Hide unnecessary itemmeta from clients (#6318)

Co-authored-by: Nassim Jahnke <jahnke.nassim@gmail.com>
Co-authored-by: Jake Potrebic <jake.m.potrebic@gmail.com>

LICENSE.md

@@ -48,4 +48,5 @@ Bjarne Koll <lynxplay101@gmail.com>
 MeFisto94 <MeFisto94@users.noreply.github.com>
 Owen1212055 <23108066+Owen1212055@users.noreply.github.com>
 LemonCaramel <admin@caramel.moe>
+Noah van der Aa <ndvdaa@gmail.com>
 ```

patches/server/0815-Hide-unnecessary-itemmeta-from-clients.patch

@@ -0,0 +1,100 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Noah van der Aa <ndvdaa@gmail.com>
+Date: Tue, 3 Aug 2021 17:28:27 +0200
+Subject: [PATCH] Hide unnecessary itemmeta from clients
+
+
+diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+index b64fbce003c00a6371a849d4835632c18ad730bb..7e2d31737bd4977c9589541e1ebdcfe4ac40a335 100644
+--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
++++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+@@ -912,6 +912,13 @@ public class PaperWorldConfig {
+         behaviorTickRates = loadTickRates("behavior");
+     }
+ 
++    public boolean hideItemmetaFromClients = true;
++    public boolean hideDurabilityFromClients = false;
++    private void getHideItemmetaFromClients() {
++        hideItemmetaFromClients = getBoolean("anticheat.obfuscation.items.hide-itemmeta", hideItemmetaFromClients);
++        hideDurabilityFromClients = getBoolean("anticheat.obfuscation.items.hide-durability", hideDurabilityFromClients);
++    }
++
+     private com.google.common.collect.Table<String, String, Integer> loadTickRates(String type) {
+         log("  " + type + ":");
+         com.google.common.collect.Table<String, String, Integer> table = com.google.common.collect.HashBasedTable.create();
+diff --git a/src/main/java/net/minecraft/network/syncher/EntityDataSerializers.java b/src/main/java/net/minecraft/network/syncher/EntityDataSerializers.java
+index 3eb6bf4258b1de4697f96c2011df493cf7414a0c..0feadee6077dd6a8d8fd05b7a7d15ec1aa728fbb 100644
+--- a/src/main/java/net/minecraft/network/syncher/EntityDataSerializers.java
++++ b/src/main/java/net/minecraft/network/syncher/EntityDataSerializers.java
+@@ -127,6 +127,7 @@ public class EntityDataSerializers {
+     public static final EntityDataSerializer<ItemStack> ITEM_STACK = new EntityDataSerializer<ItemStack>() {
+         @Override
+         public void write(FriendlyByteBuf buf, ItemStack value) {
++            net.minecraft.world.entity.LivingEntity.stripMeta(value, null); // Paper - strip items to prevent oversized data
+             buf.writeItem(value);
+         }
+ 
+diff --git a/src/main/java/net/minecraft/world/entity/LivingEntity.java b/src/main/java/net/minecraft/world/entity/LivingEntity.java
+index 62daf918d4ab00963041ca869ae718f14f2e3337..50d0280f3df59952d682f137197fd73644ba2cfe 100644
+--- a/src/main/java/net/minecraft/world/entity/LivingEntity.java
++++ b/src/main/java/net/minecraft/world/entity/LivingEntity.java
+@@ -3047,11 +3047,59 @@ public abstract class LivingEntity extends Entity {
+ 
+     }
+ 
++    public static void stripMeta(ItemStack itemStack, @org.jetbrains.annotations.Nullable Level level) {
++        if (itemStack.getTag() != null) {
++            CompoundTag nbt = itemStack.getTag();
++            if (level != null && level.paperConfig.hideDurabilityFromClients) {
++                // Only show damage values for elytra's, since they show a different texture when broken.
++                if (!itemStack.is(Items.ELYTRA) || itemStack.getDamageValue() < itemStack.getMaxDamage() - 1) {
++                    itemStack.setDamageValue(0);
++                }
++            }
++
++            if (level != null && level.paperConfig.hideItemmetaFromClients) {
++                // Some resource packs show different textures when there is more than one item. Since this shouldn't provide a big advantage,
++                // we'll tell the client if there's one or (more than) two items.
++                itemStack.setCount(itemStack.getCount() > 1 ? 2 : 1);
++                // We can't just strip out display, leather helmets still use the display.color tag.
++                if (nbt.get("display") instanceof CompoundTag displayTag) {
++                    displayTag.remove("Lore");
++                    displayTag.remove("Name");
++                }
++
++                if (nbt.get("Enchantments") instanceof ListTag enchantmentsTag && !enchantmentsTag.isEmpty()) {
++                    // The client still renders items with the enchantment glow if the enchantments tag contains at least one (empty) child.
++                    ListTag enchantments = new ListTag();
++                    enchantments.add(new CompoundTag());
++                    nbt.put("Enchantments", enchantments);
++                }
++                nbt.remove("AttributeModifiers");
++            }
++            // Always remove items to prevent oversized data
++            // Bundles change their texture based on their fullness.
++            if (itemStack.is(Items.BUNDLE) && nbt.get("Items") instanceof ListTag oldItems && !oldItems.isEmpty()) {
++                org.bukkit.inventory.meta.BundleMeta bundleMeta = (org.bukkit.inventory.meta.BundleMeta) itemStack.asBukkitMirror().getItemMeta();
++                int sizeUsed = 0;
++                for (org.bukkit.inventory.ItemStack item : bundleMeta.getItems()) {
++                    int scale = 64 / item.getMaxStackSize();
++                    sizeUsed += scale * item.getAmount();
++                }
++                // Now we add a single fake item that uses the same amount of slots as all other items.
++                ListTag items = new ListTag();
++                items.add(new ItemStack(Items.PAPER, sizeUsed).save(new CompoundTag()));
++                nbt.put("Items", items);
++            }
++            nbt.remove("BlockEntityTag");
++            nbt.remove("EntityTag");
++        }
++    }
++
+     private void handleEquipmentChanges(Map<EquipmentSlot, ItemStack> equipmentChanges) {
+         List<Pair<EquipmentSlot, ItemStack>> list = Lists.newArrayListWithCapacity(equipmentChanges.size());
+ 
+         equipmentChanges.forEach((enumitemslot, itemstack) -> {
+             ItemStack itemstack1 = itemstack.copy();
++            stripMeta(itemstack1, this.level); // Paper - hide unnecessary itemmeta from clients
+ 
+             list.add(Pair.of(enumitemslot, itemstack1));
+             switch (enumitemslot.getType()) {