fix(otlp-exporter-base): avoid use of a wrapped fetch

experimental/CHANGELOG.md

@@ -21,6 +21,7 @@ feat(configuration): parse config for rc 3 [#6304](https://github.com/open-telem
 
 * fix(exporter-prometheus): add missing `@opentelemetry/semantic-conventions` dependency [#6330](https://github.com/open-telemetry/opentelemetry-js/pull/6330) @omizha
 * fix(otlp-transformer): correctly handle Uint8Array attribute values when serializing to JSON [#6348](https://github.com/open-telemetry/opentelemetry-js/pull/6348) @pichlermarc
+* fix(otlp-exporter-base): fix unwanted instrumentation of the fetch exports when context is not propagated [#6353](https://github.com/open-telemetry/opentelemetry-js/pull/6353) @david-luna
 
 ### :books: Documentation
 

experimental/packages/otlp-exporter-base/src/transport/fetch-transport.ts

@@ -38,10 +38,23 @@ class FetchTransport implements IExporterTransport {
   async send(data: Uint8Array, timeoutMillis: number): Promise<ExportResponse> {
     const abortController = new AbortController();
     const timeout = setTimeout(() => abortController.abort(), timeoutMillis);
+    // Fetch API may be wrapped by an instrumentation like `@opentelemetry/instrumentation-fetch`.
+    // In that case the instrumentation would create a new Span for this request
+    // because the context manager cannot keep the context after `await` calls.
+    // This creates an indirect endless loop Export -> Span -> Export
+    // By using the `__original` function the instrumentation can't intercept the call
+    // and no Span will be created breaking the vicious cycle
+    let fetchApi = globalThis.fetch;
+    // @ts-expect-error -- fetch could be wrapped
+    if (typeof fetchApi.__original === 'function') {
+      // @ts-expect-error -- fetch could be wrapped
+      fetchApi = fetchApi.__original;
+    }
+
     try {
       const isBrowserEnvironment = !!globalThis.location;
       const url = new URL(this._parameters.url);
-      const response = await fetch(url.href, {
+      const response = await fetchApi(url.href, {
         method: 'POST',
         headers: await this._parameters.headers(),
         body: data,

experimental/packages/otlp-exporter-base/test/browser/fetch-transport.test.ts

@@ -41,6 +41,30 @@ describe('FetchTransport', function () {
   });
 
   describe('send', function () {
+    it('it uses global fetch API and is not affected by patching', function (done) {
+      // arrange
+      const fetchStub = sinon
+        .stub(globalThis, 'fetch')
+        .resolves(new Response('test response', { status: 200 }));
+      const transport = createFetchTransport(testTransportParameters);
+      // We patch fetch simulating what an instrumentation would do
+      const patchedStub = sinon.stub().callsFake(fetchStub);
+      globalThis.fetch = patchedStub;
+      (globalThis.fetch as any).__original = fetchStub;
+
+      //act
+      transport.send(testPayload, requestTimeout).then(response => {
+        // assert
+        try {
+          assert.strictEqual(response.status, 'success');
+          sinon.assert.notCalled(patchedStub);
+          sinon.assert.called(fetchStub);
+        } catch (e) {
+          done(e);
+        }
+        done();
+      }, done /* catch any rejections */);
+    });
     it('returns success when request succeeds', function (done) {
       // arrange
       const fetchStub = sinon