contracts/

README

Kroma Smart Contracts

This package contains the smart contracts that compose the on-chain component of Kroma. You can find detailed specifications for the contracts contained within this package here.

Contracts Overview

Contracts deployed to L1

Name	Proxy Type	Description
L1CrossDomainMessenger	Proxy
High-level interface for sending messages to and receiving messages from Kroma
L1StandardBridge	Proxy
Standardized system for transfering ERC20 tokens to/from Kroma
L2OutputOracle	Proxy
Stores commitments to the state of Kroma which can be used by contracts on L1 to access L2 state
KromaPortal	Proxy
Low-level message passing interface
KromaMintableERC20Factory	Proxy
Deploys standard KromaMintableERC20 tokens that are compatible with either StandardBridge
ProxyAdmin	-
Contract that can upgrade L1 contracts

Contracts deployed to L2

Name	Proxy Type	Description
GasPriceOracle	Proxy	Stores L2 gas price configuration values
L1Block	Proxy	Stores L1 block context information (e.g., latest known L1 block hash)
L2CrossDomainMessenger	Proxy	High-level interface for sending messages to and receiving messages from L1
L2StandardBridge	Proxy	Standardized system for transferring ERC20 tokens to/from L1
L2ToL1MessagePasser	Proxy	Low-level message passing interface
ValidatorRewardVault	Proxy	Vault for L2 transaction fees
KromaMintableERC20Factory	Proxy	Deploys standard KromaMintableERC20 tokens that are compatible with either StandardBridge
L2ProxyAdmin	-	Contract that can upgrade L2 contracts when sent a transaction from L1

Installation

We export contract ABIs, contract source code, and contract deployment information for this package via npm:

> npm install @kroma/contracts

Development

Dependencies

We work on this repository with a combination of Hardhat and Foundry.

1. Install Foundry by following the instructions located here. A specific version must be used.

   > foundryup --version nightly-d369d2486f85576eec4ca41d277391dfdae21ba7
   

2. Install node modules with pnpm and Node.js:

   > pnpm i
   

Build

> pnpm build

Test

> pnpm test

Running Echidna tests

You must have Echidna installed.

Contracts targeted for Echidna testing are located in ./contracts/echidna Each target contract is tested with a separate pnpm command, for example:

> pnpm echidna:aliasing

Deployment

Configuration

1. Create or modify a file <network-name>.ts inside of the deploy-config folder.
2. Fill out this file according to the deployConfigSpec located inside of the hardhat.config.ts.
3. Optionally: Run npx hardhat generate-deploy-config --network <network-name> to generate the associated JSON file. This is required if using utils/chain-ops.

Execution

1. Copy .env.example into .env
2. Fill out the L1_RPC and PRIVATE_KEY_DEPLOYER environment variables in .env
3. Run npx hardhat deploy --network <network-name> to deploy the L1 contracts
4. Run npx hardhat etherscan-verify --network <network-name> --sleep to verify contracts on Etherscan

Tools

Layout Locking

We use a system called "layout locking" as a safety mechanism to prevent certain contract variables from being moved to different storage slots accidentally. To lock a contract variable, add it to the layout-lock.json file which has the following format:

{
  "MyContractName": {
    "myVariableName": {
      "slot": 1,
      "offset": 0,
      "length": 32
    }
  }
}

With the above config, the validate-spacers hardhat task will check that we have a contract called MyContractName, that the contract has a variable named myVariableName, and that the variable is in the correct position as defined in the lock file. You should add things to the layout-lock.json file when you want those variables to never change. Layout locking should be used in combination with diffing the .storage-layout file in CI.

Standards and Conventions

Style

Comments

We use Seaport-style comments with some minor modifications. Some basic rules:

• Always use @notice since it has the same general effect as @dev but avoids confusion about when to use one over the other.
• Include a newline between @notice and the first @param.
• Include a newline between @param and the first @return.
• Use a line-length of 100 characters.

We also have the following custom tags:

• @custom:proxied: Add to a contract whenever it's meant to live behind a proxy.
• @custom:upgradeable: Add to a contract whenever it's meant to be used in an upgradeable contract.
• @custom:semver: Add to a constructor to indicate the version of a contract.

Errors

• Use require statements when making simple assertions.
• Use revert if throwing an error where an assertion is not being made (no custom errors).
• Error strings MUST have the format "{ContractName}: {message}" where message is a lower case string.

Function Parameters

• Function parameters should be prefixed with an underscore.

Event Parameters

• Event parameters should NOT be prefixed with an underscore.

Spacers

We use spacer variables to account for old storage slots that are no longer being used. The name of a spacer variable MUST be in the format spacer_<slot>_<offset>_<length> where <slot> is the original storage slot number, <offset> is the original offset position within the storage slot, and <length> is the original size of the variable. Spacers MUST be private.

Proxy by Default

All contracts should be assumed to live behind proxies (except in certain special circumstances). This means that new contracts MUST be built under the assumption of upgradeability. We use a minimal Proxy contract designed to be owned by a corresponding ProxyAdmin which follow the interfaces of OpenZeppelin's Proxy and ProxyAdmin contracts, respectively.

Unless explicitly discussed otherwise, you MUST include the following basic upgradeability pattern for each new implementation contract:

1. Extend OpenZeppelin's Initializable base contract.
2. Include a uint8 public constant VERSION = X at the TOP of your contract.
3. Include a function initialize with the modifier reinitializer(VERSION).
4. In the constructor, set any immutable variables and call the initialize function for setting mutables.

Versioning

All (non-library and non-abstract) contracts MUST extend the Semver base contract which exposes a version() function that returns a semver-compliant version string. Before mainnet release, the development process the Semver value for all contracts SHOULD return 0.1.0

After the mainnet release, contracts MUST use the following versioning scheme:

• patch releases are to be used only for changes that do NOT modify contract bytecode (such as updating comments).
• minor releases are to be used for changes that modify bytecode OR changes that expand the contract ABI provided that these changes do NOT break the existing interface.
• major releases are to be used for changes that break the existing contract interface OR changes that modify the security model of a contract.

Exceptions

We have made an exception to the Semver rule for the WETH contract to avoid making changes to a well-known, simple, and recognizable contract.

Tests

Tests are written using Foundry.

All test contracts and functions should be organized and named according to the following guidelines.

These guidelines are also encoded in a script which can be run with:

> ts-node scripts/forge-test-names.ts

Note: This is a work in progress, not all test files are compliant with these guidelines.

Organizing Principles

• Solidity contracts are used to organize the test suite similar to how mocha uses describe.
• Every non-trivial state changing function should have a separate contract for happy and sad path tests. This helps to make it very obvious where there are not yet sad path tests.
• Simpler functions like getters and setters are grouped together into test contracts.

Test function naming convention

Test function names are split by underscores, into 3 or 4 parts. An example function name is test_onlyOwner_callerIsNotOwner_reverts().

The parts are: [method]_[FunctionName]_[reason]_[success], where:

• [method] is either test, testFuzz, or testDiff
• [FunctionName] is the name of the function or higher level behavior being tested.
• [reason] is an optional description for the behavior being tested.
• [status] must be one of:
  • succeeds: used for most happy path cases
  • reverts: used for most sad path cases
  • works: used for tests which include a mix of happy and sad assertions (these should be broken up if possible)
  • fails: used for tests which 'fail' in some way other than reverting
  • benchmark: used for tests intended to establish gas costs

Contract Naming Conventions

Test contracts should be named one of the following according to their use:

• TargetContract_Init for contracts that perform basic setup to be reused in other test contracts.
• TargetContract_Function_Test for contracts containing happy path tests for a given function.
• TargetContract_Function_TestFail for contracts containing sad path tests for a given function.

Withdrawing From Fee Vaults

See the file scripts/FeeVaultWithdrawal.s.sol to withdraw from the L2 fee vaults. It includes instructions on how to run it. foundry is required.