Send an L1 to L2 transaction


Send an L1 to L2 transaction

The zkSync Era smart contractsopen in new window allow the sender to request transactions on Ethereum L1 and pass data to zkSync Era L2.

Common use cases

Along with zkSync Era's built-in censorship resistance that requires multi-layer interoperability, there are some common use cases that need L1 to L2 transaction functionality, such as:

  • Custom bridges.
  • Multi-layer governing smart contracts.

Step-by-step

  1. Import the zkSync Era library or contract containing the required functionality.

    The import gives access to the IZkSync.solopen in new window inherited interfaces that include the gas estimation functionality.

    You can do it using yarn (recommended), or download the contractsopen in new window from the repo.

    yarn init -y
    yarn add -D @matterlabs/zksync-contracts
    
  2. Get the current L1 gas price with Ethereum JSON-RPC method eth_gasPriceopen in new window called with the Ethers implementationopen in new window.

    async getGasPrice(): Promise<BigNumber> {
        await this.getNetwork();
    
        const result = await this.perform("getGasPrice", { });
        try {
            return BigNumber.from(result);
        } catch (error) {
            return logger.throwError("bad result from backend", Logger.errors.SERVER_ERROR, {
                method: "getGasPrice",
                result, error
            });
        }
    }
    
  3. Apply an alias to the addresses in the request if the sender address is a contract.

    If the sender is an EOA, no aliasing is required. Aliasing is implemented by the applyL1ToL2Aliasopen in new window Solidity function and called by the JavaScript SDKopen in new window.

    function applyL1ToL2Alias(address l1Address) internal pure returns (address l2Address) {
        unchecked {
            l2Address = address(uint160(l1Address) + offset);
        }
    }
    
  4. Call the JSON-RPC method zks_estimateGasL1toL2, wrapping the transaction data in a CallRequest JSON object parameter.

    The method returns the amount of gas required for the transaction to succeed.

    Important

    This value is often referred to as limit, or gas limit, or L2 gas limit in our documented examples.

    // available on a zkSync Era JS SDK Provider object
    async estimateGasL1(transaction: utils.Deferrable<TransactionRequest>): Promise<BigNumber> {
        await this.getNetwork();
        const params = await utils.resolveProperties({
          transaction: this._getTransactionRequest(transaction)
        });
        if (transaction.customData != null) {
            // @ts-ignore
            params.transaction.customData = transaction.customData;
        }
        const result = await this.send('zks_estimateGasL1ToL2', [
            Provider.hexlifyTransaction(params.transaction, { from: true })
        ]);
        try {
            return BigNumber.from(result);
        } catch (error) {
            throw new Error(`bad result from backend (zks_estimateGasL1ToL2): ${result}`);
        }
    }
    
  5. Get the base cost by calling the l2TransactionBaseCostopen in new window function with:

    • The gas price returned at step 2 as _gasPrice.
    • The gas value returned at step 3 as _l2GasLimit.
    • A constant representing how much gas is required to publish a byte of data from L1 to L2 as _l2GasPerPubdataByteLimit. At the time of writing, the JavaScript API provides this constant as REQUIRED_L1_TO_L2_GAS_PER_PUBDATA_LIMIT.
    function l2TransactionBaseCost(
        uint256 _gasPrice,
        uint256 _l2GasLimit,
        uint256 _l2GasPerPubdataByteLimit
    ) external view returns (uint256);
    
  6. The return value is a 256-bit unsigned integer in hexadecimal representing the amount of gas the transaction uses.

    {
      "jsonrpc": "2.0",
      "result": "0x25f64db",
      "id": 2
    }
    
  7. Send the transaction, including the gas price and base cost in the value parameters, by calling the requestL2Transactionopen in new window function.

    Include the gas limit value from step 3 as _l2GasLimit and the REQUIRED_L1_TO_L2_GAS_PER_PUBDATA_LIMIT constant as _l2GasPerPubdataByteLimit.

    The _refundRecipient address receives any remaining fee after the transaction completes. If _refundRecipient = 0 then L2 msg.sender is used.

    function requestL2Transaction(
        address _contractL2,
        uint256 _l2Value,
        bytes calldata _calldata,
        uint256 _l2GasLimit,
        uint256 _l2GasPerPubdataByteLimit,
        bytes[] calldata _factoryDeps,
        address _refundRecipient
    ) external payable returns (bytes32 canonicalTxHash);
    

    Solidity parameters description

    • _contractL2: L2 address of the contract to be called.
    • _l2Value: Amount of ETH to pass with the call to L2; used as msg.value for the transaction.
    • _calldata: Calldata of the transaction call; encoded the same way as in Ethereum.
    • _l2GasLimit: Gas limit of the transaction call obtained in step 3 above.
    • _l2GasPerPubdataByteLimit: Constant described in step 4 above.
    • _factoryDeps: Bytecodes array containing the bytecode of the contract being deployed. If the contract is a factory contract, the array contains the bytecodes of the contracts it can deploy.
    • _refundRecipient: Address that receives the rest of the fee after the transaction execution. If refundRecipient == 0, L2 msg.sender is used.

    Note: If the _refundRecipient is a smart contract, then during the L1 to L2 transaction its address is aliased.

  8. Wait for a transaction response and output the details.

    Responses

    • A successful L1 to L2 transaction produces an L2Log with key = l2TxHash, and value = bytes32(1).
    • A failed L1 to L2 transaction produces an L2Log with key = l2TxHash, and value = bytes32(0).

Example code

User needs to perform next steps:

  1. Run local node dockerized containers. Instructions how to run itopen in new window or use zksync-cliopen in new window:
  npx zksync-cli dev config
  // choose: Dockerized node - Persistent state, includes L1 and L2 nodes
  // choose: BE and Portal (optional)
  npx zksync-cli dev start
  1. In the root folder of the imported project (step 1) create file.js and insert there code from example below
  2. In the root folder add .env file with private key of wallet to use
"RICH_WALLET_PRIV_KEY=0x..";
  1. Add script to package.json file next script:
`"scripts": {  "run": "node file.js"},``"type": "module",`;
  1. Run npm i --save-dev ethers (in case it is not installed)
  2. Run command npm run

Please note, that if you want to run on local-node Dockerized setup use next hardhat.config.ts:

export const zkSyncTestnet = {
  url: "https://localhost:3051",
  ethNetwork: "https://localhost:8545",
  zksync: true,
};

For Testnet (recommended):

export const zkSyncTestnet = {
  url: "https://sepolia.era.zksync.dev",
  ethNetwork: "https://rpc.ankr.com/eth_sepolia",
  zksync: true,
};

And also insert same credentials in file.js:

const L1_RPC_ENDPOINT = "<insert network config here>"; //ethNetwork from instruction above
const L2_RPC_ENDPOINT = "<insert network config here>"; //url from instruction above

Example code

import { Contract, Wallet, Provider } from "zksync-ethers";
import * as ethers from "ethers";

// load env file
import dotenv from "dotenv";
dotenv.config();

// Greeter contract ABI for example
const ABI = [
  {
    inputs: [
      {
        internalType: "string",
        name: "_greeting",
        type: "string",
      },
    ],
    stateMutability: "nonpayable",
    type: "constructor",
  },
  {
    inputs: [],
    name: "greet",
    outputs: [
      {
        internalType: "string",
        name: "",
        type: "string",
      },
    ],
    stateMutability: "view",
    type: "function",
  },
  {
    inputs: [
      {
        internalType: "string",
        name: "_greeting",
        type: "string",
      },
    ],
    name: "setGreeting",
    outputs: [],
    stateMutability: "nonpayable",
    type: "function",
  },
];

// HTTPS RPC endpoints (from local node)
const L1_RPC_ENDPOINT = "http://localhost:8545";
const L2_RPC_ENDPOINT = "http://localhost:3050";

const WALLET_PRIV_KEY = process.env.RICH_WALLET_PRIV_KEY || "";

if (!WALLET_PRIV_KEY) {
  throw new Error("Wallet private key is not configured in env file");
}

const L2_CONTRACT_ADDRESS = "0x..."; //

async function main() {
  console.log(`Running script for L1-L2 transaction`);

  // Initialize the wallet.
  const l1provider = new Provider(L1_RPC_ENDPOINT);
  const l2provider = new Provider(L2_RPC_ENDPOINT);
  const wallet = new Wallet(WALLET_PRIV_KEY, l2provider, l1provider);

  // console.log(`L1 Balance is ${await wallet.getBalanceL1()}`);
  console.log(`L2 Balance is ${await wallet.getBalance()}`);

  // retrieve L1 gas price
  const l1GasPrice = await l1provider.getGasPrice();
  console.log(`L1 gasPrice ${ethers.utils.formatEther(l1GasPrice)} ETH`);

  const contract = new Contract(L2_CONTRACT_ADDRESS, ABI, wallet);

  const msg = await contract.greet();

  console.log(`Message in contract is ${msg}`);

  const message = `Updated at ${new Date().toUTCString()}`;

  const tx = await contract.populateTransaction.setGreeting(message);

  // call to RPC method zks_estimateGasL1ToL2 to estimate L2 gas limit
  const l2GasLimit = await l2provider.estimateGasL1(tx);

  console.log(`L2 gasLimit ${l2GasLimit.toString()}`);

  const baseCost = await wallet.getBaseCost({
    // L2 computation
    gasLimit: l2GasLimit,
    // L1 gas price
    gasPrice: l1GasPrice,
  });

  console.log(`Executing this transaction will cost ${ethers.utils.formatEther(baseCost)} ETH`);

  const iface = new ethers.utils.Interface(ABI);
  const calldata = iface.encodeFunctionData("setGreeting", [message]);

  const txReceipt = await wallet.requestExecute({
    contractAddress: L2_CONTRACT_ADDRESS,
    calldata,
    l2GasLimit: l2GasLimit,
    refundRecipient: wallet.address,
    overrides: {
      // send the required amount of ETH
      value: baseCost,
      gasPrice: l1GasPrice,
    },
  });

  console.log("L1 tx hash is :>> ", txReceipt.hash);

  txReceipt.wait();
}

main()
  .then()
  .catch((error) => {
    console.error(error);
    process.exitCode = 1;
  });