Create Custom Contracts

The following will guide you through an example implementation of using SKALE’s Native Messaging Layer to send custom information back and forth between SKALE Chains. The following implements a bi-directional flow of data to showcase both sending and receiving clearly, however, contracts can easily implement a one-way flow.

Custom Contract

// SDPX-License-Identifier: MIT
pragma solidity 0.8.9;

import { IMessageProxyForSchain } from "./IMessageProxyForSchain.sol";

contract SendNumber {

  /// @notice lastNumber is the last value recieved via IMA. This is for testing purposes
  uint256 public lastNumber;

  /// @notice the dstChainHash is the keccak256 hash of the SKALE Chain name i.e keccak256(abi.encodePacked("elated-tan-skat"))
  bytes32 public dstChainHash;

  /// @notice the dstContractAddr is the address of the receiving contract on the other chain
  address public dstContractAddr;

  /// @notice messageProxy is a predeployed contract on all SKALE Chains
  IMessageProxyForSchain public messageProxy = IMessageProxyForSchain(0xd2AAa00100000000000000000000000000000000);

  event NumberReceived(uint256 indexed number, address indexed sender);

  constructor(
    bytes32 _dstChainHash,
    address _dstContractAddr
  ) {
    dstChainHash = _dstChainHash;
    dstContractAddr = _dstContractAddr;
  }

  function sendNumberToChain(uint256 number) external {
    /// this is how you post a message to IMA
    messageProxy.postOutgoingMessage(
      dstChainHash,
      dstContractAddr,
      abi.encode(number)
    );
  }

  /// @notice this is how you recieve a message from IMA
  function postMessage(
    bytes32 schainHash,
    address sender,
    bytes calldata data
  ) external {
    if (schainHash != dstChainHash) revert("Invalid Chain Hash");
    (uint256 number) = abi.decode(data, (uint256));
    lastNumber = number;
    emit NumberReceived(number, sender);
  }
}

Key Notes

This contract is both a sender and receiver via IMA
This means it implements both postOutgoingMessage via MessageProxy interface AND postMessage which is the receiving part
This contract takes two constructor arguments to set the destination (dst) chain and contract which are later used to check and validate messages