How can I use FileUpload in a Quarkus RestClient to upload file to a external rest service?

I'm using org.jboss.resteasy.reactive.multipart.FileUpload in a server endpoint, and it is working well.

Now I need to send a generated file to an external Rest service.

I found org.jboss.resteasy.reactive.server.core.multipart.DefaultFileUpload, but it need org.jboss.resteasy.reactive.server.multipart.FormValue as parameter, and a non-public implementation.

I'm supposed to create a class implementing that interface or am I missing something easier ?

Let's assume that the server receives a multipart request that looks like this:

public class ServerRequest { 

  @RestForm("files")
  @PartType(MediaType.APPLICATION_OCTET_STREAM)
  List<FileUpload> files;

  @RestForm("jsonPayload")
  @PartType(MediaType.TEXT_PLAIN)
  String jsonPayload;
}

Then you can create a client request like this:

public ClientMultipartForm buildClientMultipartForm(ServerRequest request) { 
  ClientMultipartForm multiPartForm = ClientMultipartForm.create();
  multiPartForm.attribute("jsonPayload", request.getJsonPayload(), "jsonPayload"); 
  request.getFiles().forEach(fu -> {
    multiPartForm.fileUpload(fu); 
  });
  return multiPartForm;
}

More details can be found https://quarkus.io/guides/rest-client#converting-a-received-multipart-object-into-a-client-request