Item duplication through dragging

[Supersonic159]

Describe the bug
Item A replaces item B and inherits the stack number. Duplicating item A.

To Reproduce
Steps to reproduce the behavior:
Take item A (quantity 10), drag it over item B (quantity 7), place it, item B is now gone, you now have two stacks of item A (10 and 7). Item A replaces item B and inherits the stack number.

Screenshots

[abitofBaileys]

The dupe brought another issue to light: integer underflowing, which makes you able to get a stack of 65,486 items of your choice. Furthermore, you can transfer that stack beyond the Item Bag Stack Maximum (IBSM) to your Storage, allowing you to mass sell the item at 999 times per sell transaction.

Steps to reproduce

1. Get an item with a high IBSM (e.g. kindlings at 99)
   
2. Get a 2nd item with a low IBSM and high sell value (e. g. Cure-All)
   
3. Drag the item with the low IBSM over the one with the high IBSM and swap them
   
4. You now have a duped item
   
5. Discard the original low IBSM stack completely
   
6. You now have 65486 (displayed number) of the duped item.
   
7. Access your Storage Box, send 1 of the original low IBSM stack to your left box
   
8. Send the duped item to the left box (the image is not accurate in numbers here, this is the 65k+ one)
   
9. Send the duped item in the left box back to the right box (image not accurate in numbers, this should be 11)
   
10. You now have the 65k+ stack in your Storage Box.
    
11. Shift select the whole stack in your Storage Box, select Sell, confirm, repeat xN. Once depleted, the stack will fill back to 65k+ again.
    

[abitofBaileys]

Attempting to provide more information what happens on client and what on server side. Relogs done after every step:

Initial dupe using 99 kindlings and 1 Miracle Cure (See step 4 above), after relog

You end up with 2 stacks with 10 of each

After discarding (step 5), before relog

After discarding, after relog

After sending 1 of the original low IBSM stack to your left box (step 7), before relog

Yes, the 1 gets subtracted from the DUPED item, not the original item. Possible memory pointer issue.

After sending, after relog

After sending duped to left box + back (steps 8+), before relog

After sending, after relog

After selling the storage box stack (step 11), before relog

After selling, after relog

Further testing, using an already duped stack

After relog

After selling 999 pieces, before relog

After selling, after relog

We can assume that most of this issue happens on the client side and at various points bypasses server side validation. When doing the integer underflow, the server (allegedly) accepts that invalid stack number. After relogging, the 999 stack size is purely visual and 999 is likely set when the client initializes the game and/or storage, despite the stack size being negative (and thus, much higher).

The initial dupe still happens (steps 1-4)

Server-side: Both stacks are (allegedly) set to the IBSM of the duped item
Client-side: Miscalculation or wrong memory pointer issue

Discarding the original IBSM item (steps 5-6)

Server-side: Both stacks are still set to ISBM
Client-side: (allegedly) adds half a stack to the duped item. Can hint at said memory pointer issue.

[alborrajo]

Fixed in PR #284