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Bridging L1 and L2 (Portal)

In Thanos, the Portal supports asset transfers between networks by using the OptimismPortal contract on L1 and the L2ToL1MessagePasser contract on L2. However, assets that can be transferred through the Portal are limited to NativeToken, and it handles transactions with lower gas fees compared to using CrossChainMessenger.

This document explores the functions of the Portal used for deposits and withdrawals and provides a step-by-step guide on how to import and use the Portal to transfer NativeToken between L1 and L2.

You can find detailed code on the Portal here. Examples of how to use the Thanos SDK’s Portal for depositing and withdrawing NativeTokens between L1 and L2 can be found here.

Constructor

The constructor sets up the necessary information for initializing a CrossChainProvider instance. Each constructor is composed of essential elements to facilitate smooth Cross-Chain interactions between L1 and L2.

  • l1SignerOrProvider: Signer or Provider for the L1 chain, or a JSON-RPC url

  • l2SignerOrProvider: Signer or Provider for the L2 chain, or a JSON-RPC url

  • l1ChainId: Chain ID for the L1 chain

  • l2ChainId: Chain ID for the L2 chain

  • depositConfirmationBlocks: Optional number of blocks before a deposit is confirmed

  • l1BlockTimeSeconds: Optional estimated block time in seconds for the L1 chain

  • contracts: Optional contract address overrides

/**
   * Creates a new CrossChainProvider instance.
   *
   * @param opts Options for the provider.
   * @param opts.l1SignerOrProvider Signer or Provider for the L1 chain, or a JSON-RPC url.
   * @param opts.l2SignerOrProvider Signer or Provider for the L2 chain, or a JSON-RPC url.
   * @param opts.l1ChainId Chain ID for the L1 chain.
   * @param opts.l2ChainId Chain ID for the L2 chain.
   * @param opts.depositConfirmationBlocks Optional number of blocks before a deposit is confirmed.
   * @param opts.l1BlockTimeSeconds Optional estimated block time in seconds for the L1 chain.
   * @param opts.contracts Optional contract address overrides.
   */
  constructor(opts: {
    l1SignerOrProvider: SignerOrProviderLike
    l2SignerOrProvider: SignerOrProviderLike
    l1ChainId: NumberLike
    l2ChainId: NumberLike
    depositConfirmationBlocks?: NumberLike
    l1BlockTimeSeconds?: NumberLike
    contracts?: DeepPartial<OEContractsLike>
  })

Set Up

Import the ethers library for interacting with the Ethereum blockchain and the @tokamak-network/thanos-sdk package. Additionally, create an instance for L1 and L2 interactions using the Portal's constructor, and prepare to use the various functions provided by the Portal.

import { ethers } from 'ethers'
import { Portals } from '@tokamak-network/thanos-sdk'

const l1Provider = new ethers.providers.StaticJsonRpcProvider(
  process.env.L1_URL
)
const l2Provider = new ethers.providers.StaticJsonRpcProvider(
  process.env.L2_URL
)

const l1ChainId = (await l1Provider.getNetwork()).chainId
const l2ChainId = (await l2Provider.getNetwork()).chainId

const l1Wallet = new ethers.Wallet(privateKey, l1Provider)
const l2Wallet = new ethers.Wallet(privateKey, l2Provider)

const l1Contracts = {
  AddressManager: addressManager,
  OptimismPortal: optimismPortal,
  L2OutputOracle: l2OutputOracle,
}

const portals = new Portals({
  contracts: {
    l1: l1Contracts,
  },
  l1ChainId,
  l2ChainId,
  l1SignerOrProvider: l1Wallet,
  l2SignerOrProvider: l2Wallet,
})

Deposit

  1. NativeToken Creation: Create an instance to interface with the NativeToken contract on L1. This instance will be used for subsequent token approval and transfer operations. By using the contract's address and the ERC20 standard ABI, you generate a NativeToken contract object, which enables interaction with the OptimismPortal contract.

// NativeTokenContract in L1 (like TON)
const l2NativeTokenContract = new ethers.Contract(
  l2NativeToken,
  erc20ABI,
  l1Wallet
)

  1. Approve: Before depositing NativeToken into L1, you need to approve the OptimismPortal contract to use the tokens. This is done by calling the approve function to allow the OptimismPortal to handle a specified amount of tokens. This step is essential for the deposit process, and once approval is granted, the deposit transaction can proceed successfully.

// approve
const approveTx = await l2NativeTokenContract.approve(optimismPortal, amount)
await approveTx.wait()
console.log('approveTx:', approveTx.hash)

  1. Deposit Execution: Use the portals.depositTransaction function to deposit NativeToken into L2. In this process, parameters such as to, value, gasLimit, and data are set to execute the transaction. Once the transaction is included in a block, you can verify the transaction hash through depositReceipt.

    • to: The L2 address where the deposit is directed.

    • value: The amount of tokens to deposit.

    • gasLimit: The gas limit required to execute the transaction, which should be greater than data.length * 16 + 21000

    • data: Additional data to be sent, with a default value of 0x.

// deposit NativeToken in L1
const depositTx = await portals.depositTransaction({
  to: l2Wallet.address,
  value: BigNumber.from(amount),
  gasLimit: BigNumber.from('200000'), // It will be greater than data.length * 16 + 21000
  data: '0x',
})
const depositReceipt = await depositTx.wait()
console.log('depositTx:', depositReceipt.transactionHash)

  1. Deposit verification: Use the portals.waitingDepositTransactionRelayed function to verify that the deposit was processed successfully. This function returns the associated transaction hash after verifying that the transaction reached L2 and was finally processed. Verify that the deposit was processed correctly with getTransactionReceipt.

// get relayedTxHash in L2
const relayedTxHash = await portals.waitingDepositTransactionRelayed(
  depositReceipt,
  {}
)
console.log('relayedTxHash:', relayedTxHash)
const depositedTxReceipt = await l2Provider.getTransactionReceipt(
  relayedTxHash
)

Withdrawal

  1. Initiating Withdrawal: Use the portals.initiateWithdrawal function to initiate a withdrawal from L2 to L1. This function creates a withdrawal transaction and uses parameters such as target, value, gasLimit, and data to request the withdrawal. The process waits for the transaction to complete through the withdrawalReceipt.

    • target: L1 address where the withdrawal will be sent

    • value: Amount to withdraw

    • gasLimit: Set the gas limit

    • data: Additional data to be sent, with a default value of 0x.

const withdrawalTx = await portals.initiateWithdrawal({
  target: l1Wallet.address,
  value: BigNumber.from(amount),
  gasLimit: BigNumber.from('200000'),
  data: '0x12345678',
})
const withdrawalReceipt = await withdrawalTx.wait()

  1. Waiting for Relay: Use the portals.waitForWithdrawalTxReadyForRelayUsingL2Tx function to wait until the withdrawal transaction, based on the L2 transaction hash, is ready to be relayed to L1.

await portals.waitForWithdrawalTxReadyForRelayUsingL2Tx(
  withdrawalReceipt.transactionHash
)

  1. Withdrawal Prove: After confirming that the withdrawal transaction is ready to be relayed from L2 to L1, use the portals.proveWithdrawalTransactionUsingL2Tx function to prove the withdrawal transaction based on the L2 transaction hash. At this stage, a proof transaction is submitted to verify the validity of the withdrawal transaction.

const proveTransaction = await portals.proveWithdrawalTransactionUsingL2Tx(
  withdrawalReceipt.transactionHash
)
await proveTransaction.wait()

  1. Wait for Finalization: Use the portals.waitForFinalizationUsingL2Tx function to wait for the withdrawal transaction to finalize. Once finalization is complete, the withdrawal is processed successfully.

await portals.waitForFinalizationUsingL2Tx(withdrawalReceipt.transactionHash)

  1. Finalizing Withdrawal: Use the portals.finalizeWithdrawalTransactionUsingL2Tx function to finalize the withdrawal transaction based on the L2 transaction hash. At this stage, the withdrawal transaction is fully processed, and the finalized finalizedTransactionReceipt can be confirmed.

const finalizedTransaction =
  await portals.finalizeWithdrawalTransactionUsingL2Tx(
    withdrawalReceipt.transactionHash
  )
const finalizedTransactionReceipt = await finalizedTransaction.wait()
console.log('finalized transaction receipt:', finalizedTransactionReceipt)

  1. Token Transfer: After the withdrawal is finalized, use the OptimismPortal contract to transfer tokens to the user's wallet address. This process transfers tokens to L1 based on the finalized withdrawal transaction.

// Transferfrom (after finalization, user have to transferFrom to get his token)
const transferTx = await l2NativeTokenContract.transferFrom(
  l1Contracts.OptimismPortal,
  l1Wallet.address,
  amount
)
await transferTx.wait()

getMessageStatus

getMessageStatus is used to check the status of deposit and withdrawal transactions between L1 and L2 when using OptimismPortal and L2ToL1MessagePasser. Through getMessageStatus, it helps verify which stage the transaction is at within the network.

OptimismPortal

  1. Transaction Creation: Use the portals.depositTransaction function to create a NativeToken deposit transaction from L1 to L2.

const depositTx = await portals.depositTransaction({
    to: l2Wallet.address,
    value: BigNumber.from(amount),
    gasLimit: BigNumber.from('200000'),
    data: '0x',
  })

  1. Transaction Waiting: Call depositTx.wait() to wait for the transaction to complete and receive the transaction receipt, depositReceipt. This receipt includes important information such as the transactionHash.

const depositReceipt = await depositTx.wait()
console.log('depositTx:', depositReceipt.transactionHash)

  1. Relay Hash: After the transaction is successfully processed on L1, you need to wait for it to be relayed to L2. Use the portals.waitingDepositTransactionRelayed function to verify that the transaction submitted on L1 has been successfully relayed to L2 and obtain the relayedTxHash. This hash is used to track the transaction on L2.

const relayedTxHash = await portals.waitingDepositTransactionRelayed(
  depositReceipt,
  {}
)

  1. Status Check: Use portals.getMessageStatus to check the status of the deposit transaction and verify whether it has been successfully relayed on L2.

const status = await portals.getMessageStatus(depositReceipt)
console.log('deposit status relayed:', status === MessageStatus.RELAYED)

Through this process, you can deposit NativeToken from L1 to L2 and use getMessageStatus to monitor the final status of the transaction, ensuring that the entire deposit process has been completed successfully.

L2ToL1MessagePasser

  1. Withdrawal Transaction Creation and Submission: Use portals.initiateWithdrawal to create a withdrawal transaction from L2 to L1. The result of the created transaction is returned as withdrawalReceipt, which is then used to track the status of the withdrawal transaction.

const withdrawalTx = await portals.initiateWithdrawal({
    target: l1Wallet.address,
    value: BigNumber.from(amount),
    gasLimit: BigNumber.from('200000'),
    data: '0x12345678',
  })
const withdrawalReceipt = await withdrawalTx.wait()

  1. Calculate Withdrawal Message Information: The portals.calculateWithdrawalMessage function calculates information about the withdrawal message. This information is used in the subsequent steps of the withdrawal transaction, including the proving and finalization processes.

const withdrawalMessageInfo = await portals.calculateWithdrawalMessage(
  withdrawalReceipt
)
console.log('withdrawalMessageInfo:', withdrawalMessageInfo)

  1. Check Withdrawal Transaction Status 1: Use portals.getMessageStatus to check the status of the withdrawal transaction. At this stage, you verify whether the root has been successfully posted on L2.

let status = await portals.getMessageStatus(withdrawalReceipt)
console.log('[Withdrawal Status] check publish L2 root:', status)

  1. Wait for Relay Readiness: Use the portals.waitForWithdrawalTxReadyForRelay function to wait until the withdrawal transaction is ready to be relayed to L1. This process indicates that the withdrawal message created on L2 is prepared for transmission to L1.

await portals.waitForWithdrawalTxReadyForRelay(withdrawalReceipt)

  1. Check Withdrawal Transaction Status 2: Call getMessageStatus again to verify if the withdrawal transaction is ready to be proven on L1.

status = await portals.getMessageStatus(withdrawalReceipt)
console.log('[Withdrawal Status] check ready for proving:', status)

  1. Proof of Withdrawal Transaction: Use portals.proveWithdrawalTransaction to prove the withdrawal transaction on L1. This step involves verifying the withdrawal transaction on L1.

const proveTransaction = await portals.proveWithdrawalTransaction(
  withdrawalMessageInfo
)
await proveTransaction.wait()

  1. Check Withdrawal Transaction Status: Use getMessageStatus to verify if the transaction is in a challenging state on L1. This status indicates that the transaction is still being processed.

status = await portals.getMessageStatus(withdrawalReceipt)
console.log('[Withdrawal Status] check in challenging:', status)

  1. Wait for Finalization: Use portals.waitForFinalization to wait until the transaction is finalized. Afterward, you can finalize the transaction.

await portals.waitForFinalization(withdrawalMessageInfo)
const finalizedTransaction = await portals.finalizeWithdrawalTransaction(
  withdrawalMessageInfo

  1. Finalize and Check Withdrawal Transaction: Use portals.finalizeWithdrawalTransaction to finalize the withdrawal transaction. This process indicates that the transaction has been successfully completed. Finally, call getMessageStatus to confirm that the withdrawal transaction was successfully relayed on L1.

const finalizedTransactionReceipt = await finalizedTransaction.wait()
console.log('finalized transaction receipt:', finalizedTransactionReceipt)

status = await portals.getMessageStatus(withdrawalReceipt)
console.log('[Withdrawal Status] check relayed:', status)
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