2-way Communication Smart Contract with Solidity and Axelar

SendMessage.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import { AxelarExecutable } from '@axelar-network/axelar-gmp-sdk-solidity/contracts/executable/AxelarExecutable.sol';
import { IAxelarGateway } from '@axelar-network/axelar-gmp-sdk-solidity/contracts/interfaces/IAxelarGateway.sol';
import { IAxelarGasService } from '@axelar-network/axelar-gmp-sdk-solidity/contracts/interfaces/IAxelarGasService.sol';
import { IERC20 } from '@axelar-network/axelar-gmp-sdk-solidity/contracts/interfaces/IERC20.sol';

contract ExecutableSample is AxelarExecutable {
    string public message;
    IAxelarGasService public immutable gasService;

    constructor(address gateway_, address gasReceiver_) AxelarExecutable(gateway_) {
        gasService = IAxelarGasService(gasReceiver_);
    }

    // Call this function to update the value of this contract along with all its siblings'.
    function sendMessage(
        string calldata destinationChain,
        string calldata destinationAddress,
        string calldata value_
    ) external payable {
        require(msg.value > 0, 'Gas payment is required');

        bytes memory payload = abi.encode(value_);
        gasService.payNativeGasForContractCall{ value: msg.value }(
            address(this),
            destinationChain,
            destinationAddress,
            payload,
            msg.sender
        );
        gateway.callContract(destinationChain, destinationAddress, payload);
    }

    // Handles calls created by setAndSend. Updates this contract's value
    function _execute(
        string calldata sourceChain_,
        string calldata sourceAddress_,
        bytes calldata payload_
    ) internal override {
        // Decode the payload to retrieve the new message value
        (message) = abi.decode(payload_, (string));

        // Check if the new message is "Hello", then respond with "World"
        if (keccak256(abi.encode(message)) == keccak256(abi.encode("Hello"))) {
            gateway.callContract(sourceChain_, sourceAddress_, abi.encode("World"));
        }
    }
}