Helios

Helios is a fully trustless, efficient, and portable Ethereum light client written in Rust.

Helios converts an untrusted centralized RPC endpoint into a safe unmanipulable local RPC for its users. It syncs in seconds, requires no storage, and is lightweight enough to run on mobile devices.

The entire size of Helios's binary is 13Mb and should be easy to compile into WebAssembly. This makes it a perfect target to embed directly inside wallets and dapps.

Installing

First install heliosup, Helios's installer:

curl https://raw.githubusercontent.com/a16z/helios/master/heliosup/install | bash

To install Helios, run heliosup.

Usage

To run Helios, run the below command, replacing $ETH_RPC_URL with an RPC provider URL such as Alchemy or Infura:

helios --execution-rpc $ETH_RPC_URL

$ETH_RPC_URL must be an Ethereum provider that supports the eth_getProof endpoint. Infura does not currently support this. We recommend using Alchemy.

Helios will now run a local RPC server at http://127.0.0.1:8545.

Warning

Helios is still experimental software. While we hope you try it out, we do not suggest adding it as your main RPC in wallets yet. Sending high-value transactions from a wallet connected to Helios is discouraged.

Additional Options

--consensus-rpc or -c can be used to set a custom consensus layer rpc endpoint. This must be a consenus node that supports the light client beaconchain api. We recommend using Nimbus for this. If no consensus rpc is supplied, it defaults to https://www.lightclientdata.org which is run by us.

--checkpoint or -w can be used to set a custom weak subjectivity checkpoint. This must be equal the first beacon blockhash of an epoch. Weak subjectivity checkpoints are the root of trust in the system. If this is set to a malicious value, an attacker can cause the client to sync to the wrong chain. Helios sets a default value initially, then caches the most recent finalized block it has seen for later use.

--network or -n sets the network to sync to. Current valid options are mainnet and goerli, however users can add custom networks in their configuration files.

--rpc-port or -p sets the port that the local RPC should run on. The default value is 8545.

--data-dir or -d sets the directory that Helios should use to store cached weak subjectivity checkpoints in. Each network only stores the latest checkpoint, which is just 32 bytes.

Configuration Files

All configuration options can be set on a per-network level in ~/.helios/helios.toml. Here is an example config file:

[mainnet]
consensus_rpc = "https://www.lightclientdata.org"
execution_rpc = "https://eth-mainnet.g.alchemy.com/v2/XXXXX"
checkpoint = "0x85e6151a246e8fdba36db27a0c7678a575346272fe978c9281e13a8b26cdfa68"

[goerli]
consensus_rpc = "http://testing.prater.beacon-api.nimbus.team"
execution_rpc = "https://eth-goerli.g.alchemy.com/v2/XXXXX"
checkpoint = "0xb5c375696913865d7c0e166d87bc7c772b6210dc9edf149f4c7ddc6da0dd4495"

Using Helios as a Library

Helios can be imported into any Rust project. Helios requires the Rust nightly toolchain to compile.

use std::{str::FromStr, env};

use helios::{client::ClientBuilder, config::networks::Network, types::BlockTag};
use ethers::{types::Address, utils};
use eyre::Result;

#[tokio::main]
async fn main() -> Result<()> {
    let untrusted_rpc_url = env::var("UNTRUSTED_RPC_URL")?;

    let mut client = ClientBuilder::new()
        .network(Network::MAINNET)
        .consensus_rpc("https://www.lightclientdata.org")
        .execution_rpc(&untrusted_rpc_url)
        .build()?;

    client.start().await?;

    let head_block_num = client.get_block_number().await?;
    let addr = Address::from_str("0x00000000219ab540356cBB839Cbe05303d7705Fa")?;
    let block = BlockTag::Latest;
    let balance = client.get_balance(&addr, block).await?;

    println!("synced up to block: {}", head_block_num);
    println!("balance of deposit contract: {}", utils::format_ether(balance));

    Ok(())
}

Contributing

All contributions to Helios are welcome. Before opening a PR, please submit an issue detailing the bug or feature. When opening a PR, please ensure that your contribution builds on the nightly rust toolchain, has been linted with cargo fmt, and contains tests when applicable.

Telegram

If you are having trouble with Helios or are considering contributing, feel free to join our telegram here.

Disclaimer

This code is being provided as is. No guarantee, representation or warranty is being made, express or implied, as to the safety or correctness of the code. It has not been audited and as such there can be no assurance it will work as intended, and users may experience delays, failures, errors, omissions or loss of transmitted information. Nothing in this repo should be construed as investment advice or legal advice for any particular facts or circumstances and is not meant to replace competent counsel. It is strongly advised for you to contact a reputable attorney in your jurisdiction for any questions or concerns with respect thereto. a16z is not liable for any use of the foregoing, and users should proceed with caution and use at their own risk. See a16z.com/disclosures for more info.