code: @Override
      public Promise<List<String>> readDir(String path, String filter) {
          return adapter.toPromise(handler -> vertx.fileSystem().readDir(path, filter, handler));
      }
docs: Read the contents of the directory specified by {@code path}, asynchronously.
  <p>
  The parameter {@code filter} is a regular expression. If {@code filter} is specified then only the paths that
  match  @{filter}will be returned.
  <p>
  The result is an array of String representing the paths of the files inside the directory.
  
  @param path   path to the directory
  @param filter the filter expression
  @return a promise for the contents