Expose IItemHandler on vanilla entities

patches/minecraft/net/minecraft/entity/EntityLivingBase.java.patch

@@ -285,3 +285,38 @@
          }
  
          this.func_184602_cy();
+@@ -2626,4 +2707,34 @@
+     {
+         return true;
+     }
++
++    // FORGE
++    private final net.minecraftforge.items.IItemHandlerModifiable handHandler = new net.minecraftforge.items.ItemStackHandler(field_184630_bs);
++    private final net.minecraftforge.items.IItemHandlerModifiable armorHandler = new net.minecraftforge.items.ItemStackHandler(field_184631_bt);
++    private final net.minecraftforge.items.IItemHandler joinedHandler = new net.minecraftforge.items.wrapper.CombinedInvWrapper(armorHandler, handHandler);
++
++    @Override
++    public <T> T getCapability(net.minecraftforge.common.capabilities.Capability<T> capability, net.minecraft.util.EnumFacing facing)
++    {
++        if (capability == net.minecraftforge.items.CapabilityItemHandler.ITEM_HANDLER_CAPABILITY)
++        {
++            if (facing == net.minecraft.util.EnumFacing.UP)
++            {
++                return (T) armorHandler;
++            } else if (facing.func_176740_k().func_176722_c())
++            {
++                return (T) handHandler;
++            } else
++            {
++                return (T) joinedHandler;
++            }
++        }
++        return super.getCapability(capability, facing);
++    }
++
++    @Override
++    public boolean hasCapability(net.minecraftforge.common.capabilities.Capability<?> capability, net.minecraft.util.EnumFacing facing)
++    {
++        return capability == net.minecraftforge.items.CapabilityItemHandler.ITEM_HANDLER_CAPABILITY || super.hasCapability(capability, facing);
++    }
+ }

patches/minecraft/net/minecraft/entity/passive/EntityHorse.java.patch

@@ -1,6 +1,14 @@
 --- ../src-base/minecraft/net/minecraft/entity/passive/EntityHorse.java
 +++ ../src-work/minecraft/net/minecraft/entity/passive/EntityHorse.java
-@@ -1200,6 +1200,7 @@
+@@ -433,6 +433,7 @@
+ 
+         this.field_110296_bG.func_110134_a(this);
+         this.func_110232_cE();
++        this.itemHandler = new net.minecraftforge.items.wrapper.InvWrapper(this.field_110296_bG);
+     }
+ 
+     private void func_110232_cE()
+@@ -1200,6 +1201,7 @@
                  }
  
                  this.field_110277_bt = 0.0F;
@@ -8,3 +16,29 @@
              }
  
              this.field_70138_W = 1.0F;
+@@ -1793,4 +1795,25 @@
+                 this.field_188477_b = p_i46589_2_;
+             }
+         }
++
++    // FORGE
++    private net.minecraftforge.items.IItemHandler itemHandler = null; // Initialized by initHorseChest above.
++
++    @Override
++    public <T> T getCapability(net.minecraftforge.common.capabilities.Capability<T> capability, net.minecraft.util.EnumFacing facing)
++    {
++        if (capability == net.minecraftforge.items.CapabilityItemHandler.ITEM_HANDLER_CAPABILITY
++                && itemHandler != null)
++        {
++            return (T) itemHandler;
++        }
++        return super.getCapability(capability, facing);
++    }
++
++    @Override
++    public boolean hasCapability(net.minecraftforge.common.capabilities.Capability<?> capability, net.minecraft.util.EnumFacing facing)
++    {
++        return capability == net.minecraftforge.items.CapabilityItemHandler.ITEM_HANDLER_CAPABILITY && itemHandler != null
++                || super.hasCapability(capability, facing);
++    }
+ }

patches/minecraft/net/minecraft/entity/player/EntityPlayer.java.patch

@@ -401,7 +401,7 @@
  
          if (this.func_70608_bn())
          {
-@@ -2340,6 +2447,136 @@
+@@ -2340,6 +2447,169 @@
          return (float)this.func_110148_a(SharedMonsterAttributes.field_188792_h).func_111126_e();
      }
  
@@ -533,6 +533,39 @@
 +    public java.util.Collection<ITextComponent> getPrefixes() { return this.prefixes; }
 +    public java.util.Collection<ITextComponent> getSuffixes() { return this.suffixes; }
 +
++    private final net.minecraftforge.items.IItemHandler playerMainHandler = new net.minecraftforge.items.wrapper.PlayerMainInvWrapper(field_71071_by);
++    private final net.minecraftforge.items.IItemHandler playerArmorHandler = new net.minecraftforge.items.wrapper.PlayerArmorInvWrapper(field_71071_by);
++    private final net.minecraftforge.items.IItemHandler playerOffhandHandler = new net.minecraftforge.items.wrapper.PlayerOffhandInvWrapper(field_71071_by);
++    private final net.minecraftforge.items.IItemHandler playerJoinedHandler = new net.minecraftforge.items.wrapper.PlayerInvWrapper(field_71071_by);
++
++    @Override
++    public <T> T getCapability(net.minecraftforge.common.capabilities.Capability<T> capability, net.minecraft.util.EnumFacing facing)
++    {
++        if (capability == net.minecraftforge.items.CapabilityItemHandler.ITEM_HANDLER_CAPABILITY)
++        {
++            if (facing == net.minecraft.util.EnumFacing.UP)
++            {
++                return (T) playerArmorHandler;
++            } else if (facing == net.minecraft.util.EnumFacing.DOWN)
++            {
++                return (T) playerMainHandler;
++            } else if (facing.func_176740_k().func_176722_c())
++            {
++                return (T) playerOffhandHandler;
++            } else
++            {
++                return (T) playerJoinedHandler;
++            }
++        }
++        return super.getCapability(capability, facing);
++    }
++
++    @Override
++    public boolean hasCapability(net.minecraftforge.common.capabilities.Capability<?> capability, net.minecraft.util.EnumFacing facing)
++    {
++        return capability == net.minecraftforge.items.CapabilityItemHandler.ITEM_HANDLER_CAPABILITY || super.hasCapability(capability, facing);
++    }
++
 +    /* ======================================== FORGE END  =====================================*/
 +
      public static enum EnumChatVisibility

src/main/java/net/minecraftforge/items/ItemStackHandler.java

@@ -20,6 +20,11 @@ public class ItemStackHandler implements IItemHandler, IItemHandlerModifiable, I
         stacks = new ItemStack[size];
     }
 
+    public ItemStackHandler(ItemStack[] stacks)
+    {
+        this.stacks = stacks;
+    }
+
     public void setSize(int size)
     {
         stacks = new ItemStack[size];

src/main/java/net/minecraftforge/items/wrapper/PlayerArmorInvWrapper.java

@@ -7,7 +7,7 @@ import net.minecraft.item.ItemStack;
 public class PlayerArmorInvWrapper extends InvWrapper
 {
     public final InventoryPlayer inventoryPlayer;
-    public final int offset;
+    private final int offset;
 
     public PlayerArmorInvWrapper(InventoryPlayer inv)
     {

src/main/java/net/minecraftforge/items/wrapper/PlayerInvWrapper.java

@@ -6,6 +6,6 @@ public class PlayerInvWrapper extends CombinedInvWrapper
 {
     public PlayerInvWrapper(InventoryPlayer inv)
     {
-        super(new PlayerMainInvWrapper(inv), new PlayerArmorInvWrapper(inv));
+        super(new PlayerMainInvWrapper(inv), new PlayerArmorInvWrapper(inv), new PlayerOffhandInvWrapper(inv));
     }
 }

src/main/java/net/minecraftforge/items/wrapper/PlayerMainInvWrapper.java

@@ -10,7 +10,6 @@ import net.minecraft.item.ItemStack;
  */
 public class PlayerMainInvWrapper extends InvWrapper
 {
-
     public final InventoryPlayer inventoryPlayer;
 
     public PlayerMainInvWrapper(InventoryPlayer inv)
@@ -29,7 +28,7 @@ public class PlayerMainInvWrapper extends InvWrapper
     @Override
     public void setStackInSlot(int slot, ItemStack stack)
     {
-        // prevent setting of armor inventory
+        // prevent setting of armor and offhand
         if (slot > getSlots())
         {
             return;
@@ -40,7 +39,7 @@ public class PlayerMainInvWrapper extends InvWrapper
     @Override
     public ItemStack getStackInSlot(int slot)
     {
-        // prevent getting of armor inventory
+        // prevent getting of armor and offhand
         if (slot > getSlots())
         {
             return null;
@@ -51,7 +50,7 @@ public class PlayerMainInvWrapper extends InvWrapper
     @Override
     public ItemStack insertItem(int slot, ItemStack stack, boolean simulate)
     {
-        // prevent inserting into armor inventory
+        // prevent inserting into armor and offhand
         if (slot > getSlots())
         {
             return stack;
@@ -79,7 +78,7 @@ public class PlayerMainInvWrapper extends InvWrapper
     @Override
     public ItemStack extractItem(int slot, int amount, boolean simulate)
     {
-        // prevent extraction from armor inventory
+        // prevent extraction from armor and offhand
         if (slot > getSlots())
         {
             return null;

src/main/java/net/minecraftforge/items/wrapper/PlayerOffhandInvWrapper.java

@@ -0,0 +1,49 @@
+package net.minecraftforge.items.wrapper;
+
+import net.minecraft.entity.player.InventoryPlayer;
+import net.minecraft.item.ItemStack;
+
+public class PlayerOffhandInvWrapper extends InvWrapper
+{
+    public final InventoryPlayer inventoryPlayer;
+    private final int offset;
+
+    public PlayerOffhandInvWrapper(InventoryPlayer inv)
+    {
+        super(inv);
+
+        inventoryPlayer = inv;
+        offset = inventoryPlayer.mainInventory.length + inventoryPlayer.armorInventory.length;
+    }
+
+    @Override
+    public int getSlots()
+    {
+        return inventoryPlayer.offHandInventory.length;
+    }
+
+    @Override
+    public ItemStack getStackInSlot(int slot)
+    {
+        return super.getStackInSlot(slot + offset);
+    }
+
+    @Override
+    public ItemStack insertItem(int slot, ItemStack stack, boolean simulate)
+    {
+        return super.insertItem(slot + offset, stack, simulate);
+    }
+
+    @Override
+    public void setStackInSlot(int slot, ItemStack stack)
+    {
+        super.setStackInSlot(slot + offset, stack);
+    }
+
+    @Override
+    public ItemStack extractItem(int slot, int amount, boolean simulate)
+    {
+        return super.extractItem(slot + offset, amount, simulate);
+    }
+
+}