DHCPv4-over-DHCPv6 Wireshark dissector

dhcpv6_4o6.lua

--
-- DHCPv4-over-DHCPv6 Wireshark dissector
-- Copyright (C) 2020  Mikael Magnusson
--
-- This work is licensed under the terms of GPLv2 (or any later version).
--

do
   local DHCPV6_OPTION_DHCPV4_MSG = 87
   local DHCPV6_OPTION_6O4_SERVER = 88
   
   local original_dhcpv6_dissector = Dissector.get("dhcpv6")
   local dhcpv4_dissector = Dissector.get("dhcp") -- was bootp
   local dhcpv6_wrapper_proto = Proto("dhcpv6_4o6", "DHCPv4-over-DHCPv6");
   local F_4o6server = ProtoField.ipv6("dhcpv6.4o6.server", "DHCP 4o6 Server Address")
   dhcpv6_wrapper_proto.fields = {F_4o6server}
   -- declare the fields we need to read
   local f_option_type = Field.new("dhcpv6.option.type")
   local f_option_length = Field.new("dhcpv6.option.length")
   local f_option_value = Field.new("dhcpv6.option.value")

   function dhcpv6_wrapper_proto.dissector(tvbuffer, pinfo, treeitem)
      -- we've replaced the original dhcpv6 dissector in the dissector table,
      -- but we still want the original to run, especially because we need to read its data
      original_dhcpv6_dissector:call(tvbuffer, pinfo, treeitem)

      local subtreeitem
      local option_types = {f_option_type()}
      local option_lengths = {f_option_length()}
      local option_values = {f_option_value()}
      local pos = 0
      for i, _ in pairs(option_types) do
	 local option_type = option_types[i].value
	 local option_length = option_lengths[i].value
	 local option_value

	 -- The option_values table doesn't contain options with empty values
	 if option_length > 0 then
	    pos = pos + 1
	    option_value = option_values[pos]
	 end

	 if option_value then
	    if option_type == DHCPV6_OPTION_6O4_SERVER then
	       if not subtreeitem then
		  subtreeitem = treeitem:add(dhcpv6_wrapper_proto, tvbuffer)
	       end

	       server_tvb = option_value.range:tvb()
	       offset = 0
	       length = 16
	       while offset < server_tvb:len() do
		  subtreeitem:add(F_4o6server, server_tvb:range(offset, length))
		  offset = offset + length
	       end
	    else if option_type == DHCPV6_OPTION_DHCPV4_MSG then
		  if not subtreeitem then
		     subtreeitem = treeitem:add(dhcpv6_wrapper_proto, tvbuffer)
		  end
		  dhcpv4_dissector:call(option_value.range:tvb(), pinfo, subtreeitem)
		 end
	    end
	 end
      end
   end
   local udp_dissector_table = DissectorTable.get("udp.port")
   udp_dissector_table:add(546, dhcpv6_wrapper_proto)
   udp_dissector_table:add(547, dhcpv6_wrapper_proto)
end