SDK: Support for L2 direct bridging

[lukasz-zimnoch]

Closes: #750

This pull request enhances the tBTC Typescript SDK with support of the L2 direct bridging mechanism introduced by #792. Moreover, we are adding Base as the first L2 chain with direct bridging enabled.

Initialization of the cross-chain contracts

To enable the SDK to work with a supported L2 chain, we introduce a new initializeCrossChain method that is exposed from the main TBTC component. This function sets up the SDK to work with the given L2 chain and attaches the provided signer to the tBTC cross-chain contracts deployed there. It's worth noting that the signer can be read-only (e.g. Ethers provider) but in that case, only read functions of the L2 contracts will be available.

After initialization, the cross-chain contracts for the given chain can be directly accessed using the new TBTC.crossChainContracts method. This low-level access method is especially useful for reading data, e.g. get canonical L2 TBTC balance for the given address.

Cross-chain deposits

To leverage the new L2 direct bridging mechanism, the SDK adds the concept of a cross-chain deposit. A cross-chain deposit is a deposit that targets an L2 chain other than the L1 chain the tBTC system is deployed on. Such a deposit is currently initiated using a transaction on the L2 chain (plans for the future include gas-less initiation). On the technical level, this is handled by the new initiateCrossChainDeposit method exposed by the DepositsService component.

Usage

import { Hex, TBTC } from "../src"
import { JsonRpcProvider, Provider } from "@ethersproject/providers"
import { Signer, Wallet } from "ethers"

async function main() {
  // Create a readonly Ethers provider for the Ethereum L1 chain.
  const ethereumProvider: Provider = new JsonRpcProvider("...")
  // Create an instance of the tBTC SDK. It is enough to pass a readonly
  // Ethers provider as parameter. In this example, the SDK does not issue
  // transactions on the Ethereum L1 chain.
  const sdk: TBTC = await TBTC.initializeMainnet(ethereumProvider)

  // Create a signer for Base. This signer will be used to issue transactions
  // on the Base chain and will be used as the owner of the deposit.
  const baseSigner: Signer = new Wallet("...", new JsonRpcProvider("..."))
  // Initialize cross-chain contracts for the Base chain.
  await sdk.initializeCrossChain("Base", baseSigner)

  // Get BTC recovery address for the deposit.
  const bitcoinRecoveryAddress: string = "..."

  // Initiate a cross-chain deposit to the Base chain.
  const deposit = await sdk.deposits.initiateCrossChainDeposit(
    bitcoinRecoveryAddress,
    "Base"
  )
  // Get BTC deposit address and send funds to it.
  const depositAddress: string = await deposit.getBitcoinAddress()
  // Initiate minting once BTC transaction is made. This will call
  // revealDepositOnBehalf function of the ExampleDepositor contract
  // under the hood.
  const baseTxHash: Hex = await deposit.initiateMinting()

  console.log(
    `Minting initiated. Base transaction hash: ${baseTxHash.toPrefixedString()}`
  )
}

[michalsmiarowski]

LGTM 🔥

[michalsmiarowski]

Let's not forget about those TODOs, when the mainnet contracts will be available on Ethereum mainnet. I assume it's a non-blocking issue and we can merge anyway.

[lukasz-zimnoch]

Yep. We will open another PR just before the release.