account for older platforms where ReadableStream can't tee()

packages/opentelemetry-sdk-trace-web/src/utils.ts

@@ -131,8 +131,18 @@ export function addSpanNetworkEvents(
 
 function _getBodyNonDestructively(body: ReadableStream) {
   // can't read a ReadableStream without destroying it
-  // we CAN "tee" the body stream, which lets us split it, but that still locks the original stream
-  // so we end up needing to return one of the forks.
+  // on most platforms, we CAN tee the body stream, which lets us split it,
+  // but that still locks the original stream, so we end up needing to return one of the forks.
+  //
+  // some (older) platforms don't expose the tee method and in that scenario, we're out of luck;
+  //   there's no way to read the stream without consuming it.
+  if (!body.tee) {
+    return {
+      body,
+      length: Promise.resolve(null),
+    };
+  }
+
   const [bodyToReturn, bodyToConsume] = body.tee();
 
   const lengthPromise = async () => {

packages/opentelemetry-sdk-trace-web/test/utils.test.ts

@@ -699,6 +699,34 @@ describe('utils', () => {
       assert.strictEqual(value, jsonString);
     });
 
+    it('should handle readablestream objects without a tee method', async () => {
+      const jsonString = JSON.stringify({
+        key1: 'true',
+        key2: 'hello world',
+      });
+      const stream = textToReadableStream(jsonString);
+
+      // remove the .tee() method to mimic older environments where this method isn't available
+      // @ts-expect-error
+      stream.tee = undefined;
+
+      const requestParams = { body: stream };
+      const length = await getFetchBodyLength(
+        'https://example.com',
+        requestParams
+      );
+
+      // we got the correct length
+      assert.strictEqual(length, null);
+
+      // AND the body is still readable
+      assert.strictEqual(requestParams.body.locked, false);
+
+      // AND the body is still correct
+      const { value } = await requestParams.body.getReader().read();
+      assert.strictEqual(value, jsonString);
+    });
+
     it('should read the body of the first param when recieving a request', async () => {
       const bodyContent = JSON.stringify({
         key1: 'true',