protected int flush(byte[] buf, int offset, int len) throws IOException
    {
        if (flushHandler != null)
            return flushHandler.flush(this, buf, offset, len);

        out.write(buf, offset, len);
        return offset;
    }
Returns a single byte array containg all the contents written to the buffer(s).
protostuff-api/src/main/java/io/protostuff/WriteSession.java