path: root/lib/ssl/src/dtls_connection.erl

%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2013-2015. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%
-module(dtls_connection).

%% Internal application API

-behaviour(gen_statem).

-include("dtls_connection.hrl").
-include("dtls_handshake.hrl").
-include("ssl_alert.hrl").
-include("dtls_record.hrl").
-include("ssl_cipher.hrl").
-include("ssl_api.hrl").
-include("ssl_internal.hrl").
-include("ssl_srp.hrl").
-include_lib("public_key/include/public_key.hrl"). 

%% Internal application API

%% Setup
-export([start_fsm/8, start_link/7, init/1]).

%% State transition handling	 
-export([next_record/1, next_event/3]).

%% Handshake handling
-export([%%renegotiate/2, 
	 reinit_handshake_data/1, 
	 send_handshake/2, queue_handshake/2, queue_change_cipher/2]).

%% Alert and close handling
-export([%%send_alert/2, handle_own_alert/4, handle_close_alert/3,
	 handle_normal_shutdown/3 %%, close/5
	 %%alert_user/6, alert_user/9
	]).

%% Data handling

-export([%%write_application_data/3, 
	 read_application_data/2,
	 passive_receive/2,  next_record_if_active/1%, 
	 %%handle_common_event/4,

%% gen_statem state functions
-export([init/3, error/3, downgrade/3, %% Initiation and take down states
	 hello/3, certify/3, cipher/3, abbreviated/3, %% Handshake states 
	 connection/3]). 
%% gen_statem callbacks
-export([callback_mode/0, terminate/3, code_change/4, format_status/2]).

%%====================================================================
%% Internal application API
%%====================================================================	     
start_fsm(Role, Host, Port, Socket, {#ssl_options{erl_dist = false},_, Tracker} = Opts,
	  User, {CbModule, _,_, _} = CbInfo, 
	  Timeout) -> 
    try 
	{ok, Pid} = dtls_connection_sup:start_child([Role, Host, Port, Socket, 
						     Opts, User, CbInfo]), 
	{ok, SslSocket} = ssl_connection:socket_control(?MODULE, Socket, Pid, CbModule, Tracker),
	ok = ssl_connection:handshake(SslSocket, Timeout),
	{ok, SslSocket} 
    catch
	error:{badmatch, {error, _} = Error} ->
	    Error
    end;

start_fsm(Role, Host, Port, Socket, {#ssl_options{erl_dist = true},_, Tracker} = Opts,
	  User, {CbModule, _,_, _} = CbInfo, 
	  Timeout) -> 
    try 
	{ok, Pid} = dtls_connection_sup:start_child_dist([Role, Host, Port, Socket, 
							  Opts, User, CbInfo]), 
	{ok, SslSocket} = ssl_connection:socket_control(?MODULE, Socket, Pid, CbModule, Tracker),
	ok = ssl_connection:handshake(SslSocket, Timeout),
	{ok, SslSocket} 
    catch
	error:{badmatch, {error, _} = Error} ->
	    Error
    end.

send_handshake(Handshake, State) ->
    send_handshake_flight(queue_handshake(Handshake, State)).

queue_flight_buffer(Msg, #state{negotiated_version = Version,
				connection_states = #connection_states{
				  current_write =
				      #connection_state{epoch = Epoch}},
				flight_buffer = Flight} = State) ->
    State#state{flight_buffer = Flight ++ [{Version, Epoch, Msg}]}.

queue_handshake(Handshake, #state{negotiated_version = Version,
				  tls_handshake_history = Hist0,
				  connection_states = ConnectionStates0} = State0) ->
    {Frag, ConnectionStates, Hist} =
	encode_handshake(Handshake, Version, ConnectionStates0, Hist0),
    queue_flight_buffer(Frag, State0#state{connection_states = ConnectionStates,
					   tls_handshake_history = Hist}).

send_handshake_flight(#state{socket = Socket,
			     transport_cb = Transport,
			     flight_buffer = Flight,
			     connection_states = ConnectionStates0} = State0) ->

    {Encoded, ConnectionStates} =
	encode_handshake_flight(Flight, ConnectionStates0),

    Transport:send(Socket, Encoded),
    State0#state{flight_buffer = [], connection_states = ConnectionStates}.

queue_change_cipher(Msg, State) ->
    queue_flight_buffer(Msg, State).

send_alert(Alert, #state{negotiated_version = Version,
			 socket = Socket,
			 transport_cb = Transport,
			 connection_states = ConnectionStates0} = State0) ->
    {BinMsg, ConnectionStates} =
	ssl_alert:encode(Alert, Version, ConnectionStates0),
    Transport:send(Socket, BinMsg),
    State0#state{connection_states = ConnectionStates}.

reinit_handshake_data(#state{protocol_buffers = Buffers} = State) ->
    State#state{premaster_secret = undefined,
		public_key_info = undefined,
		tls_handshake_history = ssl_handshake:init_handshake_history(),
		protocol_buffers =
		    Buffers#protocol_buffers{dtls_fragment_state =
						 dtls_handshake:dtls_handshake_new_flight(0)}}.

%%====================================================================
%% tls_connection_sup API
%%====================================================================

%%--------------------------------------------------------------------
-spec start_link(atom(), host(), inet:port_number(), port(), list(), pid(), tuple()) ->
    {ok, pid()} | ignore |  {error, reason()}.
%%
%% Description: Creates a gen_fsm process which calls Module:init/1 to
%% initialize. To ensure a synchronized start-up procedure, this function
%% does not return until Module:init/1 has returned.  
%%--------------------------------------------------------------------
start_link(Role, Host, Port, Socket, Options, User, CbInfo) ->
    {ok, proc_lib:spawn_link(?MODULE, init, [[Role, Host, Port, Socket, Options, User, CbInfo]])}.

init([Role, Host, Port, Socket, Options,  User, CbInfo]) ->
    process_flag(trap_exit, true),
    State0 =  initial_state(Role, Host, Port, Socket, Options, User, CbInfo),
    try
	State = ssl_connection:ssl_config(State0#state.ssl_options, Role, State0),
	gen_statem:enter_loop(?MODULE, [], init, State)
    catch
	throw:Error ->
	    gen_statem:enter_loop(?MODULE, [], error, {Error,State0})
    end.

callback_mode() ->
    state_functions.

%%--------------------------------------------------------------------
%% State functionsconnection/2
%%--------------------------------------------------------------------

init({call, From}, {start, Timeout}, 
     #state{host = Host, port = Port, role = client,
	    ssl_options = SslOpts,
	    session = #session{own_certificate = Cert} = Session0,
	    transport_cb = Transport, socket = Socket,
	    connection_states = ConnectionStates0,
	    renegotiation = {Renegotiation, _},
	    session_cache = Cache,
	    session_cache_cb = CacheCb
	   } = State0) ->
    Timer = ssl_connection:start_or_recv_cancel_timer(Timeout, From),
    Hello = dtls_handshake:client_hello(Host, Port, ConnectionStates0, SslOpts,
				       Cache, CacheCb, Renegotiation, Cert),
    
    Version = Hello#client_hello.client_version,
    HelloVersion = dtls_record:lowest_protocol_version(SslOpts#ssl_options.versions),
    Handshake0 = ssl_handshake:init_handshake_history(),
    {BinMsg, ConnectionStates, Handshake} =
        encode_handshake(Hello,  HelloVersion, ConnectionStates0, Handshake0),
    Transport:send(Socket, BinMsg),
    State1 = State0#state{connection_states = ConnectionStates,
			  negotiated_version = Version, %% Requested version
			  session =
			      Session0#session{session_id = Hello#client_hello.session_id},
			  tls_handshake_history = Handshake,
			  start_or_recv_from = From,
			  timer = Timer},
    {Record, State} = next_record(State1),
    next_event(hello, Record, State);
init(Type, Event, State) ->
    ssl_connection:init(Type, Event, State, ?MODULE).
 
error({call, From}, {start, _Timeout}, {Error, State}) ->
    {stop_and_reply, normal, {reply, From, {error, Error}}, State};
error({call, From}, Msg, State) ->
    handle_call(Msg, From, error, State);
error(_, _, _) ->
     {keep_state_and_data, [postpone]}.

%%--------------------------------------------------------------------
-spec hello(gen_statem:event_type(),
	    #hello_request{} | #client_hello{} | #server_hello{} | term(),
	    #state{}) ->
		   gen_statem:state_function_result().
%%--------------------------------------------------------------------
hello(internal, #client_hello{client_version = ClientVersion,
			      extensions = #hello_extensions{ec_point_formats = EcPointFormats,
							     elliptic_curves = EllipticCurves}} = Hello,
      State = #state{connection_states = ConnectionStates0,
		     port = Port, session = #session{own_certificate = Cert} = Session0,
		     renegotiation = {Renegotiation, _},
		     session_cache = Cache,
		     session_cache_cb = CacheCb,
		     negotiated_protocol = CurrentProtocol,
		     key_algorithm = KeyExAlg,
		     ssl_options = SslOpts}) ->

    case dtls_handshake:hello(Hello, SslOpts, {Port, Session0, Cache, CacheCb,
					      ConnectionStates0, Cert, KeyExAlg}, Renegotiation) of
	#alert{} = Alert ->
	   ssl_connection:handle_own_alert(Alert, ClientVersion, hello, State);
	{Version, {Type, Session},
	 ConnectionStates, Protocol0, ServerHelloExt, HashSign} ->
	    Protocol = case Protocol0 of
			   undefined -> CurrentProtocol;
			   _ -> Protocol0
		       end,

	    ssl_connection:hello(internal, {common_client_hello, Type, ServerHelloExt},
				 State#state{connection_states	= ConnectionStates,
					     negotiated_version = Version,
					     hashsign_algorithm = HashSign,
					     session = Session,
					     client_ecc = {EllipticCurves, EcPointFormats},
					     negotiated_protocol = Protocol}, ?MODULE)
    end;
hello(internal, #server_hello{} = Hello,
      #state{connection_states = ConnectionStates0,
	     negotiated_version = ReqVersion,
	     role = client,
	     renegotiation = {Renegotiation, _},
	     ssl_options = SslOptions} = State) ->
    case dtls_handshake:hello(Hello, SslOptions, ConnectionStates0, Renegotiation) of
	#alert{} = Alert ->
	    ssl_connection:handle_own_alert(Alert, ReqVersion, hello, State);
	{Version, NewId, ConnectionStates, ProtoExt, Protocol} ->
	    ssl_connection:handle_session(Hello, 
					  Version, NewId, ConnectionStates, ProtoExt, Protocol, State)
    end;
hello(info, Event, State) ->
    handle_info(Event, hello, State);

hello(Type, Event, State) ->
    ssl_connection:hello(Type, Event, State, ?MODULE).

abbreviated(info, Event, State) ->
    handle_info(Event, abbreviated, State);
abbreviated(Type, Event, State) ->
    ssl_connection:abbreviated(Type, Event, State, ?MODULE).

certify(info, Event, State) ->
    handle_info(Event, certify, State);
certify(Type, Event, State) ->
    ssl_connection:certify(Type, Event, State, ?MODULE).

cipher(info, Event, State) ->
    handle_info(Event, cipher, State);
cipher(Type, Event, State) ->
     ssl_connection:cipher(Type, Event, State, ?MODULE).

connection(info, Event, State) ->
    handle_info(Event, connection, State);
connection(internal, #hello_request{}, #state{host = Host, port = Port,
				    session = #session{own_certificate = Cert} = Session0,
				    session_cache = Cache, session_cache_cb = CacheCb,
				    ssl_options = SslOpts,
				    connection_states = ConnectionStates0,
				    renegotiation = {Renegotiation, _}} = State0) ->
    Hello = dtls_handshake:client_hello(Host, Port, ConnectionStates0, SslOpts,
					Cache, CacheCb, Renegotiation, Cert),
    State1 = send_handshake(Hello, State0),
    {Record, State} =
	next_record(
	  State1#state{session = Session0#session{session_id
						  = Hello#client_hello.session_id}}),
    next_event(hello, Record, State);

connection(internal, #client_hello{} = Hello, #state{role = server, allow_renegotiate = true} = State) ->
    %% Mitigate Computational DoS attack
    %% http://www.educatedguesswork.org/2011/10/ssltls_and_computational_dos.html
    %% http://www.thc.org/thc-ssl-dos/ Rather than disabling client
    %% initiated renegotiation we will disallow many client initiated
    %% renegotiations immediately after each other.
    erlang:send_after(?WAIT_TO_ALLOW_RENEGOTIATION, self(), allow_renegotiate),
    {next_state, hello, State#state{allow_renegotiate = false}, [{next_event, internal, Hello}]};


connection(internal, #client_hello{}, #state{role = server, allow_renegotiate = false} = State0) ->
    Alert = ?ALERT_REC(?WARNING, ?NO_RENEGOTIATION),
    State1 = send_alert(Alert, State0),
    {Record, State} = ssl_connection:prepare_connection(State1, ?MODULE),
    next_event(connection, Record, State);
  
connection(Type, Event, State) ->
     ssl_connection:connection(Type, Event, State, ?MODULE).

downgrade(Type, Event, State) ->
     ssl_connection:downgrade(Type, Event, State, ?MODULE).


%%--------------------------------------------------------------------
%% Description: This function is called by a gen_fsm when it receives any
%% other message than a synchronous or asynchronous event
%% (or a system message).
%%--------------------------------------------------------------------

%% raw data from socket, unpack records
handle_info({Protocol, _, Data}, StateName,
            #state{data_tag = Protocol} = State0) ->
     case next_tls_record(Data, State0) of
	{Record, State} ->
	    next_event(StateName, Record, State);
	#alert{} = Alert ->
	    ssl_connection:handle_normal_shutdown(Alert, StateName, State0), 
	    {stop, {shutdown, own_alert}}
     end;
handle_info({CloseTag, Socket}, StateName,
	    #state{socket = Socket, close_tag = CloseTag,
		   negotiated_version = Version} = State) ->
    %% Note that as of DTLS 1.2 (TLS 1.1),
    %% failure to properly close a connection no longer requires that a
    %% session not be resumed.	This is a change from DTLS 1.0 to conform
    %% with widespread implementation practice.
    case Version of
	{254, N} when N =< 253 ->
	    ok;
	_ ->
	    %% As invalidate_sessions here causes performance issues,
	    %% we will conform to the widespread implementation
	    %% practice and go aginst the spec
	    %%invalidate_session(Role, Host, Port, Session)
	    ok
    end,
    ssl_connection:handle_normal_shutdown(?ALERT_REC(?FATAL, ?CLOSE_NOTIFY), StateName, State),
    {stop, {shutdown, transport_closed}};
handle_info(Msg, StateName, State) ->
    ssl_connection:handle_info(Msg, StateName, State).

handle_call(Event, From, StateName, State) ->
    ssl_connection:handle_call(Event, From, StateName, State, ?MODULE).

%%--------------------------------------------------------------------
%% Description:This function is called by a gen_fsm when it is about
%% to terminate. It should be the opposite of Module:init/1 and do any
%% necessary cleaning up. When it returns, the gen_fsm terminates with
%% Reason. The return value is ignored.
%%--------------------------------------------------------------------
terminate(Reason, StateName, State) ->
    ssl_connection:terminate(Reason, StateName, State).

%%--------------------------------------------------------------------
%% code_change(OldVsn, StateName, State, Extra) -> {ok, StateName, NewState}
%% Description: Convert process state when code is changed
%%--------------------------------------------------------------------
code_change(_OldVsn, StateName, State, _Extra) ->
    {ok, StateName, State}.

format_status(Type, Data) ->
    ssl_connection:format_status(Type, Data).

%%--------------------------------------------------------------------
%%% Internal functions
%%--------------------------------------------------------------------
encode_handshake(Handshake, Version, ConnectionStates0, Hist0) ->
    {Seq, ConnectionStates} = sequence(ConnectionStates0),
    {EncHandshake, Frag} = dtls_handshake:encode_handshake(Handshake, Version, Seq),
    %% DTLS does not have an equivalent version to SSLv2. So v2 hello compatibility
    %% will always be false
    Hist = ssl_handshake:update_handshake_history(Hist0, EncHandshake, false),
    {Frag, ConnectionStates, Hist}.

encode_change_cipher(#change_cipher_spec{}, Version, ConnectionStates) ->
    dtls_record:encode_change_cipher_spec(Version, ConnectionStates).

encode_handshake_flight(Flight, ConnectionStates) ->
    MSS = 1400,
    encode_handshake_records(Flight, ConnectionStates, MSS, init_pack_records()).

encode_handshake_records([], CS, _MSS, Recs) ->
    {finish_pack_records(Recs), CS};

encode_handshake_records([{Version, _Epoch, Frag = #change_cipher_spec{}}|Tail], ConnectionStates0, MSS, Recs0) ->
    {Encoded, ConnectionStates} =
        encode_change_cipher(Frag, Version, ConnectionStates0),
    Recs = append_pack_records([Encoded], MSS, Recs0),
    encode_handshake_records(Tail, ConnectionStates, MSS, Recs);

encode_handshake_records([{Version, Epoch, {MsgType, MsgSeq, Bin}}|Tail], CS0, MSS, Recs0 = {Buf0, _}) ->
    Space = MSS - iolist_size(Buf0),
    Len = byte_size(Bin),
    {Encoded, CS} =
	encode_handshake_record(Version, Epoch, Space, MsgType, MsgSeq, Len, Bin, 0, MSS, [], CS0),
    Recs = append_pack_records(Encoded, MSS, Recs0),
    encode_handshake_records(Tail, CS, MSS, Recs).

%% TODO: move to dtls_handshake????
encode_handshake_record(_Version, _Epoch, _Space, _MsgType, _MsgSeq, _Len, <<>>, _Offset, _MRS, Encoded, CS)
  when length(Encoded) > 0 ->
    %% make sure we encode at least one segment (for empty messages like Server Hello Done
    {lists:reverse(Encoded), CS};

encode_handshake_record(Version, Epoch, Space, MsgType, MsgSeq, Len, Bin,
			Offset, MRS, Encoded0, CS0) ->
    MaxFragmentLen = Space - 25,
    case Bin of
	<<BinFragment:MaxFragmentLen/bytes, Rest/binary>> ->
	    ok;
	_ ->
	    BinFragment = Bin,
	    Rest = <<>>
    end,
    FragLength = byte_size(BinFragment),
    Frag = [MsgType, ?uint24(Len), ?uint16(MsgSeq), ?uint24(Offset), ?uint24(FragLength), BinFragment],
    %% TODO Real solution, now avoid dialyzer error {Encoded, CS} = ssl_record:encode_handshake({Epoch, Frag}, Version, CS0),
    {Encoded, CS} = ssl_record:encode_handshake(Frag, Version, CS0),
    encode_handshake_record(Version, Epoch, MRS, MsgType, MsgSeq, Len, Rest, Offset + FragLength, MRS, [Encoded|Encoded0], CS).

init_pack_records() ->
    {[], []}.

append_pack_records([], MSS, Recs = {Buf0, Acc0}) ->
    Remaining = MSS - iolist_size(Buf0),
    if Remaining < 12 ->
	    {[], [lists:reverse(Buf0)|Acc0]};
       true ->
	    Recs
    end;
append_pack_records([Head|Tail], MSS, {Buf0, Acc0}) ->
    TotLen = iolist_size(Buf0) + iolist_size(Head),
    if TotLen > MSS ->
	    append_pack_records(Tail, MSS, {[Head], [lists:reverse(Buf0)|Acc0]});
       true ->
	    append_pack_records(Tail, MSS, {[Head|Buf0], Acc0})
    end.

finish_pack_records({[], Acc}) ->
    lists:reverse(Acc);
finish_pack_records({Buf, Acc}) ->
    lists:reverse([lists:reverse(Buf)|Acc]).

decode_alerts(Bin) ->
    ssl_alert:decode(Bin).

initial_state(Role, Host, Port, Socket, {SSLOptions, SocketOptions}, User,
	      {CbModule, DataTag, CloseTag, ErrorTag}) ->
    #ssl_options{beast_mitigation = BeastMitigation} = SSLOptions,
    ConnectionStates = ssl_record:init_connection_states(Role, BeastMitigation),
    
    SessionCacheCb = case application:get_env(ssl, session_cb) of
			 {ok, Cb} when is_atom(Cb) ->
			    Cb;
			 _  ->
			     ssl_session_cache
		     end,
    
    Monitor = erlang:monitor(process, User),

    #state{socket_options = SocketOptions,
	   %% We do not want to save the password in the state so that
	   %% could be written in the clear into error logs.
	   ssl_options = SSLOptions#ssl_options{password = undefined},	   
	   session = #session{is_resumable = new},
	   transport_cb = CbModule,
	   data_tag = DataTag,
	   close_tag = CloseTag,
	   error_tag = ErrorTag,
	   role = Role,
	   host = Host,
	   port = Port,
	   socket = Socket,
	   connection_states = ConnectionStates,
	   protocol_buffers = #protocol_buffers{},
	   user_application = {Monitor, User},
	   user_data_buffer = <<>>,
	   session_cache_cb = SessionCacheCb,
	   renegotiation = {false, first},
	   allow_renegotiate = SSLOptions#ssl_options.client_renegotiation,
	   start_or_recv_from = undefined,
	   protocol_cb = ?MODULE
	  }.

next_tls_record(Data, #state{protocol_buffers = #protocol_buffers{
						   dtls_record_buffer = Buf0,
						   dtls_cipher_texts = CT0} = Buffers} = State0) ->
    case dtls_record:get_dtls_records(Data, Buf0) of
	{Records, Buf1} ->
	    CT1 = CT0 ++ Records,
	    next_record(State0#state{protocol_buffers =
					 Buffers#protocol_buffers{dtls_record_buffer = Buf1,
								  dtls_cipher_texts = CT1}});

	#alert{} = Alert ->
	    Alert
   end.

next_record(#state{%%flight = #flight{state = finished}, 
		   protocol_buffers =
		       #protocol_buffers{dtls_packets = [], dtls_cipher_texts = [CT | Rest]}
		   = Buffers,
		   connection_states = ConnStates0} = State) ->
    case dtls_record:decode_cipher_text(CT, ConnStates0) of
	{Plain, ConnStates} ->		      
	    {Plain, State#state{protocol_buffers =
				    Buffers#protocol_buffers{dtls_cipher_texts = Rest},
				connection_states = ConnStates}};
	#alert{} = Alert ->
	    {Alert, State}
    end;
next_record(#state{socket = Socket,
		   transport_cb = Transport} = State) -> %% when FlightState =/= finished
    ssl_socket:setopts(Transport, Socket, [{active,once}]),
    {no_record, State};
next_record(State) ->
    {no_record, State}.

next_record_if_active(State =
		      #state{socket_options =
			     #socket_options{active = false}}) ->
    {no_record ,State};

next_record_if_active(State) ->
    next_record(State).

passive_receive(State0 = #state{user_data_buffer = Buffer}, StateName) ->
    case Buffer of
	<<>> ->
	    {Record, State} = next_record(State0),
	    next_event(StateName, Record, State);
	_ ->
	    {Record, State} = ssl_connection:read_application_data(<<>>, State0),
	    next_event(StateName, Record, State)
    end.

next_event(StateName, Record, State) ->
    next_event(StateName, Record, State, []).

next_event(connection = StateName, no_record, State0, Actions) ->
    case next_record_if_active(State0) of
	{no_record, State} ->
	    ssl_connection:hibernate_after(StateName, State, Actions);
	{#ssl_tls{} = Record, State} ->
	    {next_state, StateName, State, [{next_event, internal, {dtls_record, Record}} | Actions]};
	{#alert{} = Alert, State} ->
	    {next_state, StateName, State, [{next_event, internal, Alert} | Actions]}
    end;
next_event(StateName, Record, State, Actions) ->
    case Record of
	no_record ->
	    {next_state, StateName, State, Actions};
	#ssl_tls{} = Record ->
	    {next_state, StateName, State, [{next_event, internal, {dtls_record, Record}} | Actions]};
	#alert{} = Alert ->
	    {next_state, StateName, State, [{next_event, internal, Alert} | Actions]}
    end.

read_application_data(_,State) ->
    {#ssl_tls{fragment = <<"place holder">>}, State}.

handle_own_alert(_,_,_, State) -> %% Place holder
    {stop, {shutdown, own_alert}, State}.

handle_normal_shutdown(_, _, _State) -> %% Place holder
    ok.

%% TODO This generates dialyzer warnings, has to be handled differently.
%% handle_packet(Address, Port, Packet) ->
%%     try dtls_record:get_dtls_records(Packet, <<>>) of
%% 	%% expect client hello
%% 	{[#ssl_tls{type = ?HANDSHAKE, version = {254, _}} = Record], <<>>} ->
%% 	    handle_dtls_client_hello(Address, Port, Record);
%% 	_Other ->
%% 	    {error, not_dtls}
%%     catch
%% 	_Class:_Error ->
%% 	    {error, not_dtls}
%%     end.

%% handle_dtls_client_hello(Address, Port,
%% 			 #ssl_tls{epoch = Epoch, sequence_number = Seq,
%% 				  version = Version} = Record) ->
%%     {[{Hello, _}], _} =
%% 	dtls_handshake:get_dtls_handshake(Record,
%% 					 dtls_handshake:dtls_handshake_new_flight(undefined)),
%%     #client_hello{client_version = {Major, Minor},
%% 		  random = Random,
%% 		  session_id = SessionId,
%% 		  cipher_suites = CipherSuites,
%% 		  compression_methods = CompressionMethods} = Hello,
%%     CookieData = [address_to_bin(Address, Port),
%% 		  <<?BYTE(Major), ?BYTE(Minor)>>,
%% 		  Random, SessionId, CipherSuites, CompressionMethods],
%%     Cookie = crypto:hmac(sha, <<"secret">>, CookieData),

%%     case Hello of
%% 	#client_hello{cookie = Cookie} ->
%% 	    accept;

%% 	_ ->
%% 	    %% generate HelloVerifyRequest
%% 	    {RequestFragment, _} = dtls_handshake:encode_handshake(
%% 				     dtls_handshake:hello_verify_request(Cookie),
%% 				     Version, 0),
%% 	    HelloVerifyRequest =
%% 		dtls_record:encode_tls_cipher_text(?HANDSHAKE, Version, Epoch, Seq, RequestFragment),
%% 	    {reply, HelloVerifyRequest}
%%     end.

%% address_to_bin({A,B,C,D}, Port) ->
%%     <<0:80,16#ffff:16,A,B,C,D,Port:16>>;
%% address_to_bin({A,B,C,D,E,F,G,H}, Port) ->
%%     <<A:16,B:16,C:16,D:16,E:16,F:16,G:16,H:16,Port:16>>.

sequence(#connection_states{dtls_write_msg_seq = Seq} = CS) ->
    {Seq, CS#connection_states{dtls_write_msg_seq = Seq + 1}}.