Transfer of Tokens with an Arbitrary Instruction

function iDepositMessage(
    uint256 partnerId,
    bytes32 destChainIdBytes,
    bytes calldata recipient,
    address srcToken,
    uint256 amount,
    uint256 destAmount,
    bytes memory message
) external payable {}

The flow is just the same as that of the token transfer explained before. The only difference here is the addition of the message that you need to pass.

Parameters

partnerId	Unique ID for each partner who integrates this functionality and has a fee sharing model with Router. This helps them to track and analyze their cross-chain transactions easily.
destChainIdBytes	Network IDs of the chains in bytes32 format. These can be found here.
recipient	Wallet address that will receive the tokens on the destination chain.
srcToken	Address of the token that has to be transferred from the source chain.
amount	Decimal-adjusted amount of the token that has to be transferred from the source chain.
destAmount	Minimum amount of tokens expected to be received by the recipient on the destination chain. This can be achieved by subtracting the forwarder fee from the source chain amount.
message	ABI-encoded data that we need on the destination chain to execute an instruction whenever a cross-chain request is received.

The arbitrary instruction or message that you provide here will be executed on the destination chain on the recipient contract address that you specify. That contract must implement handleMessage function given below:

    function handleMessage(
    address tokenSent,
    uint256 amount,
    bytes memory message
) external;

With this function, the following information will be received on the destination chain:

• tokenSent: Address of the token that has been received by the recipient contract.
• amount: The amount of the aforementioned tokens received by the recipient.
• message: The data that was sent from the source chain to be used for execution of the instruction on the destination chain.

Inside the handleMessage function on the destination chain, you will decode the data according to the requirements of the function which will complete the instruction execution.

Examples

Example of a function on the source chain to generate a cross-chain sequenced request

address public nitro = “address of nitro contract”;

bytes4 public constant I_DEPOSIT_MESSAGE_SELECTOR = bytes4(keccak256("iDepositMessage(uint256,bytes32,bytes,address,uint256,uint256,bytes)"));


function callNitro(
uint256 partnerId,
bytes32 destChainIdBytes,
bytes calldata recipient,
address srcToken,
uint256 amount,
uint256 destAmount,
bytes memory message
) public payable {
bool success;


(success, ) = nitro.call{ value: msg.value }(
abi.encodeWithSelector(I_DEPOSIT_MESSAGE_SELECTOR, partnerId, destChainIdBytes,recipient, srcToken, amount, destAmount, message)
);


require(success, "Nitro deposit unsuccessful");
}

Example of a function on the destinaton chain to handle the incoming cross-chain request

In this example, we are demonstrating how to handle a cross-chain staking request (transfer funds and stake them on a contract).

address public nitro = “address of the nitro;


function handleMessage(
address tokenSent,
uint256 amount,
bytes memory message
) external {
// Checking if the sender is the nitro contract
require(msg.sender == nitro,"only nitro");
// decoding the data we sent from the source chain
address user = abi.decode(message, (address));
// calling the stake function
stake(user, tokenSent, amount);
}
// The handler function for the stake request
function stake(
address user,
address token,
address amount
) internal {
// Updating the staked balances mapping
stakedBalance[user][token] += amount;
}

info

Check out this guide to learn how to create an end-to-end cross-chain staking dApp using Nitro sequencer.