zksync-era-withdrawal-finalizer

A Withdrawal Finalizer in Rust.

Purpose

Withdrawal Finalizer is a component of zksync-era responsible for monitoring and finalizing L2->L1 withdrawals. It does so by continuously monitoring events happening on both L2 and L1, keeping some state in persistent storage (which is PostgreSQL) and sending withdrawal finalization transactions whenever necessary.

Building

Building the project is straightforward:

cargo build

Deploying

To deploy this service you will need the following prerequisites:

1. Websocket RPC endpoint on Ethereum.
2. Websocket RPC endpoint on zkSync Era.
3. An instance of PostgreSQL database.

Running DB migrations

Prior to deployment of the service the database migrations have to be run with sqlx-cli component of sqlx:

$ cd ./storage
$ env DATABASE_URL=postgres://mycreds@myhost/mydb sqlx database create
$ env DATABASE_URL=postgres://mycreds@myhost/mydb sqlx migrate run

Configuration

Configuration is done via environment variables that can also be read from .env file if it is present. Deployment is done by deploying a dockerized image of the service.

Variable	Description
ETH_CLIENT_WS_URL	The address of Ethereum WebSocket RPC endpoint
ETH_CLIENT_HTTP_URL	The address of Ethereum HTTP RPC endpoint
CONTRACTS_L1_ERC20_BRIDGE_PROXY_ADDR	Address of the L1 ERC20 bridge contract**
CONTRACTS_L2_ERC20_BRIDGE_ADDR	Address of the L2 ERC20 bridge contract**
CONTRACTS_DIAMOND_PROXY_ADDR	Address of the L1 diamond proxy contract**
CONTRACTS_WITHDRAWAL_FINALIZER_CONTRACT	Address of the Withdrawal Finalizer contract **
API_WEB3_JSON_RPC_WS_URL	Address of the zkSync Era WebSocket RPC endpoint
API_WEB3_JSON_RPC_HTTP_URL	Address of the zkSync Era HTTP RPC endpoint
DATABSE_URL	The url of PostgreSQL database the service stores its state into
GAS_LIMIT	The gas limit of a single withdrawal finalization within the batch of withdrawals finalized in a call to finalizeWithdrawals in WithdrawalFinalizerContract
BATCH_FINALIZATION_GAS_LIMIT	The gas limit of the finalization of the whole batch in a call to finalizeWithdrawals in Withdrawal Finalizer Contract
WITHDRAWAL_FINALIZER_ACCOUNT_PRIVATE_KEY	The private key of the account that is going to be submit finalization transactions
TX_RETRY_TIMEOUT_SECS	Number of seconds to wait for a potentially stuck finalization transaction before readjusting its fees
TOKENS_TO_FINALIZE	Configures the sets of tokens this instance of finalizer will finalize. It may be configured as a whitelist, a blacklist, a wildcard or completely disable any finalization. For more info see below.
FINALIZE_ETH_TOKEN	(Optional) Configure, whether the Ethereum withdrawal events should be monitored. Useful to turn off for custom bridges that are only interested in a particular ERC20 token and have nothing to do with main Ethereum withdrawals
CUSTOM_TOKEN_DEPLOYER_ADDRESSES	(Optional) Normally ERC20 tokens are deployed by the bridge contract. However, in custom cases it may be necessary to override that behavior with a custom set of addresses that have deployed tokens
CUSTOM_TOKEN_ADDRESSES	(Optional) Adds a predefined list of tokens to finalize. May be useful in case of custom bridge setups when the regular technique of finding token deployments does not work.
ENABLE_WITHDRAWAL_METERING	(Optional, default: "true") By default Finalizer collects metrics about withdrawn token volumens. Users may optionally switch off this metering.
ETH_FINALIZATION_THRESHOLD	(Optional, default: "0") Finalizer will only finalize ETH withdrawals that are greater or equal to this value

The configuration structure describing the service config can be found in config.rs

** more about zkSync contracts can be found here

Configuring Tokens to finalize.

It may be handy to limit a set of tokens the Finalizer is finalizing. This configuration may be specified by setting a rule in the TOKENS_TO_FINALIZE value. If this environment variable is not set then by default Finalizer will only finalize ETH token (0x000...0800a).

You may specify All, None, BlackList or WhiteList as json documents:

1. TOKENS_TO_FINALIZE = '"All"' - Finalize everything
2. TOKENS_TO_FINALIZE = '"None"' - Finalize nothing
3. TOKENS_TO_FINALIZE = '{ "WhiteList":[ "0x3355df6D4c9C3035724Fd0e3914dE96A5a83aaf4" ] }' - Finalize only these tokens
4. TOKENS_TO_FINALIZE = '{ "BlackList":[ "0x3355df6D4c9C3035724Fd0e3914dE96A5a83aaf4" ] }' - Finalize all tokens but these

Deploying the finalizer smart contract

The finalizer smart contract needs to reference the addresses of the diamond proxy contract and l1 erc20 proxy contract. You also need to know the key of the account you want to use to deploy the finalizer contract.

When you know those to deploy the contract you need to run (assume you are create .env from .env.example):

$ npm install
$ npx hardhat compile
$ npx hardhat deploy --network lineatest

If all goes well the the result would be

...
Compiled 18 Solidity files successfully (evm target: paris).
CONTRACTS_WITHDRAWAL_FINALIZER_ADDRESS=0x712516e61C8B383dF4A63CFe83d7701Bce54B03e

And so you know the address of the deployed contract.

License

zkSync Withdrawal Finalizer is distributed under the terms of either

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Official Links

• Website
• GitHub
• Twitter
• Twitter for Devs
• Discord

Disclaimer

zkSync Era has been through lots of testing and audits. Although it is live, it is still in alpha state and will go through more audits and bug bounties programs. We would love to hear our community's thoughts and suggestions about it! It is important to state that forking it now can potentially lead to missing important security updates, critical features, and performance improvements.