Write (Fee Delegation)

You can make a "transaction" that including payment request to feepayer when you want to execute the Smart Contract.

Import the web3 and @kaiachain/web3js-ext packages to add kaia features on web3

Define sender, fee payer addresses and private keys

Set up the provider with the specified kairos testnet URL. A provider in web3 is a read-only abstraction to access the blockchain data.

Also, you can change the provider URL from kairos to quicknode

Create a sender and fee payer account from defined private key using web3.eth.accounts.privateKeyToAccount

Define contract Abi and contract address

Create a contract instance using Web3.eth.Contract with defined contractAbi and address. You can read and write the contract through this instance

Get the value of number before update

Encoded the contract method data with contract.methods.increment().encodeABI()

Create a transaction to update the value number with type: FeeDelegatedSmartContractExecution

Sign the transaction with sender account using signTransaction

Sign the transaction with fee payer account using signTransactionAsFeePayer

Send the transaction to blockchain. It will return the transaction receipt

Get the updated value of number

smartContractWriteFeeDelegated.js


const { Web3, TxType } = require("@kaiachain/web3js-ext");
const senderAddr = "0x24e8efd18d65bcb6b3ba15a4698c0b0d69d13ff7";
const senderPriv = "0x4a72b3d09c3d5e28e8652e0111f9c4ce252e8299aad95bb219a38eb0a3f4da49";
const feePayerAddr = "0xcb0eb737dfda52756495a5e08a9b37aab3b271da";
const feePayerPriv = "0x9435261ed483b6efa3886d6ad9f64c12078a0e28d8d80715c773e16fc000cff4";
const provider = new Web3.providers.HttpProvider("https://public-en-kairos.node.kaia.io");
const web3 = new Web3(provider);
const senderAccount = web3.eth.accounts.privateKeyToAccount(senderPriv);
const feePayerAccount = web3.eth.accounts.privateKeyToAccount(feePayerPriv);
/* compiled in remix.ethereum.org (compiler: 0.8.18, optimizer: false)
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;
contract Counter {
    uint256 public number;
    event SetNumber(uint256 number);
    constructor(uint256 initNumber) {
        number = initNumber;
    }
    function setNumber(uint256 newNumber) public {
        number = newNumber;
        emit SetNumber(number);
    }
    function increment() public {
        number++;
        emit SetNumber(number);
    }
}
*/
const contractAbi = JSON.parse('[{"inputs":[{"internalType":"uint256","name":"initNumber","type":"uint256"}],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":false,"internalType":"uint256","name":"number","type":"uint256"}],"name":"SetNumber","type":"event"},{"inputs":[],"name":"increment","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"number","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"newNumber","type":"uint256"}],"name":"setNumber","outputs":[],"stateMutability":"nonpayable","type":"function"}]');
const contractAddr = "0x95Be48607498109030592C08aDC9577c7C2dD505";
async function main() {
  const contract = new web3.eth.Contract(contractAbi, contractAddr);
  console.log("number before", (await contract.methods.number().call()).toString());
  const data = contract.methods.increment().encodeABI();
  const tx = {
    type: TxType.FeeDelegatedSmartContractExecution,
    from: senderAddr,
    to: contractAddr,
    data: data,
  };
  // Sign transaction by sender
  const signResult1 = await senderAccount.signTransaction(tx);
  console.log("senderTxHashRLP", signResult1.rawTransaction);
  // Sign and send transaction by fee payer
  const signResult2 = await feePayerAccount.signTransactionAsFeePayer(signResult1.rawTransaction);
  console.log("signedTx", signResult2.transactionHash);
  const receipt = await web3.eth.sendSignedTransaction(signResult2.rawTransaction);
  console.log("receipt", receipt);
  console.log("number after", (await contract.methods.number().call()).toString());
}
main();

output


❯ node smartContractWriteFeeDelegated.js
number before 296
senderTxHashRLP 0x31f8844c850ba43b7400830111939495be48607498109030592c08adc9577c7c2dd505809424e8efd18d65bcb6b3ba15a4698c0b0d69d13ff784d09de08af847f8458207f6a03a9ade9fb5c2e4e513c56341ab64ad0a70613d826479f2117b53d3b57cee5021a07612c8538ee5b895f44b50858164dd67da473e264c29d331437273e581652eea
signedTx 0x66f7d99d2236145baa4bb84f66d283c508639bd6150c68b300323f7aa016676f
receipt {
  blockHash: '0x6b2201b6bcc999395e247fc8b85062b1a9313cc0db53a50a746203c9995af8b9',
  blockNumber: 148743711n,
  cumulativeGasUsed: 38014n,
  effectiveGasPrice: 25000000000n,
  from: '0x24e8efd18d65bcb6b3ba15a4698c0b0d69d13ff7',
  gasUsed: 38014n,
  logs: [
    {
      address: '0x95be48607498109030592c08adc9577c7c2dd505',
      topics: [Array],
      data: '0x0000000000000000000000000000000000000000000000000000000000000129',
      blockNumber: 148743711n,
      transactionHash: '0x66f7d99d2236145baa4bb84f66d283c508639bd6150c68b300323f7aa016676f',
      transactionIndex: 0n,
      blockHash: '0x6b2201b6bcc999395e247fc8b85062b1a9313cc0db53a50a746203c9995af8b9',
      logIndex: 0n,
      removed: false
    }
  ],
  logsBloom: '0x00000000000040000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000000000001200000002',
  status: 1n,
  to: '0x95be48607498109030592c08adc9577c7c2dd505',
  transactionHash: '0x66f7d99d2236145baa4bb84f66d283c508639bd6150c68b300323f7aa016676f',
  transactionIndex: 0n,
  type: 0n
}
number after 297