PaperMC/paper-server/patches/sources/net/minecraft/world/InventorySubcontainer.patch

--- a/net/minecraft/world/InventorySubcontainer.java
+++ b/net/minecraft/world/InventorySubcontainer.java
@@ -14,6 +14,12 @@
 import net.minecraft.world.item.Item;
 import net.minecraft.world.item.ItemStack;
 
+// CraftBukkit start
+import org.bukkit.Location;
+import org.bukkit.craftbukkit.entity.CraftHumanEntity;
+import org.bukkit.entity.HumanEntity;
+// CraftBukkit end
+
 public class InventorySubcontainer implements IInventory, AutoRecipeOutput {
 
     private final int size;
@@ -21,7 +27,59 @@
     @Nullable
     private List<IInventoryListener> listeners;
 
+    // CraftBukkit start - add fields and methods
+    public List<HumanEntity> transaction = new java.util.ArrayList<HumanEntity>();
+    private int maxStack = MAX_STACK;
+    protected org.bukkit.inventory.InventoryHolder bukkitOwner;
+
+    public List<ItemStack> getContents() {
+        return this.items;
+    }
+
+    public void onOpen(CraftHumanEntity who) {
+        transaction.add(who);
+    }
+
+    public void onClose(CraftHumanEntity who) {
+        transaction.remove(who);
+    }
+
+    public List<HumanEntity> getViewers() {
+        return transaction;
+    }
+
+    @Override
+    public int getMaxStackSize() {
+        return maxStack;
+    }
+
+    public void setMaxStackSize(int i) {
+        maxStack = i;
+    }
+
+    public org.bukkit.inventory.InventoryHolder getOwner() {
+        return bukkitOwner;
+    }
+
+    @Override
+    public Location getLocation() {
+        return null;
+    }
+
+    public InventorySubcontainer(InventorySubcontainer original) {
+        this(original.size);
+        for (int slot = 0; slot < original.size; slot++) {
+            this.items.set(slot, original.items.get(slot).copy());
+        }
+    }
+
     public InventorySubcontainer(int i) {
+        this(i, null);
+    }
+
+    public InventorySubcontainer(int i, org.bukkit.inventory.InventoryHolder owner) {
+        this.bukkitOwner = owner;
+        // CraftBukkit end
         this.size = i;
         this.items = NonNullList.withSize(i, ItemStack.EMPTY);
     }