Paper/nms-patches/TileEntityBarrel.patch

--- a/net/minecraft/server/TileEntityBarrel.java
+++ b/net/minecraft/server/TileEntityBarrel.java
@@ -1,7 +1,55 @@
 package net.minecraft.server;
 
+// CraftBukkit start
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import org.bukkit.Location;
+import org.bukkit.block.Barrel;
+import org.bukkit.block.Lectern;
+import org.bukkit.craftbukkit.block.CraftBlock;
+import org.bukkit.craftbukkit.entity.CraftHumanEntity;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.inventory.InventoryHolder;
+// CraftBukkit end
+
 public class TileEntityBarrel extends TileEntityLootable {
 
+    // CraftBukkit start - add fields and methods
+    public List<HumanEntity> transaction = new ArrayList<>();
+    private int maxStack = MAX_STACK;
+    public boolean opened;
+
+    @Override
+    public List<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 int getMaxStackSize() {
+       return maxStack;
+    }
+
+    @Override
+    public void setMaxStackSize(int i) {
+        maxStack = i;
+    }
+    // CraftBukkit end
     private NonNullList<ItemStack> items;
     private int b;
 
@@ -100,7 +148,7 @@
                 return;
             }
 
-            boolean flag = (Boolean) iblockdata.get(BlockBarrel.b);
+            boolean flag = (Boolean) iblockdata.get(BlockBarrel.b) && !opened; // CraftBukkit - only set flag if Barrel isn't set open by API.
 
             if (flag) {
                 this.playOpenSound(iblockdata, SoundEffects.BLOCK_BARREL_CLOSE);