DCM: Duplication Bug

[Turcul]

I have a small modded server on Minecraft version 1.19.2. I have made a custom economy on the server which uses coins from the Dot Coin Mod. Today, myself and some of my friends discovered a huge duplication bug which is based on fps. I will try my best to explain how it works and we also made a small video to showcase the bug.

For the bug to work, you must have a free slot in your action bar. The next step is to put the wallet over the inventory menu, with the coin you want to dupe on top of the free slot in your action bar. All you need to do now is to spam left click. For the bug to work thought, you need to have as few fps as possible. I could not make it work with 80 fps, but it works really well with 30, 15, 5 etc. In the video, my friend limited his fps to 5 with OptiFine.

The bug is really weird and its super easy to replicate. We run the 19.15.3 version and, as I said, we were able to replicate it on both the server and single player. I tried to limit the wallet slots to 0 and to disable it but it still works. Also, here is the link to the presentation video: https://www.youtube.com/watch?v=MYJ7c9b7SW0

[SpaceCat97]

@Turcul I cannot seem to replicate this on the latest version of DCM (20.16.0). Please could you test this and let me know how it goes?

Some further information would be helpful:

• Does this happen on single player?
• What key combo are you using, and what mouse buttons are you clicking?

[Turcul]

I will try to replicate it on 20.16.0 and tell you how it goes.

• It does happen on both singleplayer and multiplayer. But , as i said, it depends on your fps. I have a pretty hard time replicating it because my pc is good, but a friend of mine who plays with 15/20 fps normally can do this without sweating.
• There is no key combo, just spam left click on the coin as is shown in the video.

[Turcul]

I made another short video to show you exactly how the bug works on my server. it seems like the money get duped when you get lag spikes. I can't try the 20.16.0 version of DCM on the server because it runs on 1.19.2. I will come forth with more video evidence after we do some more tests on different versions of the game and the mod.

Here is the video: https://www.youtube.com/watch?v=7CRwQiLOkRQ

[Turcul]

So, i came back with the results of our tests. My friend Shadow (the guy who can replicate this bug without even sweating) made two videos showcasing the bug. One is made on our modpack (MC version 1.19.2), on singleplayer. The second one was made on MC version 1.20.2 with the latest version of DCM (20.16.0), on singleplayer. Also, the only mod we installed for the second test is DCM, so the problem is not caused by another mod in our modpack.

1.19.2 singleplayer test: https://youtu.be/YiYnc9JRilM

1.20.2 singleplayer test: https://youtu.be/qNOm9MM3aQI

We think that the bug is cuased by a weird interaction between the wallet and inventory which dupes the coins when a lagspike occurs. A quick fix may be to make the wallet so that it cannot be placed over the inventory or integrate it directly into the inventory menu.

[SpaceCat97]

This will be fixed in the next release of DCM. I am currently going through backporting the 1.20 version to 1.19