EntityMetadata packet and data watchers

[stable mango]

I'd like to change some entity metadata (custom name visible) and send it to only one client using a packet. I'm aware that the packet constructor takes a data watcher object and there is a static field in the Entity.class

My question is how do I get a fresh data watcher? Something like this would actually modify the entity which I don't want:java DataWatcher dw = ((CraftEntity) entity).getHandle().getDataWatcher(); dw.set(...)(oh, and, I've wanted to see how setCustomNameVisible method works, but there's no source code I can see for some reason)

[astral cliff]

DataWatcher? Are you using an ancient version, or not using mojang maps?

[stable mango]

eh, I guess I'm screwed

1.16.5

maybe it's called SynchedEntityData for yall

[astral cliff]

yeah can't you just create a new instance of that?

[stable mango]

it takes the entity as a constructor
wouldn't that make the data watcher modify the entity too?

[astral cliff]

maybe, I'm not sure, but it's worth a try

[stable mango]

I actually managed to pull out the DataWatcher.Item that i'm looking for```java
List<DataWatcher.Item<?>> items = ((CraftLivingEntity) entity).getHandle().getDataWatcher().c(); // .getAll()
if (items != null) {
for (DataWatcher.Item<?> item : items) {
// index 3 is "is custom name visible"
if (item.a().a() == 3) { // item.getAccessor().getId()
// this is unchecked cast, but sure works because entity is LivingEntity
DataWatcher.Item<Boolean> newItem = (DataWatcher.Item<Boolean>) item.d(); // item.copy()
newItem.a(false); // item.setValue(false)

            PacketPlayOutEntityMetadata packet = new PacketPlayOutEntityMetadata();
            FieldUtils.writeField(packet, "a", entity.getEntityId(), true);
            FieldUtils.writeField(packet, "b", List.of(newItem), true);
            ((CraftPlayer) player).getHandle().playerConnection.sendPacket(packet);
            player.sendMessage("Sent packet to hide name for entity " + entity.getEntityId());
            set.remove(entity.getEntityId());
            return;
        }
    }
}```

but yeah I'll try instantiating a new one

do you by any chance know why doesn't the decompiler show code for craftbukkit methods?

  // IntelliJ API Decompiler stub source generated from a class file
  // Implementation of methods is not available```

[astral cliff]

hm it works fine for me

[stable mango]

that's nms

try
org.bukkit.craftbukkit.v1_16_R3.entity.CraftEntity (it's abstract class, but go under setCustomNameVisible and look for implementations)

[astral cliff]

works fine too

[stable mango]

🤨

[astral cliff]

no idea why it doesn't work for you :/

have you tried to disable the mc dev plugin lol

that causes 99% of issues in IJ

[stable mango]

wait i forgot i even have it

(updated to 2023.2 few days ago)

yeah it shows the code now lmao

ty

[stable mango]

anyway I'll try this now and report back

[stable mango]

unfortunately it doesn't hide the custom name

DataWatcherObject<Boolean> dwobj = (DataWatcherObject<Boolean>) FieldUtils.readStaticField(net.minecraft.server.v1_16_R3.Entity.class, "ar");
        
DataWatcher dwNew = new DataWatcher(((CraftLivingEntity) entity).getHandle());
dwNew.register(dwobj, true);
dwNew.set(dwobj, true);
PacketPlayOutEntityMetadata pckt = new PacketPlayOutEntityMetadata(entity.getEntityId(), dwNew, true);
((CraftPlayer) player).getHandle().playerConnection.sendPacket(pckt);
set.add(entity.getEntityId()); // keeps track of which entities'custom names are visible to the player
player.sendMessage("Sent packet to show entity " + entity.getEntityId());```

i'm now trying to get the DataWatcherObject<Boolean> directly from the entity class but struggling with reflection: java.lang.IllegalArgumentException: Cannot locate field ar on class net.minecraft.server.v1_16_R3.Entity

[astral cliff]

hm sorry no clue

[stable mango]

its alright

could you by any chance spot the issue here?

[astral cliff]

in theory... you can ofc always construct the packet from the FriendlyByteBuf

[stable mango]

DataWatcherObject<Boolean> dwobj = (DataWatcherObject<Boolean>) FieldUtils.readStaticField(net.minecraft.server.v1_16_R3.Entity.class, "ar");```

[stable mango]

wait what

[astral cliff]

then check wiki.vg for the actual fields required

[stable mango]

you mean convert bytes into the packet?

[astral cliff]

yeah well, one sec

[stable mango]

that works too

(i was in doubt of that because of encryption and stuff)

[astral cliff]

basiucally this. you'd create a FriendlyByteBuf or whatever it's called, then you write the first field (writeByte(0) for the animation or what's it called), then you write an int for the air ticks, etc. the fourth field is "isCustomNameVisible"

that way you don't need any actual entity data whatsoever

https://wiki.vg/Entity_metadata#Entity_Metadata_Format

ofc that's going to be a bit annoying but this would definitely work

[stable mango]

I don't think it requires all that data, only the field that will be changed

https://wiki.vg/index.php?title=Protocol&oldid=16657#Entity_Metadata
packet ^

[astral cliff]

idk about that, I never used packets this way

[stable mango]

so i believe this would be packet id, then entity id as a varint, then 3 (for that property), then 7 (meaning that it's a boolean), then 1 (probably??) and then 0xff stating it's the end

[stable mango]

it would in theory be faster than datawatcher stuff, no?

how would I get the raw bytes of a packet? (ik each packet has methods for that)

[astral cliff]

actually the opposite seems to be true, the constructor that takes in a bytebuf puts it back together in a List<DataValue>

[stable mango]

yeah, for me I have to use an empty constructor and then call one of these (it's a friendlybytebuf)

it doesn't include the packet id anywhere though

one sec

[astral cliff]

the id is coming from the packet's id() method

you get the whole bytes from a packet through the write(FriendlyByteBuf) method

this

[stable mango]

it's the entity id not packet id

I'm confused

what do I pass to the constructor of FriendlyByteBuf?

[astral cliff]

oh yikes I'm stupid

[stable mango]

it has to be io.netty.ByteBuf and copilot autocompleted to this java new PacketDataSerializer(Unpooled.buffer());

[astral cliff]

the packet ID is extracted in Connection#sendPacket through ConnectionProtocol#getProtocolForPacket

[stable mango]

nvm I found friendly bytebuf has a method to convert to bytearray

[stable mango]

so while the packet serializer won't give me packet length and packet id, I don't need them, right?

[astral cliff]

correct

[stable mango]

okay, i'll now test with protocollib what does the data look like

ah io.netty.handler.codec.DecoderException: ByteArray with size 181 is bigger than allowed 65 at net.minecraft.server.v1_16_R3.PacketDataSerializer.b(PacketDataSerializer.java:101) ~[patched_1.16.5.jar:git-Purpur-1171] at net.minecraft.server.v1_16_R3.PacketDataSerializer.a(PacketDataSerializer.java:94) ~[patched_1.16.5.jar:git-Purpur-1171]``````java PacketDataSerializer friendlybytebuf = new PacketDataSerializer(Unpooled.buffer()); packet.b(friendlybytebuf); String rawPacketData = ABCUtils.bytesToHex(friendlybytebuf.a());I still do believe the problem is in how i'm handling the friendly bytebuf

alright I found out about the existence of ByteBufUtil and got the data of this packet that changes, the bytes 03 07 01 ff are correct, time to get this done now

[stable mango]

thanks, this works beautifully