fix: headers are appended to existing one (open-telemetry#2335)

packages/opentelemetry-exporter-collector/src/platform/browser/util.ts

@@ -55,8 +55,11 @@ export function sendWithXhr(
 ) {
   const xhr = new XMLHttpRequest();
   xhr.open('POST', url);
-  xhr.setRequestHeader('Accept', 'application/json');
-  xhr.setRequestHeader('Content-Type', 'application/json');
+
+  if (!Object.keys(headers).includes('Accept'))
+    xhr.setRequestHeader('Accept', 'application/json');
+  if (!Object.keys(headers).includes('Content-Type'))
+    xhr.setRequestHeader('Content-Type', 'application/json');
   Object.entries(headers).forEach(([k, v]) => {
     xhr.setRequestHeader(k, v);
   });

packages/opentelemetry-exporter-collector/test/browser/util.test.ts

@@ -0,0 +1,63 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as sinon from 'sinon';
+import { sendWithXhr } from "../../src/platform/browser/util";
+import {
+  ensureHeadersContain,
+} from '../helper';
+
+
+describe('util - browser', () => {
+
+  describe('when Content-Type and Accept headers are set explicit', () => {
+    let server: any;
+
+    const explicitContentTypeAndAcceptHeaders = {
+      'Content-Type': 'application/json',
+      'Accept': 'application/json',
+    };
+    const body = "";
+    const url = "";
+
+    let onSuccessStub: sinon.SinonStub;
+    let onErrorStub: sinon.SinonStub;
+
+    beforeEach(() => {
+      onSuccessStub = sinon.stub();
+      onErrorStub = sinon.stub();
+      server = sinon.fakeServer.create();
+    });
+    afterEach(() => {
+      server.restore();
+      sinon.restore();
+    });
+
+    it('should successfully use XMLHttpRequest and Request Headers contain the expilicit defined Content-Type and Accept Header Values', done => {
+      sendWithXhr(body, url, explicitContentTypeAndAcceptHeaders, onSuccessStub, onErrorStub)
+
+      // ;charset=utf-8 is applied by sinon.fakeServer
+      const expectedHeaders = { ...explicitContentTypeAndAcceptHeaders, "Content-Type": "application/json;charset=utf-8" }
+
+      setTimeout(() => {
+        const { requestHeaders } = server.requests[0];
+        ensureHeadersContain(requestHeaders, expectedHeaders);
+        done();
+      });
+    });
+  });
+});
+