vertx.fileSystem().open(testDir + pathSep + fileName, new OpenOptions(), ar -> {
if (ar.succeeded()) {
AsyncFile rs = ar.result();
rs.setReadPos(chunkSize * chunks / 2);
Buffer buff = Buffer.buffer();
rs.handler(buff::appendBuffer);
rs.exceptionHandler(t -> fail(t.getMessage()));
rs.endHandler(v -> {
ar.result().close(ar2 -> {
if (ar2.failed()) {
fail(ar2.cause().getMessage());