From 0bc6c124ed1c6be43add0164f7711220f38af6a8 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sun, 14 Jan 2018 17:01:31 -0500
Subject: [PATCH] PreCreatureSpawnEvent

Adds an event to fire before an Entity is created, so that plugins that need to cancel
CreatureSpawnEvent can do so from this event instead.

Cancelling CreatureSpawnEvent rapidly causes a lot of garbage collection and CPU waste
as it's done after the Entity object has been fully created.

Mob Limiting plugins and blanket "ban this type of monster" plugins should use this event
instead and save a lot of server resources.

See: https://github.com/PaperMC/Paper/issues/917

diff --git a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
index c76dbe74ac..b88160a2ed 100644
--- a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
+++ b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
@@ -1,6 +1,7 @@
 package net.minecraft.server;
 
 import com.google.common.collect.Lists;
+
 import java.util.Iterator;
 import java.util.List;
 import javax.annotation.Nullable;
@@ -94,6 +95,27 @@ public abstract class MobSpawnerAbstract {
                     double d3 = j >= 1 ? nbttaglist.k(0) : (double) blockposition.getX() + (world.random.nextDouble() - world.random.nextDouble()) * (double) this.spawnRange + 0.5D;
                     double d4 = j >= 2 ? nbttaglist.k(1) : (double) (blockposition.getY() + world.random.nextInt(3) - 1);
                     double d5 = j >= 3 ? nbttaglist.k(2) : (double) blockposition.getZ() + (world.random.nextDouble() - world.random.nextDouble()) * (double) this.spawnRange + 0.5D;
+                    // Paper start
+                    if (this.getMobName() == null) {
+                        return;
+                    }
+                    String key = this.getMobName().getKey();
+                    org.bukkit.entity.EntityType type = org.bukkit.entity.EntityType.fromName(key);
+                    if (type != null) {
+                        com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent event;
+                        event = new com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent(
+                                MCUtil.toLocation(world, d3, d4, d5),
+                                type,
+                                org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.SPAWNER
+                        );
+                        if (!event.callEvent()) {
+                            if (event.shouldAbortSpawn()) {
+                                break;
+                            }
+                            continue;
+                        }
+                    }
+                    // Paper end
                     Entity entity = ChunkRegionLoader.a(nbttagcompound, world, d3, d4, d5, false);
 
                     if (entity == null) {
diff --git a/src/main/java/net/minecraft/server/SpawnerCreature.java b/src/main/java/net/minecraft/server/SpawnerCreature.java
index 342a15db5e..973c3d1e9e 100644
--- a/src/main/java/net/minecraft/server/SpawnerCreature.java
+++ b/src/main/java/net/minecraft/server/SpawnerCreature.java
@@ -160,10 +160,30 @@ public final class SpawnerCreature {
 
                                                     if (worldserver.a(enumcreaturetype, biomebase_biomemeta, (BlockPosition) blockposition_mutableblockposition)) {
                                                         EntityPositionTypes.Surface entitypositiontypes_surface = EntityPositionTypes.a(biomebase_biomemeta.b);
-
                                                         if (entitypositiontypes_surface != null && a(entitypositiontypes_surface, worldserver, blockposition_mutableblockposition, biomebase_biomemeta.b)) {
                                                             EntityInsentient entityinsentient;
 
+                                                            // Paper start
+                                                            com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent event;
+                                                            EntityTypes<? extends EntityInsentient> cls = biomebase_biomemeta.b;
+                                                            org.bukkit.entity.EntityType type = EntityTypes.clsToTypeMap.get(cls);
+                                                            if (type != null) {
+                                                                event = new com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent(
+                                                                        MCUtil.toLocation(worldserver, blockposition_mutableblockposition),
+                                                                        type, SpawnReason.NATURAL
+                                                                );
+                                                                if (!event.callEvent()) {
+                                                                    if (event.shouldAbortSpawn()) {
+                                                                        continue label128; // right above the iterator for c (Chunk Pos Set)
+                                                                    }
+                                                                    j1 += l2;
+                                                                    ++j4;
+                                                                    continue;
+                                                                }
+                                                            }
+                                                            // Paper end
+
+
                                                             try {
                                                                 entityinsentient = (EntityInsentient) biomebase_biomemeta.b.a((World) worldserver);
                                                             } catch (Exception exception) {
-- 
2.18.0