From 0000000000000000000000000000000000000000 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/world/level/chunk/storage/ChunkSerializer.java b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkSerializer.java
index 83fa00de1a7cb690c763cec9c8d4b3fcd44e7c74..670e4f65680ca36fba1c84cb334c470ea8fa9b60 100644
--- a/src/main/java/net/minecraft/world/level/chunk/storage/ChunkSerializer.java
+++ b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkSerializer.java
@@ -67,6 +67,13 @@ public class ChunkSerializer {
 
     public ChunkSerializer() {}
 
+    // Paper start - guard against serializing mismatching coordinates
+    // TODO Note: This needs to be re-checked each update
+    public static ChunkPos getChunkCoordinate(CompoundTag chunkData) {
+        CompoundTag levelData = chunkData.getCompound("Level");
+        return new ChunkPos(levelData.getInt("xPos"), levelData.getInt("zPos"));
+    }
+    // Paper end
     // Paper start
     public static final class InProgressChunkHolder {
 
@@ -93,8 +100,8 @@ public class ChunkSerializer {
         // Paper end
         ChunkGenerator chunkgenerator = world.getChunkSource().getGenerator();
         BiomeSource worldchunkmanager = chunkgenerator.getBiomeSource();
-        CompoundTag nbttagcompound1 = nbt.getCompound("Level");
-        ChunkPos chunkcoordintpair1 = new ChunkPos(nbttagcompound1.getInt("xPos"), nbttagcompound1.getInt("zPos"));
+        CompoundTag nbttagcompound1 = nbt.getCompound("Level"); // Paper - diff on change, see ChunkSerializer#getChunkCoordinate
+        ChunkPos chunkcoordintpair1 = new ChunkPos(nbttagcompound1.getInt("xPos"), nbttagcompound1.getInt("zPos")); // Paper - diff on change, see ChunkSerializer#getChunkCoordinate
 
         if (!Objects.equals(pos, chunkcoordintpair1)) {
             ChunkSerializer.LOGGER.error("Chunk file at {} is in the wrong location; relocating. (Expected {}, got {})", pos, pos, chunkcoordintpair1);
diff --git a/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java
index 6f13c7adce7d4b3d170045ea5ef2a841d34ae7b0..176610b31f66b890afe61f4de46c412382bb8d22 100644
--- a/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java
+++ b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java
@@ -117,6 +117,13 @@ public class ChunkStorage implements AutoCloseable {
 
     // Paper start - async chunk io
     public void write(ChunkPos chunkPos, CompoundTag nbt) throws IOException {
+        // Paper start
+        if (!chunkPos.equals(ChunkSerializer.getChunkCoordinate(nbt))) {
+            String world = (this instanceof net.minecraft.server.level.ChunkMap) ? ((net.minecraft.server.level.ChunkMap)this).level.getWorld().getName() : null;
+            throw new IllegalArgumentException("Chunk coordinate and serialized data do not have matching coordinates, trying to serialize coordinate " + chunkPos.toString()
+                + " but compound says coordinate is " + ChunkSerializer.getChunkCoordinate(nbt).toString() + (world == null ? " for an unknown world" : (" for world: " + world)));
+        }
+        // Paper end
         this.regionFileCache.write(chunkPos, nbt);
         // Paper end - Async chunk loading
         if (this.legacyStructureHandler != null) {