is it possible to get gas refunded if a smart contract call fails to complete?

Question

I am using trust wallet, and whilst using a number of exchanges (for example - uniswap, balancer liquidity pool) I have paid gas prices without the exchange actually taking place. Is it possible to get the gas price refunded?

I am using a digital wallet and because of needing to undertake one task on a website and one task in my wallet as i flip between the two, it isn't clear that the trade hasn't completed or that a smart contract call has gone through as you come back to the same page on the wallet asking to agree the contract. Network fees are never defined and so I do not therefore get to boost the amount as i have no control and therefore did not know that i paid multiple times for a single trade to occur or that i paid particularly high gas prices in some cases (and it still didn't go through). Right now network gas prices are crazy (prohibitively high to most people / low level trades)and so it becomes impossible to consider undertaking the same activity again until it's easier to control the value in ethereum I have going out - as right now it isn't in my control other than to simply not agree the contract and not go ahead.

Any help greatly appreciated. (fingers crossed I've used the right terminology in the right places).

I understand similar questions have been asked but I still had to ask as in some cases haven't related to the answer completely.

Thank you

Answer 1

There are a few different scenarios how a transaction can "fail" - depending on what you mean with "fails to complete".

1. The given gas price is too low. In this case the transaction will simply wait until someone agrees to mine it - it might take an hour or a year, depending on when it becomes profitable for a miner to include the transaction. In this case it is possible to replace/cancel the transaction. You can find more info for example here: https://medium.com/@nonseodion/7-easy-steps-to-resolve-cancel-pending-ethereum-transactions-88d7d8bce053

2. The transaction runs out of gas. If you provide too small gas limit there might not be enough gas for the transaction to process completely. In this case the transaction will revert and the gas is spent.

3. The transaction causes an exception. For example if it doesn't meet some requirements of the used smart contracts. In this case the transaction will revert and the gas used until the exception is spent (but the rest is returned).

4. The transaction causes a coding exception. This is quite rare - for example when a smart contract tries to divide by zero. Basically this is a coding bug. In this case the transaction will revert but all gas is spent (as a sort of a punishment).