From 7e311ab9df129b843e4fbcf0905834673624f220 Mon Sep 17 00:00:00 2001
From: Florian Schmaus <flo@geekplace.eu>
Date: Sun, 8 Nov 2020 21:46:06 +0100
Subject: [PATCH] [muc] Prevent race condition on enter() by waiting

This prevents a race condition of enter() with the presence listern by
waiting until all presences have been processed.

Reported-by: Guus der Kinderen <guus@goodbytes.nl>
---
 .../smackx/muc/MultiUserChat.java             | 30 +++++++++++++++----
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/smack-extensions/src/main/java/org/jivesoftware/smackx/muc/MultiUserChat.java b/smack-extensions/src/main/java/org/jivesoftware/smackx/muc/MultiUserChat.java
index b75f44d5e..51f267694 100644
--- a/smack-extensions/src/main/java/org/jivesoftware/smackx/muc/MultiUserChat.java
+++ b/smack-extensions/src/main/java/org/jivesoftware/smackx/muc/MultiUserChat.java
@@ -149,6 +149,11 @@ public class MultiUserChat {
     private EntityFullJid myRoomJid;
     private StanzaCollector messageCollector;
 
+    /**
+     * Used to signal that the reflected self-presence was received <b>and</b> processed by us.
+     */
+    private volatile boolean processedReflectedSelfPresence;
+
     MultiUserChat(XMPPConnection connection, EntityBareJid room, MultiUserChatManager multiUserChatManager) {
         this.connection = connection;
         this.room = room;
@@ -216,13 +221,15 @@ public class MultiUserChat {
                             newAffiliation,
                             isUserStatusModification,
                             from);
-                    }
-                    else {
+                    } else if (mucUser.getStatus().contains(MUCUser.Status.PRESENCE_TO_SELF_110)) {
+                        processedReflectedSelfPresence = true;
+                        synchronized (this) {
+                            notify();
+                        }
+                    } else {
                         // A new occupant has joined the room
-                        if (!isUserStatusModification) {
-                            for (ParticipantStatusListener listener : participantStatusListeners) {
-                                listener.joined(from);
-                            }
+                        for (ParticipantStatusListener listener : participantStatusListeners) {
+                            listener.joined(from);
                         }
                     }
                     break;
@@ -376,6 +383,7 @@ public class MultiUserChat {
                         )
                     );
         // @formatter:on
+        processedReflectedSelfPresence = false;
         StanzaCollector presenceStanzaCollector = null;
         final Presence reflectedSelfPresence;
         try {
@@ -398,6 +406,16 @@ public class MultiUserChat {
             }
         }
 
+        synchronized (presenceListener) {
+            // Only continue after we have received *and* processed the reflected self-presence. Since presences are
+            // handled in an extra listener, we may return from enter() without having processed all presences of the
+            // participants, resulting in a e.g. to low participant counter after enter(). Hence we wait here until the
+            // processing is done.
+            while (!processedReflectedSelfPresence) {
+                presenceListener.wait();
+            }
+        }
+
         // This presence must be send from a full JID. We use the resourcepart of this JID as nick, since the room may
         // performed roomnick rewriting
         Resourcepart receivedNickname = reflectedSelfPresence.getFrom().getResourceOrThrow();