Transfer and Call Pattern

Overview

The Transfer and Call Pattern enables a contract to both bridge assets via Hyperlane Warp Routes and execute an action on the destination chain after the assets arrive.

This pattern is useful for cases where an action depends on token balances after bridging, such as:

• automated deposits
• staking
• contract interactions.

While Warp Routes handle cross-chain token transfers, this pattern extends their capabilities by using Interchain Accounts (ICA) to execute arbitrary logic on the destination chain.

Use Cases

Some scenarios include:

• A user deposits assets on an L2, mints a derivative, and then needs to bridge the underlying asset to an L1 vault for further use.
• A protocol facilitates faster withdrawals by using an L1 liquidity pool, allowing users to bypass extended bridge withdrawal delays, while still ensuring final settlement occurs through the rollup bridge.

How It Works

1. Tokens are transferred from the sender to the contract.
2. An Interchain Account (ICA) is derived for the contract on the destination chain.
3. The Warp Route transfer is initiated, sending the tokens cross-chain.
4. A remote contract call is executed after the tokens arrive.

The Solidity function below demonstrates this pattern:

function transferAndCall(
    uint32 destination,
    uint256 amount,
    IERC20 asset, // Tokens to transfer (not derivable from TokenRouter)
    TokenRouter warpRoute,
    CallLib.Call[] calldata calls // Array of calls to execute on the destination chain
) external payable {

    // Transfer the specified amount of tokens from the sender to this contract
    asset.transferFrom(msg.sender, address(this), amount);

    // Get the interchain account address for the contract on the destination chain
    bytes32 self = interchainAccountRouter
        .getRemoteInterchainAccount(destination, address(this))
        .addressToBytes32();

    // Quote the gas fee for the warp route payment
    uint256 warpFee = warpRoute.quoteGasPayment(destination);

    // Initiate the warp route transfer to send tokens cross-chain
    warpRoute.transferRemote{value: warpFee}(destination, self, amount);

    // Execute the specified interchain calls using the remaining gas funds
    interchainAccountRouter.callRemote{value: msg.value - warpFee}(
        destination,
        calls
    );
}

Diagram

[to_do]

Considerations

• The contract must ensure the tokens arrive before executing the follow-up action.
• If the contract executing the action is not permissioned, anyone could call it (depending on its implementation).