L1->L2 Main

Step-by-step

Sending an L1->L2 transaction requires following these steps:

1. Initialise the providers and the wallet that will send the transaction:

     const [wallet] = await ethers.getWallets();
   
     // Initialize the L2 provider.
     const l2Provider = ethers.providerL2;
   
     // Initialize the L1 provider.
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     const networkInfo = network as any;
     const l1RPCEndpoint =
       networkInfo.config.ethNetwork === 'http://localhost:8545'
         ? networkInfo.config.ethNetwork
         : '<YOUR_L1_RPC_ENDPOINT>';
     const l1Provider = new ethers.Provider(l1RPCEndpoint);
   

2. Retrieve the current gas price on L1.

     // retrieve L1 gas price
     const l1GasPrice = await l1Provider.getGasPrice();
     console.log(`L1 gasPrice ${ethers.formatEther(l1GasPrice)} ETH`);
   

3. Populate the transaction that you want to execute on L2:

     const contract = new ethers.Contract(L2_CONTRACT_ADDRESS, GREETER_ABI_JSON.abi, wallet);
     const message = `Message sent from L1 at ${new Date().toUTCString()}`;
     // populate tx object
     const tx = await contract.setGreeting.populateTransaction(message);
   

4. Retrieve the gas limit for sending the populated transaction to L2 using estimateGasL1(). This function calls the zks_estimateGasL1ToL2 RPC method under the hood:

     // Estimate gas limit for L1-L2 tx
     const l2GasLimit = await l2Provider.estimateL1ToL2Execute({
       contractAddress: L2_CONTRACT_ADDRESS,
       calldata: tx.data,
       caller: wallet.address,
     });
     console.log(`L2 gasLimit ${l2GasLimit.toString()}`);
   

5. Calculate the total transaction fee to cover the cost of sending the transaction on L1 and executing the transaction on L2 using getBaseCost from the Wallet class. This method:
   • Retrieves the ZKsync BridgeHub contract address by calling zks_getBridgehubContract RPC method.
   • Calls the l2TransactionBaseCost function on the ZKsync BridgeHub system contract to retrieve the fee.

     const baseCost = await wallet.getBaseCost({
       // L2 computation
       gasLimit: l2GasLimit,
       // L1 gas price
       gasPrice: l1GasPrice,
     });
   
     console.log(`Executing this transaction will cost ${ethers.formatEther(baseCost)} ETH`);
   

6. Encode the transaction calldata:

     const iface = new ethers.Interface(GREETER_ABI_JSON.abi);
     const calldata = iface.encodeFunctionData('setGreeting', [message]);
   

7. Finally, send the transaction from your wallet using the requestExecute method. This helper method:
   • Retrieves the Zksync BridgeHub contract address calling zks_getBridgehubContract.
   • Populates the L1-L2 transaction.
   • Sends the transaction to the requestL2TransactionDirect function of the ZKsync BridgeHub system contract on L1.

     const txReceipt = await wallet.requestExecute({
       // destination contract in L2
       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}`);
     console.log('🎉 Transaction sent successfully');
     txReceipt.wait(1);
   

Full example

Create a new script file in the scripts folder called l1tol2tx.ts, and copy/paste the full script.

touch scripts/l1tol2tx.ts