code: public int readBodyData(OutputStream output)
              throws MalformedStreamException, IOException {
          final InputStream istream = newInputStream();
          return (int) Streams.copy(istream, output, false);
      }
docs: <p>Reads <code>body-data</code> from the current
  <code>encapsulation</code> and writes its contents into the
  output <code>Stream</code>.
  
  <p>Arbitrary large amounts of data can be processed by this
  method using a constant size buffer. (see {@link
  #MultipartStream(InputStream,byte[],int, ProgressNotifier) constructor}).
  
  @param output The <code>Stream</code> to write data into. May
  be null, in which case this method is equivalent
  to {@link #discardBodyData()}.
  
  @return the amount of data written.
  
  @throws MalformedStreamException if the stream ends unexpectedly.
  @throws IOException              if an i/o error occurs.