From b27bbefc11af081a7e8e7e5212b964c8fc814777 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 c29df55fa..d6c73a5a0 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;
@@ -87,6 +88,23 @@ public abstract class MobSpawnerAbstract {
                     double d3 = j >= 1 ? nbttaglist.f(0) : (double) blockposition.getX() + (world.random.nextDouble() - world.random.nextDouble()) * (double) this.spawnRange + 0.5D;
                     double d4 = j >= 2 ? nbttaglist.f(1) : (double) (blockposition.getY() + world.random.nextInt(3) - 1);
                     double d5 = j >= 3 ? nbttaglist.f(2) : (double) blockposition.getZ() + (world.random.nextDouble() - world.random.nextDouble()) * (double) this.spawnRange + 0.5D;
+                    // Paper start
+                    if (this.getMobName() == null) {
+                        return;
+                    }
+                    com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent event;
+                    event = new com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent(
+                            MCUtil.toLocation(world, d3, d4, d5),
+                            org.bukkit.entity.EntityType.fromName(this.getMobName().getKey()),
+                            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 2cd063829..1137dda86 100644
--- a/src/main/java/net/minecraft/server/SpawnerCreature.java
+++ b/src/main/java/net/minecraft/server/SpawnerCreature.java
@@ -184,6 +184,22 @@ public final class SpawnerCreature {
                                                     }
 
                                                     if (worldserver.a(enumcreaturetype, biomebase_biomemeta, (BlockPosition) blockposition_mutableblockposition) && a(EntityPositionTypes.a(biomebase_biomemeta.b), worldserver, blockposition_mutableblockposition)) {
+                                                        // Paper start
+                                                        com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent event;
+                                                        event = new com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent(
+                                                                MCUtil.toLocation(worldserver,  blockposition_mutableblockposition),
+                                                                EntityTypes.clsToTypeMap.get(biomebase_biomemeta.b),
+                                                                SpawnReason.NATURAL
+                                                                );
+                                                        if (!event.callEvent()) {
+                                                            if (event.shouldAbortSpawn()) {
+                                                                continue label120;
+                                                            }
+                                                            j1 += l2;
+                                                            ++j4;
+                                                            continue;
+                                                        }
+                                                        // Paper end
                                                         EntityInsentient entityinsentient;
 
                                                         try {
-- 
2.15.1