Capture.open_offline.
    Objectopen(capture, filename)
          Return a Dumper to dump packets captured by
          capture to filename.
        
close
          close Dumper.
        
dump(packet)
          Dump packet to this Dumper.
          packet must be a packet captured by
          Capture specified when opening this Dumper.
        
dump_raw(buf)
          Dump buf to this Dumper as a packet.