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Hello World

Objective

Create a HelloWorld style example for using Wormhole's generic-messaging layer for developing xDapps (Cross-Chain Decentralized Applications).

Background

Currently, no production grade examples exist that detail how to safely integrate with Wormhole's generic-messaging layer on all available networks. Network-specific test cases and smart contract design are critical to safely operating an xDapp.

Goals

Provide a complete example for integrating with Wormhole's generic-messaging layer by providing the following components:

  • Fully documented smart contracts
  • Unit and integration test suite
  • Deployment scripts
  • Dependencies for interacting with the Wormhole smart contracts

Non-Goals

This design focuses only on providing an example of interaction with Wormhole's generic-message layer. It does not provide:

  • An example off-chain relayer
  • Testnet or mainnet deployment funds
  • An example User Interface

Detailed Design

The HelloWorld example xDapp utilizes the Wormhole generic-messaging layer to send and receive arbitrary messages/payload between smart contracts which for the sake of this example is HelloWorld.

Before the HelloWorld contracts can send and receive messages, the owner (see Registering Foreign Emitters) of the contract must invoke the registerEmitter method to register trusted HelloWorld contracts on other blockchains. The HelloWorld contracts will confirm that all messages that it receives are sent by trusted HelloWorld contracts on other blockchains.

To send a HelloWorld message, one will invoke the sendMessage method and pass an arbitrary message as an argument. The HelloWorld contract will then invoke the Wormhole core contract to publish the message. The Wormhole guardians will then attest the message after waiting for the specified number of block confirmations (referred to as wormholeFinality in the contracts).

Once the message is attested by the Wormhole guardians, one will invoke the receiveMessage method and pass the attested Wormhole message as an argument. The receiving HelloWorld contract will parse and verify the attested Wormhole message, and save the arbitrary HelloWorld message in its state.

To summarise all the Cross program invocations that interact with Wormhole core contract made->

  1. registerEmitter to flag the user's HelloWorld contract.
  2. sendMessage invoke the message parsing of wormhole which is picked by Guardians.
  3. receiveMessage to receive VAAs from the wormhole contract and verify the payload.
Screenshot 2023-08-19 at 7 41 58 PM

EVM Interface

    function sendMessage(string memory helloWorldMessage)
        public
        payable
        returns (uint64 messageSequence)
    function receiveMessage(bytes memory encodedMessage) public
    function registerEmitter(uint16 emitterChainId, bytes32 emitterAddress) public

EVM core HelloWorld contracts

Solana Interface

    pub fn initialize(ctx: Context<Initialize>)
    // creates a public function (open for cpi)
    pub fn register_emitter(
        ctx: Context<RegisterEmitter>,
        chain: u16,
        address: [u8; 32],
    )
    // register_emitter can only be invoked by the account owner 
    pub fn send_message(ctx: Context<SendMessage>, message: Vec<u8>)
    pub fn receive_message(ctx: Context<ReceiveMessage>, vaa_hash: [u8; 32])

Solana HelloWorld contracts

Registering Foreign Emitters

registerEmitter is an owner-only methods, meaning that only the owner of the contract (EVM contract deployer, payer of Solana initialize instruction) can invoke these methods.