on('spanEnd', span => {
+        spans.push(span);
+      });
+
+      const entry: ResourceEntry = {
+        initiatorType: 'css',
+        transferSize: 0,
+        encodedBodySize: 0,
+        decodedBodySize: 0,
+        deliveryType,
+      };
+
+      _addResourceSpans(span, entry, resourceEntryName, 100, 23, 345);
+
+      expect(spans).toHaveLength(1);
+      expect(spanToJSON(spans[0]!).data).toMatchObject({ 'http.response_delivery_type': deliveryType });
+    },
+  );
 });
 
 const setGlobalLocation = (location: Location) => {