Hello world scout script in assemblyscript

README.md

A simple scout script which simply increments the last byte of the pre state root, and saves that as post state root.

Build

Install assemblyscript:

npm i -D AssemblyScript/assemblyscript

Compile source:

asc index.ts -b build/optimized.wasm -t build/optimized.wat --sourceMap --validate --optimize --noAssert

Run

Put astest.yaml in scout's directory, fix the path to point to the built wasm module and run:

target/release/phase2-scout astest.yaml

astest.yaml

beacon_state:
  execution_scripts:
    - path/to/module.wasm
shard_pre_state:
  exec_env_states:
    - "0000000000000000000000000000000000000000000000000000000000000002"
shard_blocks:
  - env: 0
    data: ""
  - env: 0
    data: ""
shard_post_state:
  exec_env_states:
    - "0000000000000000000000000000000000000000000000000000000000000004"

env.ts

export declare function eth2_loadPreStateRoot(offset: u32): void;
export declare function eth2_blockDataSize(): u32;
export declare function eth2_blockDataCopy(outputOffset: u32, offset: u32, length: u32): void;
export declare function eth2_savePostStateRoot(offset: u32): void;
export declare function eth2_pushNewDeposit(offset: u32, length: u32): void;

index.ts

import "allocator/tlsf"
import * as env from './env'

export function main(): void {
  var preStateRootPtr: usize = memory.allocate(32)
  env.eth2_loadPreStateRoot(preStateRootPtr)

  var postStateRootPtr: usize = memory.allocate(32)
  memory.copy(postStateRootPtr, preStateRootPtr, 32)

  var lastByte: u8 = load<u8>(preStateRootPtr, 31)
  store<u8>(postStateRootPtr, lastByte + 1, 31)

  env.eth2_savePostStateRoot(postStateRootPtr)
}

tsconfig.json

{
  "extends": "node_modules/assemblyscript/std/assembly.json",
  "include": [
    "./**/*.ts"
  ]
}