Go-Ethereum EstimateGas Errors

Question

Been struggling in finding a way to estimate gas for calling a function. I was getting the error - Error: VM Exception while processing transaction: revert locally on ganache and getting Error: The execution failed due to an exception. on Kovan.

Here's a sample solidity function:

This is what my code looks like:

sig := []byte("withdraw(address)")
methodID := crypto.Keccak256(sig)[:4]
toAddress := common.HexToAddress(myAddr)
paddedAddress := common.LeftPadBytes(toAddress.Bytes(), 32)

var data []byte
data = append(data, methodID...)
data = append(data, paddedAddress...)

sendTo := common.HexToAddress(myAddress)

callMsg := ethereum.CallMsg{
        From:     Wallet.Address,
        To:       &sendTo,
        Gas:      0,
        GasPrice: big.NewInt(0),
        Value:    big.NewInt(0),
        Data:     data,
}
gasAmount, err := eth.EthClient.EstimateGas(context.Background(), callMsg)

Why am I getting the complaint - Error: VM Exception while processing transaction: revert

Answer 1

Invalid opcode is a generic EVM error, so there is a problem in your transaction.

Are you sure about the to address? I don't think is possible to send transaction to null address (even if you are only make a gas estimation).

Try to set a valid address in to field.

Answer 2

Here's how I managed to solve the problem:

1. Like Dibi91 mentioned, the to address has to be a valid address.
2. Found this way on this PR, refer to the snippet below. https://github.com/ethereum/go-ethereum/pull/15768/files

var iargs []interface{}
iargs = append(iargs, "0x...") //fill out your arguments

input, err := Abi.Pack("withdraw", iargs...)

sendTo := common.HexToAddress(myAddress)

callMsg := ethereum.CallMsg{
        From:     Wallet.Address,
        To:       &sendTo,
        Gas:      0,
        GasPrice: big.NewInt(0),
        Value:    big.NewInt(0),
        Data:     input,
    }
gasLimit, err := eth.EthClient.EstimateGas(context.Background(), callMsg)