From c6274ef5bb718e98a8abbd177d3945b36f794ffa Mon Sep 17 00:00:00 2001
From: Philip Szalla <philip@szalla.de>
Date: Mon, 23 Aug 2021 23:39:27 +0200
Subject: [PATCH] fix(opentelemetry-instrumentation-fetch): fixed override of
 headers

Signed-off-by: Philip Szalla <philip@szalla.de>
---
 packages/opentelemetry-instrumentation-fetch/src/fetch.ts | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/packages/opentelemetry-instrumentation-fetch/src/fetch.ts b/packages/opentelemetry-instrumentation-fetch/src/fetch.ts
index d82f6cdc35..7315a8c71f 100644
--- a/packages/opentelemetry-instrumentation-fetch/src/fetch.ts
+++ b/packages/opentelemetry-instrumentation-fetch/src/fetch.ts
@@ -158,6 +158,11 @@ 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) {
+      // ||-operator causes ts type error
+      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);