From a70d91950f8c66201711ffc5d8505979f0403332 Mon Sep 17 00:00:00 2001
From: Jocelyn Boullier <jocelyn@boullier.bzh>
Date: Sun, 8 Jun 2025 04:31:28 +0200
Subject: [PATCH] feat(otel): record uncaught expections (#1191)

---
 .changeset/rude-squids-shout.md |  5 +++++
 packages/otel/src/index.test.ts | 12 ++++++++++++
 packages/otel/src/index.ts      |  4 ++++
 3 files changed, 21 insertions(+)
 create mode 100644 .changeset/rude-squids-shout.md

diff --git a/.changeset/rude-squids-shout.md b/.changeset/rude-squids-shout.md
new file mode 100644
index 00000000..3db0124d
--- /dev/null
+++ b/.changeset/rude-squids-shout.md
@@ -0,0 +1,5 @@
+---
+'@hono/otel': patch
+---
+
+Record uncaught exceptions as events attached to the request span
diff --git a/packages/otel/src/index.test.ts b/packages/otel/src/index.test.ts
index 1908840c..24eb5bab 100644
--- a/packages/otel/src/index.test.ts
+++ b/packages/otel/src/index.test.ts
@@ -7,6 +7,9 @@ import {
   ATTR_HTTP_RESPONSE_STATUS_CODE,
   ATTR_URL_FULL,
   ATTR_HTTP_ROUTE,
+  ATTR_EXCEPTION_MESSAGE,
+  ATTR_EXCEPTION_TYPE,
+  ATTR_EXCEPTION_STACKTRACE,
 } from '@opentelemetry/semantic-conventions'
 import { Hono } from 'hono'
 import { otel } from '.'
@@ -65,6 +68,15 @@ describe('OpenTelemetry middleware', () => {
     expect(span.attributes[ATTR_HTTP_REQUEST_METHOD]).toBe('POST')
     expect(span.attributes[ATTR_URL_FULL]).toBe('http://localhost/error')
     expect(span.attributes[ATTR_HTTP_ROUTE]).toBe('/error')
+    expect(span.events.length).toBe(1)
+    const [event] = span.events
+    expect(event.attributes).toBeDefined()
+    const attributes = event.attributes!
+    expect(attributes[ATTR_EXCEPTION_TYPE]).toBe('Error')
+    expect(attributes[ATTR_EXCEPTION_MESSAGE]).toBe('error message')
+    expect(attributes[ATTR_EXCEPTION_STACKTRACE]).toEqual(
+      expect.stringMatching(/Error: error message\n.*at \S+\/src\/index.test.ts:\d+:\d+\n/)
+    )
   })
 
   it('Should update the active span', async () => {
diff --git a/packages/otel/src/index.ts b/packages/otel/src/index.ts
index 064e64be..e359199d 100644
--- a/packages/otel/src/index.ts
+++ b/packages/otel/src/index.ts
@@ -75,9 +75,13 @@ export const otel = <E extends Env = any, P extends string = any, I extends Inpu
             span.setAttribute(ATTR_HTTP_RESPONSE_HEADER(name), value)
           }
           if (c.error) {
+            span.recordException(c.error)
             span.setStatus({ code: SpanStatusCode.ERROR, message: String(c.error) })
           }
         } catch (e) {
+          if (e instanceof Error) {
+            span.recordException(e)
+          }
           span.setStatus({ code: SpanStatusCode.ERROR, message: String(e) })
           throw e
         } finally {