Paper/patches/server/0341-Duplicate-UUID-Resolve-Option.patch

From 0000000000000000000000000000000000000000 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/net/minecraft/server/ChunkSystem.java b/src/main/java/net/minecraft/server/ChunkSystem.java
index 1b1bfd5f92f85f46ad9661a0a64a2a1b4c33a80d..2a099fe0d514f181bf2b452d5333bc29b0d29e43 100644
--- a/src/main/java/net/minecraft/server/ChunkSystem.java
+++ b/src/main/java/net/minecraft/server/ChunkSystem.java
@@ -260,7 +260,9 @@ public final class ChunkSystem {
     }
 
     public static void onEntityPreAdd(final ServerLevel level, final Entity entity) {
-
+        if (net.minecraft.server.level.ChunkMap.checkDupeUUID(level, entity)) {
+            return;
+        }
     }
 
     public static void onChunkHolderCreate(final ServerLevel level, final ChunkHolder holder) {
diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 245f60eb904e26d6e7f7ca02bfa778d4f6db5d76..4b24e4d947e96ea0720f8f6bc33470e07c00310d 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -982,6 +982,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
                     entity.discard();
                     needsRemoval = true;
                 }
+                checkDupeUUID(world, entity); // Paper
                 return !needsRemoval;
             }));
             // CraftBukkit end
@@ -1032,6 +1033,49 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         });
     }
 
+    // Paper start
+    // rets true if to prevent the entity from being added
+    public static boolean checkDupeUUID(ServerLevel level, Entity entity) {
+        io.papermc.paper.configuration.WorldConfiguration.Entities.Spawning.DuplicateUUID.DuplicateUUIDMode mode = level.paperConfig().entities.spawning.duplicateUuid.mode;
+        if (mode != io.papermc.paper.configuration.WorldConfiguration.Entities.Spawning.DuplicateUUID.DuplicateUUIDMode.WARN
+            && mode != io.papermc.paper.configuration.WorldConfiguration.Entities.Spawning.DuplicateUUID.DuplicateUUIDMode.DELETE
+            && mode != io.papermc.paper.configuration.WorldConfiguration.Entities.Spawning.DuplicateUUID.DuplicateUUIDMode.SAFE_REGEN) {
+            return false;
+        }
+        Entity other = level.getEntity(entity.getUUID());
+
+        if (other == null || other == entity) {
+            return false;
+        }
+
+        if (mode == io.papermc.paper.configuration.WorldConfiguration.Entities.Spawning.DuplicateUUID.DuplicateUUIDMode.SAFE_REGEN && other != null && !other.isRemoved()
+            && Objects.equals(other.getEncodeId(), entity.getEncodeId())
+            && entity.getBukkitEntity().getLocation().distance(other.getBukkitEntity().getLocation()) < level.paperConfig().entities.spawning.duplicateUuid.safeRegenDeleteRange
+        ) {
+            if (ServerLevel.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.discard();
+            return true;
+        }
+        if (other != null && !other.isRemoved()) {
+            switch (mode) {
+                case SAFE_REGEN: {
+                    entity.setUUID(java.util.UUID.randomUUID());
+                    if (ServerLevel.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 (ServerLevel.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.discard();
+                    return true;
+                }
+                default:
+                    if (ServerLevel.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;
+            }
+        }
+        return false;
+    }
+    // Paper end
     public CompletableFuture<Either<LevelChunk, ChunkHolder.ChunkLoadingFailure>> prepareTickingChunk(ChunkHolder holder) {
         ChunkPos chunkcoordintpair = holder.getPos();
         CompletableFuture<Either<List<ChunkAccess>, ChunkHolder.ChunkLoadingFailure>> completablefuture = this.getChunkRangeFuture(chunkcoordintpair, 1, (i) -> {
diff --git a/src/main/java/net/minecraft/world/level/entity/PersistentEntitySectionManager.java b/src/main/java/net/minecraft/world/level/entity/PersistentEntitySectionManager.java
index ab7eadf2fc4c4598fa89068332eaaf9a8e0a100f..16519a6414f6f6418de40b714555a52631980617 100644
--- a/src/main/java/net/minecraft/world/level/entity/PersistentEntitySectionManager.java
+++ b/src/main/java/net/minecraft/world/level/entity/PersistentEntitySectionManager.java
@@ -78,7 +78,22 @@ public class PersistentEntitySectionManager<T extends EntityAccess> implements A
 
     private boolean addEntityUuid(T entity) {
         if (!this.knownUuids.add(entity.getUUID())) {
+            // Paper start
+            T conflict = this.visibleEntityStorage.getEntity(entity.getUUID());
+            if (conflict != null && ((Entity) conflict).isRemoved()) {
+                stopTracking(conflict); // remove the existing entity
+                return true;
+            }
+            // Paper end
             PersistentEntitySectionManager.LOGGER.warn("UUID of added entity already exists: {}", entity);
+            // Paper start
+            if (net.minecraft.world.level.Level.DEBUG_ENTITIES && ((Entity) entity).level.paperConfig().entities.spawning.duplicateUuid.mode != io.papermc.paper.configuration.WorldConfiguration.Entities.Spawning.DuplicateUUID.DuplicateUUIDMode.NOTHING) {
+                if (((Entity) entity).addedToWorldStack != null) {
+                    ((Entity) entity).addedToWorldStack.printStackTrace();
+                }
+                net.minecraft.server.level.ServerLevel.getAddToWorldStackTrace((Entity) entity).printStackTrace();
+            }
+            // Paper end
             return false;
         } else {
             return true;