class External {

  public static <InputT extends PInput, OutputT>
      SingleOutputExpandableTransform<InputT, OutputT> of(
          String urn, byte[] payload, String endpoint) {
    Endpoints.ApiServiceDescriptor apiDesc =
        Endpoints.ApiServiceDescriptor.newBuilder().setUrl(endpoint).build();
    return new SingleOutputExpandableTransform<>(urn, payload, apiDesc, getFreshNamespaceIndex());
  }

}