ConveyorV2 Design

Summary

ConveyorV2 is an upgrade of Automata's ConveyorV1 to support a better user experience. Tokens that are traded in the ConveyorV2 liquidity pools enjoy the MEV protection and transaction ordering enforcement capabilities without the need to wrap existing ERC20 tokens into gTokens.

Similar with ConveyorV1 (formerly known as GTokens), users must sign an EIP712 message to authorize Geode to submit a transaction on the user's behalf. Users would still enjoy the benefit of gasless trading, meaning they are not required to hold native tokens like MATIC or BNB to pay for gas. However, users are subjected to pay a service fee with an acceptable form of ERC20 tokens, such as DAI, USDC or ATA tokens.

Codebase

The ConveyorV2 smart contracts are a fork of UniswapV2. To learn more about the DEX protocol, read the UniswapV2 docs.

There are certain modifications applied to the contracts. Check out the next section for details.

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Comparison between the UniswapV2 Protocol and ConveyorV2

This section highlights the modification that has been applied to the DEX protocol contracts.

ConveyorV2Pair

• The addition of the onlyRouter() modifier. This modifier guards the mint(), burn() and swap() methods, such that it is made callable by the Router contract only. This modifier is the most viable for enforcing MEV protection, because it prevents any other addresses from bypassing our relayers to perform sandwich attacks.

ConveyorV2Factory

• The router() address variable, the ConveyorV2Pair contract uses this value to match with the caller address. If the caller address does not match with router(), then the pair contract rejects the transaction. Using this approach also allows the "upgradeability" of the router. After the deployment of a newer version of the Router contract, the owner of the DEX can invoke the setRouter() method to map it to the new router address. At this point, all existing pair contracts would only accept function calls from the new Router contract.

ConveyorV2Router01

• The ConveyorV2 router introduces the ability for gasless trading. The user signs the EIP712 message, which is then submitted to the trusted relayer. The trusted relayer then executes the executeMetaTx() method, and pays gas on the user's behalf. After completion of execution, the Forwarder contract collects a service fee from the user to compensate for gas. Check out the ERC20Forwarder section to learn more about the Forwarder contract.

• In an unlikely event when the relayer service is not available, the protocol owner can disable the meta-transaction functionality by invoking the metaSwitch() method to toggle the metaOnly modifier. This would allow users to directly interact with the router contract as a temporary workaround for such an extenuating circumstance.

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ERC20 Forwarder

The gas forwarder contract enables meta-transaction executions, which allows gas relayers to be compensated for the gas payment with ERC20 tokens. The gas forwarder contract has the ability to calculate a better estimation of the actual gas usage, including transactions that are being reverted. This way, the relayers are only compensated for the equivalent amount of ERC20 token in gas usage.

constructor()

Initializes the contract and assigns msg.sender as the default feeHolder. The feeHolder is the recipient of the ERC20 fee payment.

setConstantFee()

function setConstantFee(uint256 _newConstantFee) public onlyOwner

Updates the constantFee value, defaults at 21000. Requires owner() privilege.

Parameter	Type
_newConstantFee	uint256	constant gas limit value

setTransferFee()

function setTransferFee(uint256 _newTransferFee) public onlyOwner

Updates the ERC20 transfer gas limit, the transferFee value, defaults at 65000. Requires owner() privilege.

Parameter	Type
_newTransfeFee	uint256	ERC20 transfer limit value

setRelayer()

function setRelayer(address _relayer, bool _trusted) public onlyOwner

Assigns or revokes relayer role. Requires owner() privilege.

Parameter	Type
_relayer	address	Relayer address
_trusted	bool	True: grant authorization; false: revoke authorization

setFeeHolder()

function setFeeHolder(address _feeHolder) public onlyOwner

Transfers feeHolder role over to the input address. Requires owner() privilege.

Parameter	Type
_feeHolder	address	Fee holder address

MetaTransaction

struct MetaTransaction {
    address from;
    address feeToken;
    uint256 maxTokenAmount;
    uint256 deadline;
    uint256 nonce;
    bytes data;
    bytes32 hashedPayload;
}

Parameter	Type
from	address	the user's address
feeToken	address	The address of the ERC20 fee token
maxAmountToken	uint256	The maximum amount of fee tokens that the users are willing to pay for the meta-tx
deadline	uint256	Meta-transactions that are executed past the deadline will be reverted
nonce	uint256	Replay protection
data	bytes	The encoded function data that is to be executed
hashedPayload	bytes32	EIP712-compliant hash struct

executeMetaTx()

function executeMetaTx(MetaTransaction memory metatx, string memory domainName, uint256 tokenPricePerNativeToken, uint256 feeOffset, SIGNATURE_TYPE memory sig) public relayerOnly

This function executes the encoded function data, as defined in MetaTransaction.data. It calculates the amount of gas consumption within the enveloped function call and charges the user the fee amount that is based on the token/ETH price tokenPricePerNativeToken. This value is given by the Geode, calculated by an aggregation of token prices fetched from multiple sources. There are certain situations that could cause the transaction to revert, which the relayers will not be compensated for gas fee. The point of reverts are:

• Insufficient fee token balance
• Insufficient maxAmountToken
• Invalid EIP 712 signature
• Out of gas error

Parameter	Type
metatx	MetaTransaction	The meta-transaction body
domainName	string	The EIP712 domain name
tokenPricePerNativeToken	uint256	ERC20 token price per ETH
feeOffset	uint256	An additional amount of token to be taken into consideration when verifying the user's balance
sig	SIGNATURE_TYPR	The user's EIP712 signature

MetaStatus

event MetaStatus(address sender, bool success, string error)

The executeMetaTx logs the event to indicate the status of the meta-tx. Execution failure within the meta-tx will not cause the function to revert. To view the error logs of a meta transaction, the client can simply listen for the error message emitted by this event.

Parameter	Type
sender	address	user address
success	bool	status of the meta-tx
error	string	reason of a reverted meta-tx