From dbfabd2bff113b6cfd17096b12f287472c30c751 Mon Sep 17 00:00:00 2001
From: Philip Szalla <philip@szalla.de>
Date: Sat, 28 Aug 2021 01:11:30 +0200
Subject: [PATCH] fix(opentelemetry-instrumentation-fetch): fixed override of
 headers (#2426)

* fix(opentelemetry-instrumentation-fetch): fixed override of headers

Signed-off-by: Philip Szalla <philip@szalla.de>

* style(opentelemetry-instrumentation-fetch): removed irritating comment

Signed-off-by: Philip Szalla <philip@szalla.de>

* test(opentelemetry-instrumentation-fetch): added tests for custom headers

Signed-off-by: Philip Szalla <philip@szalla.de>

Co-authored-by: Daniel Dyla <dyladan@users.noreply.github.com>
---
 .../src/fetch.ts                              |  4 +++
 .../test/fetch.test.ts                        | 26 +++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/packages/opentelemetry-instrumentation-fetch/src/fetch.ts b/packages/opentelemetry-instrumentation-fetch/src/fetch.ts
index d82f6cdc35..01ff72cb2f 100644
--- a/packages/opentelemetry-instrumentation-fetch/src/fetch.ts
+++ b/packages/opentelemetry-instrumentation-fetch/src/fetch.ts
@@ -158,6 +158,10 @@ export class FetchInstrumentation extends InstrumentationBase<
       api.propagation.inject(api.context.active(), options.headers, {
         set: (h, k, v) => h.set(k, typeof v === 'string' ? v : String(v)),
       });
+    } else if(options.headers instanceof Headers) {
+      api.propagation.inject(api.context.active(), options.headers, {
+        set: (h, k, v) => h.set(k, typeof v === 'string' ? v : String(v)),
+      });
     } else {
       const headers: Partial<Record<string, unknown>> = {};
       api.propagation.inject(api.context.active(), headers);
diff --git a/packages/opentelemetry-instrumentation-fetch/test/fetch.test.ts b/packages/opentelemetry-instrumentation-fetch/test/fetch.test.ts
index 1fa0d465c7..1de5b795d0 100644
--- a/packages/opentelemetry-instrumentation-fetch/test/fetch.test.ts
+++ b/packages/opentelemetry-instrumentation-fetch/test/fetch.test.ts
@@ -535,6 +535,32 @@ describe('fetch', () => {
       assert.ok(typeof r.headers.get(X_B3_TRACE_ID) === 'string');
     });
 
+    it('should keep custom headers with a request object and a headers object', () => {
+      const r = new Request('url', {
+        headers: new Headers({'foo': 'bar'})
+      });
+      window.fetch(r).catch(() => {});
+      assert.ok(r.headers.get('foo') === 'bar');
+    });
+
+    it('should keep custom headers with url, untyped request object and typed headers object', () => {
+      const url = 'url';
+      const init = {
+        headers: new Headers({'foo': 'bar'})
+      };
+      window.fetch(url, init).catch(() => {});
+      assert.ok(init.headers.get('foo') === 'bar');
+    });
+
+    it('should keep custom headers with url, untyped request object and untyped headers object', () => {
+      const url = 'url';
+      const init = {
+        headers: {'foo': 'bar'}
+      };
+      window.fetch(url, init).catch(() => {});
+      assert.ok(init.headers['foo'] === 'bar');
+    });
+
     it('should pass request object as first parameter to the original function (#2411)', () => {
       const r = new Request(url);
       return window.fetch(r).then(() => {