udp.erl

-module(udp).

-export([parse/1]).

-record(udp_packet, { src_port, dst_port, length, checksum, message_type, payload }).

-record(bootp_packet, { hw_type, addr_length, hops, transaction_id, elapsed, bootp_flags, 
  client_ip, your_client_ip, next_server_ip, relay_agent_ip, client_mac, dhcp_server_name, 
  boot_file, cookie, options }).

-record(bootp_option, { type, value }).


parse(Dgram) ->
	<<SrcPrt:16, DstPrt:16, Length:16, Checksum:16, MessageType, Message/binary>> = Dgram,

	case MessageType of
		1 -> Dhcp = parse_bootp(Message),
			#udp_packet{ src_port = SrcPrt, dst_port = DstPrt, length = Length, checksum = Checksum, payload = Dhcp };
		2 -> Dhcp = parse_bootp(Message),
			#udp_packet{ src_port = SrcPrt, dst_port = DstPrt, length = Length, checksum = Checksum, payload = Dhcp };
		true -> io:format("Don't know about ~w~n", [ MessageType ])
	end.

parse_bootp(Message) ->
	<<HwType,AddrLength,Hops,TransactionID:32,Elapsed:16,BootpFlags:16, 
	  ClientIP:4/binary,YourClientIP:4/binary,NextServerIP:4/binary,
	  RelayAgentIP:4/binary,ClientMAC:6/binary,DHCPServerName:64/binary, BootFile:128/binary,
	  _Pad:10/binary, Cookie:32, Options/binary>> = Message,
	
	#bootp_packet{
		hw_type = HwType, addr_length = AddrLength, hops = Hops, transaction_id = TransactionID, 
		elapsed = Elapsed, bootp_flags = BootpFlags, client_ip = util:extract_ip(ClientIP), 
		your_client_ip = util:extract_ip(YourClientIP), next_server_ip = util:extract_ip(NextServerIP), 
		relay_agent_ip = util:extract_ip(RelayAgentIP), client_mac = util:extract_mac(ClientMAC), 
		dhcp_server_name = binary_to_list(DHCPServerName), boot_file = binary_to_list(BootFile), 
		cookie = Cookie, options = listify_bootp_options(Options)
	}.

listify_bootp_options(Data) ->
	case Data of
		<<255>> -> [];
		Data -> 
			if size(Data) > 0 ->
				<<Type, Length, Rest/binary>> = Data,
				<<Value:Length/binary, Next/binary>> = Rest,
				[ #bootp_option{ type = Type, value = binary_to_list(Value) } ] ++ listify_bootp_options(Next)
			end
	end.