Zetachain — deploy and interact with your own omnichain contract

Zetachain is a PoS blockchain developed using the Cosmos SDK that hosts Ethereum Virtual Machine (zEVM) which is capable of running omnichain smartcontracts. Those contracts allow you to execute transactions from any supported source to destination networks. Let’s explore how this is done in practice

Download or clone example repository from github

https://github.com/stanisloe/zetachain-swap-example.git

Navigate to the folder and you should see the following structure

Project structure

I’ve highlighted core files that we’ll go through to better understand what is happening here:

1. hardhat.config.ts: This is the configuration file for the Ethereum development environment called Hardhat. It allows you to easily deploy and interact with smart contracts using JavaScript code. If you were to do it from scratch, you would need to configure RPC providers, chain settings, etc. However, in this example, everything is already pre-configured for you, so you don't need to add anything there.
2. .env file ( it won’t be in the downloaded project, but we will create it later ): This is where you will insert your EVM account private key, which Hardhat will use for contract deployment and interaction. Please ensure that this account has some native tokens to cover gas costs.
3. tasks/deploy.ts and tasks/interact.ts: These are Hardhat tasks for deploying and interacting with the Swap.sol smart contract. Later, you'll execute commands to trigger those tasks.
4. Swap.sol file: This contains the Ethereum Virtual Machine (EVM) compatible smart contract code that will perform cross-chain swap transactions.

Now, let’s prepare our environment for contract deployment.

First, let’s install npm and Node.js if you haven’t done so already. You can follow any of the following guides:

How to Install NPM and Node.js on Windows and Mac Devices?

Downloading and installing Node.js and npm | npm Docs

After this is done let’s navigate to downloaded example repository in the command line and run

npm install yarn && yarn && yarn add --dev @uniswap/v2-periphery @uniswap/v2-core

Next, you’ll need to create a file named .env in the project directory and place the private key from an account that holds Matic Mumbai testnet tokens.

PRIVATE_KEY=<your private key here>

Run

npx hardhat balances

and you should see similar output

EVM: 0xA72745c17596E4Bd4E4424e8d827176087F5870a
BTC: tb1qgxuumr0ctan0x4u8jthcw4gvxz0q5pfhemyazs

┌─────────┬──────────────────┬────────┬─────────┬───────┐
│ (index) │   networkName    │ native │  zeta   │ zrc20 │
├─────────┼──────────────────┼────────┼─────────┼───────┤
│    0    │ 'mumbai_testnet' │ '0.58' │ '57.00' │       │
│    1    │  'zeta_testnet'  │ '5.82' │ '0.00'  │  ''   │
│    2    │  'bsc_testnet'   │ '0.10' │ '0.98'  │       │
│    3    │ 'goerli_testnet' │ '0.16' │ '30.00' │       │
│    4    │  'btc_testnet'   │  '0'   │         │       │
└─────────┴──────────────────┴────────┴─────────┴───────┘

Pay attention to your Mumbai and Goerli native balances. If you don’t have matic tokens request them here.

Next compile smart contracts

npx hardhat compile --force

Once everything is compiled we are ready to deploy our contract by running:

npx hardhat deploy --network zeta_testnet

Note the naming for the deploy task — it’s the same as the task file tasks/deploy.ts we discussed previously. interact task will be called in a similar manner later, but with different arguements.

You should see similar output with your account and contract addresses. They will be different from mine.

🔑 Using account: 0xA72745c17596E4Bd4E4424e8d827176087F5870a

🚀 Successfully deployed contract on ZetaChain.
📜 Contract address: 0xFAfE767BB2AbC2B68AE4466FCcbd8afc9d1B7079
🌍 Explorer: https://athens3.explorer.zetachain.com/address/0xFAfE767BB2AbC2B68AE4466FCcbd8afc9d1B7079

Once the contract is deployed it’s time to interact with it. Run the following command

npx hardhat interact --contract 0xFAfE767BB2AbC2B68AE4466FCcbd8afc9d1B7079 --amount 0.2 --network mumbai_testnet --destination goerli_testnet --recipient 0xA72745c17596E4Bd4E4424e8d827176087F5870a

Note that you need to replace contract and recipient arguments. You should see the following output after few minutes

🔑 Using account: 0xA72745c17596E4Bd4E4424e8d827176087F5870a


🚀 Successfully broadcasted a token transfer transaction on mumbai_testnet network.
📝 Transaction hash: 0x6a85f07eef914ddd7eae76355e9d6c12e4d72082f22bbedcbfee56ccfadf5a84

✔ CCTX hash found: 0xabd5a19e33a772086680403028a2a0a4bd528321e64755eb5c9b84c89641754c

ℹ Status updated to "OutboundMined": Remote omnichain contract call completed

✔ CCTX has been finalized on ZetaChain

Let’s inspect what was done byinteract task and it’s output in more detail.

Transaction hash

📝 Transaction hash: 0x6a85f07eef914ddd7eae76355e9d6c12e4d72082f22bbedcbfee56ccfadf5a84

corresponds to a transfer made from your mumbai test network account to zetachain account on mumbai blockchain called the TSS ( Threshold Signature Scheme ) On every connected network there is such TSS ( actuall addresses for supported chains could be found here ) owned by zetachain team. Typically, you’ll send some tokens and metadata about your desired actions with those tokens to the TSS. In this exeample you have send 0.2 matic tokens and told zetachain to withdraw what is left after fees to your wallet in goerli network.

By sending this Mumbai blockchain transaction you have triggered transaction on the Zetachain blockchain, known as a cross-chain transaction (CCTX), which you can find in the output as well.

✔ CCTX hash found: 0xabd5a19e33a772086680403028a2a0a4bd528321e64755eb5c9b84c89641754c

Now lets investigate it a little bit further. Navigate to ( don’t forget to use your CCTX hash in explorer )

https://athens3.explorer.zetachain.com/cc/tx/0xabd5a19e33a772086680403028a2a0a4bd528321e64755eb5c9b84c89641754c

to explore this CCTX in detail. You should see the following screen.

CCTX example

From it you should be able to see how your omnichain swap was performed:

1. This your initial transaction on polygon mumbai blockchain where you interacted with TSS and sent your tokens with metadata about recipient and destination chain
2. This is another CCTX on zetachain that will initiate tokens withdrawal from goerli TSS to recipient account
3. Deposit transaction hash on destination network

After some time, when zetachain processes your transaction, you will receive tokens in your destination network

To check the balance

npx hardhat balances

Notice that goerli_testnet native value increased by 0.01 from the previous run. The rest was payed for the interchain transaction commission to zetachain protocol.

EVM: 0xA72745c17596E4Bd4E4424e8d827176087F5870a
BTC: tb1qgxuumr0ctan0x4u8jthcw4gvxz0q5pfhemyazs

┌─────────┬──────────────────┬────────┬─────────┬───────┐
│ (index) │   networkName    │ native │  zeta   │ zrc20 │
├─────────┼──────────────────┼────────┼─────────┼───────┤
│    0    │ 'mumbai_testnet' │ '0.38' │ '57.00' │       │
│    1    │  'zeta_testnet'  │ '5.82' │ '0.00'  │  ''   │
│    2    │  'bsc_testnet'   │ '0.10' │ '0.98'  │       │
│    3    │ 'goerli_testnet' │ '0.17' │ '30.00' │       │
│    4    │  'btc_testnet'   │  '0'   │         │       │
└─────────┴──────────────────┴────────┴─────────┴───────┘

And that’s it. By simply running

npx hardhat deploy --network zeta_testnet

you have deployed your own smart contract that is reusing audited and battle-tested uniswap code base. You do not need to implement all the complex multichain swap logic from scratch.

And by running

npx hardhat interact --contract 0xFAfE767BB2AbC2B68AE4466FCcbd8afc9d1B7079 --amount 0.2 --network mumbai_testnet --destination goerli_testnet --recipient 0xA72745c17596E4Bd4E4424e8d827176087F5870a

you’ve bridged your native mumbai polygon tokens to goerli eth tokens.

One cool feature of omnichain contracts is that they eliminate the need for smart contracts on both source and destination networks. Smart contracts are only deployed on Zetachain. To initiate a cross-chain transaction, you simply send data to the TSS address on the supported source chain. The advantage of TSS being just an account is that it enables the triggering of smart contracts even on chains like Bitcoin/Dogecoin, which lack the capacity or efficiency to support general-purpose smart contracts.

Feel free to explore more from the official docs.