From d39b091e6993517819763e6e209249e36aaca293 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 ef882b897f..385b3ac0ce 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -449,4 +449,43 @@ public class PaperWorldConfig {
             log("Using vanilla redstone algorithm.");
         }
     }
+
+    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 197c0fe169..ef07f665b7 100644
--- a/src/main/java/net/minecraft/server/Chunk.java
+++ b/src/main/java/net/minecraft/server/Chunk.java
@@ -397,6 +397,7 @@ public class Chunk implements IChunkAccess {
         if (i != this.loc.x || j != this.loc.z) {
             Chunk.LOGGER.warn("Wrong location! ({}, {}) should be ({}, {}), {}", i, j, this.loc.x, this.loc.z, entity);
             entity.dead = true;
+            return; // Paper
         }
 
         int k = MathHelper.floor(entity.locY / 16.0D);
diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
index 658c493cd3..fae57a0998 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -2674,6 +2674,7 @@ 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.ap = this.uniqueID.toString();
diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
index 8fcd721eeb..34db8c8247 100644
--- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
@@ -1,5 +1,6 @@
 package net.minecraft.server;
 
+import com.destroystokyo.paper.PaperWorldConfig; // Paper
 import com.google.common.collect.ImmutableList;
 import co.aikar.timings.Timing;
 import com.google.common.collect.ComparisonChain;
@@ -20,12 +21,15 @@ import it.unimi.dsi.fastutil.objects.ObjectIterator;
 import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.HashMap; // Paper
 import java.util.Iterator;
 import java.util.List;
+import java.util.Map; // Paper
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Queue;
 import java.util.Set;
+import java.util.UUID; // Paper
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -559,12 +563,49 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
 
                     for (int j = 0; j < i; ++j) {
                         List<Entity> entityslice = aentityslice[j]; // Spigot
-                        Iterator iterator = entityslice.iterator();
 
-                        while (iterator.hasNext()) {
-                            Entity entity = (Entity) iterator.next();
+                        // Paper start
+                        PaperWorldConfig.DuplicateUUIDMode mode = world.paperConfig.duplicateUUIDMode;
+                        if (mode == PaperWorldConfig.DuplicateUUIDMode.WARN || mode == PaperWorldConfig.DuplicateUUIDMode.DELETE || mode == PaperWorldConfig.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).getEntity(entity.uniqueID);
+                                if (other == null || other.dead) {
+                                    other = thisChunk.get(entity.uniqueID);
+                                }
+
+                                if (mode == PaperWorldConfig.DuplicateUUIDMode.SAFE_REGEN && other != null && !other.dead
+                                        && 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.dead = true;
+                                    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.dead = true;
+                                            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;
+                                    }
+                                }
+
 
-                            if (!(entity instanceof EntityHuman) && !this.world.addEntityChunk(entity)) {
+                            if (!(entity instanceof EntityHuman) && (entity.dead || !this.world.addEntityChunk(entity))) { // Paper
                                 if (list == null) {
                                     list = Lists.newArrayList(new Entity[]{entity});
                                 } else {
@@ -572,6 +613,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
                                 }
                             }
                         }
+                        } // Paper
                     }
 
                     if (list != null) {
diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
index e61381221f..e9e5ecf747 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -2,6 +2,8 @@ package net.minecraft.server;
 
 import co.aikar.timings.TimingHistory;
 import co.aikar.timings.Timings;
+
+import com.destroystokyo.paper.PaperWorldConfig;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Queues;
@@ -977,8 +979,23 @@ public class WorldServer extends World {
         if (entity1 == null) {
             return false;
         } else {
-            WorldServer.LOGGER.error("Keeping entity {} that already exists with UUID {}", EntityTypes.getName(entity1.getEntityType()), entity.getUniqueID().toString()); // CraftBukkit // paper
-            WorldServer.LOGGER.error("Deleting duplicate entity {}", entity); // CraftBukkit // paper
+            // Paper start
+            if (entity1.dead) {
+                unregisterEntity(entity1); // remove the existing entity
+                return false;
+            }
+
+            if (DEBUG_ENTITIES && entity.world.paperConfig.duplicateUUIDMode != PaperWorldConfig.DuplicateUUIDMode.NOTHING) {
+                WorldServer.LOGGER.error("Keeping entity {} that already exists with UUID {}", EntityTypes.getName(entity1.getEntityType()), entity.getUniqueID().toString()); // CraftBukkit // paper
+                WorldServer.LOGGER.error("Deleting duplicate entity {}", entity); // CraftBukkit // paper
+
+                if (entity1.addedToWorldStack != null) {
+                    entity1.addedToWorldStack.printStackTrace();
+                }
+
+                getAddToWorldStackTrace(entity).printStackTrace();
+            }
+            // Paper end
             return true;
         }
     }
@@ -1109,7 +1126,7 @@ public class WorldServer extends World {
             }
 
             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) { // Paper
                 Logger logger = LogManager.getLogger();
                 logger.error("Overwrote an existing entity " + old + " with " + entity);
                 if (DEBUG_ENTITIES) {
-- 
2.21.0

