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Omnichain Contracts
Overview

Overview

Omnichain Smart Contracts are contracts deployed on ZetaChain that can use and orchestrate assets on connected chains, as well as on ZetaChain. With omnichain smart contracts you are able to have a single place of logic that can maintain the state of assets and data across all connected chains.

For a contract to be considered omnichain it must inherit from the zContract interface and implement the onCrossChainCall function:

pragma solidity 0.8.7;

import "@zetachain/protocol-contracts/contracts/zevm/interfaces/IZRC20.sol";
import "@zetachain/protocol-contracts/contracts/zevm/interfaces/zContract.sol";

contract YourContract is zContract {
    function onCrossChainCall(
        zContext calldata context,
        address zrc20,
        uint256 amount,
        bytes calldata message
    ) external virtual override {
        bytes32 recipient = abi.decode(message, (bytes32));

        (, uint256 gasFee) = IZRC20(zrc20).withdrawGasFee();

        IZRC20(zrc20).approve(zrc20, gasFee);
        IZRC20(zrc20).withdraw(abi.encodePacked(recipient), amount - gasFee);
    }
}

The contract above is a very simple example of an omnichain contract. Check out the introductory omnichain tutorial for a more in-depth example.

An omnichain contract is deployed on ZetaChain and can be called from any connected chain.

To call an omnichain contract from a connected chain a user sends native gas tokens to the TSS address or deposits supported ERC-20 tokens to ERC-20 custody contract. The amount of deposited tokens becomes available an omnichain contract in a ZRC-20 form and the payload of the deposit is passed as the message to the contract.

Omnichain Smart Contracts are ideal for more complex applications where state management between different chains is core to the application. Some use case examples include:

  • Complex trading or DeFi applications that involve liquidity on multiple chains.
  • Adding smart contract layer to non-smart-contract chains like Bitcoin and Dogecoin, or incorporating these chains/assets with other pieces of the DeFi ecosystem natively.
  • Multichain smart-contract wallet applications like portfolio management across all chains.
  • Leveraging existing implementations of protocols like Aave, Uniswap, Curve, etc. for omnichain. Since zEVM is EVM-compatible, one can build on top of these implementations (just as they would on Ethereum) to adapt them for omnichain interoperability.