mod_multicast not delivering correct address stanza to receivers

Multicast service is not delivering all "to" attributes to all the recipient of address stanza.

UserA sends a packet to UserB and UserC

<message type="chat" to="multicast.example.com" id="">
  <addresses xmlns="http://jabber.org/protocol/address">
    <address type="to" jid="[email protected]"/>
    <address type="to" jid="[email protected]"/>
  </addresses>
  <body>One</body>
  <active xmlns="http://jabber.org/protocol/chatstates"/>
</message>

However UserB receives

<message xmlns="jabber:client" from="[email protected]/iPhone" to="[email protected]" type="chat" id="">
  <addresses xmlns="http://jabber.org/protocol/address">
    <address type="to" jid="[email protected]"/>
  </addresses>
  <body>One</body>
  <active xmlns="http://jabber.org/protocol/chatstates"/>
</message>

And UserC receives

<message xmlns="jabber:client" from="[email protected]/iPhone" to="[email protected]" type="chat" id="">
  <addresses xmlns="http://jabber.org/protocol/address">
    <address type="to" jid="[email protected]"/>
  </addresses>
  <body>One</body>
  <active xmlns="http://jabber.org/protocol/chatstates"/>
</message>

So, UserB and UserC are missing 'to' attribute for each other in the address stanza.

I use ejabberd 16.01 and I use https://docs.ejabberd.im/admin/guide/configuration/#modmulticast to configure

Solution

Try this change. It's strange, because those lines haven't changed since many years ago. Maybe the bug is somewhere else, and this is only a workaround:

--- a/src/mod_multicast.erl
+++ b/src/mod_multicast.erl
@@ -599,7 +599,7 @@ add_addresses(Delivereds, Groups) ->
 add_addresses2(_, [], Res, _, []) -> Res;
 add_addresses2(Delivereds, [Group | Groups], Res, Pa,
               [Pi | Pz]) ->
-    Addresses = lists:append([Delivereds] ++ Pa ++ Pz),
+    Addresses = lists:append([Delivereds] ++ Pa ++ [Pi] ++ Pz),
     Group2 = Group#group{addresses = Addresses},
     add_addresses2(Delivereds, Groups, [Group2 | Res],
                   [Pi | Pa], Pz).
@@ -655,7 +655,7 @@ route_packet_multicast(From, ToS, Packet, AAttrs, Dests,
 route_packet2(From, ToS, Dests, Packet, AAttrs,
              Addresses) ->
     #xmlel{name = T, attrs = A, children = C} = Packet,
-    C2 = case append_dests(Dests, Addresses) of
+    C2 = case Addresses of
           [] -> C;
           ACs ->
               [#xmlel{name = <<"addresses">>, attrs = AAttrs,