foo.java

    Vertx vertx = Vertx.vertx();
    HttpClient client = vertx.createHttpClient();
    HttpServer server = vertx.createHttpServer();
    server.requestHandler(req -> {
      Trace trace = Trace.create(req);
      HttpClientRequest clientReq = client.get("some-uri", ar -> {
        trace.close();
      });
      trace.propagateTo(clientReq);
      clientReq.end();
    });