opbnb-bridge-bot

Description

The opbnb-bridge-bot project primarily maintains a Layer2 contract named L2StandardBridgeBot. This contract, when called, initiates withdrawal transactions and collects a fixed fee for every withdrawals. The project promises that after the withdrawal transaction has can be proven and finalized after the required time window, a third-party account would complete the corresponding L1 proven withdrawal transactions and L1 finalized withdrawal transactions, thus completing the entire withdrawal process.

Motivation

A withdrawal request must be completed in three steps:

1. Send a L2 initiating transaction
2. Send the L1 proven transaction after the proposer submits the next L2 output root
3. Send L1 finalized transaction after the challenge window has passed

Completing these three steps might not be a good user experience. Firstly, users need to send 3 transactions; secondly, they need to wait 2 periods before sending the next transaction.

See also

• opBNB testnet bridge: https://opbnb-testnet-bridge.bnbchain.org

• withdrawal example: https://testnet.opbnbscan.com/tx/0xadb6b8d8bffb4dc7177ef1e27e202035f0861a71521c3cdff66a4aeb4464e501

Design Principle and Working Mechanism

This project consists of an on-chain contract contracts/src/L2StandardBridgeBot.sol and an off-chain bot.

The L2StandardBridgeBot contract provides a withdrawTo function, which charges a fixed fee for every execution and then forwards the call to the L2StandardBridge.withdraw.

The off-chain bot watches the L2StandardBridgeBot.WithdrawTo events and based on these events, re-constructs the corresponding withdrawals. We name these withdrawals as bot-delegated withdrawals. As time go out of the bot-delegated withdrawal's proven and finalized time window, our bot will send proven and finalized transactions to complete the entire withdrawal process.

references

• contracts
  • L2StandardBridge.sol which concludes the withdrawTo function.
    • opBNB Mainnet address.
    • opBNB Testnet address
  • OptimismPortal.sol which concludes the proveWithdrawalTransaction and finalizeWithdrawalTransaction functions.
    • BSC Mainnet address.
    • BSC Testnet address
• opbnb bridge
• tutorial of interacting with bridge with js-sdk.

User Guide

Getting Started at opBNB testnet

1. Prepare a MySQL database

docker-compose up -d

2. Compile the off-chain bot and output the artifact to ./bot

make build-go

3. Run the off-chain bot

OPBNB_BRIDGE_BOT_PRIVKEY=<bot privkey> ./bot --config ./bot.toml

Deploy and Use Contracts

1. Compile the contract using forge

make build-solidity

2. Deploy contract

cd contracts

export DELEGATE_FEE=1000000000000000
forge create \
    --rpc-url $OPBNB_TESTNET \
    --private-key $OP_DEPLOYER_PRIVKEY \
    src/L2StandardBridgeBot.sol:L2StandardBridgeBot --constructor-args $OP_DEPLOYER_ADDRESS $DELEGATE_FEE

3. Withdraw via the deployed contract

export DELEGATE_FEE=1000000000000000
export amount=2000000000000001
export contract_addr=<deployed contract address>

cast send --rpc-url $OPBNB_TESTNET \
          --private-key $OP_DEPLOYER_PRIVKEY \
          --value $(($DELEGATE_FEE + $amount)) \
          $contract_addr \
          $(cast calldata 'withdrawTo( address _l2Token, address _to, uint256 _amount, uint32 _minGasLimit, bytes calldata _extraData)' 0xDeadDeAddeAddEAddeadDEaDDEAdDeaDDeAD0000 $OP_DEPLOYER_ADDRESS $amount 150469 "")

License

MIT