From dbf60c4aea0812474c4a45c78473fafcb0ca11e9 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Fri, 27 Dec 2019 09:42:26 -0800
Subject: [PATCH] Guard against serializing mismatching chunk coordinate

Should help if something dumb happens

diff --git a/src/main/java/net/minecraft/server/ChunkRegionLoader.java b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
index 34cd09a503b..fa893b14bce 100644
--- a/src/main/java/net/minecraft/server/ChunkRegionLoader.java
+++ b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
@@ -23,6 +23,13 @@ public class ChunkRegionLoader {
 
     private static final Logger LOGGER = LogManager.getLogger();
 
+    // Paper start - guard against serializing mismatching coordinates
+    // TODO Note: This needs to be re-checked each update
+    public static ChunkCoordIntPair getChunkCoordinate(NBTTagCompound chunkData) {
+        NBTTagCompound levelData = chunkData.getCompound("Level");
+        return new ChunkCoordIntPair(levelData.getInt("xPos"), levelData.getInt("zPos"));
+    }
+    // Paper end
     // Paper start
     public static final class InProgressChunkHolder {
 
@@ -48,8 +55,8 @@ public class ChunkRegionLoader {
         // Paper end
         ChunkGenerator<?> chunkgenerator = worldserver.getChunkProvider().getChunkGenerator();
         WorldChunkManager worldchunkmanager = chunkgenerator.getWorldChunkManager();
-        NBTTagCompound nbttagcompound1 = nbttagcompound.getCompound("Level");
-        ChunkCoordIntPair chunkcoordintpair1 = new ChunkCoordIntPair(nbttagcompound1.getInt("xPos"), nbttagcompound1.getInt("zPos"));
+        NBTTagCompound nbttagcompound1 = nbttagcompound.getCompound("Level"); // Paper - diff on change, see ChunkRegionLoader#getChunkCoordinate
+        ChunkCoordIntPair chunkcoordintpair1 = new ChunkCoordIntPair(nbttagcompound1.getInt("xPos"), nbttagcompound1.getInt("zPos")); // Paper - diff on change, see ChunkRegionLoader#getChunkCoordinate
 
         if (!Objects.equals(chunkcoordintpair, chunkcoordintpair1)) {
             ChunkRegionLoader.LOGGER.error("Chunk file at {} is in the wrong location; relocating. (Expected {}, got {})", chunkcoordintpair, chunkcoordintpair, chunkcoordintpair1);
diff --git a/src/main/java/net/minecraft/server/IChunkLoader.java b/src/main/java/net/minecraft/server/IChunkLoader.java
index 134c76065bf..25c8b131fec 100644
--- a/src/main/java/net/minecraft/server/IChunkLoader.java
+++ b/src/main/java/net/minecraft/server/IChunkLoader.java
@@ -106,6 +106,13 @@ public class IChunkLoader extends RegionFileCache implements AutoCloseable {
 //
     public void a(ChunkCoordIntPair chunkcoordintpair, NBTTagCompound nbttagcompound) throws IOException { write(chunkcoordintpair, nbttagcompound); } // Paper OBFHELPER
     public void write(ChunkCoordIntPair chunkcoordintpair, NBTTagCompound nbttagcompound) throws IOException { // Paper - OBFHELPER - (Switched around for safety)
+        // Paper start
+        if (!chunkcoordintpair.equals(ChunkRegionLoader.getChunkCoordinate(nbttagcompound))) {
+            String world = (this instanceof PlayerChunkMap) ? ((PlayerChunkMap)this).world.getWorld().getName() : null;
+            throw new IllegalArgumentException("Chunk coordinate and serialized data do not have matching coordinates, trying to serialize coordinate " + chunkcoordintpair.toString()
+                + " but compound says coordinate is " + ChunkRegionLoader.getChunkCoordinate(nbttagcompound).toString() + (world == null ? " for an unknown world" : (" for world: " + world)));
+        }
+        // Paper end
         super.write(chunkcoordintpair, nbttagcompound);
         if (this.c != null) {
             synchronized (this.persistentDataLock) { // Paper - Async chunk loading
-- 
2.26.2