chore(frontend): add TODO for ERC20 token conversion issue for approval

[AntonioVentilii-DFINITY]

Context

A partner encountered an issue not specific to Oisy, but somehow can be food for thought for improvement.

It may happen that after the approval transaction is done, the transfer transaction may fail for whatever reasons. In this case, the next approval transaction will be rejected, since there is already an approved amount. So, the next transfer transaction will work only if the amount is below the one already approved. Otherwise, the user is blocked until it consumes all the approved amount.

Example

1. The user wants to convert 10 USDT to ckUSDT:
   1. approve transaction for 10 USDT --> successful
   2. transfer_from transaction for 10 USDT --> failed (for whatever reason)
2. The user wants to convert 20 USDT to ckUSDT:
   1. approve transaction for 20 USDT --> failed (the previous approved amount is still there)
   2. transfer_from transaction for 20 USDT --> failed (not enough approved amount)
3. The user wants to convert 7 USDT to ckUSDT:
   1. approve transaction for 7 USDT --> failed (the previous approved amount is still there)
   2. transfer_from transaction for 7 USDT --> successful (remaining approved amount is 3 USDT)

Practical example

We had a practical example with USDT. Please check the sender wallet transaction history backwards from this one: https://etherscan.io/tx/0x084432404a919c1ee720c906bb5c7a565b6e1fdcd5bb9da32049dddfa21ad23f

[peterpeterparker]

Instead of resetting, couldn't we potentially know if the spender is already entitled to spend the amount and skip the approval if it's the case?

I guess this has been discussed with cross-chain team?

[AntonioVentilii-DFINITY]

yes, correct, we could query the allowance endpoint of the ERC20 to check. For example:

Case 1:

• query allowance
• no amount approved --> ask for approval

Case 2:

• query allowance
• old amount approved --> reset amount
• ask for new approval

That what you mean?

[peterpeterparker]

No, I mean:

Case 3:

• query allowance
• is allowance still valid?
• yes, do stuffs
• no, ask for new approval, do stuffs

Would that be possible ? I really don't know, just a question.

[AntonioVentilii-DFINITY]

ah! understood! well, it is possible only if the allowance is greater or equal that the current amount that the user requested;

we can check that, and if it is still ok, we can use that for sure, yes; otherwise we reset

[peterpeterparker]

Cool. Can you extend the TODO accordingly if this is a potential solution too?