From ae6e94856d0fbd8c97993488e2f970d65ff0e330 Mon Sep 17 00:00:00 2001
From: Nick Dobie <nick@dobie.me>
Date: Wed, 7 May 2025 00:36:21 -0500
Subject: [PATCH 1/2] feat(otel): Added support for W3C Trace Context format

---
 .changeset/salty-bags-shop.md |  5 +++++
 packages/otel/src/index.ts    | 11 +++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/salty-bags-shop.md

diff --git a/.changeset/salty-bags-shop.md b/.changeset/salty-bags-shop.md
new file mode 100644
index 00000000..dee41796
--- /dev/null
+++ b/.changeset/salty-bags-shop.md
@@ -0,0 +1,5 @@
+---
+'@hono/otel': minor
+---
+
+Added support for W3C Trace Context format
diff --git a/packages/otel/src/index.ts b/packages/otel/src/index.ts
index 06c382d5..fb34457a 100644
--- a/packages/otel/src/index.ts
+++ b/packages/otel/src/index.ts
@@ -1,5 +1,5 @@
 import type { TracerProvider } from '@opentelemetry/api'
-import { SpanKind, SpanStatusCode, trace } from '@opentelemetry/api'
+import { SpanKind, SpanStatusCode, trace, context, propagation } from '@opentelemetry/api'
 import {
   ATTR_HTTP_REQUEST_HEADER,
   ATTR_HTTP_REQUEST_METHOD,
@@ -8,7 +8,7 @@ import {
   ATTR_URL_FULL,
   ATTR_HTTP_ROUTE,
 } from '@opentelemetry/semantic-conventions'
-import type { Env, Input } from 'hono'
+import type { Env, HonoRequest, Input } from 'hono'
 import { createMiddleware } from 'hono/factory'
 import metadata from '../package.json' with { type: 'json' }
 
@@ -42,6 +42,12 @@ export const otel = <E extends Env = any, P extends string = any, I extends Inpu
   const tracerProvider = options.tracerProvider ?? trace.getTracerProvider()
   const tracer = tracerProvider.getTracer(PACKAGE_NAME, PACKAGE_VERSION)
   return createMiddleware<E, P, I>(async (c, next) => {
+    // Handle propagation of trace context from a request using the W3C Trace Context format
+    let activeContext = context.active()
+    if (c.req.header('traceparent')) {
+      activeContext = propagation.extract(context.active(), c.req.header())
+    }
+
     const routePath = c.req.routePath
     await tracer.startActiveSpan(
       `${c.req.method} ${c.req.routePath}`,
@@ -53,6 +59,7 @@ export const otel = <E extends Env = any, P extends string = any, I extends Inpu
           [ATTR_HTTP_ROUTE]: routePath,
         },
       },
+      activeContext,
       async (span) => {
         for (const [name, value] of Object.entries(c.req.header())) {
           span.setAttribute(ATTR_HTTP_REQUEST_HEADER(name), value)

From 19d55ea2d3921c5d4240bfcfebce4d22e2fffbe1 Mon Sep 17 00:00:00 2001
From: Nicholas Dobie <nrdobie@users.noreply.github.com>
Date: Wed, 7 May 2025 09:56:23 -0500
Subject: [PATCH 2/2] removed unneeded HonoRequest

---
 packages/otel/src/index.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/otel/src/index.ts b/packages/otel/src/index.ts
index fb34457a..064e64be 100644
--- a/packages/otel/src/index.ts
+++ b/packages/otel/src/index.ts
@@ -8,7 +8,7 @@ import {
   ATTR_URL_FULL,
   ATTR_HTTP_ROUTE,
 } from '@opentelemetry/semantic-conventions'
-import type { Env, HonoRequest, Input } from 'hono'
+import type { Env, Input } from 'hono'
 import { createMiddleware } from 'hono/factory'
 import metadata from '../package.json' with { type: 'json' }