Send Entire Balance

Question

web3 = new Web3(new Web3.providers.HttpProvider("https://kovan.infura.io/"));

router.post('/sendEth', (req, res) => {

    var fromaddress = req.body._fromaddress;
    var amount = req.body._amount;
    var privatekey = req.body._privatekey;
    var toAddress = req.body._toAddress;

    // Step 1
    var payloadData = web3.toHex(web3.toWei(amount, 'ether'));
    var transactionObject = {
        'from': fromaddress,
        'to': toAddress,
        'value': payloadData
    }
    gasLimit = web3.eth.estimateGas(transactionObject);

    // Step 2
    gasPrice = web3.eth.gasPrice;
    totalGas = gasPrice * gasLimit;

    var amountToSend = web3.toWei(amount, 'ether') - totalGas;

    payloadData = web3.toHex(amountToSend);
    gasPriceHex = web3.toHex(gasPrice);
    gasLimitHex = web3.toHex(gasLimit);


    nonce = web3.eth.getTransactionCount(fromaddress, "pending");
    nonceHex = web3.toHex(nonce);

    var rawTx = {
        nonce: nonceHex,
        gasPrice: gasPriceHex,
        gasLimit: gasLimitHex,
        to: toAddress,
        from: fromaddress,
        value: payloadData,
        data: '0x00'
    };

    // Step 3
    var key = Buffer.from(privatekey, 'hex');
    var tx = new Tx(rawTx);
    tx.sign(key);

    var serializedTx = tx.serialize();

    web3.eth.sendRawTransaction('0x' + serializedTx.toString('hex'), function (err, hash) {
        if (err) {
            res.status(401).json("" + err);
        }
        else {
            res.json({"status": true, "hash": hash});
        }
    });

});

Above is my code in nodejs for sending entire balance in ether where I get error for gas price:

Error: Transaction gas is too low. There is not enough gas to cover minimal cost of the transaction (minimal: 21004, got: 21000). Try increasing supplied gas.

This is the correct method to send ether, but still get this error.

Answer 1

The error is quite clear, so I assume your question is about why the gas cost is 21004 instead of what you expected (21000).

The extra 4 gas is because you're sending a data field with one byte in it, and that byte is zero. Each zero you send costs 4 gas.

Just remove the data field and you should see the gas cost be 21000.