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Build with Vea

This page covers how to integrate Vea into a cross-chain application. For protocol-level details, see the Vea Bridge overview.

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Integration Pattern

To integrate Vea, you deploy two gateway contracts:
  1. Sender Gateway on the sending chain, which interfaces with VeaInbox
  2. Receiver Gateway on the receiving chain, which interfaces with VeaOutbox
Sender Gateway (Chain A) -> VeaInbox -> [Vea Bridge] -> VeaOutbox -> Receiver Gateway (Chain B)
For each sending-receiving chain pair supported by Vea, there is a separate set of Vea contract deployments. For each chain, there is exactly one deployed contract.

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1. Sender Gateway

The Sender Gateway calls sendMessage() on VeaInbox to initiate cross-chain communication. 
interface IVeaInbox {
    function sendMessage(
        address _to,        // address of Receiver Gateway on destination chain
        bytes4 _fnSelector, // function selector to call on Receiver Gateway
        bytes memory _data  // encoded parameters
    ) external;
}
You specify:
  • The target contract address on the receiving chain (_to)
  • The function to call on the target (_fnSelector)
  • The encoded parameters (_data)

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Example: Sender Gateway

contract SenderGateway {
    IVeaInbox public immutable veaInbox;
    address public immutable receiverGateway;

    constructor(IVeaInbox _veaInbox, address _receiverGateway) {
        veaInbox = _veaInbox;
        receiverGateway = _receiverGateway;
    }

    function sendMyMessage(uint256 _data) external {
        bytes4 selector = IReceiverGateway.receiveMessage.selector;
        bytes memory data = abi.encode(_data);
        veaInbox.sendMessage(receiverGateway, selector, data);
    }
}

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2. Receiver Gateway

The Receiver Gateway receives the relayed message on the destination chain. Vea passes the msg.sender from the sending chain as the first argument of any cross-chain call. 
interface IReceiverGateway {
    function veaOutbox() external view returns (address);
    function senderGateway() external view returns (address);
}
Your receiver function must always include address msgSender as the first parameter: 
contract ReceiverGateway is IReceiverGateway {
    address public override veaOutbox;
    address public override senderGateway;

    modifier onlyFromVea() {
        require(msg.sender == veaOutbox, "Only VeaOutbox");
        _;
    }

    function receiveMessage(address msgSender, uint256 _data) external onlyFromVea {
        require(msgSender == senderGateway, "Only SenderGateway");
        // Process _data
    }
}
The msgSender parameter is inserted by Vea for security. Your interface must always have address msgSender as the first argument. The actual parameters you sent follow after it.

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3. Relaying Messages

After the challenge period passes, a relayer calls verifyAndRelay() on VeaOutbox to deliver the message to the Receiver Gateway. The Vea SDK provides utility functions to calculate merkle inclusion proofs and fetch message data for relaying: 
import VeaSdk from "@kleros/vea-sdk";

// Create client for a specific route
  const vea = VeaSdk.ClientFactory.arbitrumSepoliaToChiadoDevnet(
  "https://sepolia-rollup.arbitrum.io/rpc",
  "https://rpc.chiadochain.net"
  
);

// Get message info by ID
const messageInfo = await vea.getMessageInfo(messageId);

// Calculate proof and relay
// ... relay logic using proof data
The SDK is under active development. Check the Vea SDK package for the latest API.

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Lightbulb Demo

The Vea Lightbulb Demo is a minimal cross-chain application where a switch on one chain controls a lightbulb on another chain via Vea. The tutorial repository walks through deploying the contracts for each chain pair. Bridge status can be tracked on VeaScan.

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Deployment Addresses

See Vea Deployment Addresses for contract addresses on each supported route.

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Further Reading

Full Build Guide

Complete integration guide on docs.vea.ninja

Lightbulb Demo

Interactive cross-chain demo application

Run a Validator

Run a Vea bridge validator node

Vea Bridge Architecture

Protocol architecture and bridge types