RotMG proof-of-concept server in Erlang

rotmgs.erl

%% RotMG game module

-module(rotmgs).
-export([start/0, read/1, processpacket/2, send/2]).

-define(PORT, 2050).
-define(TCP_OPTIONS, [binary,
	{packet, 0},
	{active, false},
	{backlog, 1024},
	{reuseaddr, true}]).
-define(RC4R, [16#31, 16#1f, 16#80, 16#69, 16#14, 16#51, 16#c7, 16#1d, 16#09, 16#a1, 16#3a, 16#2a, 16#6e]).
-define(RC4S, [16#72, 16#c5, 16#58, 16#3c, 16#af, 16#b6, 16#81, 16#89, 16#95, 16#cd, 16#d7, 16#4b, 16#80]).

start() ->
	io:format("Starting~n"),
	crypto:start(),
	listen().

listen() ->
	{ok, Listener} = gen_tcp:listen(?PORT, ?TCP_OPTIONS),
	io:format("Listening on ~b~n", [?PORT]),
	accept(Listener).

accept(Listener) ->
	{ok, Client} = gen_tcp:accept(Listener),
	io:format("Accepted client~n"),
	spawn(?MODULE, read, [Client]),
	accept(Listener).

read(Client) ->
	case gen_tcp:recv(Client, 4) of
		{ok, Data} ->
			<<Length:32/big-unsigned-integer>> = Data,
			readpacket(Client, Length);
		{error, _} ->
			ok
	end.

readpacket(Client, Length) ->
	io:format("Packet length: ~b~n", [Length]),
	case gen_tcp:recv(Client, Length - 4) of
		{ok, Data} ->
			spawn_link(?MODULE, processpacket, [Client, Data]);
		{error, _} ->
			ok
	end,
	read(Client).

processpacket(Client, Packet) ->
	<<Ty, EData/binary>> = Packet,
	io:format("Packet type: ~b~n", [Ty]),
	Type =
		case Ty of
			13 ->
				hello
		end,
	Data = crypto:rc4_encrypt(?RC4R, EData),
	processpacket(Type, Client, Data).

processpacket(hello, Client, Data) ->
	<<BVLn:16/big-unsigned-integer, BuildVersion:BVLn/binary,
	  GmId:32/big-unsigned-integer,
	  GLen:16/big-unsigned-integer, Guid:GLen/binary,
	  Rnd1:32/big-unsigned-integer,
	  PLen:16/big-unsigned-integer, Password:PLen/binary,
	  Rnd2:32/big-unsigned-integer,
	  SLen:16/big-unsigned-integer, Secret:SLen/binary,
	  KTim:32/big-unsigned-integer,
	  KLen:16/big-unsigned-integer, Key:KLen/binary,
	  MLen:32/big-unsigned-integer, MapInfo:MLen/binary,
	  OLn1:16/big-unsigned-integer, Obf1:OLn1/binary,
	  OLn2:16/big-unsigned-integer, Obf2:OLn2/binary,
	  OLn3:16/big-unsigned-integer, Obf3:OLn3/binary,
	  OLn4:16/big-unsigned-integer, Obf4:OLn4/binary,
	  OLn5:16/big-unsigned-integer, Obf5:OLn5/binary>> = Data,
	io:format("Received HELLO: ~s~n", [BuildVersion]),
	%failure(Client, 55, "Test error")
	mapinfo(Client, 10, 10, "Nexus", "Nexuss", 0, 0, 1, true, true).

failure(Client, Id, LMessage) ->
	Message = list_to_binary(LMessage),
	MsgSize = byte_size(Message),
	Base = <<0, MsgSize:16/big-unsigned-integer, Message/binary>>,
	BaseSize = byte_size(Base) + 4,
	Packet = <<BaseSize:32/big-unsigned-integer, Base/binary>>,
	spawn_link(?MODULE, send, [Client, Packet]).

mapinfo(Client, Width, Height, Name, WorldName, Fp, Background, Difficulty, AllowTeleport, ShowDisplays) ->
	LName = list_to_binary(Name),
	LWorldName = list_to_binary(WorldName),
	NLen = byte_size(LName),
	WNLen = byte_size(LWorldName),
	AllowTeleportB =
		case AllowTeleport of
			true ->
				16#1;
			false ->
				16#0
		end,
	ShowDisplaysB =
		case ShowDisplays of
			true ->
				16#1;
			false ->
				16#0
		end,
	Base = <<16#62,
			 Width:32/big-unsigned-integer,
			 Height:32/big-unsigned-integer,
			 NLen:16/big-unsigned-integer, LName:NLen/binary,
			 WNLen:16/big-unsigned-integer, LWorldName:WNLen/binary,
			 Fp:32/big-unsigned-integer,
			 Background:32/big-unsigned-integer,
			 Difficulty:32/big-unsigned-integer,
			 AllowTeleportB, ShowDisplaysB, 0:16, 0:16>>,
			 %CXLen:16/big-unsigned-integer, ClientXML:CXLen/binary,
			 %EXLen:16/big-unsigned-integer, ExtraXML:EXLen/binary>>,
	BaseSize = byte_size(Base) + 4,
	Packet = <<BaseSize:32/big-unsigned-integer, Base/binary>>,
	spawn_link(?MODULE, send, [Client, Packet]).

send(Client, Data) ->
	case gen_tcp:send(Client, Data) of
		ok ->
			ok;
		{error, _} ->
			ok
	end.