Go-Ethereum Gas Estimate – How to Properly Estimate Gas Costs of Function Calls with Go-Ethereum and Golang

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I'm attempting to build out a program in golang to model ethereum gas costs of function calls for the smart contracts I write. I've successfully been able to estimate them using ethclient.EstimateGas however the reported gas costs seem incredibly underpriced, anywhere from 22K->24K gas to send tokens, and alter some boolean variables in storage? There is no way that's the correct gas cost. I'm unable to find out how websites like ethgasstation can reliably estimate gas costs, if the costs reported back by go-ethereum library barely even match real world costs?

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I can't tell you why the ethclient.EstimateGas underreports the consumed gas. I remember facing the same problem once and my lazy solution was to multiply whatever it reported by 3.

In order to calculate the correct gas price for a method call, you need the binary EVM code of the contract. Once you have that, you can look up the price of each instruction in the Yellow Paper in Appendix G and H. The hard part of this calculation is, however, that the precise gas cost will depend upon the state of the virtual machine executing the code (the EVM). In order to calculate that correctly, you probably need to simulate the whole virtual machine. And in the general case, the whole Ethereum blockchain, i.e., you need an Ethereum blockchain node.

If you for example call the ERC20 function transfer, you will end up paying at least 21,000 gas just to make the function call and between 10,000 and 40,000 to update the balances and 400 to read the balances plus additional gas to pay for the jump table logic at the beginning of the contract. The amount paid to update each balance (sender and receiver) will depend on whether the address has a balance or not (5,000 gas vs. 20,000 gas for each update) so you need to know the whole state of the virtual machine. In other cases, you would need to know the state of other Ethereum accounts such as balances or deployed smart contracts.

Related Solutions

[Ethereum] How Ethereum estimate the gas for running a contract

Geth does estimate the gas cost of a transaction, but theoretically no one--not geth, not the miners, nor anyone else--can know the gas cost of a transaction before it executed while creating a block. This is because something else could happen in a block before the transaction is executed (or even in the same block), thus changing the result that geth got when it made the estimate. It's even possible that geth made the estimate on a block that didn't even make it into the canonical blockchain.

Which brings the second point. geth gets its estimate by simulating the transaction itself, based on the latest block. There is essentially no other way to do so. This is called the Halting Problem, if you want to look it up, and it's why gas exists in the first place.

However, in most situations, sending the estimate is sufficient. It's even possible, in (IMHO) the majority of situations, to determine how much gas a transaction could ever possibly consume, and then use that.

Gas Estimation – How to Estimate Gas Cost for Smart Contracts

Using Truffle and testrpc. It's actually pretty easy to build a development environment and test different use cases.

For the gas estimation, it's mostly based on Web3 native functions:

You can retrieve the gas price (in wei) using web3.eth.getGasPrice
The function estimateGas will give the gas estimation for a function (with the parameters passed)
Multiply number of gas by gas price to get the gas cost estimation.

For example

var TestContract = artifacts.require("./Test.sol");

// Run unit tests to populate my contract
// ...
// ...

// getGasPrice returns the gas price on the current network
TestContract.web3.eth.getGasPrice(function(error, result){ 
    var gasPrice = Number(result);
    console.log("Gas Price is " + gasPrice + " wei"); // "10000000000000"

    // Get Contract instance
    TestContract.deployed().then(function(instance) {

        // Use the keyword 'estimateGas' after the function name to get the gas estimation for this particular function 
        return instance.giveAwayDividend.estimateGas(1);

    }).then(function(result) {
        var gas = Number(result);

        console.log("gas estimation = " + gas + " units");
        console.log("gas cost estimation = " + (gas * gasPrice) + " wei");
        console.log("gas cost estimation = " + TestContract.web3.fromWei((gas * gasPrice), 'ether') + " ether");
    });
});

Result in my case (private network):

> truffle test
Using network 'test'.

Compiling .\contracts\Migrations.sol...
Compiling .\contracts\Test.sol...

Gas Price is 20000000000 wei
gas estimation = 26794 units
gas cost estimation = 535880000000000 wei
gas cost estimation = 0.00053588 ether

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[Ethereum] How Ethereum estimate the gas for running a contract

Gas Estimation – How to Estimate Gas Cost for Smart Contracts

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