Standard Exit Format for L2s built on EVM chains

We present a general standard for such a format, along with coders written in Typescript, which will aid L2 interoperability and support arbitrary tokens.

Description

The idea behind this library is to standardise the data structures used in exiting a layer 2 system: whether that is a Celer, Connext, or Nitro state channel or a rollup such as Arbitrum or Optimism. An exit format allows one to specify how assets locked up and redistributed in an L2 should be paid out in L1. Standard utilities, built against a standard format, can undergo a higher concentration of scrutiny from the community and auditors — a major benefit.

We hope to receive feedback from as many layer 2 projects as possible, to help towards writing a standards track EIP. Adoption of this standard improves interoperability between L2s, and enables the sharing of L2 entrance & exit utilities, such as exit meta transactions.

We have concentrated so far on a format that works for Nitro state channels. The new format enables us to streamline our virtual channel construction, simplifying the protocol while lowering the gas costs for channel disputes. Find out more at https://www.notion.so/statechannels/Streamlining-Virtual-Channels-8a8650ba849d4221b7e93c125a794ecf

The standard is extensible enough to support future token standards and even to describe cross-chain assets.

How It's Made

The main content is the definition of an exit format, with some exit-transformations implemented in Typescript and Solidity.

This repo depends on ethers-js for ABI encoding.

How to install this package

yarn add @statechannels/exit-format

Example usage

// SPDX-License-Identifier: MIT
pragma solidity 0.8.4;

import "@statechannels/exit-format/contracts/ExitFormat.sol";

contract MyLayer2 {
  bytes32 exitHash;

  function storeExitHash(ExitFormat.SingleAssetExit[] memory exit) public {
    if (msg.sender == 0x0737369d5F8525D039038Da1EdBAC4C4f161b949) {
      exitHash = keccak256(ExitFormat.encodeExit(exit));
    }
  }

  function payout(ExitFormat.SingleAssetExit[] memory exit) public {
    if (keccak256(ExitFormat.encodeExit(exit)) == exitHash) {
      ExitFormat.executeExit(exit);
    }
  }
}

import {
  Exit,
  SingleAssetExit,
  NullAssetMetadata,
} from "@statechannels/exit-format";

const ethExit: SingleAssetExit = {
  asset: "0x0000000000000000000000000000000000000000", // this implies the native token (e.g. ETH)
  assetMetadata: NullAssetMetadata,
  allocations: [
    {
      destination: "0x96f7123E3A80C9813eF50213ADEd0e4511CB820f", // Alice
      amount: "0x05",
      allocationType: AllocationType.simple, // a regular ETH transfer
      metadata: "0x",
    },
    {
      destination: "0x0737369d5F8525D039038Da1EdBAC4C4f161b949", // Bob
      amount: "0x05",
      allocationType: AllocationType.withdrawHelper, // call a WithdrawHelper
      metadata: "0x0123", // at the address, and with the calldata, encoded within
    },
  ],
};

const daiExit: SingleAssetExit = {
  asset: "0x6b175474e89094c44da98b954eedeac495271d0f", // this implies DAI (an ERC20 token)
  assetMetadata: {
    assetType: AssetType.ERC20, // The format supports Native, ERC20, ERC721 and ERC1155 tokens and can be extended to others.
    metadata: "0x",
  },
  allocations: [
    {
      destination: "0x96f7123E3A80C9813eF50213ADEd0e4511CB820f", // Alice
      amount: "0x05",
      allocationType: AllocationType.simple, // a regular ERC20.transfer
      metadata: "0x",
    },
    {
      destination: "0x96f7123E3A80C9813eF50213ADEd0e4511CB820f", // Bob
      amount: "0x05",
      allocationType: AllocationType.simple, // a regular ERC20.transfer
      metadata: "0x",
    },
  ],
};

const exit: Exit = [ethExit, daiExit];