Nomad

Nomad is a cross-chain communication standard that supports passing messages between blockchains easily and inexpensively. Like IBC light clients and similar systems, Nomad establishes message-passing channels between chains. Once a channel is established, any application on that chain can use it to send messages to others chains.

Nomad is an implementation and extension of the Optics protocol (OPTimistic Interchain Communication), originally developed at Celo.

Compared to light clients, Nomad has weaker security guarantees and a longer latency period. However, these tradeoffs allow Nomad to be implemented on any smart contract chain without expensive light client development. Unlike light clients, Nomad does not use gas verifying remote chain block headers.

Nomad is designed to prioritize:

• Operating costs: No gas-intensive header verification or state management
• Implementation speed and cost: Uses simple smart contracts without complex cryptography
• Ease of use: Straightforward interface for maintaining xApp connections
• Security: Relies on a 1/n honest watcher assumption for security

You can read more about Nomad's architecture at our main documentation site.

Nomad Rust Repository

Nomad's off-chain systems are written in Rust for speed, safety and reliability. (Nomad's on-chain systems are written in Solidity and are available here.)

Rust Setup

• Install rustup from here and run it

Note: You should be running at least version 1.52.1 of the rustc compiler. Check it with rustup --version

$ 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)`

Rust uses cargo for package management, building, testing and other essential tasks.

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

Nomad uses the tokio async runtime environment. Please see the docs here.

Running the Test Suite

• cargo test --workspace --all-features

This will run the full suite of tests for this repository.

Generate Documentation

• cargo doc --open

This will generate this repos documentation and open it in a web browser.

Agent Architecture

The off-chain portion of Nomad is a set of agents each with a specific role:

• updater
  • Signs update attestations and submits them to the home chain
• watcher
  • Observes the home chain
  • Observes one or more replica chains
  • Check for fraud
  • Submits fraud to the home chain
  • If configured, issues emergency stop transactions
• relayer
  • Relays signed updates from the home chain to the replicas
• processor
  • Retrieves Merkle leaves from home chain
  • Observes one or more replica chains
  • Generates proofs for passed messages
  • Submits messages with proofs to replica chains

Repository Layout

• nomad-base
  • A VM-agnostic toolkit for building agents
    • Common agent structs
    • Agent traits
    • Agent settings
    • NomadDB (RocksDB)
    • Concrete contract objects (for calling contracts)
    • VM-agnostic contract sync
    • Common metrics
• nomad-core
  • Contains implementations of core primitives
    • Core primitives
    • Core data types
    • Contract and chain traits
• nomad-types
  • Common types used throughout the stack
• chains
  • A collection of crates for interacting with different VMs
    • Ethereum
    • More coming...
• accumulator
  • Contains Merkle tree implementations
• agents
  • A collection of VM-agnostic agent implementations
• configuration
  • An interface for persisting and accessing config data
    • JSON config files (for development, staging, production)
    • An interface for retrieving agent and system config
    • An interface for retrieving agent secrets

Contributing

All contributions, big and small, are welcome. All contributions require signature verification and contributions that touch code will have to pass linting and formatting checks as well as tests.

Commit signature verification

Commits (and tags) for this repository require signature verification. You can learn about signing commits here.

After signing is set up, commits can be signed with the -S flag.

• git commit -S -m "your commit message"

Testing, Linting and Formatting

If your commits have changed code, please ensure the following have been run and pass before submitting a PR:

cargo check --workspace
cargo test --workspace --all-features
cargo fmt --all
cargo clippy --workspace --all-features -- -D warnings

Advanced Usage

Building Agent Images

There exists a docker build for the agent binaries. These docker images are used for deploying the agents in a production environment.

./build.sh <image_tag>
./release.sh <image_tag>

Adding a New Agent

• Run 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
  • Add your own new settings
  • Make sure to read the docs :)
• In $AGENT_NAME/src/main.rs:
  • Add mod declarations for your agent and settings modules
  • Create main and setup functions
  • Use the implementation in agents/kathy/src/main.rs as a guide
• Add required config to configuration/configs/* for the agent

Miscellaneous

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