Estimating gas cost of function with multiple inputs

Question

I have the contract

pragma solidity ^0.4.11;

contract UserBasic {
    struct Record {
        bytes32 _id;
        address _addedBy;
        uint _dateAdded;
        bytes32 _transactionHash;
        bytes32 _type;
        bytes32 _hash;
        bytes32 _signature;
    }
    // Type to records array
    mapping(bytes32 => bytes32[]) typeRecords;
    // Record ID to record
    mapping(bytes32 => Record) idRecord;
    // Search for record
    function searchRecord(bytes32 _id) constant returns (bytes32, address, uint, bytes32, bytes32, bytes32, bytes32) {
        Record storage temp = idRecord[_id];
        return (temp._id, temp._addedBy, temp._dateAdded, temp._transactionHash, temp._type, temp._hash, temp._signature);
    }
    // Add a record
    function addRecord(bytes32 _type, bytes32 _id) {
        typeRecords[_type].push(_id);
        var _new = Record(_id, tx.origin, now, "", _type, "", "");
        idRecord[_id] = _new;
    }
    // Get all records of a given type
    function getRecordsByType(bytes32 _type) constant returns(bytes32[]) {
        return typeRecords[_type];
    }
}

My addRecord method isn't working (I figure because of gas costs). I wanted to estimate how much gas that method costs but not sure how. This answer explains a way for a function with one parameter but it seems too complex of a process, I was wondering if there is a simpler way.

I'm calling it from node with

function addRecord(publicAddress, contractAddress, _type, _id) {
    const contract = contractInstance("UserBasic", contractAddress);
    // Interaction with the contract
    contract.addRecord(_type, _id, {from: publicAddress}, (err, res) => {
        // Log transaction to explore
        if (err) {
            console.log(err);
        } else {
            console.log('tx: ' + res);
            helpers.addTransaction(publicAddress, res);
        }
    });
}

I read the docs but the only part I don't know is how to convert multiple parameters to data.

Answer 1

If you have the contract address and abi you can estimate the method call directly

const Web3 = require('web3');

const web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"));

const contractAbi = [.....] ;// Contract abi goes here
const contractAddress = "0x....."; // Contract address goes here

const contract = new web3.eth.Contract(contractAbi, contractAddress);


// Estimate gas for:
//     contractInstance.methods.MethodToCalll(param1, param2, param3);
const gas = contract.methods.MethodToCall.estimateGas(param1, param2, param3);

console.log(`Gas estimated: ${gas}`);

Will output something like

Gas estimation: 26818

Answer 2

Data param is a signature of method, In geth, you can run the following command to find the signature of the addRecord(bytes32,bytes32) function:

> web3.sha3("addRecord(bytes32,bytes32)")
"0x3193195597c87745d51912ca6cbef014b04b9d925f94235ee2ed5c1819afb2cb"

And take the first 4 bytes to create the data parameter:

0x319319550000000000000000000000000000000000000000000000000000000000000001

Now you have a data param. Hope it helps~