Don't store mucsub presence events in offline storage

This is expanded version of pull request #3959

src/misc.erl

@@ -43,7 +43,7 @@
 	 get_my_ipv4_address/0, get_my_ipv6_address/0, parse_ip_mask/1,
 	 crypto_hmac/3, crypto_hmac/4, uri_parse/1, uri_parse/2,
 	 match_ip_mask/3, format_hosts_list/1, format_cycle/1, delete_dir/1,
-	 semver_to_xxyy/1, logical_processors/0]).
+	 semver_to_xxyy/1, logical_processors/0, get_mucsub_event_type/1]).
 
 %% Deprecated functions
 -export([decode_base64/1, encode_base64/1]).
@@ -168,7 +168,11 @@ unwrap_mucsub_message(_Packet) ->
     false.
 
 -spec is_mucsub_message(xmpp_element()) -> boolean().
-is_mucsub_message(#message{} = OuterMsg) ->
+is_mucsub_message(Packet) ->
+    get_mucsub_event_type(Packet) /= false.
+
+-spec get_mucsub_event_type(xmpp_element()) -> binary() | false.
+get_mucsub_event_type(#message{} = OuterMsg) ->
     case xmpp:get_subtag(OuterMsg, #ps_event{}) of
 	#ps_event{
 	    items = #ps_items{
@@ -180,11 +184,11 @@ is_mucsub_message(#message{} = OuterMsg) ->
 		 Node == ?NS_MUCSUB_NODES_PARTICIPANTS;
 		 Node == ?NS_MUCSUB_NODES_PRESENCE;
 		 Node == ?NS_MUCSUB_NODES_SUBSCRIBERS ->
-	    true;
+	    Node;
 	_ ->
 	    false
     end;
-is_mucsub_message(_Packet) ->
+get_mucsub_event_type(_Packet) ->
     false.
 
 -spec is_standalone_chat_state(stanza()) -> boolean().

src/mod_offline.erl

@@ -473,14 +473,17 @@ need_to_store(LServer, #message{type = Type} = Packet) ->
 					_ ->
 					    true
 				    end,
-			    case {Store, mod_offline_opt:store_empty_body(LServer)} of
-				{false, _} ->
+			    case {misc:get_mucsub_event_type(Packet), Store,
+				  mod_offline_opt:store_empty_body(LServer)} of
+				{?NS_MUCSUB_NODES_PRESENCE, _, _} ->
 				    false;
-				{_, true} ->
+				{_, false, _} ->
+				    false;
+				{_, _, true} ->
 				    true;
-				{_, false} ->
+				{_, _, false} ->
 				    Packet#message.body /= [];
-				{_, unless_chat_state} ->
+				{_, _, _, unless_chat_state} ->
 				    not misc:is_standalone_chat_state(Packet)
 			    end
 		    end