erc-metatransaction-forwarder

A Forwarder (aka. Bouncer) smart-contract to facilitate meta-transactions via a relayer(s) built in solidity. This contract can serve as the meta abstraction for any type of smart-contract. In the tests, I use an ERC20.

Meta-transactions provide various advantages for a web3 ecosystem, including gas-less transactions for new users - specifically aiding in new user onboarding, as well as incentivises mining for internal ecosytems where users can be whitelisted and "mine" these metatransactions from a pool while recieving a fee to do so.

features

• nonce collision detection for replay protection (may not be necessary depending on your impl)
• batching for gas efficiency/ higher volume
• whitelisting for both relayers (e.g hotwallet, or Infura), as well as signers (original senders); either can be toggled on/off
• fee (for relayer gas fee) to be paid in either native ERC20 token, or ETH

tests

1. yarn (for dependencies)
2. yarn test:waffle

(see /test/Forwarder.test.js for how a signed transaction is constructed)

const constructMetaTransfer = async (to, amount, recipientContract, signer) => { 
  const iface = new utils.Interface(['function transfer(address,uint256)'])
  const data = iface.encodeFunctionData('transfer', [to, amount])

  const hash = ethers.utils.keccak256(
    ethers.utils.defaultAbiCoder.encode(
    ['address','bytes'],
    [recipientContract,data]
    )
  )

  const signature = await signer.signMessage(utils.arrayify(hash));
  return { data, signature };
}