Paper/nms-patches/InventoryHorseChest.patch

--- a/net/minecraft/server/InventoryHorseChest.java
+++ b/net/minecraft/server/InventoryHorseChest.java
@@ -1,8 +1,60 @@
 package net.minecraft.server;
 
+// CraftBukkit start
+import java.util.List;
+import org.bukkit.craftbukkit.entity.CraftHumanEntity;
+import org.bukkit.entity.HumanEntity;
+// CraftBukkit end
+
 public class InventoryHorseChest extends InventorySubcontainer {
 
     public InventoryHorseChest(String s, int i) {
         super(s, false, i);
     }
+
+    // CraftBukkit start - add fields and methods
+    public List<HumanEntity> transaction = new java.util.ArrayList<HumanEntity>();
+    private EntityHorse horse;
+    private int maxStack = MAX_STACK;
+
+    public InventoryHorseChest(String s, int i, EntityHorse horse) {
+        super(s, false, i, (org.bukkit.craftbukkit.entity.CraftHorse) horse.getBukkitEntity());
+        this.horse = horse;
+    }
+
+    @Override
+    public ItemStack[] getContents() {
+        return this.items;
+    }
+
+    @Override
+    public void onOpen(CraftHumanEntity who) {
+        transaction.add(who);
+    }
+
+    @Override
+    public void onClose(CraftHumanEntity who) {
+        transaction.remove(who);
+    }
+
+    @Override
+    public List<HumanEntity> getViewers() {
+        return transaction;
+    }
+
+    @Override
+    public org.bukkit.inventory.InventoryHolder getOwner() {
+        return (org.bukkit.entity.Horse) this.horse.getBukkitEntity();
+    }
+
+    @Override
+    public void setMaxStackSize(int size) {
+        maxStack = size;
+    }
+
+    @Override
+    public int getMaxStackSize() {
+        return maxStack;
+    }
+    // CraftBukkit end
 }