gistfile1.txt

      my $tx = $self->ua->build_tx(POST => $url);
      $tx->req->headers->content_length($file->size);

      my $offset = 0;
      my $chunk_size = 4096;
      my $drain;
      $drain = sub {
        my $req = shift;
        my $chunk = $file->get_chunk($offset, $chunk_size);
        $drain = undef unless length $chunk;
        $offset += length $chunk;
        $req->write($chunk, $drain);
      };

      $tx->req->$drain;
      $self->ua->start($tx, $delay->begin);