Simulate transactions at the beginning of a block

[thegostep]

Cross posting a ticket that I think would be useful to have on hardhat fork

flashbots/mev-geth#9

[alcuadrado]

This is really interesting @thegostep, thanks for sharing.

Do you see this being useful for forked networks exclusively, or also for local ones?

[thegostep]

This is mostly useful for asking "what if" questions at a specific point in chain history. I don't think that is as useful with a local chain since chain history is usually ephemeral / easy to replicate. That being said, maybe some people are doing more complex things with local chains than I am.

[alcuadrado]

I may be missing something, but isn't this equivalent as forking from block N and send a tx/call to simulate a tx in the block N+1?

[thegostep]

woah that's right! nice.

only thing missing is ability to send more than one tx per block

[thegostep]

Here is a simple test written to take advantage of this:

import { expect } from 'chai'
import { Contract } from 'ethers'
import { ethers, network } from 'hardhat'
import { ERC20s } from '../src/constants'

const resetFork = async (blockNumber: number) =>
  network.provider.request({
    method: 'hardhat_reset',
    params: [
      {
        forking: {
          jsonRpcUrl: process.env.ETHEREUM_ARCHIVE_URL,
          blockNumber,
        },
      },
    ],
  })

describe('Epoch', function () {
  let contract: Contract
  before(async () => {
    // fork at target block
    await resetFork(11592051)
    // deploy execution contract
    contract = await (await ethers.getContractFactory('Epoch')).deploy()
    await contract.deployed()
    console.log(await ethers.provider.getBlockNumber())
  })
  it('should execute transaction at top of block', async function () {
    const signer = (await ethers.getSigners())[0]
    const preBal = await signer.getBalance()
    
    // try execution
    const tx = await contract.advance(
      '0x6A2E6510B2BBF8C9AD7bC817D0Dc711711E8d747',
      [ERC20s.ZAI, ERC20s.DAI, ERC20s.WETH9],
      1,
      { gasPrice: 0 },
    )
    await tx.wait()

    // assert increase balance
    const postBal = await signer.getBalance()
    console.log(`Profit`, ethers.utils.formatEther(postBal.sub(preBal)))
    expect(postBal).to.be.gt(preBal)
  })
})