fix some NPEs caused by race conditions in chunk conversion (#1396)

* fix some NPEs caused by race conditions in chunk conversion

tbh the whole session should be read-write locked for every operation

* fix code style issues

connector/src/main/java/org/geysermc/connector/network/translators/java/world/JavaChunkDataTranslator.java

@@ -66,11 +66,11 @@ public class JavaChunkDataTranslator extends PacketTranslator<ServerChunkDataPac
             return;
         }
 
+        GeyserConnector.getInstance().getGeneralThreadPool().execute(() -> {
+            try {
                 // Non-full chunks don't have all the chunk data, and Bedrock won't accept that
                 final boolean isNonFullChunk = (packet.getColumn().getBiomeData() == null);
 
-        GeyserConnector.getInstance().getGeneralThreadPool().execute(() -> {
-            try {
                 ChunkUtils.ChunkData chunkData = ChunkUtils.translateToBedrock(session, packet.getColumn(), isNonFullChunk);
                 ByteBuf byteBuf = Unpooled.buffer(32);
                 ChunkSection[] sections = chunkData.sections;

connector/src/main/java/org/geysermc/connector/network/translators/world/GeyserWorldManager.java

@@ -25,12 +25,14 @@
 
 package org.geysermc.connector.network.translators.world;
 
+import com.github.steveice10.mc.protocol.data.game.chunk.Column;
 import com.github.steveice10.mc.protocol.data.game.entity.player.GameMode;
 import com.github.steveice10.mc.protocol.data.game.setting.Difficulty;
 import com.github.steveice10.mc.protocol.packet.ingame.client.ClientChatPacket;
 import it.unimi.dsi.fastutil.objects.Object2ObjectMap;
 import it.unimi.dsi.fastutil.objects.Object2ObjectOpenHashMap;
 import org.geysermc.connector.network.session.GeyserSession;
+import org.geysermc.connector.network.session.cache.ChunkCache;
 import org.geysermc.connector.utils.GameRule;
 
 public class GeyserWorldManager extends WorldManager {
@@ -39,14 +41,25 @@ public class GeyserWorldManager extends WorldManager {
 
     @Override
     public int getBlockAt(GeyserSession session, int x, int y, int z) {
-        return session.getChunkCache().getBlockAt(x, y, z);
+        ChunkCache chunkCache = session.getChunkCache();
+        if (chunkCache != null) { // Chunk cache can be null if the session is closed asynchronously
+            return chunkCache.getBlockAt(x, y, z);
+        }
+        return 0;
     }
 
     @Override
     public int[] getBiomeDataAt(GeyserSession session, int x, int z) {
-        if (!session.getConnector().getConfig().isCacheChunks())
+        if (session.getConnector().getConfig().isCacheChunks()) {
+            ChunkCache chunkCache = session.getChunkCache();
+            if (chunkCache != null) { // Chunk cache can be null if the session is closed asynchronously
+                Column column = chunkCache.getChunk(x, z);
+                if (column != null) { // Column can be null if the server sent a partial chunk update before the first ground-up-continuous one
+                    return column.getBiomeData();
+                }
+            }
+        }
         return new int[1024];
-        return session.getChunkCache().getChunk(x, z).getBiomeData();
     }
 
     @Override