PaperMC/paper-server/nms-patches/net/minecraft/world/item/ItemArmor.patch

--- a/net/minecraft/world/item/ItemArmor.java
+++ b/net/minecraft/world/item/ItemArmor.java
@@ -28,6 +28,11 @@
 import net.minecraft.world.level.block.BlockDispenser;
 import net.minecraft.world.phys.AxisAlignedBB;
 
+// CraftBukkit start
+import org.bukkit.craftbukkit.inventory.CraftItemStack;
+import org.bukkit.event.block.BlockDispenseArmorEvent;
+// CraftBukkit end
+
 public class ItemArmor extends Item implements ItemWearable {
 
     private static final UUID[] ARMOR_MODIFIER_UUID_PER_SLOT = new UUID[]{UUID.fromString("845DB27C-C624-495F-8C9F-6020A9A58B6B"), UUID.fromString("D8499B04-0E66-4726-AB29-64469D734E0D"), UUID.fromString("9F3D476D-C118-4544-8365-64846904B48E"), UUID.fromString("2AD3F246-FEE1-4E67-B886-69FD380BB150")};
@@ -54,8 +59,34 @@
             EntityLiving entityliving = (EntityLiving) list.get(0);
             EnumItemSlot enumitemslot = EntityInsentient.getEquipmentSlotForItem(itemstack);
             ItemStack itemstack1 = itemstack.cloneAndSubtract(1);
+            // CraftBukkit start
+            World world = isourceblock.getWorld();
+            org.bukkit.block.Block block = world.getWorld().getBlockAt(isourceblock.getBlockPosition().getX(), isourceblock.getBlockPosition().getY(), isourceblock.getBlockPosition().getZ());
+            CraftItemStack craftItem = CraftItemStack.asCraftMirror(itemstack1);
+
+            BlockDispenseArmorEvent event = new BlockDispenseArmorEvent(block, craftItem.clone(), (org.bukkit.craftbukkit.entity.CraftLivingEntity) entityliving.getBukkitEntity());
+            if (!BlockDispenser.eventFired) {
+                world.getCraftServer().getPluginManager().callEvent(event);
+            }
+
+            if (event.isCancelled()) {
+                itemstack.add(1);
+                return false;
+            }
+
+            if (!event.getItem().equals(craftItem)) {
+                itemstack.add(1);
+                // Chain to handler for new item
+                ItemStack eventStack = CraftItemStack.asNMSCopy(event.getItem());
+                IDispenseBehavior idispensebehavior = (IDispenseBehavior) BlockDispenser.DISPENSER_REGISTRY.get(eventStack.getItem());
+                if (idispensebehavior != IDispenseBehavior.NOOP && idispensebehavior != ItemArmor.DISPENSE_ITEM_BEHAVIOR) {
+                    idispensebehavior.dispense(isourceblock, eventStack);
+                    return true;
+                }
+            }
 
-            entityliving.setSlot(enumitemslot, itemstack1);
+            entityliving.setSlot(enumitemslot, CraftItemStack.asNMSCopy(event.getItem()));
+            // CraftBukkit end
             if (entityliving instanceof EntityInsentient) {
                 ((EntityInsentient) entityliving).a(enumitemslot, 2.0F);
                 ((EntityInsentient) entityliving).setPersistent();