Relayer Calls on BEX

Relayer calls allow an end-user to sign a BEX command using an off-chain EIP-712 signature. This signed command can then be executed inside an Ethereum transaction sent by a third-party relayer. The user can optionally "tip" the relayer to compensate for the gas cost.

function userCmdRelayer(
    uint16 callpathIdx,
    bytes cmd,
    bytes conds,
    bytes tip,
    bytes signature
) returns (bytes memory)

Parameters

Parameter	Type	Description
callpathIdx	uint16	The same parameter in standard userCmd and will behave identically
cmd	bytes	The same parameter in standard userCmd and will behave identically
conds	bytes	A bytestring encoded in a fixed format that governs the conditions of the relayer call (explained below)
tip	bytes	A bytestring that can be empty or set using a fixed encoding scheme to specify the relayer tip (explained below)
signature	bytes	The EIP-712 signature of the command and conditions (explained below)

Conds

The conds bytestring is encoded as follows:

conds = abi.encode(
    deadline, // uint48
    alive,    // uint48
    salt,     // bytes32
    nonce,    // uint32
    relayer   // address
)

Parameters

Parameter	Type	Description
deadline	uint48	The timestamp before which the transaction must occur, otherwise it will fail
alive	uint48	The timestamp after which the transaction must occur, otherwise it will fail
salt	bytes32	A unique value that defines a unique nonce tracking (starting at 0), allowing for multidimensional nonces
nonce	uint32	A user-specific relayer nonce that increments by one on every relayer call, preventing replay attacks
relayer	address	The address of the relayer that can execute the command; if set to address(0), the condition is unenforced

Tip

The tip bytestring can either be empty (no tip paid) or set using the following fixed encoding scheme:

tip = abi.encode(
    token,  // address
    amount, // uint128
    recv    // address
)

Parameters

Parameter	Type	Description
token	address	The address of the token in which the tip is being paid
amount	uint128	The total amount of the token being paid as a tip to the relayer
recv	address	The recipient of the relayer tip, which can be a specific address or a magic value (address(256) for msg.sender or address(512) for tx.origin)

Tips are always paid from the surplus collateral balance of the end-user. If the end-user has insufficient surplus collateral, the contract call will revert.

signature

The signature is the EIP-712 signature of the command and conditions, constructed from the standard v, r, and s recovery signature:

signature = abi.encode(
    v, // uint8
    r, // uint256
    s  // uint256
)

The EIP-712 domain hash is constructed as:

const domain = {
    name: "CrocSwap",
    chainId: [chain ID],
    verifyingContract: [BEXSwapDex contract address],
    version: "1.0"
};

The typed content hash is constructed as:

CrocRelayerCall: [
  { name: "callpath", type: "uint8" },
  { name: "cmd", type: "bytes" },
  { name: "conds", type: "bytes" },
  { name: "tip", type: "bytes" },
];

Example Signature Construction in Javascript/Ethersjs

const { ethers } = require("ethers");

const signer = new ethers.Wallet("0x... private key ...");

const domain = {
  name: "CrocSwap",
  version: "1.0",
  chainId: 31337,
  verifyingContract: BEX_DEX_CONTRACT_ADDRESS,
};

const types = {
  CrocRelayerCall: [
    { name: "callpath", type: "uint8" },
    { name: "cmd", type: "bytes" },
    { name: "conds", type: "bytes" },
    { name: "tip", type: "bytes" },
  ],
};

const value = {
  callpath: callpath,
  cmd: cmd,
  conds: conds,
  tip: tip,
};

const signature = (await signer._signTypedData(domain, types, value)).substring(
  2
);

const r = "0x" + signature.substring(0, 64);
const s = "0x" + signature.substring(64, 128);
const v = parseInt(signature.substring(128, 130), 16);

const abiCoder = new ethers.utils.AbiCoder();
const encodedSignature = abiCoder.encode(
  ["uint8", "bytes32", "bytes32"],
  [v, r, s]
);