fix: fix a rare NPE exception that may occur if player disconnect whe…

…n joining the server.

CHANGELOG.md

@@ -35,13 +35,15 @@ Unless otherwise specified, any version comparison below is the comparison of se
 - Main thread will sleep a short time if gui is enabled when the server exits abnormally. This gives user time to see what goes wrong.
 - Server won't crash if failed to load the descriptor of a plugin now. An error message will be print to the console instead.
 - Server won't crash if failed to create world generator. Void world generator will be used instead.
+- It is not allowed to reset the dimension of player back to null now, and doing such thing will result in an exception.
 
 ### Fixed
 
 - Plugins are able to create their own world generator implementation now. In previous versions a ClassCastException would be thrown when
   initializing the dimension.
 - Explosion now calculates entity exposure correctly. In previous version any non-air block will block the explosion ray.
 - Explosion damage now scales with game difficulty, and a bug was fixed that cause the damage two times bigger than the correct damage.
+- Fixed a rare NPE exception that may occur if player disconnect when joining the server.
 
 ### Removed
 

server/src/main/java/org/allaymc/server/AllayServer.java

@@ -300,9 +300,15 @@ public void onDisconnect(EntityPlayer player) {
             // the server without waiting for the status change to IN_GAME, which is why the session remains and the
             // server thinks that the player is still on the server, but after such manipulations, the player client
             // will crash every time he logs on to the server
-            player.getDimension().removePlayer(player);
-            playerStorage.savePlayerData(player);
-            removeFromPlayerList(player);
+            if (player.getDimension() != null) {
+                // The dimension of the player may be null, that because the client is still handling resource packs
+                // and is not added or going to be added (willBeSpawnedNextTick == true) to any dimension. After handled
+                // resources packs, the dimension of the player should always be non-null regardless the status of the
+                // player because there is a check in EntityPlayerBaseComponentImpl#setLocationBeforeSpawn()
+                player.getDimension().removePlayer(player);
+                playerStorage.savePlayerData(player);
+                removeFromPlayerList(player);
+            }
         }
 
         ((AllayNetworkInterface) networkInterface).setPlayerCount(players.size());

server/src/main/java/org/allaymc/server/entity/component/EntityBaseComponentImpl.java

@@ -290,6 +290,7 @@ protected void setLocation(Location3fc location, boolean calculateFallDistance)
         if (MathUtils.hasNaN(location)) {
             throw new IllegalArgumentException("Trying to set the location of entity " + runtimeId + " to a new location which contains NaN: " + location);
         }
+
         if (calculateFallDistance && !this.onGround) {
             if (this.fallDistance < 0) {
                 // Entity start falling

server/src/main/java/org/allaymc/server/entity/component/player/EntityPlayerBaseComponentImpl.java

@@ -941,6 +941,16 @@ public void setMotion(Vector3fc motion) {
         networkComponent.sendPacket(packet);
     }
 
+    @Override
+    public void setLocationBeforeSpawn(Location3fc location) {
+        if (this.location.dimension() != null && location.dimension() == null) {
+            // Different from normal entity, reset the dimension of player entity back to null is not allowed
+            throw new IllegalArgumentException("Reset dimension back to null is not allowed for player!");
+        }
+
+        super.setLocationBeforeSpawn(location);
+    }
+
     @Override
     public void sendMetadata() {
         super.sendMetadata();

server/src/main/java/org/allaymc/server/entity/component/player/EntityPlayerNetworkComponentImpl.java

@@ -220,7 +220,8 @@ protected void onFullyJoin() {
 
         world.getWorldData().sendTimeOfDay(thisPlayer);
         ((AllayWorld) world).sendWeather(thisPlayer);
-        // Save player data the first time
+
+        // Save player data the first time it joins
         server.getPlayerStorage().savePlayerData(thisPlayer);
     }