Paper/patches/server/0327-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/io/papermc/paper/chunk/system/ChunkSystem.java b/src/main/java/io/papermc/paper/chunk/system/ChunkSystem.java
index 56c35149fd142af6ffe31434fec0064cf6ea3be5..14e24e3bd8695c7038e8e1f4fb92ca3fd20c6258 100644
--- a/src/main/java/io/papermc/paper/chunk/system/ChunkSystem.java
+++ b/src/main/java/io/papermc/paper/chunk/system/ChunkSystem.java
@@ -74,7 +74,17 @@ public final class ChunkSystem {
     }
 
     public static void onEntityPreAdd(final ServerLevel level, final Entity entity) {
-
+        // Paper start - duplicate uuid resolving
+        if (net.minecraft.server.level.ChunkMap.checkDupeUUID(level, entity)) {
+            return;
+        }
+        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 - duplicate uuid resolving
     }
 
     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 a8533bbac77c6024cd6163149affe4f4733019b5..de89863bae07b6e1264b0c70287c085a716862e4 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -520,6 +520,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
                     entity.discard();
                     needsRemoval = true;
                 }
+                checkDupeUUID(world, entity); // Paper
                 return !needsRemoval;
             }), position); // Paper - rewrite chunk system
             // CraftBukkit end
@@ -531,6 +532,49 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         throw new UnsupportedOperationException(); // Paper - rewrite chunk system
     }
 
+    // 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) {
         throw new UnsupportedOperationException(); // Paper - rewrite chunk system
     }