$sfh = $sftp->do_open($target_file ...);
  .
  .
  .
 #loop over source file, reading blocks of $data
  $status = $sftp->do_write($sfh, $offset, $data)
  &bail_out($status) if ($status != SSH2_FX_OK);
  .
  .
  .
 $sftp->do_close($sfh);