EVM CCIP-Read Gateway

This repository implements a generic CCIP-Read gateway framework for fetching state proofs of data on other EVM chains. This allows L1 smart contracts to fetch and verify state from L2s. The library is built to be as modular and interchangeable as possible. This means:

Anyone can operate their own gateway, but...
Only one gateway needs to be operated for each chain, regardless of the applications requesting data from it.
Gateways do not need to be trusted; their responses are fully verified on L1.
Contracts can fetch L2 state using a simple builder interface and callbacks.
Contracts can change targets (eg, a different L2) just by swapping out the address of a verifier contract for another.

While this functionality is written primarily with read calls in mind, it also functions for transactions; using a compliant library like Ethers, a transaction that includes relevant L2 proofs can be generated and signed.

Usage

Have your contract extend EVMFetcher.
In a view/pure context, use EVMFetcher to fetch the value of slots from another contract (potentially on another chain). Calling EVMFetcher.fetch() terminates execution and generates a callback to the same contract on a function you specify.
In the callback function, use the information from the relevant slots as you see fit.

Example

The example below fetches another contract's storage value testUint.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

import { EVMFetcher } from '@ensdomains/evm-verifier/contracts/EVMFetcher.sol';
import { EVMFetchTarget } from '@ensdomains/evm-verifier/contracts/EVMFetchTarget.sol';
import { IEVMVerifier } from '@ensdomains/evm-verifier/contracts/IEVMVerifier.sol';

contract TestL2 {
    uint256 testUint; // Slot 0
    
    constructor() {
        testUint = 42;
    }
}

contract TestL1 is EVMFetchTarget {
    using EVMFetcher for EVMFetcher.EVMFetchRequest;

    IEVMVerifier verifier;
    address target;

    constructor(IEVMVerifier _verifier, address _target) {
        verifier = _verifier;
        target = _target;
    }

    function getTestUint() public view returns(uint256) {
        EVMFetcher.newFetchRequest(verifier, target)
            .getStatic(0)
            .fetch(this.getSingleStorageSlotCallback.selector, "");
    }

    function getSingleStorageSlotCallback(bytes[] memory values, bytes memory) public pure returns(uint256) {
        return uint256(bytes32(values[0]));
    }
}

Packages

This is a monorepo divided up into several packages:

evm-gateway

A framework for constructing generic CCIP-Read gateways targeting different EVM-compatible chains. This repository implements all the functionality required to fetch and verify multiple storage slots from an EVM-compatible chain, omitting only the L2-specific logic of determining a block to target, and verifying the root of the generated proof.

l1-gateway

An instantiation of evm-gateway that targets Ethereum L1 - that is, it implements a CCIP-Read gateway that generates proofs of contract state on L1.

This may at first seem useless, but as the simplest possible practical EVM gateway implementation, it acts as an excellent target for testing the entire framework end-to-end.

It may also prove useful for contracts that wish to trustlessly establish the content of storage variables of other contracts, or historic values for storage variables of any contract.

evm-verifier

A Solidity library that verifies state proofs generated by an evm-gateway instance. This library implements all the functionality required make CCIP-Read calls to an EVM gateway and verify the responses, except for verifying the root of the proof. This library is intended to be used by libraries for specific EVM-compatible chains that implement the missing functionality.

Osas-dot/evmgateway