From d4952e11a8163210b2a750f4c22b03b57a118632 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 21 Jul 2018 14:27:34 -0400
Subject: [PATCH] Duplicate UUID Resolve Option

Due to a bug in https://github.com/PaperMC/Paper/commit/2e29af3df05ec0a383f48be549d1c03200756d24
which was added all the way back in March of 2016, it was unknown (potentially not at the time)
that an entity might actually change the seed of the random object.

At some point, EntitySquid did start setting the seed. Due to this shared random, this caused
every entity to use a Random object with a predictable seed.

This has caused entities to potentially generate with the same UUID....

Over the years, servers have had entities disappear, but no sign of trouble
because CraftBukkit removed the log lines indicating that something was wrong.

We have fixed the root issue causing duplicate UUID's, however we now have chunk
files full of entities that have the same UUID as another entity!

When these chunks load, the 2nd entity will not be added to the world correctly.

If that chunk loads in a different order in the future, then it will reverse and the
missing one is now the one added to the world and not the other. This results in very
inconsistent entity behavior.

This change allows you to recover any duplicate entity by generating a new UUID for it.
This also lets you delete them instead if you don't want to risk having new entities added to
the world that you previously did not see.

But for those who are ok with leaving this inconsistent behavior, you may use WARN or NOTHING options.

It is recommended you regenerate the entities, as these were legit entities, and deserve your love.

diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index f5b2e88f3b..8c4ff18868 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -463,4 +463,43 @@ public class PaperWorldConfig {
             log("Bed Search Radius: " + bedSearchRadius);
         }
     }
+
+    public enum DuplicateUUIDMode {
+        SAFE_REGEN, DELETE, NOTHING, WARN
+    }
+    public DuplicateUUIDMode duplicateUUIDMode = DuplicateUUIDMode.SAFE_REGEN;
+    public int duplicateUUIDDeleteRange = 32;
+    private void repairDuplicateUUID() {
+        String desiredMode = getString("duplicate-uuid-resolver", "saferegen").toLowerCase().trim();
+        duplicateUUIDDeleteRange = getInt("duplicate-uuid-saferegen-delete-range", duplicateUUIDDeleteRange);
+        switch (desiredMode.toLowerCase()) {
+            case "regen":
+            case "regenerate":
+            case "saferegen":
+            case "saferegenerate":
+                duplicateUUIDMode = DuplicateUUIDMode.SAFE_REGEN;
+                log("Duplicate UUID Resolve: Regenerate New UUID if distant (Delete likely duplicates within " + duplicateUUIDDeleteRange + " blocks)");
+                break;
+            case "remove":
+            case "delete":
+                duplicateUUIDMode = DuplicateUUIDMode.DELETE;
+                log("Duplicate UUID Resolve: Delete Entity");
+                break;
+            case "silent":
+            case "nothing":
+                duplicateUUIDMode = DuplicateUUIDMode.NOTHING;
+                logError("Duplicate UUID Resolve: Do Nothing (no logs) - Warning, may lose indication of bad things happening");
+                break;
+            case "log":
+            case "warn":
+                duplicateUUIDMode = DuplicateUUIDMode.WARN;
+                log("Duplicate UUID Resolve: Warn (do nothing but log it happened, may be spammy)");
+                break;
+            default:
+                duplicateUUIDMode = DuplicateUUIDMode.WARN;
+                logError("Warning: Invalid duplicate-uuid-resolver config " + desiredMode + " - must be one of: regen, delete, nothing, warn");
+                log("Duplicate UUID Resolve: Warn (do nothing but log it happened, may be spammy)");
+                break;
+        }
+    }
 }
diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
index c2f12f92b0..e8c06e01b4 100644
--- a/src/main/java/net/minecraft/server/Chunk.java
+++ b/src/main/java/net/minecraft/server/Chunk.java
@@ -1,5 +1,10 @@
 package net.minecraft.server;
 
+// Paper start
+import com.destroystokyo.paper.PaperWorldConfig.DuplicateUUIDMode;
+import java.util.HashMap;
+import java.util.UUID;
+// Paper end
 import com.destroystokyo.paper.exception.ServerInternalException;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Queues;
@@ -41,6 +46,7 @@ public class Chunk implements IChunkAccess {
     public final World world;
     public final Map<HeightMap.Type, HeightMap> heightMap;
     public Long scheduledForUnload; // Paper - delay chunk unloads
+    private static final Logger logger = LogManager.getLogger(); // Paper
     public final int locX;
     public final int locZ;
     private boolean l;
@@ -691,6 +697,7 @@ public class Chunk implements IChunkAccess {
         if (i != this.locX || j != this.locZ) {
             Chunk.d.warn("Wrong location! ({}, {}) should be ({}, {}), {}", i, j, this.locX, this.locZ, entity);
             entity.die();
+            return; // Paper
         }
 
         int k = MathHelper.floor(entity.locY / 16.0D);
@@ -879,6 +886,50 @@ public class Chunk implements IChunkAccess {
 
         for (int j = 0; j < i; ++j) {
             List<Entity> entityslice = aentityslice[j]; // Spigot
+            // Paper start
+            DuplicateUUIDMode mode = world.paperConfig.duplicateUUIDMode;
+            if (mode == DuplicateUUIDMode.WARN || mode == DuplicateUUIDMode.DELETE || mode == DuplicateUUIDMode.SAFE_REGEN) {
+                Map<UUID, Entity> thisChunk = new HashMap<>();
+                for (Iterator<Entity> iterator = ((List<Entity>) entityslice).iterator(); iterator.hasNext(); ) {
+                    Entity entity = iterator.next();
+                    if (entity.dead || entity.valid) continue;
+                    Entity other = ((WorldServer) world).entitiesByUUID.get(entity.uniqueID);
+                    if (other == null || other.dead || world.getEntityUnloadQueue().contains(other)) {
+                        other = thisChunk.get(entity.uniqueID);
+                    }
+
+                    if (mode == DuplicateUUIDMode.SAFE_REGEN && other != null && !other.dead &&
+                        !world.getEntityUnloadQueue().contains(other)
+                        && java.util.Objects.equals(other.getSaveID(), entity.getSaveID())
+                        && entity.getBukkitEntity().getLocation().distance(other.getBukkitEntity().getLocation()) < world.paperConfig.duplicateUUIDDeleteRange
+                    ) {
+                        if (World.DEBUG_ENTITIES) logger.warn("[DUPE-UUID] Duplicate UUID found used by " + other + ", deleted entity " + entity + " because it was near the duplicate and likely an actual duplicate. See https://github.com/PaperMC/Paper/issues/1223 for discussion on what this is about.");
+                        entity.die();
+                        iterator.remove();
+                        continue;
+                    }
+                    if (other != null && !other.dead) {
+                        switch (mode) {
+                            case SAFE_REGEN: {
+                                entity.setUUID(UUID.randomUUID());
+                                if (World.DEBUG_ENTITIES) logger.warn("[DUPE-UUID] Duplicate UUID found used by " + other + ", regenerated UUID for " + entity + ". See https://github.com/PaperMC/Paper/issues/1223 for discussion on what this is about.");
+                                break;
+                            }
+                            case DELETE: {
+                                if (World.DEBUG_ENTITIES) logger.warn("[DUPE-UUID] Duplicate UUID found used by " + other + ", deleted entity " + entity + ". See https://github.com/PaperMC/Paper/issues/1223 for discussion on what this is about.");
+                                entity.die();
+                                iterator.remove();
+                                break;
+                            }
+                            default:
+                                if (World.DEBUG_ENTITIES) logger.warn("[DUPE-UUID] Duplicate UUID found used by " + other + ", doing nothing to " + entity + ". See https://github.com/PaperMC/Paper/issues/1223 for discussion on what this is about.");
+                                break;
+                        }
+                    }
+                    thisChunk.put(entity.uniqueID, entity);
+                }
+            }
+            // Paper end
 
             // CraftBukkit start
             List<Entity> toRemove = new LinkedList<>();
diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
index b6c46e01d9..6598b87eef 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -2739,6 +2739,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
         });
     }
 
+    public void setUUID(UUID uuid) { a(uuid); } // Paper - OBFHELPER
     public void a(UUID uuid) {
         this.uniqueID = uuid;
         this.au = this.uniqueID.toString();
diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
index 1496125ddf..a5f4b9ad94 100644
--- a/src/main/java/net/minecraft/server/World.java
+++ b/src/main/java/net/minecraft/server/World.java
@@ -70,7 +70,7 @@ public abstract class World implements IEntityAccess, GeneratorAccess, IIBlockAc
         }
     };
     // Spigot end
-    protected final Set<Entity> g = com.google.common.collect.Sets.newHashSet(); // Paper
+    protected final Set<Entity> g = com.google.common.collect.Sets.newHashSet(); public Set<Entity> getEntityUnloadQueue() { return g; };// Paper - OBFHELPER
     //public final List<TileEntity> tileEntityList = Lists.newArrayList(); // Paper - remove unused list
     public final List<TileEntity> tileEntityListTick = Lists.newArrayList();
     private final List<TileEntity> c = Lists.newArrayList();
diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
index 6d1f70b39e..293818b196 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -37,7 +37,7 @@ public class WorldServer extends World implements IAsyncTaskHandler {
     private final MinecraftServer server;
     public EntityTracker tracker;
     private final PlayerChunkMap manager;
-    private final Map<UUID, Entity> entitiesByUUID = Maps.newHashMap();
+    public final Map<UUID, Entity> entitiesByUUID = Maps.newHashMap(); // Paper
     public boolean savingDisabled;
     private boolean J;
     private int emptyTime;
@@ -971,7 +971,7 @@ public class WorldServer extends World implements IAsyncTaskHandler {
                     this.g.remove(entity1);
                 } else {
                     if (!(entity instanceof EntityHuman)) {
-                        if (DEBUG_ENTITIES) {
+                        if (DEBUG_ENTITIES && entity.world.paperConfig.duplicateUUIDMode != com.destroystokyo.paper.PaperWorldConfig.DuplicateUUIDMode.NOTHING) {
                             WorldServer.a.error("Keeping entity {} that already exists with UUID {}", entity1, uuid.toString()); // CraftBukkit // Paper
                             WorldServer.a.error("Deleting duplicate entity {}", entity); // Paper
 
@@ -1002,7 +1002,7 @@ public class WorldServer extends World implements IAsyncTaskHandler {
         }
 
         Entity old = this.entitiesByUUID.put(entity.getUniqueID(), entity);
-        if (old != null && old.getId() != entity.getId() && old.valid) {
+        if (old != null && old.getId() != entity.getId() && old.valid && entity.world.paperConfig.duplicateUUIDMode != com.destroystokyo.paper.PaperWorldConfig.DuplicateUUIDMode.NOTHING) {
             Logger logger = LogManager.getLogger();
             logger.error("Overwrote an existing entity " + old + " with " + entity);
             if (DEBUG_ENTITIES) {
-- 
2.21.0

