Message Ordering

// appends "01000104", the ExecutorOrderedExecutionOption, to your options bytes array
_options = OptionsBuilder.newOptions().addExecutorLzReceiveOption(200000, 0).addExecutorOrderedExecutionOption();

/**
 * @notice skips exactly the next‐in‐line message, and keeps our mapping in perfect sync
 * @param _srcEid the LayerZero source chain ID
 * @param _sender the address of the remote sender (packed as bytes32)
 * @param _nonce  the nonce to skip — must equal nextNonce(_srcEid,_sender)
 */
function skipInboundNonce(
  uint32 _srcEid,
  bytes32 _sender,
  uint64 _nonce
) public onlyOwner {
  // 1) sanity‐check that you're skipping exactly the next message
  uint64 expected = nextNonce();
  require(_nonce == expected, "OApp: invalid skip nonce");

  // 2) fire the skip on the endpoint
  IMessagingChannel(address(endpoint)).skip(
      address(this),
      _srcEid,
      _sender,
      _nonce
  );

  // 3) sync our mapping
  receivedNonce[_srcEid][_sender] = _nonce;
}

pragma solidity ^0.8.20;

import { OApp } from "@layerzerolabs/oapp-evm/contracts/oapp/OApp.sol"; // Import OApp and other necessary contracts/interfaces

/**
 * @title OmniChain Nonce Ordered Enforcement Example
 * @dev Implements nonce ordered enforcement for your OApp.
 */
contract MyNonceEnforcementExample is OApp {
    // Mapping to track the maximum received nonce for each source endpoint and sender
    mapping(uint32 eid => mapping(bytes32 sender => uint64 nonce)) private receivedNonce;

    /**
     * @dev Constructor to initialize the omnichain contract.
     * @param _endpoint Address of the LayerZero endpoint.
     * @param _owner Address of the contract owner.
     */
    constructor(address _endpoint, address _owner) OApp(_endpoint, _owner) {}

    /**
     * @dev Public function to get the next expected nonce for a given source endpoint and sender.
     * @param _srcEid Source endpoint ID.
     * @param _sender Sender's address in bytes32 format.
     * @return uint64 Next expected nonce.
     */
    function nextNonce(uint32 _srcEid, bytes32 _sender) public view virtual override returns (uint64) {
        return receivedNonce[_srcEid][_sender] + 1;
    }

    /**
     * @dev Internal function to accept nonce from the specified source endpoint and sender.
     * @param _srcEid Source endpoint ID.
     * @param _sender Sender's address in bytes32 format.
     * @param _nonce The nonce to be accepted.
     */
    function _acceptNonce(uint32 _srcEid, bytes32 _sender, uint64 _nonce) internal virtual override {
        receivedNonce[_srcEid][_sender] += 1;
        require(_nonce == receivedNonce[_srcEid][_sender], "OApp: invalid nonce");
    }

    // @dev Override receive function to enforce strict nonce enforcement.
    function _lzReceive(
        Origin calldata _origin,
        bytes32 _guid,
        bytes calldata _message,
        address _executor,
        bytes calldata _extraData
    ) public payable virtual override {
        _acceptNonce(_origin.srcEid, _origin.sender, _origin.nonce);
        // your _lzReceive(...) logic continues here
    }
}