Scout

Scout is a Ethereum 2.0 Phase 2 execution prototyping engine.

Warning: this is super experimental

Goals

1. Create a (black boxed) execution prototyping engine
2. Create some example contracts ("execution scripts")
3. Enable "easy" onboarding for creating scripts
4. By having actual real world use cases in scripts, we can benchmark the design and identify bottlenecks

What is this?

This engine intentionally avoids a lot of details and therefore it is not usable as a Eth 2.0 client. Instead of being a client, it should support reading and outputting shard/beacon states in a YAML format.

How to use this?

Install Rust first. Add the wasm32 target to the toolchain and install chisel using cargo:

rustup target add wasm32-unknown-unknown
rustup component add rustfmt
rustup update
cargo install chisel

There is a Makefile to make building easy:

• build will build all components (the runner and the example scripts)
• test will run tests using the YAML test files
• all will do both

The runner is called scout and is available at target/release/phase2-scout after being built.

The runner expects a YAML test file:

beacon_state:
  execution_scripts:
    - scripts/helloworld/target/wasm32-unknown-unknown/release/phase2_helloworld.wasm
shard_pre_state:
  exec_env_states:
    - "0000000000000000000000000000000000000000000000000000000000000000"
shard_blocks:
  - env: 0
    data: ""
  - env: 0
    data: ""
shard_post_state:
  exec_env_states:
    - "0000000000000000000000000000000000000000000000000000000000000000"

The runner expects a filename pointing to the test file or will default to test.yaml in the local directory if nothing was specified.

How to code scripts?

An example script is located in scripts/helloworld. It uses ewasm-rust-api with the experimental eth2 feature.

extern crate ewasm_api;

use ewasm_api::*;

#[cfg(not(test))]
#[no_mangle]
pub extern "C" fn main() {
    let pre_state_root = eth2::load_pre_state_root();

    assert!(eth2::block_data_size() == 0);

    // No updates were made to the state
    let post_state_root = pre_state_root;

    eth2::save_post_state_root(post_state)
}

A better example is located in scripts/bazaar which is in essence a stateless contract. It uses SSZ serialisation. A test case is included in bazaar.yaml.

It should be possible to import any Rust crate as long as it can be compiled to the wasm32 target.

Maintainer

• Alex Beregszaszi

License

Apache 2.0