[1.19.3] EntityJoinLevelEvent Clientside returns Air

[Crimson_Fluff]

Hello All,

Using the EntityJoinLevelEvent event, checking for Item Entities. When an item entity spawns in I notice that Client-side 'Air' is always returned, whereas Server-side the correct item is returned

I feel this is a bug...

[warjort]

Your issue is not something I know a lot about, but I would guess your problem is related to how minecraft sends entity data to the client.

If you look at ServerEntity.sendPairingData() it sends multiple network packets for each entity.

Relevant to your use case are the first 2 packets:

ClientboundAddEntityPacket

ClientboundSetEntityDataPacket

 

The first packet will lead to that event being called, but the itemstack inside an ItemEntity is sent in the 2nd packet.

Until the 2nd packet arrives, the entity will have default values, in your case that is ItemStack.EMPTY (air)

There is no guarantee when the 2nd packet will arrive.

 

Interestingly, Mojang added a new feature to client bound network packets in the latest snapshot

https://www.minecraft.net/en-us/article/minecraft-snapshot-23w03a

Quote

PACKET BUNDLES

Added new delimiter packet to clientbound game protocol

All packets between two delimiters are guaranteed to be processed within same tick

I don't know whether they applied this new feature to entity spawns?

[Crimson_Fluff]

hoping its something Forge can fix. As this seems wrong to get two different results.  Im wondering if previous Forge versions do the same. I might have to do some testing

Its not really important, I do my work Server side, its just something I noticed

[warjort]

I had a look at the 23w03a code and entity spawns packets ARE sent together in the new ClientboundBundlePacket.

It's not clear to me whether it will help with that event, but it will mean any entity tick processing will see a consistent view of the entity in the future.