Sending private transactions using ethers and hardhat

Question

I am using HardHat and ethers to send mint transaction:

  const ABI = (await ethers.getContractFactory("MyContract")).interface

  const contract_address = "0xABCDABCD"
  const [signer] = await ethers.getSigners()

  const MyContract = await new ethers.Contract(contract_address, ABI, signer)

  tx = await MyContract.mint({ gasPrice: price * 4 })

Now I want the mint transaction to be private. The doc I found was this:

  const provider = new ethers.providers.JsonRpcProvider("https://dark-red-uranium.discover.quiknode.pro/XXXXXXX");
  const network = await provider.send("eth_sendPrivateTransaction", ["FILL_ME_ARG_1"]);

How do I send the mint transaction using this syntax?

Answer 1

The document stating that it requires a signed transaction. With ethers.js you should sign the transaction locally and send it. The below should work:

  provider = ethers.getDefaultProvider('http://localhost:8545')
  myWallet = new ethers.Wallet("0x59c699..sample private key...", provider)
  myAddress = await myWallet.getAddress()
  raw_tx = await MyContract.populateTransaction.mint()
  console.log(raw_tx)
  //make sure "from" is "myAddress"
  raw_tx.from = myAddress
  raw_tx = await myWallet.populateTransaction(raw_tx)
  console.log(raw_tx)
  signed_tx = await myWallet.signTransaction(raw_tx)
  console.log("signed tx ", signed_tx)
  /// Continute with your eth_sendPrivateTransaction as example in document with  "tx" is the signed_tx above
  /// For example: tx = await provider.sendTransaction(signed_tx); should work with normal provider

By looking at the populated raw tx, you can modify the gas price before it's signed, it may not be gasPrice field anymore after EIP 1559, depends on the blockchain One thing to note is that the default JsonRpcSigner may not allow signTransaction, my solution is to use Wallet of ethers to import either privatekey or some menomic to sign. Not sure if there is a cleaner way to do it.