How-to: Build a hook receiver

import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract VaultDepositReceiver {
    bytes32 public constant EXECUTE_SUCCESS =
        keccak256("circle-cctpx-execute-success");

    address public immutable service;
    address public immutable vault;

    error OnlyService();

    constructor(address _service, address _vault) {
        service = _service;
        vault = _vault;
    }

    function executeWithCrossChainToken(
        uint32 /* sourceDomain */,
        bytes calldata /* sourceAddress */,
        bytes32 /* tokenId */,
        address token,
        uint256 amount,
        uint32 /* finalityThresholdExecuted */,
        bytes calldata hookData
    ) external returns (bytes32) {
        if (msg.sender != service) revert OnlyService();

        address recipient = abi.decode(hookData, (address));
        // Example app logic only — not a CCTP requirement. Replace with your own.
        IERC20(token).approve(vault, amount);
        IVault(vault).depositFor(recipient, token, amount);

        return EXECUTE_SUCCESS;
    }
}

import { encodeAbiParameters, encodePacked } from "viem";

// hookData is an application payload — ABI encoding is fine here.
const hookData = encodeAbiParameters([{ type: "address" }], [recipient]);

// destinationAddress must be raw packed address bytes (20 bytes on EVM).
// Do not use encodeAbiParameters — that pads to 32 bytes and breaks delivery.
const destinationAddress = encodePacked(["address"], [receiverAddress]);

await walletClient.writeContract({
  address: serviceAddress,
  abi: serviceAbi,
  functionName: "crossChainTransfer",
  args: [
    tokenId,
    100n * 10n ** 18n,
    destinationDomain,
    destinationAddress,
    "0x0000000000000000000000000000000000000000000000000000000000000000",
    2000, // standard finality; prefer this for hooks
    claim,
    true, // autoExecuteHookData
    hookData,
  ],
  value: feeTotalAmount,
});