From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: jmp <jasonpenilla2@me.com>
Date: Wed, 18 Nov 2020 20:52:25 -0800
Subject: [PATCH] Entity load/save limit per chunk

Adds a config option to limit the number of entities saved and loaded
to a chunk. The default values of -1 disable the limit. Although
defaults are only included for certain entites, this allows setting
limits for any entity type.

1.17: looks like tracking the count on loading should work fine just putting it in the EntityType#loadEntitiesRecursive, but
the tracking count on save needs some more work to implement.

diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index 7ebc85264a2cbfb601dfe5472b561cac1a7cf8bf..486e5438254348db68017228af131cba7defd637 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -7,6 +7,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
 import net.minecraft.world.Difficulty;
+import net.minecraft.world.entity.EntityType;
 import net.minecraft.world.entity.monster.Vindicator;
 import net.minecraft.world.entity.monster.Zombie;
 import com.destroystokyo.paper.antixray.ChunkPacketBlockControllerAntiXray.EngineMode;
@@ -762,4 +763,18 @@ public class PaperWorldConfig {
             Difficulty.class
         );
     }
+
+    public Map<EntityType<?>, Integer> entityPerChunkSaveLimits = new HashMap<>();
+    private void entityPerChunkSaveLimits() {
+        getInt("entity-per-chunk-save-limit.experience_orb", -1);
+        getInt("entity-per-chunk-save-limit.snowball", -1);
+        getInt("entity-per-chunk-save-limit.ender_pearl", -1);
+        getInt("entity-per-chunk-save-limit.arrow", -1);
+        EntityType.getEntityNameList().forEach(name -> {
+            final EntityType<?> type = EntityType.getByName(name.getPath()).orElseThrow(() -> new IllegalStateException("Unknown Entity Type: " + name.toString()));
+            final String path = ".entity-per-chunk-save-limit." + name.getPath();
+            final int value = config.getInt("world-settings." + worldName + path, config.getInt("world-settings.default" + path, -1)); // get without setting defaults
+            if (value != -1) entityPerChunkSaveLimits.put(type, value);
+        });
+    }
 }
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 f6a814f9305813eaafa56baa0327e0111cd4e38c..30f80f8549c3236d6bfe594e323e4ca6e702005d 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
@@ -539,11 +539,22 @@ public class ChunkSerializer {
 
             chunk.setLastSaveHadEntities(false);
 
+            // Paper start
+            final Map<EntityType<?>, Integer> savedEntityCounts = Maps.newHashMap();
             for (int j = 0; j < chunk.getEntitySlices().length; ++j) {
                 Iterator iterator1 = chunk.getEntitySlices()[j].iterator();
 
                 while (iterator1.hasNext()) {
                     Entity entity = (Entity) iterator1.next();
+                    final EntityType<?> entityType = entity.getType();
+                    final int saveLimit = worldserver.paperConfig.entityPerChunkSaveLimits.getOrDefault(entityType, -1);
+                    if (saveLimit > -1) {
+                        if (savedEntityCounts.getOrDefault(entityType, 0) >= saveLimit) {
+                            continue;
+                        }
+                        savedEntityCounts.merge(entityType, 1, Integer::sum);
+                    }
+                    // Paper end
                     CompoundTag nbttagcompound4 = new CompoundTag();
                     // Paper start
                     if (asyncsavedata == null && !entity.removed && (int) Math.floor(entity.getX()) >> 4 != chunk.getPos().x || (int) Math.floor(entity.getZ()) >> 4 != chunk.getPos().z) {
@@ -674,10 +685,21 @@ public class ChunkSerializer {
         ListTag nbttaglist = tag.getList("Entities", 10);
         Level world = chunk.getLevel();
 
+        // Paper start
+        final Map<EntityType<?>, Integer> loadedEntityCounts = Maps.newHashMap();
         for (int i = 0; i < nbttaglist.size(); ++i) {
             CompoundTag nbttagcompound1 = nbttaglist.getCompound(i);
 
             EntityType.loadEntityRecursive(nbttagcompound1, world, (entity) -> {
+                final EntityType<?> entityType = entity.getType();
+                final int saveLimit = world.paperConfig.entityPerChunkSaveLimits.getOrDefault(entityType, -1);
+                if (saveLimit > -1) {
+                    if (loadedEntityCounts.getOrDefault(entityType, 0) >= saveLimit) {
+                        return null;
+                    }
+                    loadedEntityCounts.merge(entityType, 1, Integer::sum);
+                }
+                // Paper end
                 chunk.addEntity(entity);
                 return entity;
             });