hyperlane-monorepo/solidity/apps/contracts/xapp-template/RouterTemplate.sol

// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity >=0.6.11;

// ============ External Imports ============
import {TypedMemView} from "@summa-tx/memview-sol/contracts/TypedMemView.sol";
import {Router} from "@abacus-network/core/contracts/router/Router.sol";
import {XAppConnectionClient} from "@abacus-network/core/contracts/router/XAppConnectionClient.sol";
// ============ Internal Imports ============
import {Message} from "./MessageTemplate.sol";

/*
============ Overview: Building a xApp ============
To implement a xApp, define the actions you would like to execute across chains.
For each type of action,
- in the xApp Router
    - implement a function like doTypeA to initiate the action from one domain to another (add your own parameters and logic)
    - implement a corresponding _handle function to receive, parse, and execute this type of message on the remote domain
    - add logic to the handle function to route incoming messages to the appropriate _handle function
- in the Message library,
    - implement functions to *format* the message to send to the other chain (encodes all necessary information for the action)
    - implement functions to *parse* the message once it is received on the other chain (decode all necessary information for the action)
*/
contract RouterTemplate is Router {
    // ============ Libraries ============

    using TypedMemView for bytes;
    using TypedMemView for bytes29;
    using Message for bytes29;

    // ============ Events ============

    event TypeAReceived(uint256 number);

    // ============ Constructor ============

    constructor(address _xAppConnectionManager) {
        __XAppConnectionClient_initialize(_xAppConnectionManager);
    }

    // ============ Handle message functions ============

    /**
     * @notice Receive messages sent via Abacus from other remote xApp Routers;
     * parse the contents of the message and enact the message's effects on the local chain
     * @dev Called by an Abacus Inbox contract while processing a message sent via Abacus
     * @param _origin The domain the message is coming from
     * @param _sender The address the message is coming from
     * @param _message The message in the form of raw bytes
     */
    function handle(
        uint32 _origin,
        bytes32 _sender,
        bytes memory _message
    ) external override onlyInbox onlyRemoteRouter(_origin, _sender) {
        bytes29 _msg = _message.ref(0);
        // route message to appropriate _handle function
        // based on what type of message is encoded
        if (_msg.isTypeA()) {
            _handleTypeA(_msg);
        } else {
            // if _message doesn't match any valid actions, revert
            require(false, "!valid action");
        }
    }

    /**
     * @notice Once the Router has parsed a message in the handle function and determined it is Type A,
     * call this internal function to parse specific information from the message,
     * and enact the message's action on this chain
     * @param _message The message in the form of raw bytes
     */
    function _handleTypeA(bytes29 _message) internal {
        // parse the information from the message
        uint256 _number = _message.number();
        // implement the logic for executing the action
        // (in this example case, emit an event with the number that was sent)
        emit TypeAReceived(_number);
    }

    // ============ Dispatch message functions ============

    /**
     * @notice Send a message of "Type A" to a remote xApp Router via Abacus;
     * this message is called to take some action in the cross-chain context
     * Example message types:
     * Sending tokens from this chain to the destination chain;
     * params would be the address of the token, the amount of the token to send, and the address of the recipient
     * @param _destinationDomain The domain to send the message to
     * @param _number Example parameter used in message TypeA - a number to send to another chain
     */
    function dispatchTypeA(uint32 _destinationDomain, uint256 _number)
        external
    {
        // get the xApp Router at the destinationDomain
        bytes32 _remoteRouterAddress = _mustHaveRemoteRouter(
            _destinationDomain
        );
        // encode a message to send to the remote xApp Router
        bytes memory _outboundMessage = Message.formatTypeA(_number);
        // send the message to the xApp Router
        _outbox().dispatch(
            _destinationDomain,
            _remoteRouterAddress,
            _outboundMessage
        );
    }
}