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Using Forks With Ethers.js

Using Forks With Ethers.js

The following code sample will guide you through:

  • Creating a Fork using the Fork API with custom chain config.
  • Connecting Ethers.js to the Fork.
  • Completing a Fork state override.
  • Sending several transactions.

In this example, we'll mint, approve, and transferFrom some DAI. We'll use the Mainnet Dai contract:

  1. TX1 – mint: We'll use an arbitrary address ($minter) to mint 2 DAI for $owner.
  2. TX2 – approve: The address $owner will approve $spender to spend 0.5 DAI.
  3. TX3 – transferFrom: The address we just approved ($spender) will transfer 0.25 DAI to $receiver.

We have three participants in this scenario: $minter, $spender, and $receiver. Instead of dealing with real addresses, we'll use accounts available on the Fork upon creation (lines 29..32).

example.ts
import axios from 'axios';
import * as dotenv from 'dotenv';
import { ethers } from 'ethers';
 
dotenv.config();
 
// assuming environment variables TENDERLY_ACCOUNT_SLUG, TENDERLY_PROJECT_SLUG and TENDERLY_ACCESS_KEY are set
// https://docs.tenderly.co/account/projects/account-project-slug
// https://docs.tenderly.co/account/projects/how-to-generate-api-access-token
const { TENDERLY_ACCOUNT_SLUG, TENDERLY_PROJECT_SLUG, TENDERLY_ACCESS_KEY } = process.env;
 
const daiOnFork = async () => {
  console.time('Fork Creation');
  const fork = await mainnetFork();
  console.timeEnd('Fork Creation');
 
  const forkId = fork.data.simulation_fork.id;
  const rpcUrl = `https://rpc.tenderly.co/fork/${forkId}`;
  // const rpcUrl = 'https://rpc.tenderly.co/fork/###-###-###-###';
  console.log('Fork URL\n\t' + rpcUrl);
 
  const forkProvider = new ethers.providers.JsonRpcProvider(rpcUrl);
 
  const [minterAddress, ownerAddress, spenderAddress, receiverAddress] =
    await forkProvider.listAccounts();
 
  const [minterSigner, ownerSigner, spenderSigner] = [
    forkProvider.getSigner(minterAddress),
    forkProvider.getSigner(ownerAddress),
    forkProvider.getSigner(spenderAddress),
    forkProvider.getSigner(receiverAddress),
  ];
 
  /*
  // alternatively, you could as well use an existing account you do have private key access to.
 
  const minterAddress = '0xdc6bdc37b2714ee601734cf55a05625c9e512461';
  const minterSigner = new ethers.Wallet(
    '0x94...5c'
  ).connect(forkProvider);
 
    await forkProvider.send('tenderly_setBalance', [
      [minterAddress],
      ethers.utils.hexValue(ethers.utils.parseUnits('10', 'ether').toHexString()),
    ]);
 
  */
 
  // override: make 0xdc6bdc37b2714ee601734cf55a05625c9e512461 a ward of DAI
  await forkProvider.send('tenderly_setStorageAt', [
    // the DAI contract address
    '0x6b175474e89094c44da98b954eedeac495271d0f',
    // storage location wards['0xdc6bdc37b2714ee601734cf55a05625c9e512461']
    ethers.utils.keccak256(
      ethers.utils.concat([
        ethers.utils.hexZeroPad(minterAddress, 32), // the ward address (address 0x000..0) - mapping key
        ethers.utils.hexZeroPad('0x0', 32), // the wards slot is 0th  in the DAI contract - the mapping variable
      ]),
    ),
    // flag 1 (at 32 bytes length)
    '0x0000000000000000000000000000000000000000000000000000000000000001',
  ]);
 
  // TX1: mint
  await minterSigner.sendTransaction({
    from: minterAddress,
    to: '0x6b175474e89094c44da98b954eedeac495271d0f',
    data: DaiAbi.encodeFunctionData('mint', [
      ethers.utils.hexZeroPad(ownerAddress.toLowerCase(), 20),
      ethers.utils.parseEther('1.0'),
    ]),
    gasLimit: 800000,
  });
 
  // TX2: approve
  await ownerSigner.sendTransaction({
    to: '0x6b175474e89094c44da98b954eedeac495271d0f',
    data: DaiAbi.encodeFunctionData('approve', [
      ethers.utils.hexZeroPad(spenderAddress.toLowerCase(), 20),
      ethers.utils.parseEther('1.0'),
    ]),
    gasLimit: 800000,
  });
 
  // TX3: transferFrom
  await spenderSigner.sendTransaction({
    to: '0x6b175474e89094c44da98b954eedeac495271d0f',
    data: DaiAbi.encodeFunctionData('transferFrom', [
      ethers.utils.hexZeroPad(ownerAddress.toLowerCase(), 20),
      ethers.utils.hexZeroPad(receiverAddress.toLowerCase(), 20),
      ethers.utils.parseEther('1.0'),
    ]),
    gasLimit: 800000,
  });
 
  // deleteFork(forkId);
};
 
const DaiAbi = new ethers.utils.Interface([
  {
    constant: false,
    inputs: [
      { internalType: 'address', name: 'usr', type: 'address' },
      { internalType: 'uint256', name: 'wad', type: 'uint256' },
    ],
    name: 'mint',
    outputs: [],
    payable: false,
    stateMutability: 'nonpayable',
    type: 'function',
  },
  {
    constant: false,
    inputs: [
      { internalType: 'address', name: 'usr', type: 'address' },
      { internalType: 'uint256', name: 'wad', type: 'uint256' },
    ],
    name: 'approve',
    outputs: [{ internalType: 'bool', name: '', type: 'bool' }],
    payable: false,
    stateMutability: 'nonpayable',
    type: 'function',
  },
  {
    constant: false,
    inputs: [
      { internalType: 'address', name: 'src', type: 'address' },
      { internalType: 'address', name: 'dst', type: 'address' },
      { internalType: 'uint256', name: 'wad', type: 'uint256' },
    ],
    name: 'transferFrom',
    outputs: [{ internalType: 'bool', name: '', type: 'bool' }],
    payable: false,
    stateMutability: 'nonpayable',
    type: 'function',
  },
]);
 
daiOnFork();
 
function deleteFork(forkId: any) {
  axios.delete(
    `https://api.tenderly.co/api/v1/account/${TENDERLY_ACCOUNT_SLUG}/project/${TENDERLY_PROJECT_SLUG}/fork/${forkId}`,
    {
      headers: {
        'X-Access-Key': TENDERLY_ACCESS_KEY as string,
      },
    },
  );
}
 
async function mainnetFork() {
  return await axios.post(
    `https://api.tenderly.co/api/v1/account/${TENDERLY_ACCOUNT_SLUG}/project/${TENDERLY_PROJECT_SLUG}/fork`,
    {
      network_id: '1',
      chain_config: {
        chain_id: 11,
        shanghai_time: 1677557088,
      },
    },
    {
      headers: {
        'X-Access-Key': TENDERLY_ACCESS_KEY as string,
      },
    },
  );
}