Assume a client with MUC elements in presence needs to join

XEP-0045 discusses how a request to join a room is the only case where a MUC
element should exist in presence. Therefore, a conformant client will always
send this whenever it believes it is not joined. This can happen in cases of
stanza loss (due to network outage) or remote server crash.

This patch assumes that a client sending a MUC element is trying to join, and
will go through much of the motions of the join, including sending history as
required, existing occupants' presence, and so on. To other existing occupants,
however, it'll look like an ordinary presence update.

src/java/org/jivesoftware/openfire/muc/spi/LocalMUCRoom.java

@@ -563,6 +563,8 @@ public class LocalMUCRoom implements MUCRoom, GroupEventListener {
         }
         LocalMUCRole joinRole = null;
         lock.writeLock().lock();
+        boolean clientOnlyJoin = false;
+        // A "client only join" here is one where the client is already joined, but has re-joined.
         try {
             // If the room has a limit of max user then check if the limit has been reached
             if (!canJoinRoom(user)) {
@@ -584,6 +586,9 @@ public class LocalMUCRoom implements MUCRoom, GroupEventListener {
                     // Nickname is already used, and not by the same JID
                     throw new UserAlreadyExistsException();
                 }
+                if (occupant.getUserAddress().equals(user.getAddress())) {
+                    clientOnlyJoin = true; // This user is already an occupant. The client thinks it isn't. (Or else this is a broken gmail).
+                }
             }
             // If the room is password protected and the provided password is incorrect raise a
             // Unauthorized exception
@@ -650,23 +655,29 @@ public class LocalMUCRoom implements MUCRoom, GroupEventListener {
                 role = (isModerated() ? MUCRole.Role.visitor : MUCRole.Role.participant);
                 affiliation = MUCRole.Affiliation.none;
             }
-            // Create a new role for this user in this room
-            joinRole = new LocalMUCRole(mucService, this, nickname, role, affiliation, user, presence, router);
-            // Add the new user as an occupant of this room
-            List<MUCRole> occupants = occupantsByNickname.get(nickname.toLowerCase());
-            if (occupants == null) {
-            	occupants = new ArrayList<>();
-            	occupantsByNickname.put(nickname.toLowerCase(), occupants);
-            }
-            occupants.add(joinRole);
-            // Update the tables of occupants based on the bare and full JID
-            List<MUCRole> list = occupantsByBareJID.get(bareJID);
-            if (list == null) {
-                list = new ArrayList<>();
-                occupantsByBareJID.put(bareJID, list);
-            }
-            list.add(joinRole);
-            occupantsByFullJID.put(user.getAddress(), joinRole);
+            if (!clientOnlyJoin) {
+                // Create a new role for this user in this room
+                joinRole = new LocalMUCRole(mucService, this, nickname, role,
+                        affiliation, user, presence, router);
+                // Add the new user as an occupant of this room
+                List<MUCRole> occupants = occupantsByNickname.get(nickname.toLowerCase());
+                if (occupants == null) {
+                    occupants = new ArrayList<>();
+                    occupantsByNickname.put(nickname.toLowerCase(), occupants);
+                }
+                occupants.add(joinRole);
+                // Update the tables of occupants based on the bare and full JID
+                List<MUCRole> list = occupantsByBareJID.get(bareJID);
+                if (list == null) {
+                    list = new ArrayList<>();
+                    occupantsByBareJID.put(bareJID, list);
+                }
+                list.add(joinRole);
+                occupantsByFullJID.put(user.getAddress(), joinRole);
+            } else {
+                // Grab the existing one.
+                joinRole = (LocalMUCRole) occupantsByFullJID.get(user.getAddress());
+           }
         }
         finally {
             lock.writeLock().unlock();
@@ -706,10 +717,13 @@ public class LocalMUCRoom implements MUCRoom, GroupEventListener {
         else {
             historyRequest.sendHistory(joinRole, roomHistory);
         }
-        // Update the date when the last occupant left the room
-        setEmptyDate(null);
-        // Fire event that occupant joined the room
-        MUCEventDispatcher.occupantJoined(getRole().getRoleAddress(), user.getAddress(), joinRole.getNickname());
+        if (!clientOnlyJoin) {
+            // Update the date when the last occupant left the room
+            setEmptyDate(null);
+            // Fire event that occupant joined the room
+            MUCEventDispatcher.occupantJoined(getRole().getRoleAddress(),
+                    user.getAddress(), joinRole.getNickname());
+       }
         return joinRole;
     }
 

src/java/org/jivesoftware/openfire/muc/spi/LocalMUCUser.java

@@ -71,7 +71,7 @@ import org.xmpp.packet.Presence;
  */
 public class LocalMUCUser implements MUCUser {
 
-	private static final Logger Log = LoggerFactory.getLogger(LocalMUCUser.class);
+    private static final Logger Log = LoggerFactory.getLogger(LocalMUCUser.class);
 
     /** The chat server this user belongs to. */
     private MultiUserChatService server;
@@ -462,9 +462,12 @@ public class LocalMUCUser implements MUCUser {
         String group = recipient.getNode();
         if (group != null) {
             MUCRole role = roles.get(group);
-            if (role == null) {
-                // If we're not already in a room, we either are joining it or it's not
+            Element mucInfo = packet.getChildElement("x",
+                    "http://jabber.org/protocol/muc");
+            if (role == null || mucInfo != null) {
+                // If we're not already in a room (role == null), we either are joining it or it's not
                 // properly addressed and we drop it silently
+                // Alternative is that mucInfo is not null, in which case the client thinks it isn't in the room, so we should join anyway.
                 if (recipient.getResource() != null
                         && recipient.getResource().trim().length() > 0) {
                     if (packet.isAvailable()) {
@@ -472,8 +475,6 @@ public class LocalMUCUser implements MUCUser {
                             // Get or create the room
                             MUCRoom room = server.getChatRoom(group, packet.getFrom());
                             // User must support MUC in order to create a room
-                            Element mucInfo = packet.getChildElement("x",
-                                    "http://jabber.org/protocol/muc");
                             HistoryRequest historyRequest = null;
                             String password = null;
                             // Check for password & requested history if client supports MUC