## Hyperlane Rust implementations

### Setup

- install `rustup`
  - [link here](https://rustup.rs/)

Note: You should be running >= version `1.63.0` of the rustc compiler, you can see that version with this command and should see similar output:

```
$ rustup --version
rustup 1.24.3 (ce5817a94 2021-05-31)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.63.0 (4b91a6ea7 2022-08-08)`
```

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

Hyperlane 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.

For Ethereum and Celo connections we use
[ethers-rs](https://github.com/gakonst/ethers-rs). Please see the docs
[here](https://docs.rs/ethers/0.2.0/ethers/).

We use the tokio async runtime environment. Please see the docs
[here](https://docs.rs/tokio/1.1.0/tokio/).

### Repo layout

- `abacus-base`
  - lowest dependency abacus utilities
  - 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
- `abacus-core`
  - depends on abacus-base
  - 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)
- `chains/abacus-ethereum`
  - depends on abacus-core (and transitively abacus-base)
  - interfaces to the ethereum contracts
- `agents`
  - each of the off-chain agents implemented thus far

### Running Locally

From within the `hyperlane-monorepo/rust` directory, run

```bash
cargo run -r -p run-locally
```

or (long-form)

```bash
cargo run --release --package run-locally
```