Ensure waitUntilTrace ends spans on errors

Author: petyosi

packages/otel-cf-workers/src/instrumentation/fetch.ts

@@ -146,8 +146,11 @@ function getParentContextFromRequest(request: Request): Context {
 export async function waitUntilTrace(fn: () => Promise<unknown>): Promise<void> {
   const tracer = trace.getTracer('waitUntil')
   return tracer.startActiveSpan('waitUntil', async (span) => {
-    await fn()
-    span.end()
+    try {
+      await fn()
+    } finally {
+      span.end()
+    }
   })
 }
 

packages/otel-cf-workers/test/instrumentation/fetch.test.ts

@@ -0,0 +1,25 @@
+import type { Span, Tracer } from '@opentelemetry/api'
+import { trace } from '@opentelemetry/api'
+import { describe, expect, it, vitest } from 'vitest'
+import { waitUntilTrace } from '../../src/instrumentation/fetch'
+
+describe('waitUntilTrace', () => {
+  it('ends the span when traced background work rejects', async () => {
+    const error = new Error('background work failed')
+    const end = vitest.fn<() => void>()
+    const span = { end } as unknown as Span
+    const tracer = {
+      async startActiveSpan(_name: string, fn: (span: Span) => Promise<void>) {
+        return fn(span)
+      },
+    } as unknown as Tracer
+    const getTracer = vitest.spyOn(trace, 'getTracer').mockReturnValue(tracer)
+
+    try {
+      await expect(waitUntilTrace(async () => Promise.reject(error))).rejects.toBe(error)
+      expect(end).toHaveBeenCalledTimes(1)
+    } finally {
+      getTracer.mockRestore()
+    }
+  })
+})