solidity – Is Gas Fee Refunded if Transaction Fails?

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I'm confusing the rule of paying gas fee when caller makes a transaction.

The gas fee is needed when the transaction is made and I know that the require() is the guard function that returns all the gas fee to the caller.

Is the gas fee paid after all operations in the function in the smart contract?

Then, if the require() function is placed at the start of the function and the codes aren't operated at all, does that mean no gas fee is needed?

And what if the value in that require() statement is false condition and the transaction therefore fails?

Is the gas fee 100% refunded to the caller or does the caller have to pay a remaining gas fee after some operations in the function worked?

Can the caller be refunded all gas?

function burn(uint256 _value) public returns (bool success) {
    require(balances[msg.sender] >= _value);
    balances[msg.sender] = balances[msg.sender].sub(_value);
    totalSupply = totalSupply.sub(_value);
    Burn(msg.sender, _value);
    return true;
}

If the gas fee has to be paid after the code has been executed, what happens if caller(msg.sender) can not pay the gas fee because caller's account has no balance after the require () conditional pass?

I doubt that I know right.

Best Answer

The gas has to be supplied with the signed transaction. The contract function cannot be called unless gas is supplied. There is no way to overdraw the account. It's like the fuel in your car. You need some to get started, and if there is enough, you will make it to your destination. If there is not enough, everything stops.

Source code is compiled into assembly code and any time something is happening, OPCODES are being used. Gas is charged for the OPCODES, as it's used, so even if the first line is a require() and it's false, it still took a lot of OPCODES to unpack the transaction data and evaluate the require() - so some gas got burned.

If gas is returned to the signer, it's the remaining gas. This is like filling your tank, then aborting your trip. You maybe burned some while the engine was running but you still have most of it.

If a lot of processing unfolds before the abortive operation that reverts everything, it's possible most of the gas was used up.

Hope it helps.

Related Solutions

[Ethereum] Token transfer: Intrinsic gas too low

I suspect that your issue is because you have not approved the transfer required to call transferFrom(...).

Here are the relevant functions:

    /* Send coins */
    function transfer(address _to, uint256 _value) {
        if (balanceOf[msg.sender] < _value) throw;           // Check if the sender has enough
        if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows
        balanceOf[msg.sender] -= _value;                     // Subtract from the sender
        balanceOf[_to] += _value;                            // Add the same to the recipient
        Transfer(msg.sender, _to, _value);                   // Notify anyone listening that this transfer took place
    }

    /* Allow another contract to spend some tokens in your behalf */
    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        tokenRecipient spender = tokenRecipient(_spender);
        spender.receiveApproval(msg.sender, _value, this, _extraData);
        return true;
    }

    /* A contract attempts to get the coins */
    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
        if (balanceOf[_from] < _value) throw;                 // Check if the sender has enough
        if (balanceOf[_to] + _value < balanceOf[_to]) throw;  // Check for overflows
        if (_value > allowance[_from][msg.sender]) throw;   // Check allowance
        balanceOf[_from] -= _value;                          // Subtract from the sender
        balanceOf[_to] += _value;                            // Add the same to the recipient
        allowance[_from][msg.sender] -= _value;
        Transfer(_from, _to, _value);
        return true;
    }

If you are the current owner of the tokens, you can call transfer(...) to transfer your balance to another address.

However if you want to transfer from another address, you will need to call transferFrom(...) which will check the allowance[...][...] data structure to confirm whether this transfer has been approved.

So, call approveAndCall(...) first to approve your transfer and you should be able to call transferFrom(...) to transfer your tokens.

When you call transferFrom(...) without first calling approveAndCall(...), and error is thrown in the line

if (_value > allowance[_from][msg.sender]) throw;   // Check allowance

This error will appear as an Out Of Gas error in the Ethereum Wallet.

If you are comfortable using geth, see How can the transaction status from a thrown error be detected when gas can be exactly the same as the gasUsed for a successful transaction? for the following code that can be used to check the exact reason for your error:

> var status = debug.traceTransaction("0xd23219e2ea10528b245deb9e47993cae2ffd3ffe9fc27aeb808e94fc4e75d37b")
undefined
> if (status.structLogs.length > 0) {
  console.log(status.structLogs[status.structLogs.length-1].error)
}
"invalid jump destination (PUSH1) 2"

Smart Contract Costs – Who Gets Paid in Smart Contract Function Calls?

A specifies a gas price.

M1 and M2 decide whether to mine A's transaction if the gas price is high enough. If A's gas price was 1.5 GWei/gas, then only M1 would choose to mine A's transaction (since M2 wants 2 GWei/gas).

A always pays 1000 (given F costs 1,000 gas) multiplied by the gas price it specified; miners cannot change the transaction fee A pays and can only choose whether to include A's transaction in a block.

Only the winning miner gets the transaction fee paid by A. Other miners and all other (full) nodes do have to verify the transaction and store its results: yes, it's unfair to them and part of the problem related to incentives and scalability.

More information, https://blog.ethereum.org/2014/02/01/on-transaction-fees-and-the-fallacy-of-market-based-solutions

For each individual transaction that a miner includes, the costs are borne not just by that miner, but by every single node in the entire network.

Best Answer

Related Solutions

[Ethereum] Token transfer: Intrinsic gas too low

Smart Contract Costs – Who Gets Paid in Smart Contract Function Calls?

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