def pack (self):
    """
    Packs this object into its wire format.
    May normalize fields.
    NOTE: If "data" has been specified, this method may actually return
          *more than just a single ofp_flow_mod* in packed form.
          Specifically, it may also have a barrier and an ofp_packet_out.
    """
    po = None
    if self.data:
      #TODO: It'd be nice to log and then ignore if not data_is_complete.
      #      Unfortunately, we currently have no logging in here, so we
      #      assert instead which is a either too drastic or too quiet.
      assert self.data.is_complete
      assert self.buffer_id is None
      self.buffer_id = self.data.buffer_id
      if self.buffer_id is None:
        po = ofp_packet_out(data=self.data)
        po.in_port = self.data.in_port
        po.actions.append(ofp_action_output(port = OFPP_TABLE))
        # Should maybe check that packet hits the new entry...
        # Or just duplicate the actions? (I think that's the best idea)

    assert self._assert()
    match = self.match.pack()
    match_len = len(match)

    command = self.command
    command |= (self.table_id << 8)

    packed = b""
    packed += ofp_header.pack(self)
    packed += struct.pack("!LL", self.vendor, self.subtype)
    packed += struct.pack("!QHHHHLHHH", self.cookie, command,
                          self.idle_timeout, self.hard_timeout,
                          self.priority, self._buffer_id, self.out_port,
                          self.flags, match_len)
    packed += _PAD6
    packed += match
    packed += _PAD * ((match_len + 7)/8*8 - match_len)
    for i in self.actions:
      packed += i.pack()

    if po:
      packed += ofp_barrier_request().pack()
      packed += po.pack()

    assert len(packed) == len(self)

    return packed
  def pack (self):
    assert self._assert()

    match_len = len(self.match)

    packed = b""
    packed += ofp_header.pack(self)
    packed += struct.pack("!LL", NX_VENDOR_ID, self.subtype)
    packed += struct.pack("!LHBBQH", self._buffer_id, self.total_len,
                          self.reason, self.table_id, self.cookie,
                          match_len)
    packed += _PAD6
    packed += match.pack()
    packed += _PAD * ((match_len + 7)/8*8 - match_len)
    packed += _PAD2
    packed += self.packed_data
    return packed