PaperMC/Spigot-Server-Patches/0468-Fix-numerous-item-duplication-issues-and-teleport-is.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 25 Apr 2020 06:46:35 -0400
Subject: [PATCH] Fix numerous item duplication issues and teleport issues

This notably fixes the newest "Donkey Dupe", but also fixes a lot
of dupe bugs in general around nether portals and entity world transfer

We also fix item duplication generically by anytime we clone an item
to drop it on the ground, destroy the source item.

This avoid an itemstack ever existing twice in the world state pre
clean up stage.

So even if something NEW comes up, it would be impossible to drop the
same item twice because the source was destroyed.

diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
index 7aa95b968af810a7bb4d7dedfacc83219f491e05..b400b04fcb733110150de800927c602180771cec 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -1911,11 +1911,12 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
         } else {
             // CraftBukkit start - Capture drops for death event
             if (this instanceof EntityLiving && !((EntityLiving) this).forceDrops) {
-                ((EntityLiving) this).drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(itemstack));
+                ((EntityLiving) this).drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asCraftMirror(itemstack)); // Paper - mirror so we can destroy it later
                 return null;
             }
             // CraftBukkit end
-            EntityItem entityitem = new EntityItem(this.world, this.locX(), this.locY() + (double) f, this.locZ(), itemstack);
+            EntityItem entityitem = new EntityItem(this.world, this.locX(), this.locY() + (double) f, this.locZ(), itemstack.cloneItemStack()); // Paper - clone so we can destroy original
+            itemstack.setCount(0); // Paper - destroy this item - if this ever leaks due to game bugs, ensure it doesn't dupe
 
             entityitem.defaultPickupDelay();
             // CraftBukkit start
@@ -2560,6 +2561,12 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
     @Nullable
     public Entity teleportTo(WorldServer worldserver, BlockPosition location) {
         // CraftBukkit end
+        // Paper start - fix bad state entities causing dupes
+        if (!isAlive() || !valid) {
+            LOGGER.warn("Illegal Entity Teleport " + this + " to " + worldserver + ":" + location, new Throwable());
+            return null;
+        }
+        // Paper end
         if (this.world instanceof WorldServer && !this.dead) {
             this.world.getMethodProfiler().enter("changeDimension");
             // CraftBukkit start
@@ -2663,7 +2670,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
                 entity.bukkitEntity = this.getBukkitEntity();
 
                 if (this instanceof EntityInsentient) {
-                    ((EntityInsentient)this).unleash(true, false); // Unleash to prevent duping of leads.
+                    ((EntityInsentient)this).unleash(true, true); // Paper drop lead
                 }
                 // CraftBukkit end
             }
@@ -2684,7 +2691,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
     }
 
     public boolean canPortal() {
-        return true;
+        return isAlive() && valid; // Paper
     }
 
     public float a(Explosion explosion, IBlockAccess iblockaccess, BlockPosition blockposition, IBlockData iblockdata, Fluid fluid, float f) {
diff --git a/src/main/java/net/minecraft/server/EntityArmorStand.java b/src/main/java/net/minecraft/server/EntityArmorStand.java
index 51e9f4a6e09474a7489d2872a800308ee3f02e46..250bccee4a27801b41c50d59e93396c696ab6974 100644
--- a/src/main/java/net/minecraft/server/EntityArmorStand.java
+++ b/src/main/java/net/minecraft/server/EntityArmorStand.java
@@ -557,7 +557,7 @@ public class EntityArmorStand extends EntityLiving {
         for (i = 0; i < this.handItems.size(); ++i) {
             itemstack = (ItemStack) this.handItems.get(i);
             if (!itemstack.isEmpty()) {
-                drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(itemstack)); // CraftBukkit - add to drops
+                drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asCraftMirror(itemstack)); // CraftBukkit - add to drops // Paper - mirror so we can destroy it later - though this call site was safe
                 this.handItems.set(i, ItemStack.b);
             }
         }
@@ -565,7 +565,7 @@ public class EntityArmorStand extends EntityLiving {
         for (i = 0; i < this.armorItems.size(); ++i) {
             itemstack = (ItemStack) this.armorItems.get(i);
             if (!itemstack.isEmpty()) {
-                drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(itemstack)); // CraftBukkit - add to drops
+                drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asCraftMirror(itemstack)); // CraftBukkit - add to drops // Paper - mirror so we can destroy it later - though this call site was safe
                 this.armorItems.set(i, ItemStack.b);
             }
         }
diff --git a/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java b/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
index d82b57f4078802acd6b4a45e1f46f7ac9c8ba1d6..3c73d81d143ade511a88d2ab46417c7aa09719d8 100644
--- a/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
+++ b/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
@@ -775,7 +775,8 @@ public class CraftEventFactory {
         for (org.bukkit.inventory.ItemStack stack : event.getDrops()) {
             if (stack == null || stack.getType() == Material.AIR || stack.getAmount() == 0) continue;
 
-            world.dropItem(entity.getLocation(), stack);
+            world.dropItem(entity.getLocation(), stack); // Paper - note: dropItem already clones due to this being bukkit -> NMS
+            if (stack instanceof CraftItemStack) stack.setAmount(0); // Paper - destroy this item - if this ever leaks due to game bugs, ensure it doesn't dupe, but don't nuke bukkit stacks of manually added items
         }
 
         return event;