From ddaa409ee2aaa9a9402a33c59aacf3cd7d3e9bbb Mon Sep 17 00:00:00 2001
From: Holger Weiss <holger@zedat.fu-berlin.de>
Date: Fri, 15 Jan 2016 01:08:22 +0100
Subject: [PATCH] XEP-0198: Let MAM take care of pending messages

If a stream management session times out for a user who appears to be
using MAM, drop any unacknowledged messages rather than resending or
bouncing them.  This avoids duplicates or bogus error messages.

However, this is only done if the new mod_mam option "assume_mam_usage"
is set to 'if_enabled' or 'on_request'.  In the former case, a user is
assumed to be using MAM if archiving is enabled for his account.  In the
latter case, MAM usage is assumed only if archiving was explicitly
requested by the client, or if archiving was enabled by means of
mod_mam's "request_activates_archiving" option.
---
 src/ejabberd_c2s.erl | 11 ++++++++-
 src/mod_mam.erl      | 59 ++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/src/ejabberd_c2s.erl b/src/ejabberd_c2s.erl
index 0035ed6d1..021fb9739 100644
--- a/src/ejabberd_c2s.erl
+++ b/src/ejabberd_c2s.erl
@@ -2878,7 +2878,16 @@ handle_unacked_stanzas(StateData)
 		      ?DEBUG("Dropping forwarded message stanza from ~s",
 			     [xml:get_attr_s(<<"from">>, El#xmlel.attrs)]);
 		  false ->
-		      ReRoute(From, To, El, Time)
+		      case ejabberd_hooks:run_fold(message_is_archived,
+						   StateData#state.server,
+						   false,
+						   [StateData, From,
+						    StateData#state.jid, El]) of
+			true ->
+			    ok;
+			false ->
+			    ReRoute(From, To, El, Time)
+		      end
 		end
 	end,
     handle_unacked_stanzas(StateData, F);
diff --git a/src/mod_mam.erl b/src/mod_mam.erl
index c20a941df..f4943b3d2 100644
--- a/src/mod_mam.erl
+++ b/src/mod_mam.erl
@@ -36,7 +36,7 @@
 -export([user_send_packet/4, user_receive_packet/5,
 	 process_iq_v0_2/3, process_iq_v0_3/3, disco_sm_features/5,
 	 remove_user/2, remove_user/3, mod_opt_type/1, muc_process_iq/4,
-	 muc_filter_message/5, delete_old_messages/2]).
+	 muc_filter_message/5, message_is_archived/5, delete_old_messages/2]).
 
 -include_lib("stdlib/include/ms_transform.hrl").
 -include("jlib.hrl").
@@ -105,6 +105,17 @@ start(Host, Opts) ->
 		       remove_user, 50),
     ejabberd_hooks:add(anonymous_purge_hook, Host, ?MODULE,
 		       remove_user, 50),
+    case gen_mod:get_opt(assume_mam_usage, Opts,
+			 fun(if_enabled) -> if_enabled;
+			    (on_request) -> on_request;
+			    (never) -> never
+			 end, never) of
+	never ->
+	    ok;
+	_ ->
+	    ejabberd_hooks:add(message_is_archived, Host, ?MODULE,
+			       message_is_archived, 50)
+    end,
     ejabberd_commands:register_commands(commands()),
     ok.
 
@@ -150,6 +161,17 @@ stop(Host) ->
 			  remove_user, 50),
     ejabberd_hooks:delete(anonymous_purge_hook, Host,
 			  ?MODULE, remove_user, 50),
+    case gen_mod:get_module_opt(Host, ?MODULE, assume_mam_usage,
+				fun(if_enabled) -> if_enabled;
+				   (on_request) -> on_request;
+				   (never) -> never
+				end, never) of
+	never ->
+	    ok;
+	_ ->
+	    ejabberd_hooks:delete(message_is_archived, Host, ?MODULE,
+				  message_is_archived, 50)
+    end,
     ejabberd_commands:unregister_commands(commands()),
     ok.
 
@@ -307,6 +329,34 @@ disco_sm_features({result, OtherFeatures},
 disco_sm_features(Acc, _From, _To, _Node, _Lang) ->
     Acc.
 
+message_is_archived(true, _C2SState, _Peer, _JID, _Pkt) ->
+    true;
+message_is_archived(false, C2SState, Peer,
+		    #jid{luser = LUser, lserver = LServer}, Pkt) ->
+    Res = case gen_mod:get_module_opt(LServer, ?MODULE, assume_mam_usage,
+				      fun(if_enabled) -> if_enabled;
+					 (on_request) -> on_request;
+					 (never) -> never
+				      end, never) of
+	      if_enabled ->
+		  get_prefs(LUser, LServer);
+	      on_request ->
+		  DBType = gen_mod:db_type(LServer, ?MODULE),
+		  cache_tab:lookup(archive_prefs, {LUser, LServer},
+				   fun() ->
+					   get_prefs(LUser, LServer, DBType)
+				   end);
+	      never ->
+		  error
+	  end,
+    case Res of
+	{ok, Prefs} ->
+	    should_archive(strip_my_archived_tag(Pkt, LServer), LServer)
+		andalso should_archive_peer(C2SState, Prefs, Peer);
+	error ->
+	    false
+    end.
+
 delete_old_messages(TypeBin, Days) when TypeBin == <<"chat">>;
 					TypeBin == <<"groupchat">>;
 					TypeBin == <<"all">> ->
@@ -1318,6 +1368,11 @@ commands() ->
 			args = [{type, binary}, {days, integer}],
 			result = {res, rescode}}].
 
+mod_opt_type(assume_mam_usage) ->
+    fun(if_enabled) -> if_enabled;
+       (on_request) -> on_request;
+       (never) -> never
+    end;
 mod_opt_type(cache_life_time) ->
     fun (I) when is_integer(I), I > 0 -> I end;
 mod_opt_type(cache_size) ->
@@ -1334,5 +1389,5 @@ mod_opt_type(request_activates_archiving) ->
 mod_opt_type(store_body_only) ->
     fun (B) when is_boolean(B) -> B end;
 mod_opt_type(_) ->
-    [cache_life_time, cache_size, db_type, default, iqdisc,
+    [assume_mam_usage, cache_life_time, cache_size, db_type, default, iqdisc,
      request_activates_archiving, store_body_only].