Validate transaction slots

src/inventory/ArmorInventory.php

@@ -23,8 +23,11 @@
 
 namespace pocketmine\inventory;
 
+use pocketmine\block\BlockTypeIds;
 use pocketmine\entity\Living;
+use pocketmine\item\Armor;
 use pocketmine\item\Item;
+use pocketmine\item\ItemBlock;
 
 class ArmorInventory extends SimpleInventory{
 	public const SLOT_HEAD = 0;
@@ -36,6 +39,14 @@ public function __construct(
 		protected Living $holder
 	){
 		parent::__construct(4);
+
+		$this->validators->add(static function (Inventory $inventory, Item $item, int $slot) : bool{
+			return ($item instanceof Armor && $item->getArmorSlot() === $slot) ||
+				($slot === ArmorInventory::SLOT_HEAD && $item instanceof ItemBlock && (
+						$item->getBlock()->getTypeId() === BlockTypeIds::CARVED_PUMPKIN ||
+						$item->getBlock()->getTypeId() === BlockTypeIds::MOB_HEAD
+					));
+		});
 	}
 
 	public function getHolder() : Living{

src/inventory/BaseInventory.php

@@ -36,8 +36,10 @@
 
 /**
  * This class provides everything needed to implement an inventory, minus the underlying storage system.
+ *
+ * @phpstan-import-type SlotValidators from SlotSafeInventory
  */
-abstract class BaseInventory implements Inventory{
+abstract class BaseInventory implements Inventory, SlotSafeInventory{
 	protected int $maxStackSize = Inventory::MAX_STACK;
 	/** @var Player[] */
 	protected array $viewers = [];
@@ -46,9 +48,12 @@ abstract class BaseInventory implements Inventory{
 	 * @phpstan-var ObjectSet<InventoryListener>
 	 */
 	protected ObjectSet $listeners;
+	/** @phpstan-var SlotValidators */
+	protected ObjectSet $validators;
 
 	public function __construct(){
 		$this->listeners = new ObjectSet();
+		$this->validators = new ObjectSet();
 	}
 
 	public function getMaxStackSize() : int{
@@ -398,4 +403,8 @@ public function slotExists(int $slot) : bool{
 	public function getListeners() : ObjectSet{
 		return $this->listeners;
 	}
+
+	public function getSlotValidators() : ObjectSet{
+		return $this->validators;
+	}
 }

src/inventory/SlotSafeInventory.php

@@ -0,0 +1,46 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+ */
+
+declare(strict_types=1);
+
+namespace pocketmine\inventory;
+
+use pocketmine\item\Item;
+use pocketmine\utils\ObjectSet;
+
+/**
+ * A "slot safe inventory" has validators which may restrict items
+ * from being placed in particular slots of the inventory.
+ *
+ * @phpstan-type SlotValidators ObjectSet<\Closure(Inventory $inventory, Item $item, int $slot): bool>
+ */
+interface SlotSafeInventory{
+	/**
+	 * Returns a set of validators that will be used to determine whether an item can be placed in a particular slot.
+	 * All validators need to return true for the transaction to be allowed.
+	 * If one of the validators returns false, the transaction will be cancelled.
+	 *
+	 * There is no guarantee that the validators will be called in any particular order.
+	 *
+	 * @phpstan-return SlotValidators
+	 */
+	public function getSlotValidators() : ObjectSet;
+}

src/inventory/transaction/action/SlotChangeAction.php

@@ -24,6 +24,7 @@
 namespace pocketmine\inventory\transaction\action;
 
 use pocketmine\inventory\Inventory;
+use pocketmine\inventory\SlotSafeInventory;
 use pocketmine\inventory\transaction\InventoryTransaction;
 use pocketmine\inventory\transaction\TransactionValidationException;
 use pocketmine\item\Item;
@@ -74,6 +75,17 @@ public function validate(Player $source) : void{
 		if($this->targetItem->getCount() > $this->inventory->getMaxStackSize()){
 			throw new TransactionValidationException("Target item exceeds inventory max stack size");
 		}
+		if($this->inventory instanceof SlotSafeInventory && !$this->targetItem->isNull()){
+			foreach($this->inventory->getSlotValidators() as $validator){
+				try{
+					if(!$validator($this->inventory, $this->targetItem, $this->inventorySlot)){
+						throw new TransactionValidationException("Target item is not accepted by the inventory");
+					}
+				}catch(TransactionValidationException $e){
+					throw new TransactionValidationException("Target item is not accepted by the inventory: " . $e->getMessage());
+				}
+			}
+		}
 	}
 
 	/**