LayerZero

Introduction

This guide aims to provide an insight into the LayerZero messaging service, which is an omnichain interoperability protocol designed for lightweight message passing across chains, and how to Setup and utilize the OmniCounter contract to demonstrate cross-chain message passing. Below is a table showcasing the zkSync Era and zkSync (Testnet) endpoint details for LayerZero:

Network	ChainID	Endpoint
zkSync Era	165	0x9b896c0e23220469C7AE69cb4BbAE391eAa4C8da
zkSync Testnet	10165	0x093D2CF57f764f09C3c2Ac58a42A2601B8C79281

Prerequisites

• Knowledge Base: Familiarity with blockchain concepts and smart contract development.
• Node.js: If not installed, download it here.

Step 1 — Understanding LayerZero messaging service

LayerZero enables authentic and guaranteed message delivery between different blockchain networks with configurable trustlessness. Messages in LayerZero are managed by LayerZero Endpoints, which comprise versioned messaging libraries and a proxy to route messages to the appropriate library version. Message states are maintained across versions, allowing for seamless library upgrades.

Messages are sent from the User Application (UA) at source srcUA to the UA at the destination dstUA. Once the message is received by dstUA, the message is considered delivered (transitioning from INFLIGHT to either SUCCESS or STORED)

More details can be found here.

Step 2 — Environment setup

Clone the GitHub repository containing the OmniCounter contract, and navigate to the repository directory:

git clone git@github.com:dutterbutter/zksync-layer0-example.git

Install dependencies:

yarn install

Update the Environment File:

• Modify the .env-example file with your private key.
• Ensure your account has a sufficient balance for both chains being interacted with. For this guide, that is zkSync Testnet, and Optimism Testnet.

Step 3 — Understanding OmniCounter

OmniCounter is a smart contract that increments a counter on another chain via LayerZero messaging service.

It utilizes _lzSend() within incrementCounter() to send messages, and _nonblockingLzReceive() to receive messages on the destination chain.

Step 4 — Deploy OmniCounter

Deploy OmniCounter contract on at least two different chains. In this example, we'll use zkSync Testnet and Optimism Testnet.

We will start with deploying on zkSync Testnet:

npx hardhat --network zksync-testnet deploy --tags OmniCounter

We should see the expected output:

[zksync-testnet] Endpoint address: 0x093D2CF57f764f09C3c2Ac58a42A2601B8C79281
OmniCounter was deployed to 0x07C89fc22B959DbaE2bF3Bb5d0F1Ac94986588fd

Note: Copy the contract address somewhere safe, we will need it in the next step!

Deploy on Optimism:

npx hardhat --network optimism-goerli deploy --tags OmniCounter

Step 5 — Configure and Send Cross-Chain Message

Open setTrustedRemote.js located in the /tasks directory. Replace "YOUR-ZKSYNC-DEPLOYED-OMNICOUNTER-ADDRESS" with the zkSync contract address.

const ZKSYNC_OMNICOUNTER = "YOUR-ZKSYNC-DEPLOYED-OMNICOUNTER-ADDRESS";

Set the remote addresses to allow each contract to receive messages:

npx hardhat --network zksync-testnet setTrustedRemote --target-network optimism-goerli --contract OmniCounter

Execute:

npx hardhat --network optimism-goerli setTrustedRemote --target-network zksync-testnet --contract OmniCounter

Time to send a cross-chain message from optimism-goerli to zksync-testnet:

npx hardhat --network optimism-goerli incrementCounter --target-network zksync-testnet

Expected output:

fees[0] (wei): 1289224800000000 / (eth): 0.0012892248
✅ Message Sent [optimism-goerli] incrementCounter on destination OmniCounter @ [10165]
tx: 0x6efca38d68bd11aae030c2b02d0dd8ae93eb32cba04152bb541309a909a0c894

Conclusion

You have now set up and demonstrated cross-chain messaging using LayerZero with the OmniCounter contract. This simplistic example serves as a gateway to understand and explore the potential of LayerZero messaging service in building interoperable blockchain applications.