Improve MUCs subject changed notification filter

Filter also messages with bodies or thread element.

smack-core/src/main/java/org/jivesoftware/smack/filter/MessageWithThreadFilter.java

@@ -0,0 +1,43 @@
+/**
+ *
+ * Copyright 2017 Florian Schmaus
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jivesoftware.smack.filter;
+
+import org.jivesoftware.smack.packet.Message;
+import org.jivesoftware.smack.util.StringUtils;
+
+/**
+ * Filters message stanzas which have at least one body.
+ */
+public final class MessageWithThreadFilter extends FlexibleStanzaTypeFilter<Message> {
+
+    public static final StanzaFilter INSTANCE = new MessageWithThreadFilter();
+
+    private MessageWithThreadFilter() {
+        super(Message.class);
+    }
+
+    @Override
+    protected boolean acceptSpecific(Message message) {
+        return StringUtils.isNotEmpty(message.getThread());
+    }
+
+    @Override
+    public String toString() {
+        return getClass().getSimpleName();
+    }
+}

smack-extensions/src/main/java/org/jivesoftware/smackx/muc/MultiUserChat.java

@@ -41,7 +41,9 @@ import org.jivesoftware.smack.chat.ChatMessageListener;
 import org.jivesoftware.smack.filter.AndFilter;
 import org.jivesoftware.smack.filter.FromMatchesFilter;
 import org.jivesoftware.smack.filter.MessageTypeFilter;
+import org.jivesoftware.smack.filter.MessageWithBodiesFilter;
 import org.jivesoftware.smack.filter.MessageWithSubjectFilter;
+import org.jivesoftware.smack.filter.MessageWithThreadFilter;
 import org.jivesoftware.smack.filter.NotFilter;
 import org.jivesoftware.smack.filter.OrFilter;
 import org.jivesoftware.smack.filter.PresenceTypeFilter;
@@ -318,8 +320,17 @@ public class MultiUserChat {
         connection.addSyncStanzaListener(messageListener, fromRoomGroupchatFilter);
         connection.addSyncStanzaListener(presenceListener, new AndFilter(fromRoomFilter,
                         StanzaTypeFilter.PRESENCE));
-        connection.addSyncStanzaListener(subjectListener, new AndFilter(fromRoomFilter,
+        // @formatter:off
-                        MessageWithSubjectFilter.INSTANCE, new NotFilter(MessageTypeFilter.ERROR)));
+        connection.addSyncStanzaListener(subjectListener,
+                        new AndFilter(fromRoomFilter,
+                                      MessageWithSubjectFilter.INSTANCE,
+                                      new NotFilter(MessageTypeFilter.ERROR),
+                                      // According to XEP-0045 § 8.1 "A message with a <subject/> and a <body/> or a <subject/> and a <thread/> is a
+                                      // legitimate message, but it SHALL NOT be interpreted as a subject change."
+                                      new NotFilter(MessageWithBodiesFilter.INSTANCE),
+                                      new NotFilter(MessageWithThreadFilter.INSTANCE))
+                        );
+        // @formatter:on
         connection.addSyncStanzaListener(declinesListener, DECLINE_FILTER);
         connection.addPacketInterceptor(presenceInterceptor, new AndFilter(ToMatchesFilter.create(room),
                         StanzaTypeFilter.PRESENCE));