Add ItemTransportingEntityValidateTargetEvent closes #13114 (#13115)

Author: jpenilla

paper-api/src/main/java/io/papermc/paper/event/entity/ItemTransportingEntityValidateTargetEvent.java

@@ -0,0 +1,71 @@
+package io.papermc.paper.event.entity;
+
+import org.bukkit.block.Block;
+import org.bukkit.entity.CopperGolem;
+import org.bukkit.entity.Entity;
+import org.bukkit.event.HandlerList;
+import org.bukkit.event.entity.EntityEvent;
+import org.jetbrains.annotations.ApiStatus;
+import org.jspecify.annotations.NullMarked;
+
+/**
+ * Called when an item-transporting entity (typically a {@link CopperGolem},
+ * although other entities may be possible through non-API means)
+ * is searching for or validating an existing target container block for
+ * taking or depositing items.
+ *
+ * <p>This may be called multiple times per entity per tick, so listeners
+ * should be careful to implement checks in an efficient manner.</p>
+ */
+@NullMarked
+public class ItemTransportingEntityValidateTargetEvent extends EntityEvent {
+    protected static final HandlerList HANDLER_LIST = new HandlerList();
+
+    private final Block block;
+    private boolean allowed = true;
+
+    @ApiStatus.Internal
+    public ItemTransportingEntityValidateTargetEvent(
+        final Entity entity,
+        final Block block
+    ) {
+        super(entity);
+        this.block = block;
+    }
+
+    /**
+     * Sets if the entity is allowed to use {@link #getBlock()} as a target.
+     *
+     * @param allowed whether the target is allowed
+     */
+    public void setAllowed(boolean allowed) {
+        this.allowed = allowed;
+    }
+
+    /**
+     * Gets if the entity is allowed to use {@link #getBlock()} as a target.
+     *
+     * @return true if the target is allowed
+     */
+    public boolean isAllowed() {
+        return this.allowed;
+    }
+
+    /**
+     * Gets the target block the entity is validating.
+     *
+     * @return the target block
+     */
+    public Block getBlock() {
+        return this.block;
+    }
+
+    public static HandlerList getHandlerList() {
+        return HANDLER_LIST;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return HANDLER_LIST;
+    }
+}

paper-server/patches/sources/net/minecraft/world/entity/ai/behavior/TransportItemsBetweenContainers.java.patch

@@ -0,0 +1,14 @@
+--- a/net/minecraft/world/entity/ai/behavior/TransportItemsBetweenContainers.java
++++ b/net/minecraft/world/entity/ai/behavior/TransportItemsBetweenContainers.java
+@@ -323,7 +_,10 @@
+             } else {
+                 boolean flag1 = this.isWantedBlock(mob, transportItemTarget.state)
+                     && !this.isPositionAlreadyVisited(visited, unreachable, transportItemTarget, level)
+-                    && !this.isContainerLocked(transportItemTarget);
++                    // Paper start - ItemTransportingEntityValidateTargetEvent
++                    && !this.isContainerLocked(transportItemTarget)
++                    && org.bukkit.craftbukkit.event.CraftEventFactory.callTransporterValidateTarget(mob, level, transportItemTarget.pos);
++                    // Paper end - ItemTransportingEntityValidateTargetEvent
+                 return flag1 ? transportItemTarget : null;
+             }
+         }

paper-server/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java

@@ -18,6 +18,7 @@
 import io.papermc.paper.connection.HorriblePlayerLoginEventHack;
 import io.papermc.paper.connection.PlayerConnection;
 import io.papermc.paper.event.connection.PlayerConnectionValidateLoginEvent;
+import io.papermc.paper.event.entity.ItemTransportingEntityValidateTargetEvent;
 import net.minecraft.core.BlockPos;
 import net.minecraft.core.Direction;
 import net.minecraft.network.Connection;
@@ -38,6 +39,7 @@
 import net.minecraft.world.entity.Entity;
 import net.minecraft.world.entity.Leashable;
 import net.minecraft.world.entity.Mob;
+import net.minecraft.world.entity.PathfinderMob;
 import net.minecraft.world.entity.animal.AbstractFish;
 import net.minecraft.world.entity.animal.AbstractGolem;
 import net.minecraft.world.entity.animal.Animal;
@@ -2112,4 +2114,13 @@ public static Component handleLoginResult(PlayerList.LoginResult result, PlayerC
 
         return disconnectReason;
     }
+
+    public static boolean callTransporterValidateTarget(final PathfinderMob mob, final Level level, final BlockPos transportItemTarget) {
+        if (ItemTransportingEntityValidateTargetEvent.getHandlerList().getRegisteredListeners().length == 0) {
+            return true; // No listeners, skip event creation
+        }
+        final ItemTransportingEntityValidateTargetEvent event = new ItemTransportingEntityValidateTargetEvent(mob.getBukkitEntity(), CraftBlock.at(level, transportItemTarget));
+        event.callEvent();
+        return event.isAllowed();
+    }
 }