Add paymaster integration for sponsored (gasless) transactions

[ch4r10t33r]

Title

Add paymaster integration for sponsored (gasless) transactions

Labels

enhancement, account-abstraction, paymaster, gasless

Description

Implement paymaster functionality to enable sponsored transactions where users don't pay gas fees directly, following the ERC-4337 paymaster specification.

Requirements

Paymaster Data Types

• Define PaymasterData struct:
  • paymaster: Address - Paymaster contract address
  • paymaster_verification_gas_limit: u256 - Gas for paymaster validation
  • paymaster_post_op_gas_limit: u256 - Gas for post-operation logic
  • paymaster_data: []u8 - Custom data for paymaster

Paymaster Middleware

• Create PaymasterMiddleware:
  • getPaymasterData(userOp: *UserOperation) PaymasterData - Get paymaster approval
  • signPaymasterData(data: PaymasterData) []u8 - Sign if needed
  • verifyPaymasterData(data: PaymasterData) bool - Validate response

Common Paymaster Patterns

• Verifying Paymaster:

  • Sponsor based on off-chain signature
  • Whitelist validation
  • Rate limiting

• Token Paymaster:

  • Pay gas fees with ERC-20 tokens
  • Automatic token approval
  • Price oracle integration

• Deposit Paymaster:

  • Pre-funded deposit system
  • Balance checking

Integration

• Integrate with UserOperation builder:

  var userOp = try UserOperationBuilder.init(allocator)
      .setSender(account)
      .setCallData(data)
      .usePaymaster(paymaster_service)  // <-- automatic paymaster
      .build();

• Add to providers:

  • withPaymaster(paymaster_url: []u8) Provider

Paymaster Service Integration

• Support for popular paymaster services:

  • Pimlico
  • Biconomy
  • Alchemy Gas Manager
  • Stackup

• Custom paymaster API integration:

  • pm_sponsorUserOperation RPC method
  • Context data passing
  • Signature validation

File Structure

src/account_abstraction/
  ├── paymaster.zig            # Paymaster types and logic
  ├── paymaster_middleware.zig # Middleware integration
  └── paymaster_services/
      ├── pimlico.zig
      ├── biconomy.zig
      └── custom.zig

Example Usage

// Using a paymaster service
const paymaster = try PimlicoPaymaster.init(allocator, api_key);

var userOp = try UserOperationBuilder.init(allocator)
    .setSender(smart_account)
    .setCallData(call_data)
    .usePaymaster(&paymaster)  // Gas will be sponsored!
    .build();

const hash = try bundler.sendUserOperation(userOp);
// User pays 0 ETH for gas! 🎉

References

• ERC-4337 Paymaster: https://eips.ethereum.org/EIPS/eip-4337#paymasters
• Viem paymaster: https://github.com/wevm/viem/tree/main/src/account-abstraction
• Pimlico docs: https://docs.pimlico.io/