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 97cdd8cd7749185230471f34f7d1ce3abcd0fd11..7862caa0f787634cec14af81fe1f39803a43f115 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
@@ -94,6 +94,18 @@ 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) {
+        final int dataVersion = ChunkStorage.getVersion(chunkData);
+        if (dataVersion < 2842) { // Level tag is removed after this version
+            final CompoundTag levelData = chunkData.getCompound("Level");
+            return new ChunkPos(levelData.getInt("xPos"), levelData.getInt("zPos"));
+        } else {
+            return new ChunkPos(chunkData.getInt("xPos"), chunkData.getInt("zPos"));
+        }
+    }
+    // Paper end - guard against serializing mismatching coordinates
     // Paper start
     public static final class InProgressChunkHolder {
 
@@ -115,7 +127,7 @@ public class ChunkSerializer {
 
     public static InProgressChunkHolder loadChunk(ServerLevel world, PoiManager poiStorage, ChunkPos chunkPos, CompoundTag nbt, boolean distinguish) {
         // Paper end
-        ChunkPos chunkcoordintpair1 = new ChunkPos(nbt.getInt("xPos"), nbt.getInt("zPos"));
+        ChunkPos chunkcoordintpair1 = new ChunkPos(nbt.getInt("xPos"), nbt.getInt("zPos")); // Paper - guard against serializing mismatching coordinates; diff on change, see ChunkSerializer#getChunkCoordinate
 
         if (!Objects.equals(chunkPos, chunkcoordintpair1)) {
             ChunkSerializer.LOGGER.error("Chunk file at {} is in the wrong location; relocating. (Expected {}, got {})", new Object[]{chunkPos, chunkPos, 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 b4e7c9b317d532d4915932f8f79dfebf2b63ff16..af8a8e85742497e8dac7a59a3cd5938e09580e45 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
@@ -178,6 +178,13 @@ public class ChunkStorage implements AutoCloseable {
 
     // Paper start - async chunk io
     public void write(ChunkPos chunkPos, CompoundTag nbt) throws IOException {
+        // Paper start - guard against serializing mismatching coordinates
+        if (nbt != null && !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 - guard against serializing mismatching coordinates
         this.regionFileCache.write(chunkPos, nbt);
         // Paper end - Async chunk loading
         if (this.legacyStructureHandler != null) {