[MC-250954] Player is assigned a new UUID in singleplayer

In the latest snapshot (22w17a) players are assigned a new UUID in singleplayer worlds. All things relating to the UUID are lost in this snapshot, including but not limited to Skins, Statistics, and Advancements

This can be confirmed by creating a world in 22w16a/22w16b, and then loading the same world in 22w17a. Checking the stats folder in the world folder will display two UUIDs despite it being the same player.

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Comments 17

Eometheous 2022-04-27T18:08:08Z

Looking at the JSON files in the stats folder, I can confirm that a new file was created and my statistics were reset. I can also see a new file was created in the advancements folder, resetting the advancements for my character.

I didn't know skins and multiplayer inventories were linked to your UUID. In singleplayer, I kept my inventory items, so I'd think this would be the same in multiplayer. Aren't the items in players inventory saved in their NBT data?

Flightning99 2022-04-27T18:16:44Z

I could be entirely wrong, but the world's inventory is used in single player. Everyone who uses a world download will have the same inventory, even if they had previously joined the world as a player on a server.

Eometheous 2022-04-27T18:20:42Z

One thing I just learned is that your ID is linked to your account when it is created. So that means that it is the same on every world, regardless on if it's singeplayer or multiplayer. This must be a huge issue then.

I wonder if this bug was caused by the new multiplayer secure chat signing added in this snapshot.

Eometheous 2022-04-27T18:27:03Z

I believe you can see what your ID is supposed to be in launcher_accounts.json
It is located in the .minecraft folder.

Eometheous 2022-04-27T18:44:26Z

You can see in the screenshots below that the ID is not what it is supposed to be. You can see the correct ID for me in 22w16b, and then the incorrect one above it in 22w17a.

[media]

I crossed out most of the ID incase this is private information that shouldn't be shared.

7 more comments

Mesa3D 2022-04-27T18:46:28Z

Can reproduce this and it seems to be one of the biggest problems since then all player data gets completely swapped to a first-time player save including blank copies of ender chest containers.

Eometheous 2022-04-27T18:56:11Z

@Mesa3D, I just tested and my inventory items and ender chest items were still present in 22w17a after updating a test world from 22w16b. I believe all inventory and enderchest items are saved in the players NBT data. I don't have a multiplayer server to test on however, so I'm not sure if this is still the case on servers.

the404 2022-04-27T19:09:52Z

I've tested this snapshot with a server, and it seems like the bug is only present in singleplayer.
Compare the UUIDs of my playerdata in multiplayer (left), and singleplayer (right), and the correct UUID shown below from launcher_accounts.json

[media]

Eometheous 2022-04-27T19:12:13Z

Hey! So I just created a minecraft server using the server jar from 22w16b. I joined it and gave myself operator to give my self a few items. I then put some of the items in an ender chest and kept some in my inventory. I left the server and closed it. I then downloaded the 22w17a server jar and ran that server jar using the with the same world. I joined it and I still had my custom skin, items in my inventory, and items in my ender chest, statistics, and advancements.

So! This bug only happens in singleplayer.

Eometheous 2022-04-27T19:20:41Z

@the404, looks like you beat me. I didn't refresh this page so I didn't see your comment when I made my post.

Earthcomputer 2022-04-27T19:50:40Z

(for future reference, your UUID isn't private information, you can see other players' UUIDs when hovering over their name in chat, and there are websites where you can look up a player's UUID by their username).

TeamArvv 2022-04-27T20:09:18Z

Jumping in:

THIS is a feature. It is suppose to replace the UUID's with new ones.

This might reset progress, but it is a feature.

ampolive 2022-04-27T20:11:36Z

@unknown Do you have a source?

Jean Dubois 2022-04-27T22:03:54Z

@unknown If it's true, the bug is in the update from the old UUIDs to the new ones 🙂

JT Knobel-Piehl 2022-04-28T08:27:09Z

This is likely related to the following changes from the patch notes:

Chat messages between players are now cryptographically signed.
Players are given a Mojang provided key-pair on startup.
Servers can require players to have a Mojang-signed public key by setting enforce-secure-profile=true in server.properties.
Enforcing secure profiles will prevent players without a Mojang-signed public key from connecting.
By default this is set to false, allowing players to connect without a Mojang-signed public key.

There is nothing in the patch notes that suggests that the UUID change or its consequences are a feature or in any way intended.

Tokes 2022-04-30T22:15:36Z

Also if it was intended it would be affecting multiplayer-only, not singleplayer-only.

Flightning99 2022-04-30T22:27:39Z

@Tokes Luckily the issue has already been labelled as resolved. We'll just have to see how it was handled in 22w18a, for if it was intentional or a complete accident