}
	t.reqCanceler[req] = cancel
	t.reqMu.Unlock()
	return cancel
}

// CancelRequest cancels an in-flight request by closing its connection.
// CancelRequest should only be called after [Transport.RoundTrip] has returned.
//
// Deprecated: Use [Request.WithContext] to create a request with a
// cancelable context instead. CancelRequest cannot cancel HTTP/2
// requests. This may become a no-op in a future release of Go.

	defer frontend.Close()
	frontendClient := frontend.Client()

	getReq, _ := http.NewRequest("GET", frontend.URL, nil)
	go func() {
		<-reqInFlight
		frontendClient.Transport.(*http.Transport).CancelRequest(getReq)
	}()
	res, err := frontendClient.Do(getReq)
	if res != nil {
		t.Errorf("got response %v; want nil", res.Status)
	}
	if err == nil {
		// This should be an error like: