# Writing a message:
  my $message = {
    data => "Some message\nthat can contain newlines\n",
    params => \%params,
  };
  nstore_fd($message, $fh);

  # Reading a message:
  my $message = fd_retrieve($fh);
  my $params = $message->{'params'};
  my $data = $message->{'data'};