Developers

Cross-Chain Messaging

Overview

Cross-Chain Messaging

Cross-chain messaging makes the most sense for applications that generally need minimal logic or state to maintain across all chains, and where data that needs only to be passed between different chains one way.

Cross-chain messaging (CCM) offers:

• Transfer of ZETA tokens between connected EVM chains, including to/from ZetaChain
• Transfer of messages with arbitrary data between connected EVM chains

note

Currently, it's not possible to send messages with arbitrary data to/from ZetaChain using CCM. For sending data to ZetaChain, check out omnichain contracts.

pragma solidity 0.8.7;

import "@zetachain/protocol-contracts/contracts/evm/tools/ZetaInteractor.sol";
import "@zetachain/protocol-contracts/contracts/evm/interfaces/ZetaInterfaces.sol";

contract YourContract is ZetaInteractor, ZetaReceiver {
    constructor(address connectorAddress)
        ZetaInteractor(connectorAddress)
    {}

    function sendMessage(uint256 destinationChainId) external payable {
        connector.send(
            ZetaInterfaces.SendInput({
                destinationChainId: destinationChainId,
                destinationAddress: interactorsByChainId[destinationChainId],
                destinationGasLimit: 300000,
                message: abi.encode("Hello, Cross-Chain World!"),
                zetaValueAndGas: msg.value,
                zetaParams: abi.encode("")
            })
        );
    }

    function onZetaMessage(ZetaInterfaces.ZetaMessage calldata zetaMessage) external override isValidMessageCall(zetaMessage) {
        // Handle the message
    }

    function onZetaRevert(ZetaInterfaces.ZetaRevert calldata zetaRevert) external override isValidRevertCall(zetaRevert) {
        // Handle the revert
    }
}

The contract above is a very simple example of a cross-chain messaging contract. Check out the Message tutorial for a more in-depth example.

CCM contracts are deployed on two or more connected chains. ZetaChain acts as a relayer transferring the messages between blockchains.

To send a message a user calls a function that executes connector.send(). ZetaChain picks up the message and sends it to the destination chain. The message is then received by a CCM contract passed to the onZetaMessage function.

A good use-case of CCM is an application that needs only to call a contract or send value to an address on a different chain. After the message is received and processed on the destination, the application ideally doesn't have to broadcast anything back to synchronize state for anything, and the sender doesn't care about the results.

Cross-chain messaging works to build a variety of applications and primitives such as:

• Omnichain NFTs that can be sent between different chains, and that don't need to know about the state of the collection on other chains
• “Simple” swap or bridge apps that use liquidity pools on existing chains
• Proving ownership of NFTs or simple action-calls to a different chain