fix(cloudflare): Forward method, headers and body when a Request is passed as fetch init

packages/cloudflare/src/instrumentations/worker/instrumentFetcher.ts

@@ -24,6 +24,22 @@ export function instrumentFetcher(fetchFn: Fetcher['fetch']): Fetcher['fetch'] {
       return fetchFn(requestWithTracing);
     }
 
+    if (init instanceof Request) {
+      // `init` is itself a Request (the `stub.fetch(url, request)` Workers idiom). A Request's
+      // `method`, `headers`, `body` and the rest are prototype getters, not own properties, so the
+      // object spread below would drop them and the call would reach the fetcher as a bare GET with
+      // no headers or body. Rebuild through the Request constructor, which reads those members by
+      // property access, then layer the tracing headers (which already include the request's own
+      // headers) on top.
+      const request = new Request(input, init);
+
+      if (!headers) {
+        return fetchFn(request);
+      }
+
+      return fetchFn(new Request(request, { headers: headers as HeadersInit }));
+    }
+
     const mergedInit = {
       ...init,
       ...(headers ? { headers } : {}),

packages/cloudflare/test/utils/instrumentFetcher.test.ts

@@ -260,6 +260,52 @@ describe('instrumentFetcher', () => {
     expect(headers.get('baggage')).toBe('sentry-environment=production');
   });
 
+  it('forwards method, headers and body when init is a Request', async () => {
+    getTraceDataMock.mockReturnValue({
+      'sentry-trace': '12345678901234567890123456789012-1234567890123456-1',
+      baggage: 'sentry-environment=production',
+    });
+
+    const mockFetch = vi.fn().mockResolvedValue(new Response('ok'));
+    const wrapped = instrumentFetcher(mockFetch);
+
+    // The `stub.fetch(url, request)` Workers idiom: `init` is itself a Request.
+    const incoming = new Request('https://example.com/room/ABC/websocket', {
+      method: 'POST',
+      headers: { Upgrade: 'websocket', 'Content-Type': 'application/json' },
+      body: '{"a":1}',
+    });
+
+    await wrapped('https://internal/websocket', incoming as unknown as RequestInit);
+
+    expect(mockFetch).toHaveBeenCalledTimes(1);
+    const forwarded = mockFetch.mock.calls[0]![0] as Request;
+    expect(forwarded.method).toBe('POST');
+    expect(forwarded.headers.get('upgrade')).toBe('websocket');
+    expect(forwarded.headers.get('content-type')).toBe('application/json');
+    expect(forwarded.headers.get('sentry-trace')).toBe('12345678901234567890123456789012-1234567890123456-1');
+    expect(await forwarded.text()).toBe('{"a":1}');
+  });
+
+  it('forwards method and body when init is a Request and tracing is disabled', async () => {
+    getTraceDataMock.mockReturnValue({});
+
+    const mockFetch = vi.fn().mockResolvedValue(new Response('ok'));
+    const wrapped = instrumentFetcher(mockFetch);
+
+    const incoming = new Request('https://example.com/upload', {
+      method: 'POST',
+      body: 'payload',
+    });
+
+    await wrapped('https://internal/upload', incoming as unknown as RequestInit);
+
+    expect(mockFetch).toHaveBeenCalledTimes(1);
+    const forwarded = mockFetch.mock.calls[0]![0] as Request;
+    expect(forwarded.method).toBe('POST');
+    expect(await forwarded.text()).toBe('payload');
+  });
+
   it('appends baggage to existing non-sentry baggage', async () => {
     getTraceDataMock.mockReturnValue({
       'sentry-trace': '12345678901234567890123456789012-1234567890123456-1',