feat(utils): Backfill stack trace on fetch errors if it is missing (#12389)

Author: Luca Forstner

dev-packages/browser-integration-tests/playwright.config.ts

@@ -11,7 +11,7 @@ const config: PlaywrightTestConfig = {
   testMatch: /test.ts/,
 
   use: {
-    trace: process.env.CI ? 'retain-on-failure' : 'off',
+    trace: 'retain-on-failure',
   },
 
   projects: [

dev-packages/browser-integration-tests/suites/integrations/globalHandlers/fetchStackTrace/subject.js

@@ -0,0 +1 @@
+fetch('http://localhost:123/fake/endpoint/that/will/fail');

dev-packages/browser-integration-tests/suites/integrations/globalHandlers/fetchStackTrace/test.ts

@@ -0,0 +1,13 @@
+import { expect } from '@playwright/test';
+import type { Event } from '@sentry/types';
+
+import { sentryTest } from '../../../../utils/fixtures';
+import { getMultipleSentryEnvelopeRequests } from '../../../../utils/helpers';
+
+sentryTest('should create errors with stack traces for failing fetch calls', async ({ getLocalTestPath, page }) => {
+  const url = await getLocalTestPath({ testDir: __dirname });
+
+  const envelopes = await getMultipleSentryEnvelopeRequests<Event>(page, 3, { url, timeout: 10000 });
+  const errorEvent = envelopes.find(event => !event.type)!;
+  expect(errorEvent?.exception?.values?.[0].stacktrace?.frames?.length).toBeGreaterThan(0);
+});

dev-packages/browser-integration-tests/suites/integrations/globalHandlers/init.js

@@ -0,0 +1,7 @@
+import * as Sentry from '@sentry/browser';
+
+window.Sentry = Sentry;
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+});

dev-packages/browser-integration-tests/suites/tracing/request/fetch/test.ts

@@ -17,12 +17,8 @@ sentryTest('should create spans for fetch requests', async ({ getLocalTestPath,
 
   // We will wait 500ms for all envelopes to be sent. Generally, in all browsers, the last sent
   // envelope contains tracing data.
-
-  // If we are on FF or webkit:
-  // 1st envelope contains CORS error
-  // 2nd envelope contains the tracing data we want to check here
-  const envelopes = await getMultipleSentryEnvelopeRequests<Event>(page, 2, { url, timeout: 10000 });
-  const tracingEvent = envelopes[envelopes.length - 1]; // last envelope contains tracing data on all browsers
+  const envelopes = await getMultipleSentryEnvelopeRequests<Event>(page, 4, { url, timeout: 10000 });
+  const tracingEvent = envelopes.find(event => event.type === 'transaction')!; // last envelope contains tracing data on all browsers
 
   const requestSpans = tracingEvent.spans?.filter(({ op }) => op === 'http.client');
 

packages/utils/src/instrument/fetch.ts

@@ -1,7 +1,8 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
 import type { HandlerDataFetch } from '@sentry/types';
 
-import { fill } from '../object';
+import { isError } from '../is';
+import { addNonEnumerableProperty, fill } from '../object';
 import { supportsNativeFetch } from '../supports';
 import { timestampInSeconds } from '../time';
 import { GLOBAL_OBJ } from '../worldwide';
@@ -45,6 +46,15 @@ function instrumentFetch(): void {
         ...handlerData,
       });
 
+      // We capture the stack right here and not in the Promise error callback because Safari (and probably other
+      // browsers too) will wipe the stack trace up to this point, only leaving us with this file which is useless.
+
+      // NOTE: If you are a Sentry user, and you are seeing this stack frame,
+      //       it means the error, that was caused by your fetch call did not
+      //       have a stack trace, so the SDK backfilled the stack trace so
+      //       you can see which fetch call failed.
+      const virtualStackTrace = new Error().stack;
+
       // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
       return originalFetch.apply(GLOBAL_OBJ, args).then(
         (response: Response) => {
@@ -65,6 +75,16 @@ function instrumentFetch(): void {
           };
 
           triggerHandlers('fetch', erroredHandlerData);
+
+          if (isError(error) && error.stack === undefined) {
+            // NOTE: If you are a Sentry user, and you are seeing this stack frame,
+            //       it means the error, that was caused by your fetch call did not
+            //       have a stack trace, so the SDK backfilled the stack trace so
+            //       you can see which fetch call failed.
+            error.stack = virtualStackTrace;
+            addNonEnumerableProperty(error, 'framesToPop', 1);
+          }
+
           // NOTE: If you are a Sentry user, and you are seeing this stack frame,
           //       it means the sentry.javascript SDK caught an error invoking your application code.
           //       This is expected behavior and NOT indicative of a bug with sentry.javascript.