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Description

The Helix Relayer is a client designed to facilitate the operation of the LnBridge (Liquidate Node Bridge) by relaying messages from the source chain to the target chain. This relayer allows you to efficiently transmit messages and receive rewards from the fees paid by users.

The relayer functions by periodically fetching user transaction data from the Helix indexer service. When it identifies a transaction that requires relaying, it proceeds to perform the relay operation.

Register

LnBridge with direction "Default"

  1. Call setProviderFee method of the LnBridge contract on the source chain to set the fee(include base fee and liquidity fee).
  2. Call depositProviderMargin method of the LnBridge contract on the target chain to deposit margin. Before calling the method, relayer should approve the contract to use the source token.
  3. Optional method depositSlashFundReserve is used to deposit for Slasher a certain amount of gas fee compensation, if there is no pledge of this compensation, the backend will reduce the probability of recommending the relayer to the user.

LnBridge with direction "Opposite"

Call updateProviderFeeAndMargin method of the LnBridge contract on the source chain to set fee and deposit margin. Before doing this, relayer should approve token transfer first.

Configure

The default configure file path is

.maintain/configure.json

You need configure the .env file as follows to indict the configure file path and store path.

# The path of the configure file
LP_BRIDGE_PATH=./.maintain/configure.json
# The store path, DB files to store the last tx hash relayer sent.
LP_BRIDGE_STORE_PATH=./.maintain/db

The details of each field in the configuration file are as follows.

Field Description
indexer The relayer relies on the trustworthiness of the indexer, which you can find in the provided GitHub repository indexer. Relayers have the option to deploy their own indexer service using this repository.
Please note that Helix also deploys an indexer service, but relayers who choose to use it should be aware that there is a risk of data correctness. It is recommended that relayers proceed with caution and assume responsibility for any potential inaccuracies.
relayGasLimit The gasLimit for relay transactions, which may be different for different chains, but we can pick the highest limit that supports them, because the actual transactions consume less gas than this limit.
chains Relayers need to configure the name(which will be used in a later field), rpc url and native token symbol (which is not used at the moment).
bridges This client supports running multiple token bridges and tokens simultaneously, bridges is an array where each element of the array represents an instance of an asset bridge in one direction

The attributes of bridges are as follows

Attributes Description
fromChain Source chain name, which needs to be in the chains field.
toChain Target chain name, which also needs to be in the chains field.
sourceBridgeAddress Source LnBridge Contract Address.
targetBridgeAddress Target LnBridge Contract Address.
encryptedPrivateKey Encrypted private key by using yarn crypto command.
minProfit & maxProfit Maximum and Minimum Profit (Native token), as the price of the gas on the target chain adjusts, the client automatically adjusts the fee to the middle of the maximum and minimum profit range when it sees that the profit has jumped out of their range.
feeLimit Relay cost cap, used to protect against programmatic exceptions and to prevent the sending of transactions with too high a gas price.
reorgThreshold This threshold is used to prevent the reorg of transactions on the source chain, and needs to be set by the relayer itself to a suitable value to prevent the loss of assets due to reorg.
direction The direction of the protocol used by the bridge, the optional values are opposite and default.
providers Is an array indicating that a relayer can provide bridge services for multiple tokens in the same direction. Include
1. fromAddress: The address of the token on the source chain, or all zeros in the case of native tokens
2. toAddress: The address of the token on the target chain, or all zeros in the case of native tokens
3. swapRate: The exchange rate between the native token on the target chain and the transfer token is used to calculate cross-chain costs and profits.
4. srcDecimals: The decimals of the token on the source chain.

Example

Here is a specific example on testnet arbitrum-goerli <-> goerli.

USDC

0xEA70a40Df1432A1b38b916A51Fb81A4cc805a963(arbitrum-goerli)

0xd35CCeEAD182dcee0F148EbaC9447DA2c4D449c4(goerli)

arbitrum-goerli -> goerli (opposite)

LnBridgeSourceAddress: 0x7B8413FA1c1033844ac813A2E6475E15FB0fb3BA

LnBridgeTargetAddress: 0x3B1A953bFa72Af4ae3494b08e453BFF30a06A550

Register:

Step1(arbitrum-goerli):
Erc20(0x7B8413FA1c1033844ac813A2E6475E15FB0fb3BA).approve(0x7B8413FA1c1033844ac813A2E6475E15FB0fb3BA, 10000000000);

Step2(arbitrum-goerli):
LnOppositeBridgeSource(0x7B8413FA1c1033844ac813A2E6475E15FB0fb3BA).updateProviderFeeAndMargin(
  0x7B8413FA1c1033844ac813A2E6475E15FB0fb3BA,
  10000000000,
  3000000,
  100
);

goerli -> arbitrum-goerli (default)

LnBridgeSourceAddress: 0xcD86cf37a4Dc6f78B4899232E7dD1b5c8130EFDA

LnBridgeTargetAddress: 0x4112c9d474951246fBC2B4D868D247e714698aE1

Register:

Step1(goerli):
LnDefaultBridgeSource(0xcD86cf37a4Dc6f78B4899232E7dD1b5c8130EFDA).setProviderFee(
  0xd35CCeEAD182dcee0F148EbaC9447DA2c4D449c4,
  3000000,
  100
);

Step2(arbitrum-goerli):
Erc20(0x4112c9d474951246fBC2B4D868D247e714698aE1).approve(0x4112c9d474951246fBC2B4D868D247e714698aE1, 10000000000);

Step3(arbitrum-goerli):
LnDefaultBridgeTarget(0xEA70a40Df1432A1b38b916A51Fb81A4cc805a963).depositProviderMargin(
  0xd35CCeEAD182dcee0F148EbaC9447DA2c4D449c4,
  0xEA70a40Df1432A1b38b916A51Fb81A4cc805a963,
  10000000000
);

configure file

Edit the configure file and put it in the path .maintain/configure.json.

{
    "indexer": "https://apollo-test.helixbridge.app/graphql",
    "relayGasLimit": 600000,
    "chains": [
        {
            "name": "arbitrum-goerli",
            "rpc": "https://goerli-rollup.arbitrum.io/rpc",
            "native": "ETH"
        },
        {
            "name": "goerli",
            "rpc": "https://rpc.ankr.com/eth_goerli",
            "native": "ETH"
        }
    ],
    "bridges": [
        {
            "fromChain": "arbitrum-goerli",
            "toChain": "goerli",
            "sourceBridgeAddress": "0x7B8413FA1c1033844ac813A2E6475E15FB0fb3BA",
            "targetBridgeAddress": "0x3B1A953bFa72Af4ae3494b08e453BFF30a06A550",
            "encryptedPrivateKey": "...",
            "minProfit": 0.005,
            "maxProfit": 0.01,
            "feeLimit": 0.01,
            "reorgThreshold": 100,
            "direction": "opposite",
            "providers": [
                {
                    "fromAddress": "0xEA70a40Df1432A1b38b916A51Fb81A4cc805a963",
                    "toAddress": "0xd35CCeEAD182dcee0F148EbaC9447DA2c4D449c4",
                    "swapRate": 2000,
                    "srcDecimals": 6
                }
            ]
        },
        {
            "fromChain": "goerli",
            "toChain": "arbitrum-goerli",
            "sourceBridgeAddress": "0xcD86cf37a4Dc6f78B4899232E7dD1b5c8130EFDA",
            "targetBridgeAddress": "0x4112c9d474951246fBC2B4D868D247e714698aE1",
            "encryptedPrivateKey": "...",
            "minProfit": 0,
            "maxProfit": 1,
            "feeLimit": 0.01,
            "reorgThreshold": 10,
            "direction": "default",
            "providers": [
                {
                    "fromAddress": "0xd35CCeEAD182dcee0F148EbaC9447DA2c4D449c4",
                    "toAddress": "0xEA70a40Df1432A1b38b916A51Fb81A4cc805a963",
                    "swapRate": 2000,
                    "srcDecimals": 6
                }
            ]
        }
    ]
}

Install & Run Client

Before start, relayers need to approve LnBridge to transferFrom their tokens.

$ yarn install

$ yarn build

$ yarn start

# Enter Password to Start

Encrypt your private key

$ yarn crypto

To execute the command mentioned above and update the .maintain/configure.json file with the encrypted private key, please follow the steps below:

  1. Run the command as specified and provide the necessary input, including the password and private key.
  2. The command will output the encrypted private key.
  3. Open the .maintain/configure.json file in a text editor.
  4. Locate the "encryptedPrivateKey" field in the JSON file.
  5. Replace the existing value of encryptedPrivateKey with the newly generated encrypted private key obtained from the command's output.
  6. Save the changes to the .maintain/configure.json file.

Please make sure to take proper precautions to protect your private key and encrypted private key.

Slash & Margin Withdraw

When the relayer is not working, Slasher needs to call the contract interface to help the user to complete the transfer and get a penalty from the relayer as a reward. When the relayer wishes to exit, it needs to call the contract interface to complete the exit and withdraw the pledge margin. There is a difference in the contract operation here for different chains, due to the different messages used in the message layer.

arbitrum -> ethereum (opposite)

  1. Slash

First call submissionRefundFee on the target chain ethereum to get the submissionFee fee. Then call slashAndRemoteRefund to send a Slash request to the source chain The cost is submissionFee + maxGas * gasPriceBid, and the excess cost is refunded to the sending account. If the execution of the target chain fails, call retryRemoteRefund to retry.

  1. Withdraw

First call submissionWithdrawFee on the target chain ethereum to get the submissionFee fee. Then call requestWithdrawMargin to send a Withdraw request to the source chain, the cost is submissionFee + maxGas * gasPriceBid, and the excess cost is refunded to the sending account.

ethereum -> arbitrum (default)

  1. Slash

First call submissionSlashFee on the source ethereum chain to get the submissionFee fee. Then call slashAndRemoteRelease to send a slash request to the target chain, the cost is submissionFee + maxGas * gasPriceBid, the excess cost will be refunded to the sending account.

  1. Withdraw

The submissionWithdrawFee is first called on the source chain ethereum to get the submissionFee fee. Then call requestWithdrawMargin to send the Withdraw request to the target chain, the cost is submissionFee + maxGas * gasPriceBid, the excess cost will be refunded to the sending account.

zkSync -> ethereum (opposite)

  1. Slash

First use l2Fee to get fees on the target chain ethereum. Then call slashAndRemoteRefund to send a Slash request to the source chain at a cost of l2Fee. If the execution of the target chain fails, call retryRemoteRefund to retry.

  1. Withdraw

First use l2Fee to get fees on the target chain ethereum. Then call requestWithdrawMargin to send an Withdraw request to the source chain, at a cost of l2Fee.

ethereum -> zkSync (default)

  1. Slash

First use l2Fee to get fees on the source chain ethereum. Then call slashAndRemoteRelease to send a slash request to the target chain with the cost of l2Fee.

  1. Withdraw

First use l2Fee to get fees on the source chain ethereum. Then call requestWithdrawMargin to send an Withdraw request to the target chain, at a cost of l2Fee

Linea -> ethereum (opposite)

  1. Slash

Execute slashAndRemoteRefund on the target chain ethereum with the cost set to 0. After waiting about 15 minutes for the transaction hash to be relayed to the source chain, execute the claimMessage interface of the Linea messageService contract on the source chain.

  1. Withdraw

Execute requestWithdrawMargin on the target chain ethereum with the cost set to 0. After the transaction hash has been relayed to the source chain in about 15 minutes, execute the claimMessage interface of the Linea messageService contract.

ethereum -> Linea (default)

  1. Slash

Execute slashAndRemoteRelease on source chain ethereum with cost set to 0. After waiting about 15 minutes for the transaction hash to be relayed to the target chain, execute the claimMessage interface of the Linea messageService contract.

  1. Withdraw

Execute requestWithdrawMargin on source chain ethereum with cost set to 0. After waiting about 15 minutes for the transaction hash to be relayed to the target chain, execute the claimMessage interface of the Linea messageService contract.

Linea<>zkSync<>arbitrum（default, based on LayerZero）

  1. Slash

The estimateSlashFee interface is used on the source chain to estimate the cost, and the slashAndRemoteRelease interface is called to send the request to the target chain. If the execution of the target chain fails and needs to be retried, use the retryPayload interface of the layerzero endpoint contract to do so.

  1. Withdraw

The estimateWithdrawFee interface is used on the source chain to estimate the cost, and the requestWithdrawMargin interface is called to send the request to the target chain. If the target chain fails and needs to be retried, use the retryPayload interface of the layerzero endpoint contract to do so. It is possible that the target chain succeeds, but the result fails, so if you want to retry, you can only retry in the source chain.

Message Channel

  • arbitrum L2
// 1. call function fee() to get submissionCost[message channel]
function fee(
    uint256 _callSize,
    uint256 _l1GasPrice,
    uint256 _l2GasPrice,
    uint256 _l2GasLimit,
    uint256 _percentIncrease
) external view returns(uint256, uint256);
// 2. call encodeParams to get _extParams[message channel]
function encodeParams(
   uint256 _maxSubmissionCost,
   uint256 _l2GasPrice,
   uint256 _l2GasLimit,
   address _refunder
);
  • linea L2
// 1. set fee to be zero
// 2. call claimMessage on target chain
  • Layerzero
// 1. call function fee to get bridge fee
function fee(
    uint256 _remoteChainId,
    bytes memory _message
)
// 2. params is the refund address
  • axelar
// 1. estimate bridge fee, more then required, example 0.001 eth on goerli
// 2. params is the refund address
// 3. on target chain, the gas fee will be refund