%%%----------------------------------------------------------------------
%%% File    : mod_pres_counter.erl
%%% Author  : Ahmed Omar
%%% Purpose : Presence subscription flood prevention
%%% Created : 23 Sep 2010 by Ahmed Omar
%%%
%%%
%%% ejabberd, Copyright (C) 2002-2016   ProcessOne
%%%
%%% This program is free software; you can redistribute it and/or
%%% modify it under the terms of the GNU General Public License as
%%% published by the Free Software Foundation; either version 2 of the
%%% License, or (at your option) any later version.
%%%
%%% This program is distributed in the hope that it will be useful,
%%% but WITHOUT ANY WARRANTY; without even the implied warranty of
%%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
%%% General Public License for more details.
%%%
%%% You should have received a copy of the GNU General Public License along
%%% with this program; if not, write to the Free Software Foundation, Inc.,
%%% 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
%%%
%%%----------------------------------------------------------------------

-module(mod_pres_counter).

-behavior(gen_mod).

-export([start/2, stop/1, check_packet/6,
	 mod_opt_type/1, depends/2]).

-include("ejabberd.hrl").
-include("logger.hrl").

-include("jlib.hrl").

-record(pres_counter,
	{dir, start, count, logged = false}).

start(Host, _Opts) ->
    ejabberd_hooks:add(privacy_check_packet, Host, ?MODULE,
		       check_packet, 25),
    ok.

stop(Host) ->
    ejabberd_hooks:delete(privacy_check_packet, Host,
			  ?MODULE, check_packet, 25),
    ok.

depends(_Host, _Opts) ->
    [].

check_packet(_, _User, Server, _PrivacyList,
	     {From, To, #xmlel{name = Name, attrs = Attrs}}, Dir) ->
    case Name of
      <<"presence">> ->
	  IsSubscription = case fxml:get_attr_s(<<"type">>, Attrs)
			       of
			     <<"subscribe">> -> true;
			     <<"subscribed">> -> true;
			     <<"unsubscribe">> -> true;
			     <<"unsubscribed">> -> true;
			     _ -> false
			   end,
	  if IsSubscription ->
		 JID = case Dir of
			 in -> To;
			 out -> From
		       end,
		 update(Server, JID, Dir);
	     true -> allow
	  end;
      _ -> allow
    end.

update(Server, JID, Dir) ->
    StormCount = gen_mod:get_module_opt(Server, ?MODULE, count,
                                        fun(I) when is_integer(I), I>0 -> I end,
                                        5),
    TimeInterval = gen_mod:get_module_opt(Server, ?MODULE, interval,
                                          fun(I) when is_integer(I), I>0 -> I end,
                                          60),
    TimeStamp = p1_time_compat:system_time(seconds),
    case read(Dir) of
      undefined ->
	  write(Dir,
		#pres_counter{dir = Dir, start = TimeStamp, count = 1}),
	  allow;
      #pres_counter{start = TimeStart, count = Count,
		    logged = Logged} =
	  R ->
	  if TimeStamp - TimeStart > TimeInterval ->
		 write(Dir,
		       R#pres_counter{start = TimeStamp, count = 1}),
		 allow;
	     (Count =:= StormCount) and Logged -> {stop, deny};
	     Count =:= StormCount ->
		 write(Dir, R#pres_counter{logged = true}),
		 case Dir of
		   in ->
		       ?WARNING_MSG("User ~s is being flooded, ignoring received "
				    "presence subscriptions",
				    [jid:to_string(JID)]);
		   out ->
		       IP = ejabberd_sm:get_user_ip(JID#jid.luser,
						    JID#jid.lserver,
						    JID#jid.lresource),
		       ?WARNING_MSG("Flooder detected: ~s, on IP: ~s ignoring "
				    "sent presence subscriptions~n",
				    [jid:to_string(JID),
				     jlib:ip_to_list(IP)])
		 end,
		 {stop, deny};
	     true ->
		 write(Dir,
		       R#pres_counter{start = TimeStamp, count = Count + 1}),
		 allow
	  end
    end.

read(K) -> get({pres_counter, K}).

write(K, V) -> put({pres_counter, K}, V).

mod_opt_type(count) ->
    fun (I) when is_integer(I), I > 0 -> I end;
mod_opt_type(interval) ->
    fun (I) when is_integer(I), I > 0 -> I end;
mod_opt_type(_) -> [count, interval].