In this tutorial, we will explore how to use deBridge to perform cross-chain royalty payments. From a high level, it involves:
  1. Constructing a deBridge API call that will return tx data to swap tokens across chains and pay an IP Asset on Story
  2. Executing the API call to receive a response
  3. Verifying the API response to see that it contains tx data to swap and pay royalties
  4. Executing the transaction (using the returned tx data) on the source chain

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Prerequisites

For easy setup, you can actually clone the Story Protocol Boilerplate and view the test in the test/6_DebridgeHook.t.sol file. This already covers steps 1-3 below.

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Step 1: Constructing the deBridge API Call

The first step is to construct a deBridge API call. The purpose of this API call is to receive back a response that will contain transaction data so we can then execute it on the source chain. Normally, this deBridge order would swap tokens from one chain to another. We can optionally attach a dlnHook that will execute an arbitrary action upon order completion (ex. after $ETH has been swapped for $WIP). In this case, the dlnHook will be a call to payRoyaltyOnBehalf on Story’s RoyaltyModule contract, which will pay royalties to an IP Asset. To summarize, we will construct a deBridge API call that says “we want to swap $ETH for $WIP, and then pay royalties using that $WIP to an IP Asset on Story”.

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Step 1a. Constructing the dlnHook

The dlnHook is a JSON object that will be attached to the deBridge API call. It will contain the following information:
  • The type of action to execute (evm_transaction_call)
  • The address of the contract to call (ROYALTY_MODULE)
  • The calldata to execute (payRoyaltyOnBehalf)
Check out the whole function by going here.
Solidity
function _buildRoyaltyPaymentHook() internal pure returns (string memory dlnHookJson) {
    // an IP Asset on Story mainnet (it is actually Ippy - Story's mascot)
    address ipAssetId = 0xB1D831271A68Db5c18c8F0B69327446f7C8D0A42;

    bytes memory calldata_ = abi.encodeCall(
        IRoyaltyModule.payRoyaltyOnBehalf,
        (
            ipAssetId, // IP asset receiving royalties
            address(0), // External payer (0x0)
            0x1514000000000000000000000000000000000000, // Payment token (WIP)
            1e18 // 1 WIP
        )
    );

    dlnHookJson = string.concat(
        '{"type":"evm_transaction_call",',
        '"data":{"to":"',
        _addressToHex(ROYALTY_MODULE),
        '",',
        '"calldata":"',
        calldata_.toHexString(),
        '",',
        '"gas":0}}'
    );
}

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Step 1b. Constructing the deBridge API Call

Now that we have the dlnHook, we can construct the whole deBridge API call, including the dlnHook.
Check out the whole function by going here.
You can view deBridge’s documentation on the create-tx endpoint here.
AttributeDescription
srcChainIdThe ID of the source blockchain (e.g., Ethereum mainnet is 1).
srcChainTokenInThe address of the token being swapped on the source chain (ETH in this case).
srcChainTokenInAmountThe amount of the source token to swap, set to auto for automatic calculation.
dstChainIdThe ID of the destination blockchain (e.g., Story mainnet is 100000013).
dstChainTokenOutThe address of the token to receive on the destination chain (WIP token).
dstChainTokenOutAmountThe amount of the destination token to receive. It should be the same as the amount we’re paying in payRoyaltyOnBehalf in step 1a.
dstChainTokenOutRecipientThis can just be the same as senderAddress.
senderAddressThe address initiating the transaction.
srcChainOrderAuthorityAddressThe address authorized to manage the order on the source chain. This can just be the same as senderAddress.
dstChainOrderAuthorityAddressThe address authorized to manage the order on the destination chain. This can just be the same as senderAddress.
enableEstimateA flag to enable transaction simulation and estimation.
prependOperatingExpensesA flag to include operating expenses in the transaction.
dlnHookThe URL-encoded hook that specifies additional actions to execute post-swap.
Solidity
function _buildApiRequest(string memory dlnHookJson) internal pure returns (string memory apiUrl) {
    address senderAddress = 0xcf0a36dEC06E90263288100C11CF69828338E826; // Example sender

    apiUrl = string.concat(
        "https://dln.debridge.finance/v1.0/dln/order/create-tx",
        "?srcChainId=1", // Ethereum mainnet
        "&srcChainTokenIn=",
        _addressToHex(address(0)), // ETH (native token)
        "&srcChainTokenInAmount=auto", // 0.01 ETH
        "&dstChainId=100000013", // Story mainnet
        "&dstChainTokenOut=",
        _addressToHex(WIP_TOKEN), // WIP token
        "&dstChainTokenOutAmount=",
        StringUtils.toString(PAYMENT_AMOUNT),
        "&dstChainTokenOutRecipient=",
        _addressToHex(senderAddress),
        "&senderAddress=",
        _addressToHex(senderAddress),
        "&srcChainOrderAuthorityAddress=",
        _addressToHex(senderAddress),
        "&dstChainOrderAuthorityAddress=",
        _addressToHex(senderAddress),
        "&enableEstimate=true", // Enable simulation
        "&prependOperatingExpenses=true",
        "&dlnHook=",
        _urlEncode(dlnHookJson) // URL-encoded hook
    );
}

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Step 2: Executing the API Call

Once the API call is constructed, execute it to receive a response. This response includes transaction data and an estimate for running the transaction on the source swap chain (e.g., Ethereum, Solana).
Check out the whole function by going here.
Solidity
function _executeApiCall(string memory apiUrl) internal returns (string memory response) {
    console.log("deBridge API Request:");
    console.log(apiUrl);
    console.log("");

    string[] memory curlCommand = new string[](3);
    curlCommand[0] = "curl";
    curlCommand[1] = "-s";
    curlCommand[2] = apiUrl;

    bytes memory responseBytes = vm.ffi(curlCommand);
    response = string(responseBytes);

    console.log("deBridge API Response:");
    console.log(response);
    console.log("");
}

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Step 3: Verifying the API Response

Verify that the API call returns transaction data and an estimate. This step ensures that the transaction can be executed on the source chain.
Solidity
function _validateApiResponse(string memory response) internal pure {
    require(bytes(response).length > 0, "Empty API response");

    require(_contains(response, '"estimation"'), "Missing estimation field");
    require(_contains(response, '"tx"'), "Missing transaction field");
    require(_contains(response, '"orderId"'), "Missing order ID");
    require(_contains(response, '"dstChainTokenOut"'), "Missing destination token info");

    require(
        _contains(response, "d2577f3b"), // payRoyaltyOnBehalf selector
        "Hook not properly integrated in transaction"
    );

    require(
        _contains(_toLower(response), _toLower(_addressToHex(WIP_TOKEN))),
        "WIP token address not found in response"
    );
}
In this response is the following:
You can view the whole API return type here.
{
    ..., // other fields
    "tx": {
        "value": string,
        "data": string,
        "to": string
    }
}

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Step 4: Executing the Transaction on the Source Chain

Next, you would take the API response and execute the transaction on the source chain.
View the docs here on submitting the transaction, including how this would be done differently on Solana.
TypeScript
import { mainnet } from "viem/chains";
import { createWalletClient, http, WalletClient } from "viem";
import { privateKeyToAccount, Address, Account } from "viem/accounts";
import dotenv from "dotenv";

dotenv.config();

// Validate environment variables
if (!process.env.WALLET_PRIVATE_KEY) {
  throw new Error("WALLET_PRIVATE_KEY is required in .env file");
}

// Create account from private key
const account: Account = privateKeyToAccount(
  `0x${process.env.WALLET_PRIVATE_KEY}` as Address
);

// Initialize the wallet client
const walletClient = createWalletClient({
  chain: mainnet,
  transport: http("https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID"), // Use Infura or another Ethereum provider
  account,
}) as WalletClient;

// Function to send a transaction
async function sendTransaction(apiResponse: ApiResponse) {
  // Extract transaction details from the API response
  const transactionRequest = {
    to: apiResponse.tx.to, // Extracted from API response
    value: BigInt(apiResponse.tx.value), // Convert value to BigInt
    data: apiResponse.tx.data, // Extracted from API response
    account, // Include the account
    chain: mainnet, // Include the chain
  };

  try {
    const txHash = await walletClient.sendTransaction(transactionRequest);
    console.log("Transaction sent:", txHash);

    // Wait for the transaction to be mined
    const receipt = await walletClient.waitForTransactionReceipt(txHash);
    console.log("Transaction mined:", receipt.transactionHash);
  } catch (error) {
    console.error("Error sending transaction:", error);
  }
}

// Example usage with a mock API response
const mockApiResponse: ApiResponse = {
  // ... other fields
  tx: {
    to: "0xRecipientAddress", // Replace with the actual recipient's address
    value: "1000000000000000000", // 1 ETH in wei
    data: "0x", // No data for a simple ETH transfer
  },
  // ... other fields
};

// Execute the function to send the transaction
sendTransaction(mockApiResponse);

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Conclusion

Congratulations! You have successfully set up cross-chain royalty payments using deBridge. This tutorial demonstrated how to construct and execute a deBridge API call, verify the response, and perform the transaction on the source chain.