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

@@ -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);

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].