Important

Bolt is an implementation of permissionless proposer commitments that is fully compatible with PBS. In its essence, it consists in a fork of the MEV-Boost stack that allows users to request commitments like preconfirmations from proposers, and then adds a way for proposers to commit to transaction inclusion in a way that is verifiable on-chain.

• How it works
• Project structure
  • Additional components
• Kurtosis Devnet
  • Requirements and setup
  • Running the devnet
  • Stopping the devnet
• License

How it works

The technical flow of Bolt can be summarized in the following steps:

1. Users submit transactions to an RPC endpoint that will forward them to the proposer opted-in to Bolt in the beacon chain lookahead window.
2. The proposer can accept this request and turn it into a commitment relative to the block that it is going to propose. This commitment acts as guarantee of inclusion of the transaction in the block, also known as a preconfirmation.
3. Near the time of block proposal, the proposer will share the list of committed transactions with the relays that are connected to block builders. This list is called a constraint.
4. Builders subscribe to proposer constraints in real time through a new relay streaming endpoint to keep informed about the outstanding preconfirmations.
5. Builders build valid blocks that adhere to all constraints, and append inclusion proofs together with the bids to the relay for trustless verification.
6. When it's time to propose a block, the proposer will fetch the best valid bid from the relay, and verify its inclusion proofs locally before signing the header.
7. If the constraints are respected, the proposer can propose the payload as usual by sending the signed header back to the relay. If not, the proposer can self-build a payload and propose it directly instead.

Here is a diagram illustrating the flow explained above:

sequenceDiagram
    participant Beacon Node as beacon node
    participant Bolt Sidecar as bolt-sidecar
    participant MEV-Boost as mev-boost
    participant PBS Relay as pbs relay

    Beacon Node->>Bolt Sidecar: /eth/v1/builder/header
    Note over Beacon Node, Bolt Sidecar: when it's time, the proposer's beacon node will ask for an externally built payload

    Bolt Sidecar->>MEV-Boost: /eth/v1/builder/header
    MEV-Boost->>PBS Relay: /eth/v1/builder/header_with_proofs
    PBS Relay->>MEV-Boost: ExecutionPayloadHeader + InclusionProofs
    MEV-Boost->>Bolt Sidecar: ExecutionPayloadHeader + InclusionProofs

    alt Inclusion proofs sent by the relay are VALID
        Bolt Sidecar->>Beacon Node: ExecutionPayloadHeader
        Bolt Sidecar->>MEV-Boost: /eth/v1/builder/blinded-blocks
        MEV-Boost->>PBS Relay: /eth/v1/builder/blinded-blocks
        Note over MEV-Boost, PBS Relay: the relay can now broadcast the full payload.
    else Inclusion proofs sent by the relay are INVALID
        PBS Relay->>MEV-Boost: nil response
        Bolt Sidecar->>Beacon Node: bolt-sidecar will generate a fallback ExecutionPayload that follows all constraints committed to by the proposer.
        Bolt Sidecar->>MEV-Boost: /eth/v1/builder/blinded-blocks
        MEV-Boost->>PBS Relay: /eth/v1/builder/blinded-blocks
        PBS Relay->>Beacon Node: ExecutionPayload
        Note over Beacon Node, Bolt Sidecar: after receiving the payload, the beacon node will broadcast it to the beacon chain p2p network.
    end

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Project structure

This repository contains most of the necessary components of the Bolt protocol stack. In particular, the core components are:

• Bolt Sidecar: New validator software (akin to mev-boost) that handles the receipt of preconfirmation requests from users, translates them into constraints, and forwards them to relays. Additionally, it handles the fallback logic to produce a block locally when relays send invalid inclusion proofs.
• Bolt Contracts: A set of smart contracts for peripheral functionality such as proposer registration and permissionless dispute resolution for attributable faults.
• Bolt Boost: A Commit-Boost module that implements the Constraints-API.
• Bolt CLI: A CLI tool to interact with Bolt components in a safe and easy way.
• Testnets: A set of guides and scripts to deploy the Bolt contracts on testnets.
• Scripts: A collection of scripts to build and run the Kurtosis devnet locally.

Additional components

Bolt also relies on a few external components that are not part of this repository:

• Ethereum Package: A fork of the Kurtosis Ethereum package with custom components for Bolt.
• Helix Relay: A fork of the Gattaca Helix relay that implements the Constraints API to proxy requests from the Bolt Sidecar to the connected builders.
• Bolt Builder: A fork of the Flashbots builder that subscribes to new constraints from relays, builds blocks that respect them, and includes the necessary proofs of inclusion in the bids submitted to relays.
• Bolt MEV-Boost: A fork of the Flashbots MEV-Boost sidecar that includes new API endpoints to proxy requests from the Bolt Sidecar to the connected relays.

List of legacy components that are not updated to the latest version of Bolt:

• Web demo: A simple web interface to interact with the Bolt Sidecar and submit preconfirmation requests to proposers for inclusion in blocks.
• MEV-Boost-Relay: A fork of the Flashbots MEV-Boost relay that includes new API endpoints to proxy requests from the Bolt Sidecar to the connected builders.

Kurtosis Devnet

We are using a forked Kurtosis devnet stack, with custom Docker images for the core components outlined above. The exact version of the Ethereum-package used in our devnet can be seen here.

Requirements and setup

8GB of RAM and a modern laptop CPU are recommended to run the devnet efficiently, but it should work on most machines. Please Open an issue if you encounter any problems.

Make sure you have the following requirements on your machine:

• Docker engine installed and running
• Just installed
• Kurtosis CLI installed
• Foundry installed
• Rust & Cargo installed

Note

The Kurtosis CLI version tested is 0.88.16. Some issues may arise if you are using a different version.

Please make sure to install the correct version.

Then, clone this repository and navigate to the root directory of the project:

git clone git@github.com:chainbound/bolt.git && cd bolt

Running the devnet

Running the devnet is straightforward once you have the requirements installed. Just run the following commands in your terminal:

# build all necessary docker images locally first
just build-local-images

# spin up the kurtosis devnet on your machine
just up

Commit-Boost support

The devnet by default will run using a fork of MEV-Boost which supports the Constraints-API. Bolt also supports Commit-Boost by providing a compatible MEV-Boost module called Bolt-Boost that implements the Constraints-API. To use it in the devnet add the appropriate bolt_boost_image in the kurtosis_config.yaml file:

# ... the rest of the file
mev_params:
  # Bolt-specific images:
  # Adding the `bolt_boost_image` will start the devnet with Bolt-Boost
  # instead of MEV-Boost
  bolt_boost_image: ghcr.io/chainbound/bolt-boost:0.1.0
  # ... the rest of the `mev_params`

Stopping the devnet

To stop the devnet, run the following command:

# if you want to simply stop all running containers
just down

# if you want to remove all the data and stop the Kurtosis engine
just clean

Note

Remember to shut down the devnet environment when you are done with it, as it consumes significant resources (CPU & RAM) on your machine.

License

MIT. Forked repositories have their own licenses.