%%%----------------------------------------------------------------------
%%% File    : mod_pres_counter.erl
%%% Author  : Ahmed Omar
%%% Purpose : Presence subscription flood prevention
%%% Created : 23 Sep 2010 by Ahmed Omar
%%%
%%%
%%% ejabberd, Copyright (C) 2002-2021   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).

-behaviour(gen_mod).

-export([start/2, stop/1, reload/3, check_packet/4,
	 mod_opt_type/1, mod_options/1, depends/2, mod_doc/0]).

-include("logger.hrl").
-include("translate.hrl").
-include_lib("xmpp/include/xmpp.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.

reload(_Host, _NewOpts, _OldOpts) ->
    ok.

depends(_Host, _Opts) ->
    [].

-spec check_packet(allow | deny, ejabberd_c2s:state() | jid(),
		   stanza(), in | out) -> allow | deny.
check_packet(Acc, #{jid := JID}, Packet, Dir) ->
    check_packet(Acc, JID, Packet, Dir);
check_packet(_, #jid{lserver = LServer},
	     #presence{from = From, to = To, type = Type}, Dir) ->
    IsSubscription = case Type of
			 subscribe -> true;
			 subscribed -> true;
			 unsubscribe -> true;
			 unsubscribed -> true;
			 _ -> false
		     end,
    if IsSubscription ->
	    JID = case Dir of
		      in -> To;
		      out -> From
		  end,
	    update(LServer, JID, Dir);
       true -> allow
    end;
check_packet(Acc, _, _, _) ->
    Acc.

update(Server, JID, Dir) ->
    StormCount = mod_pres_counter_opt:count(Server),
    TimeInterval = mod_pres_counter_opt:interval(Server),
    TimeStamp = erlang:system_time(millisecond),
    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 ~ts is being flooded, ignoring received "
				    "presence subscriptions",
				    [jid:encode(JID)]);
		   out ->
		       IP = ejabberd_sm:get_user_ip(JID#jid.luser,
						    JID#jid.lserver,
						    JID#jid.lresource),
		       ?WARNING_MSG("Flooder detected: ~ts, on IP: ~ts ignoring "
				    "sent presence subscriptions~n",
				    [jid:encode(JID),
				     misc: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) ->
    econf:pos_int();
mod_opt_type(interval) ->
    econf:timeout(second).

mod_options(_) ->
    [{count, 5}, {interval, timer:seconds(60)}].

mod_doc() ->
    #{desc =>
          ?T("This module detects flood/spam in presence "
             "subscriptions traffic. If a user sends or receives "
             "more of those stanzas in a given time interval, "
             "the exceeding stanzas are silently dropped, and a "
             "warning is logged."),
      opts =>
          [{count,
            #{value => ?T("Number"),
              desc =>
                  ?T("The number of subscription presence stanzas "
                     "(subscribe, unsubscribe, subscribed, unsubscribed) "
                     "allowed for any direction (input or output) per time "
                     "defined in 'interval' option. Please note that two "
                     "users subscribing to each other usually generate 4 "
                     "stanzas, so the recommended value is '4' or more. "
                     "The default value is '5'.")}},
           {interval,
            #{value => "timeout()",
              desc =>
                  ?T("The time interval. The default value is '1' minute.")}}],
      example =>
          ["modules:",
           "  ...",
           "  mod_pres_counter:",
           "    count: 5",
           "    interval: 30 secs",
           "  ..."]}.