Nomad Rust implementations

Setup

• install rustup
  • link here

Note: You should be running >= version 1.52.1 of the rustc compiler, you can see that version with this command and should see similar output:

$ rustup --version
rustup 1.24.2 (755e2b07e 2021-05-12)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.52.1 (9bc8c42bb 2021-05-09)`

Useful cargo commands

• cargo doc --open
  • generate documentation and open it in a web browser
• cargo build
  • compile the project
• cargo run --example example
  • run the default executable for the current project
• cargo test
  • run the tests

Useful cargo extensions

• tree
  • show the dependency tree. Allows searching for specific packages
  • install: cargo install cargo-tree
  • invoke: cargo tree
• clippy
  • search the codebase for a large number of lints and bad patterns
  • install: rustup component add clippy
  • invoke: cargo clippy
• expand
  • expand macros and procedural macros. Show the code generated by the preprocessor
  • useful for debugging #[macros] and macros!()
  • install: cargo install cargo-expand
  • invoke cargo expand path::to::module

Architecture

The on-chain portions of nomad are written in Solidity. The rust portions are exclusively off-chain. Later, there may be on-chain rust for Near/Solana/ Polkadot.

Nomad will be managed by a number of small off-chain programs ("agents"). Each of these will have a specific role. We want these roles to be simple, and easily described. Each of these agents will connect to a home chain and any number of replicas. They need to be configured with chain connection details and have access to a reliable node for each chain.

Some agent sketches:

• updater
  • Needs only a connection to the home chain
  • Signs upate attestations and submits them to the home chain
• watcher
  • Observe the home chain
  • Observe as many replicas as possible
  • Cache updates
  • Check for fraud
  • Submit fraud to the home chain
  • if configured, issue emergency stop transactions
• relayer
  • Relays signed updates from the home to the replica
• processor
  • retrieve leaves from home chain
  • observe >=1 replica
  • generate proofs for the messages
  • submit messages and proofs to the replica for processing
  • config option: gas params

For Ethereum and Celo connections we use ethers-rs. Please see the docs here.

We use the tokio async runtime environment. Please see the docs here.

Repo layout

• nomad-core
  • contains implementations of core primitives
  • this includes
    • traits (interfaces) for the on-chain contracts
    • model implementations of the contracts in rust
    • merkle tree implementations (for provers)
• nomad-base
  • contains shared utilities for building off-chain agents
  • this includes
    • trait implementations for different chains
    • shared configuration file formats
    • basic setup for an off-chain agent
• chains/nomad-ethereum
  • interfaces to the ethereum contracts
• agents
  • each of the off-chain agents implemented thus far

High-level guide to building an agent

• cargo new $AGENT_NAME
• add the new directory name to the workspace Cargo.toml
• add dependencies to the new directory's Cargo.toml
  • copy most of the dependencies from nomad-base
• create a new module in src/$AGENT_NAME.rs
  • add a new struct
  • implement nomad_base::NomadAgent for your struct
  • your run function is the business logic of your agent
• create a new settings module src/settings.rs
  • reuse the Settings objects from nomad_base::settings
  • make sure to read the docs :)
  • add your own new settings
• in $AGENT_NAME/src/main.rs
  • add mod _____ declarations for your agent and settings modules
  • create main and setup functions
  • follow the pattern in nomad-base/src/main.rs
• make a config folder and a toml file
  • Make sure to include your own settings from above