OP Stack Smart Contracts

This package contains the L1 and L2 smart contracts for the OP Stack. Detailed specifications for the contracts contained within this package can be found at specs.optimism.io. High-level information about these contracts can be found within this README and within the Optimism Developer Docs.

Table of Contents

• Architecture Overview
  • Core L1 Smart Contracts
    • Notes for Core L1 Smart Contracts
  • Core L2 Smart Contracts
    • Notes for Core L2 Smart Contracts
  • Smart Contract Proxies
• External Usage
  • Using OP Stack Contracts in Solidity
  • Using OP Stack Contracts in JavaScript
  • Deployed Addresses
• Contributing
  • Contributing Guide
  • Style Guide
• Deployment
  • Configuration
    • Custom Gas Token
  • Execution
  • Deploying a single contract
• Testing
  • Test Setup
  • Static Analysis

Architecture Overview

NOTE: Smart contract names in the architecture diagrams below are links to source code. Click them!

Core L1 Smart Contracts

Below you'll find an architecture diagram describing the core L1 smart contracts for the OP Stack. Smart contracts that are considered "peripheral" and not core to the operation of the OP Stack system are described separately.

graph LR
    subgraph "External Contracts"
        ExternalERC20(External ERC20 Contracts)
        ExternalERC721(External ERC721 Contracts)
    end

    subgraph "L1 Smart Contracts"
        BatchDataEOA(<a href="https://etherscan.io/address/0xff00000000000000000000000000000000000010">Batch Inbox Address</a>)
        L1StandardBridge(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L1/L1StandardBridge.sol">L1StandardBridge</a>)
        L1ERC721Bridge(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L1/L1ERC721Bridge.sol">L1ERC721Bridge</a>)
        L1CrossDomainMessenger(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L1/L1CrossDomainMessenger.sol">L1CrossDomainMessenger</a>)
        L2OutputOracle(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L1/L2OutputOracle.sol">L2OutputOracle</a>)
        OptimismPortal(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L1/OptimismPortal.sol">OptimismPortal</a>)
        SuperchainConfig(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L1/SuperchainConfig.sol">SuperchainConfig</a>)
        SystemConfig(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L1/SystemConfig.sol">SystemConfig</a>)
    end

    subgraph "User Interactions"
        Users(Users)
    end

    subgraph "System Interactions"
        Batcher(Batcher)
        Proposer(Proposer)
        Guardian(Guardian)
    end

    subgraph "Layer 2 Interactions"
        L2Nodes(Layer 2 Nodes)
    end

    Batcher -->|publish transaction batches| BatchDataEOA
    Proposer -->|propose state outputs| L2OutputOracle
    Guardian -->|remove invalid state outputs| L2OutputOracle

    ExternalERC20 <-->|mint/burn/transfer| L1StandardBridge
    ExternalERC721 <-->|mint/burn/transfer| L1ERC721Bridge

    L1StandardBridge <-->|send/receive message| L1CrossDomainMessenger
    L1ERC721Bridge <-->|send/receive message| L1CrossDomainMessenger
    L1CrossDomainMessenger <-->|package/send/receive message| OptimismPortal
    L1StandardBridge -.->|query pause state| SuperchainConfig
    L1ERC721Bridge -.->|query pause state| SuperchainConfig
    L1CrossDomainMessenger -.->|query pause state| SuperchainConfig
    OptimismPortal -.->|query pause state| SuperchainConfig

    OptimismPortal -.->|query config| SystemConfig
    OptimismPortal -.->|query proposed states| L2OutputOracle

    Users <-->|deposit/withdraw ETH/ERC20| L1StandardBridge
    Users <-->|deposit/withdraw ERC721| L1ERC721Bridge
    Users -->|prove/execute withdrawal transactions| OptimismPortal

    L2Nodes -.->|fetch transaction batches| BatchDataEOA
    L2Nodes -.->|verify output roots| L2OutputOracle
    L2Nodes -.->|fetch deposit events| OptimismPortal

    classDef extContracts stroke:#ff9,stroke-width:2px;
    classDef l1Contracts stroke:#bbf,stroke-width:2px;
    classDef l1EOA stroke:#bbb,stroke-width:2px;
    classDef userInt stroke:#f9a,stroke-width:2px;
    classDef systemUser stroke:#f9a,stroke-width:2px;
    classDef l2Nodes stroke:#333,stroke-width:2px
    class ExternalERC20,ExternalERC721 extContracts;
    class L1StandardBridge,L1ERC721Bridge,L1CrossDomainMessenger,L2OutputOracle,OptimismPortal,SuperchainConfig,SystemConfig l1Contracts;
    class BatchDataEOA l1EOA;
    class Users userInt;
    class Batcher,Proposer,Guardian systemUser;
    class L2Nodes l2Nodes;

Notes for Core L1 Smart Contracts

• The Batch Data Address described above (highlighted in GREY) is not a smart contract and is instead simply an arbitrarily chosen account that is assumed to have no known private key. This account is typically chosen as the account 0xFF0000....<L2 chain ID> where <L2 chain ID> is chain ID of the Layer 2 network for which the data is being posted. For instance, for OP Mainnet, this account is chosen as 0xFF00000000000000000000000000000000000010. However, this is not a strict requirement and some OP Stack chains may not follow this convention.
• Smart contracts that sit behind Proxy contracts are highlighted in BLUE. Refer to the Smart Contract Proxies section below to understand how these proxies are designed.
  • The L1CrossDomainMessenger contract sits behind the ResolvedDelegateProxy contract, a legacy proxy contract type used within older versions of the OP Stack. This proxy type is used exclusively for the L1CrossDomainMessenger to maintain backwards compatibility.
  • The L1StandardBridge contract sits behind the L1ChugSplashProxy contract, a legacy proxy contract type used within older versions of the OP Stack. This proxy type is used exclusively for the L1StandardBridge contract to maintain backwards compatibility.

Core L2 Smart Contracts

Here you'll find an architecture diagram describing the core OP Stack smart contracts that exist natively on the L2 chain itself.

graph LR
    subgraph "Layer 1 (Ethereum)"
        L1SmartContracts(L1 Smart Contracts)
    end

    subgraph "L2 Client"
        L2Node(L2 Node)
    end

    subgraph "L2 System Contracts"
        L1Block(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L2/L1Block.sol">L1Block</a>)
        GasPriceOracle(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L2/GasPriceOracle.sol">GasPriceOracle</a>)
        L1FeeVault(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L2/L1FeeVault.sol">L1FeeVault</a>)
        BaseFeeVault(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L2/BaseFeeVault.sol">BaseFeeVault</a>)
        SequencerFeeVault(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L2/SequencerFeeVault.sol">SequencerFeeVault</a>)
    end

    subgraph "L2 Bridge Contracts"
        L2CrossDomainMessenger(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L2/L2CrossDomainMessenger.sol">L2CrossDomainMessenger</a>)
        L2ToL1MessagePasser(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L2/L2ToL1MessagePasser.sol">L2ToL1MessagePasser</a>)
        L2StandardBridge(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L2/L2StandardBridge.sol">L2StandardBridge</a>)
        L2ERC721Bridge(<a href="https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/L2/L2ERC721Bridge.sol">L2ERC721Bridge</a>)
    end

    subgraph "Transactions"
        DepositTransaction(Deposit Transaction)
        UserTransaction(User Transaction)
    end

    subgraph "External Contracts"
        ExternalERC20(External ERC20 Contracts)
        ExternalERC721(External ERC721 Contracts)
    end

    subgraph "Remaining L2 Universe"
        OtherContracts(Any Contracts and Addresses)
    end

    L2Node -.->|derives chain from| L1SmartContracts
    L2Node -->|updates| L1Block
    L2Node -->|distributes fees to| L1FeeVault
    L2Node -->|distributes fees to| BaseFeeVault
    L2Node -->|distributes fees to| SequencerFeeVault
    L2Node -->|derives from deposits| DepositTransaction
    L2Node -->|derives from chain data| UserTransaction

    UserTransaction -->|can trigger| OtherContracts
    DepositTransaction -->|maybe triggers| L2CrossDomainMessenger
    DepositTransaction -->|can trigger| OtherContracts

    ExternalERC20 <-->|mint/burn/transfer| L2StandardBridge
    ExternalERC721 <-->|mint/burn/transfer| L2ERC721Bridge

    L2StandardBridge <-->|sends/receives messages| L2CrossDomainMessenger
    L2ERC721Bridge <-->|sends/receives messages| L2CrossDomainMessenger
    GasPriceOracle -.->|queries| L1Block
    L2CrossDomainMessenger -->|sends messages| L2ToL1MessagePasser

    classDef extContracts stroke:#ff9,stroke-width:2px;
    classDef l2Contracts stroke:#bbf,stroke-width:2px;
    classDef transactions stroke:#fba,stroke-width:2px;
    classDef l2Node stroke:#f9a,stroke-width:2px;

    class ExternalERC20,ExternalERC721 extContracts;
    class L2CrossDomainMessenger,L2ToL1MessagePasser,L2StandardBridge,L2ERC721Bridge l2Contracts;
    class L1Block,L1FeeVault,BaseFeeVault,SequencerFeeVault,GasPriceOracle l2Contracts;
    class UserTransaction,DepositTransaction transactions;
    class L2Node l2Node;

Notes for Core L2 Smart Contracts

• Contracts highlighted as "L2 System Contracts" are updated or mutated automatically as part of the chain derivation process. Users typically do not mutate these contracts directly, except in the case of the FeeVault contracts where any user may trigger a withdrawal of collected fees to the pre-determined withdrawal address.
• Smart contracts that sit behind Proxy contracts are highlighted in BLUE. Refer to the Smart Contract Proxies section below to understand how these proxies are designed.
• User interactions for the "L2 Bridge Contracts" have been omitted from this diagram but largely follow the same user interactions described in the architecture diagram for the Core L1 Smart Contracts.

Smart Contract Proxies

Most L1 and L2 smart contracts for OP Stack chains today sit behind Proxy contracts that themselves are managed by a ProxyAdmin contract. The ProxyAdmin contract is controlled by some owner address that can be any EOA or smart contract. Below you'll find a diagram that explains the behavior of the typical proxy contract.

graph LR
    ProxyAdminOwner(Proxy Admin Owner)
    ProxyAdmin(<a href="https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/universal/ProxyAdmin.sol">ProxyAdmin</a>)

    subgraph "Logical Smart Contract"
        Proxy(<a href="https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/universal/Proxy.sol">Proxy</a>)
        Implementation(Implementation)
    end

    ProxyAdminOwner -->|manages| ProxyAdmin
    ProxyAdmin -->|upgrades| Proxy
    Proxy -->|delegatecall| Implementation

    classDef l1Contracts stroke:#bbf,stroke-width:2px;
    classDef systemUser stroke:#f9a,stroke-width:2px;
    class Proxy l1Contracts;
    class ProxyAdminOwner systemUser;

External Usage

Using OP Stack Contracts in Solidity

OP Stack smart contracts are published to NPM and can be installed via:

npm install @eth-optimism/contracts-bedrock.

Refer to the Optimism Developer Docs for additional information about how to use this package.

Using OP Stack Contracts in JavaScript

Contract ABIs and addresses are published to NPM in a separate package and can be installed via:

npm install @eth-optimism/contracts-ts

Refer to the Optimism Developer Docs for additional information about how to use this package.

Deployed Addresses

See the Optimism Developer Docs for the deployed addresses of these smart contracts for OP Mainnet and OP Sepolia.

Contributing

Contributing Guide

Contributions to the OP Stack are always welcome. Please refer to the CONTRIBUTING.md for more information about how to contribute to the OP Stack smart contracts.

Style Guide

OP Stack smart contracts should be written according to the STYLE_GUIDE.md found within this repository. Maintaining a consistent code style makes code easier to review and maintain, ultimately making the development process safer.

Deployment

The smart contracts are deployed using foundry with a hardhat-deploy compatibility layer. When the contracts are deployed, they will write a temp file to disk that can then be formatted into a hardhat-deploy style artifact by calling another script.

The addresses in the deployments directory will be read into the script based on the backend's chain id. To manually define the set of addresses used in the script, set the CONTRACT_ADDRESSES_PATH env var to a path on the local filesystem that points to a JSON file full of key value pairs where the keys are names of contracts and the values are addresses. This works well with the JSON files in superchain-ops.

Configuration

Create or modify a file <network-name>.json inside of the deploy-config folder. Use the env var DEPLOY_CONFIG_PATH to use a particular deploy config file at runtime.

Custom Gas Token

The Custom Gas Token feature is a Beta feature of the MIT licensed OP Stack. While it has received initial review from core contributors, it is still undergoing testing, and may have bugs or other issues.

Execution

Before deploying the contracts, you can verify the state diff produced by the deploy script using the runWithStateDiff() function signature which produces the outputs inside snapshots/state-diff/. Run the deployment with state diffs by executing: forge script -vvv scripts/Deploy.s.sol:Deploy --sig 'runWithStateDiff()' --rpc-url $ETH_RPC_URL --broadcast --private-key $PRIVATE_KEY.

1. Set the env vars ETH_RPC_URL, PRIVATE_KEY and ETHERSCAN_API_KEY if contract verification is desired.
2. Set the DEPLOY_CONFIG_PATH env var to a path on the filesystem that points to a deploy config.
3. Deploy the contracts with forge script -vvv scripts/Deploy.s.sol:Deploy --rpc-url $ETH_RPC_URL --broadcast --private-key $PRIVATE_KEY Pass the --verify flag to verify the deployments automatically with Etherscan.

Deploying a single contract

All of the functions for deploying a single contract are public meaning that the --sig argument to forge script can be used to target the deployment of a single contract.

Testing

Test Setup

The Solidity unit tests use the same codepaths to set up state that are used in production. The same L1 deploy script is used to deploy the L1 contracts for the in memory tests and the L2 state is set up using the same L2 genesis generation code that is used for production and then loaded into foundry via the vm.loadAllocs cheatcode. This helps to reduce the overhead of maintaining multiple ways to set up the state as well as give additional coverage to the "actual" way that the contracts are deployed.

The L1 contract addresses are held in deployments/hardhat/.deploy and the L2 test state is held in a .testdata directory. The L1 addresses are used to create the L2 state and it is possible for stale addresses to be pulled into the L2 state, causing tests to fail. Stale addresses may happen if the order of the L1 deployments happen differently since some contracts are deployed using CREATE. Run pnpm clean and rerun the tests if they are failing for an unknown reason.

Static Analysis

contracts-bedrock uses slither as its primary static analysis tool. Slither will be run against PRs as part of CI, and new findings will be reported as a comment on the PR. CI will fail if there are any new findings of medium or higher severity, as configured in the repo's Settings > Code Security and Analysis > Code Scanning > Protection rules setting.

There are two corresponding jobs in CI: one calls "Slither Analysis" and one called "Code scanning results / Slither". The former will always pass if Slither runs successfully, and the latter will fail if there are any new findings of medium or higher severity.

Existing findings can be found in the repo's Security tab > Code Scanning section. You can view findings for a specific PR using the pr:{number} filter, such pr:9405.

For each finding, either fix it locally and push a new commit, or dismiss it through the PR comment's UI.

Note that you can run slither locally by running slither ., but because it does not contain the triaged results from GitHub, it will be noisy. Instead, you should run slither ./path/to/contract.sol to run it against a specific file.