contracts

@facilitator/contracts

EIP-7702 Delegate contract for x402 gasless payment intents. Enables any ERC-20 and native ETH transfers without the payer holding gas tokens.

Deployed Addresses

Network	Address
Ethereum Mainnet	0xD064939e706dC03699dB7Fe58bB0553afDF39fDd
Polygon	0xD064939e706dC03699dB7Fe58bB0553afDF39fDd
Base	0xD064939e706dC03699dB7Fe58bB0553afDF39fDd
Optimism	0xD064939e706dC03699dB7Fe58bB0553afDF39fDd
Arbitrum	0xD064939e706dC03699dB7Fe58bB0553afDF39fDd
BNB Chain	0xD064939e706dC03699dB7Fe58bB0553afDF39fDd
Avalanche	0xD064939e706dC03699dB7Fe58bB0553afDF39fDd

Install

forge install melonask/facilitator

Add to remappings.txt:

@facilitator/=lib/facilitator/packages/

Usage

import {Delegate} from "@facilitator/contracts/src/Delegate.sol";

Overview

Delegate is an EIP-7702 delegate contract. A relayer submits a Type 4 transaction that sets the Delegate as the EOA's code, then calls transfer() or transferEth() with the user's EIP-712 signed intent.

User signs:                  Relayer submits:
  EIP-712 PaymentIntent        Type 4 tx (EIP-7702)
  EIP-7702 Authorization       authorizationList: [user's auth]
                                to: user's EOA
                                data: Delegate.transfer(intent, sig)
                                        |
                                        v
                                SafeERC20.safeTransfer(token, to, amount)

API Reference

Structs

Struct	Fields	Description
PaymentIntent	token, amount, to, nonce, deadline	ERC-20 transfer intent
EthPaymentIntent	amount, to, nonce, deadline	Native ETH transfer intent

Functions

Function	Access	Description
transfer(intent, signature)	External	Execute a signed ERC-20 payment intent
transferEth(intent, signature)	External	Execute a signed native ETH payment intent
invalidateNonce(nonce)	Owner	Cancel a pending intent (owner only)
isValidSignature(hash, sig)	View	ERC-1271 signature validation (ERC-7739)

Events

Event	Parameters	Description
PaymentExecuted	token, to, amount, nonce	Emitted on successful ERC20 transfer
EthPaymentExecuted	to, amount, nonce	Emitted on successful ETH transfer
NonceInvalidated	nonce	Emitted when nonce is manually invalidated

Custom Errors

Error	Condition
Expired	block.timestamp > intent.deadline
NonceAlreadyUsed	Nonce was previously used or invalidated
InvalidSignature	Signature invalid or signer != EOA owner
EthTransferFailed	ETH transfer to recipient reverted
OnlyOwner	msg.sender != address(this)
ZeroAddress	intent.to == address(0)

EIP-712 Integration

For frontend/backend integrations, use the following EIP-712 domain and type definitions:

Domain

const domain = {
  name: "Delegate",
  version: "1.0",
  chainId: chainId,
  verifyingContract: userEOAAddress, // The EOA with delegated code
};

Types

// For ERC-20 transfers
const PaymentIntent = {
  PaymentIntent: [
    { name: "token", type: "address" },
    { name: "amount", type: "uint256" },
    { name: "to", type: "address" },
    { name: "nonce", type: "uint256" },
    { name: "deadline", type: "uint256" },
  ],
};

// For native ETH transfers
const EthPaymentIntent = {
  EthPaymentIntent: [
    { name: "amount", type: "uint256" },
    { name: "to", type: "address" },
    { name: "nonce", type: "uint256" },
    { name: "deadline", type: "uint256" },
  ],
};

Signing Example (ethers.js v6)

const intent = {
  token: "0x...", // ERC-20 token address
  amount: parseUnits("100", 18),
  to: "0x...", // Recipient
  nonce: 1n, // Any unique uint256
  deadline: BigInt(Math.floor(Date.now() / 1000) + 3600), // 1 hour
};

const signature = await signer.signTypedData(domain, PaymentIntent, intent);

Security

Feature	Implementation
Replay Protection	Single-use nonces per intent
Intent Expiration	Unix timestamp deadline validation
Signature Validation	EIP-712 typed data + ECDSA recovery via SignerEIP7702
ERC-1271 Support	ERC-7739 compliant
Storage Isolation	ERC-7201 namespaced storage
Zero-Address Protection	Explicit validation prevents accidental fund loss
Safe Token Transfers	OpenZeppelin SafeERC20 for ERC-20 compatibility
CEI Pattern	State changes before external calls

Dependencies

• OpenZeppelin Contracts: ECDSA, EIP712, ERC7739, SignerEIP7702, SafeERC20, ERC721Holder, ERC1155Holder

Gas Optimization

The contract is optimized for minimal gas consumption:

• Custom errors instead of string reverts (~200-500 gas saved per revert)
• Inline assembly for EIP-712 struct hashing (avoids abi.encode overhead)
• Calldata caching to stack variables before assembly access
• Optimizer enabled with via_ir = true and optimizer_runs = 1 for deployment size

Development

# Build
forge build

# Run tests
forge test -vvv

# Run tests with gas report
forge test --gas-report

# Check coverage
forge coverage

Test Coverage

| File             | Lines      | Statements | Branches  | Functions |
|------------------|------------|------------|-----------|-----------|
| src/Delegate.sol | 100.00%    | 100.00%    | 100.00%   | 100.00%   |

Deploy

Deterministic deployment via CREATE2 (same address on every chain):

Salt: 0xcabb92b3cbd6ab7eeb40c1a3415b7c452a7e3e900d53a9eb466f56e44018d5c7

export DEPLOYER_PRIVATE_KEY=0x...
# The script defaults to the correct salt if not provided
forge script script/Deploy.s.sol --rpc-url <RPC_URL> --broadcast

Audits

Note: This contract has not been audited. Use at your own risk.

License

MIT