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Setup and Installation

In this step, we’re going to

  1. Install prerequisites
  2. Create a yarn project to house everything
  3. Create a noir project for our Aztec contract
  4. Create a hardhat project for our Ethereum contract(s)
  5. Import all the Ethereum contracts we need
  6. Create a yarn project that will interact with our contracts on L1 and the sandbox

We recommend going through this setup to fully understand where things live.

However if you’d rather skip this part, our dev-rels repo contains the starter code here.

Prerequisites

/bin/sh -c "$(curl -fsSL 'https://sandbox.aztec.network')"

Create the root project and packages

Our root project will house everything ✨

mkdir aztec-token-bridge
cd aztec-token-bridge && mkdir packages

We will hold our projects inside of packages to follow the design of the project in the repo.

Create a noir project

Now inside packages create a new directory called aztec-contracts

Inside aztec-contracts, create the following file structure:

aztec-contracts
└── token_bridge
├── Nargo.toml
├── src
├── main.nr

Inside Nargo.toml add the following content:

[package]
name = "token_bridge"
authors = [""]
compiler_version = ">=0.18.0"
type = "contract"

[dependencies]
aztec = { git="https://github.com/AztecProtocol/aztec-packages/", tag="aztec-packages-v0.34.0", directory="noir-projects/aztec-nr/aztec" }
token_portal_content_hash_lib = { git="https://github.com/AztecProtocol/aztec-packages/", tag="aztec-packages-v0.34.0", directory="noir-projects/noir-contracts/contracts/token_portal_content_hash_lib" }

We will also be writing some helper functions that should exist elsewhere so we don't overcomplicated our contract. In src create two more files - one called util.nr and one called token_interface - so your dir structure should now look like this:

aztec-contracts
└── token_bridge
├── Nargo.toml
├── src
├── main.nr
├── token_interface.nr
├── util.nr

Create a JS hardhat project

In the packages dir, create a new directory called l1-contracts and run yarn init -yp && npx hardhat init inside of it. Keep hitting enter so you get the default setup (Javascript project)

mkdir l1-contracts
cd l1-contracts
yarn init -yp
npx hardhat init

Once you have a hardhat project set up, delete the existing contracts, tests, and scripts, and create a TokenPortal.sol:

rm -rf contracts test scripts
mkdir contracts && cd contracts
touch TokenPortal.sol

Now add dependencies that are required. These include interfaces to Aztec Inbox, Outbox and Registry smart contracts, OpenZeppelin contracts, and NomicFoundation.

yarn add @aztec/foundation @aztec/l1-contracts @openzeppelin/contracts && yarn add --dev @nomicfoundation/hardhat-network-helpers @nomicfoundation/hardhat-chai-matchers @nomiclabs/hardhat-ethers @nomiclabs/hardhat-etherscan @types/chai @types/mocha @typechain/ethers-v5 @typechain/hardhat chai@4.0.0 hardhat-gas-reporter solidity-coverage ts-node typechain typescript

This is what your l1-contracts should look like:

├── README.md
├── contracts
├── hardhat.config.js
├── node_modules
└── package.json

We will need to ensure we are using the correct Solidity version. Inside your hardhat.config.js update solidity version to this:

  solidity: "0.8.20",

Create src yarn project

In this directory, we will write TS code that will interact with our L1 and L2 contracts and run them against the sandbox.

We will use viem in this tutorial and jest for testing.

Inside the packages directory, run

mkdir src && cd src && yarn init -yp
yarn add typescript @aztec/aztec.js @aztec/accounts @aztec/noir-contracts.js @aztec/types @aztec/foundation @aztec/l1-artifacts viem@1.21.4 "@types/node@^20.8.2"
yarn add -D jest @jest/globals ts-jest

If you are going to track this repo using git, consider adding a .gitignore file to your src directory and adding node_modules to it.

In package.json, add:

"type": "module",
"scripts": {
"test": "NODE_NO_WARNINGS=1 node --experimental-vm-modules $(yarn bin jest)"
}

Your package.json should look something like this (do not copy and paste):

{
"name": "src",
"version": "1.0.0",
"main": "index.js",
"license": "MIT",
"private": true,
"type": "module",
"dependencies": {
"dep": "version"
},
"devDependencies": {
"dep": "version"
},
"scripts": {
"test": "NODE_NO_WARNINGS=1 node --experimental-vm-modules $(yarn bin jest)"
}
}

Create a tsconfig.json and paste this:

{
"compilerOptions": {
"rootDir": "../",
"outDir": "./dest",
"target": "es2020",
"lib": ["dom", "esnext", "es2017.object"],
"module": "NodeNext",
"moduleResolution": "NodeNext",
"strict": true,
"declaration": true,
"allowSyntheticDefaultImports": true,
"esModuleInterop": true,
"downlevelIteration": true,
"inlineSourceMap": true,
"declarationMap": true,
"importHelpers": true,
"resolveJsonModule": true,
"composite": true,
"skipLibCheck": true
},
"include": [
"packages/src/**/*",
"contracts/**/*.json",
"packages/src/**/*",
"packages/aztec-contracts/token_bridge/target/*.json"
],
"exclude": ["node_modules", "**/*.spec.ts", "contracts/**/*.ts"],
"references": []
}

The main thing this will allow us to do is to access TS artifacts that we generate later from our test.

Then create a jest config file: jest.config.json

{
"preset": "ts-jest/presets/default-esm",
"globals": {
"ts-jest": {
"useESM": true
}
},
"moduleNameMapper": {
"^(\\.{1,2}/.*)\\.js$": "$1"
},
"testRegex": "./test/.*\\.test\\.ts$",
"rootDir": "./test"
}

Finally, we will create a test file. Run this in the src directory.:

mkdir test && cd test
touch cross_chain_messaging.test.ts

Your src dir should look like:

src
├── node_modules
└── test
└── cross_chain_messaging.test.ts
├── jest.config.json
├── package.json
├── tsconfig.json

In the next step, we’ll start writing our L1 smart contract with some logic to deposit tokens to Aztec from L1.