Implementing the Hub Model

Hub is the place where assets are deposited, borrowed, and repaid.

Writing the Hub Contract

🛠️ Step 1- Create Your Contract File: 🛠️

First things first! Create a new file named Hub.sol in your src/ directory. This is where all the action happens!

Step 2: Kick things off by adding the license and the libraries you’ll need. Paste the following code:

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;
import "wormhole-solidity-sdk/WormholeRelayerSDK.sol";

Remember our Cross Chain Mailbox tutorial? Yep, we’re using wormhole-solidity-sdk again for those awesome cross-chain features! 🌉

Step 3- Declare the Hub Contract: 🎨 Time to declare our Hub contract! 🎉 Add this code snippet:

contract Hub is TokenSender, TokenReceiver {
   uint256 constant GAS_LIMIT = 250_000;
   enum Action {DEPOSIT, WITHDRAW, BORROW, REPAY}

Here, our Hub contract inherits from TokenSender and TokenReceiver. This aligns perfectly with the article’s point about the hub being the central point for all token transactions. 🔄

Step 4 - Map Out Deposits and Borrows: 🗺️ Let’s create some mappings to keep tabs on user deposits and borrows. 🗺️

   mapping(address => mapping(address => uint256)) public vaultDeposits;
   mapping(address => mapping(address => uint256)) public vaultBorrows;

This is like the hub’s own little ledger, keeping track of all the assets. 📚

Step 5 - Initialize the Contract: 🏗️ Now, let’s set up the constructor to initialize our contract. 🛠️

   constructor(address _wormholeRelayer, address _tokenBridge, address _wormhole)
   TokenBase(_wormholeRelayer, _tokenBridge, _wormhole)
   {}

Step 6- Quoting Function: 📊 Add a function that estimates the cost of returning assets to a spoke. This is like the hub’s own calculator! 🧮.

function quoteReturnDelivery(uint16 spokeChain) public view returns (uint256 cost) 
{
uint256 deliveryCost;

(deliveryCost,) = wormholeRelayer.quoteEVMDeliveryPrice(spokeChain, 0, GAS_LIMIT);
cost = deliveryCost + wormhole.messageFee();
}

Step 7- The Heart of the Hub: 🎛️ This function is the control center of the Hub. It’s a bit long, but it’s where the magic happens! 🌟

function receivePayloadAndTokens(
    bytes memory payload,
    TokenReceived[] memory receivedTokens,
    bytes32 sourceAddress,
    uint16 sourceChain,
    bytes32 deliveryHash
) 
internal override onlyWormholeRelayer isRegisteredSender(sourceChain, sourceAddress) replayProtect(deliveryHash) 
{
    if (receivedTokens.length == 0) {
        (Action action, address user, address tokenHomeAddress, uint256 amount) = abi.decode(payload, (Action, address, address, uint256));
        address tokenAddressOnThisChain = getTokenAddressOnThisChain(sourceChain, toWormholeFormat(tokenHomeAddress));

        if (action == Action.BORROW || action == Action.WITHDRAW) {
            if (updateHubState(action, user, tokenAddressOnThisChain, amount)) {
                sendTokenToUser(user, sourceChain, sourceAddress, tokenAddressOnThisChain, amount);
            }
        }
    } else if (receivedTokens.length == 1) {
        TokenReceived memory receivedToken = receivedTokens[0];
        (Action action, address user) = abi.decode(payload, (Action, address));

        if (action == Action.DEPOSIT || action == Action.REPAY) {
            updateHubState(action, user, receivedToken.tokenAddress, receivedToken.amount);
        }
    }
}

This function is like the Swiss Army knife of our Hub contract. It handles deposits, withdrawals, borrows, and repayments. It’s the real MVP, aligning with everything the article talks about. 🏆

Step 8- Update the Hub State: 🔄 Now, let’s add a function that updates the state of the Hub based on user actions. 🔄

function updateHubState(Action action, address user, address wrappedTokenAddress, uint256 amount) 
internal returns (bool success) 
{
    uint256 currentHubBalance = IERC20(wrappedTokenAddress).balanceOf(address(this));

    if (action == Action.DEPOSIT) {
        vaultDeposits[user][wrappedTokenAddress] += amount;

    } else if (action == Action.WITHDRAW) {
        if (vaultDeposits[user][wrappedTokenAddress] < amount) return false;
        if (currentHubBalance < amount) return false;
        vaultDeposits[user][wrappedTokenAddress] -= amount;

    } else if (action == Action.BORROW) {
        if (currentHubBalance < amount) return false;
        vaultBorrows[user][wrappedTokenAddress] += amount;

    } else if (action == Action.REPAY) {
        if (vaultBorrows[user][wrappedTokenAddress] < amount) {
            vaultDeposits[user][wrappedTokenAddress] += amount - vaultBorrows[user][wrappedTokenAddress];
            vaultBorrows[user][wrappedTokenAddress] = 0;
        } else {
            vaultBorrows[user][wrappedTokenAddress] -= amount;
        }
    }

    return true;
}

This function is like the hub’s personal assistant, updating records and making sure everything is in tip-top shape! 📋

Step 9- Close the Contract 🎉 You’ve made it to the end! Don’t forget to close the contract with a }. 🎉

Launching the Hub Contract 🚀

Alright, the coding marathon is over! Now let’s get this beauty off the ground and into the blockchain universe:

Step 1 - Choose Your Networks 🌐:
Wormhole is compatible with multiple blockchains, so go ahead and pick your top two. Once you’ve made your choice, head over to the ts-scripts/testnet/config.json file and update it. Don’t forget to grab some faucet tokens for your selected networks! 💦

Chain Name	Wormhole Chain ID	Network ID	Address	Faucets
Binance Smart Chain	4	97	0x80aC94316391752A193C1c47E27D382b507c93F3	BSC Faucet
Polygon (Mumbai)	5	80001	0x0591C25ebd0580E0d4F27A82Fc2e24E7489CB5e0	Polygon Faucet
Avalanche (Fuji)	6	43113	0xA3cF45939bD6260bcFe3D66bc73d60f19e49a8BB	Avalanche Faucet
Celo	14	44787	0x306B68267Deb7c5DfCDa3619E22E9Ca39C374f84	Celo Faucet
Moonbase	16	1287	0x0591C25ebd0580E0d4F27A82Fc2e24E7489CB5e0	Moonbase Faucet
Base	30	84531	0xea8029CD7FCAEFFcD1F53686430Db0Fc8ed384E1	Base Faucet

Step 2 - Build the Code 🏗️:
Once you’ve set up your networks and secured some faucet tokens, it’s time to build your code. Open your terminal and run:

bashCopy code

npm run build

This command will use Foundry to compile your code.

Step 3 - Test Run 🧪:
With your testnet faucets in place, you’re all set for a test run. To kick things off, execute the following command in your terminal:

bashCopy code

EVM_PRIVATE_KEY=${PRIVATE_KEY} npm run test

Step 4 - Check the Output 📜:
If all has gone according to plan, you’ll see an output indicating that your mock tokens have been deployed. This will be followed by Wormhole’s attestation and transfer process.

And voila! 🎉 You’ve now successfully crafted two contracts that lay the foundation for building a cross-chain borrow-lend application. 🌉💰 Onward to decentralized financial innovation! 🚀🌟