Calculate the transaction hash in advanced

[khoanguyen-yang]

Hi guys,

I want to get the transaction hash of a smart contract transaction before sending it to the network. How can I achieve that?

I tried some ways but none worked. None of the hashes match the generated one

const rawTransaction = await contract.populateTransaction.transfer(
  receiver,
  amount,
);

const signature = await signer.signTransaction(rawTransaction);
const hash1 = ethers.utils.keccak256(signature);
console.log('hash1', hash1);

const hash2 = ethers.utils.keccak256(ethers.utils.serializeTransaction(lodash.omit(rawTransaction, ['from'])));
console.log('hash2', hash2);

// this one throws error actually
// const hash3 = ethers.utils.keccak256(ethers.utils.serializeTransaction(lodash.omit(rawTransaction, ['from']), signature));
// console.log('hash3', hash3);

const tx = await signer.sendTransaction(rawTransaction);
console.log('resulted hash', tx.hash);

Really appreciate any help 🙏

[zemse]

The hash1 should be the proper hash. Is it really not equal to the resulted hash?

const signature = await signer.signTransaction(rawTransaction);
const hash1 = ethers.utils.keccak256(signature);
console.log('hash1', hash1);

[khoanguyen-yang]

Yes @zemse, totally different hashes. Running on BSC Testnet

const ethers = require("ethers");

const commonABI = ["function transfer(address to, uint amount)"];
const signer = new ethers.Wallet(
  privateKey,
  new ethers.providers.JsonRpcProvider(
    "https://data-seed-prebsc-1-s1.binance.org:8545"
  )
);
const contract = new ethers.Contract(tokenAddress, commonABI, signer);

(async () => {
  const rawTransaction = await contract.populateTransaction.transfer(
    receiver,
    amount
  );

  const signature = await signer.signTransaction(rawTransaction);
  const hash1 = ethers.utils.keccak256(signature);
  console.log("hash1", hash1);

  const tx = await signer.sendTransaction(rawTransaction);
  console.log("resulted hash", tx.hash);
})();

[phoax]

Are chainId in transactions equals to your BSC chainId?

[redcomethk]

I also encountered this problem when I use ethers.js v6.
After some trial and error, I can get the transaction hash by calling signer's populateTransaction on the rawTransaction here again.
In my environment I can get the same hash by the following change

   const rawTransaction = await contract.transfer.populateTransaction(
    receiver,
    amount
  ); // change for ethers.js v6 
  const rawTransaction2 = await signer.populateTransaction(rawTransaction); // this is the newly added line
  const signature = await signer.signTransaction(rawTransaction2);
  const hash1 = ethers.utils.keccak256(signature);
  console.log("hash1", hash1);

  const tx = await signer.sendTransaction(rawTransaction);
  console.log("resulted hash", tx.hash); // this should match hash1