Implement gas estimation for UserOperations

[ch4r10t33r]

Title

Implement gas estimation for UserOperations

Labels

enhancement, account-abstraction, gas, estimation

Description

Add accurate gas estimation for UserOperations, accounting for all ERC-4337 components including verification, execution, and paymaster gas.

Requirements

UserOperation Gas Components

• Estimate callGasLimit:

  • Simulate main execution call
  • Add buffer for safety (10-20%)

• Estimate verificationGasLimit:

  • Account's validateUserOp gas cost
  • Handle different account implementations
  • Standard accounts: ~100k gas
  • Complex validation: higher limits

• Calculate preVerificationGas:

  • Fixed overhead for bundler
  • calldata cost calculation
  • Signature length consideration
  • Formula: 21000 + calldataGas + bundlerOverhead

• Estimate paymaster gas (if used):

  • paymasterVerificationGasLimit
  • paymasterPostOpGasLimit

Estimation Strategies

• Via Bundler RPC:

  • Use eth_estimateUserOperationGas
  • Parse bundler response
  • Apply safety margins

• Local Simulation:

  • Fallback if bundler doesn't support estimation
  • Simulate via eth_call to EntryPoint
  • Extract gas usage from trace

• Heuristic-based:

  • Default values for known account types
  • Simple account: 100k verification, based on call for execution
  • Configurable defaults

Gas Optimization

• Add optimization helpers:
  • optimizeUserOpGas(userOp: *UserOperation) - Reduce gas where safe
  • Check if init_code is needed
  • Minimize signature size
  • Optimize calldata packing

Estimation Middleware

• Create UserOpGasMiddleware:
  • Automatic gas estimation before submission
  • Caching of estimation results
  • Dynamic adjustment based on network conditions

Gas Calculation Formulas

// Pre-verification gas
pub fn calculatePreVerificationGas(
    userOp: UserOperation,
    bundler_overhead: u256,
) u256 {
    const calldata_cost = calcdataGasCost(userOp);
    return 21000 + calldata_cost + bundler_overhead;
}

// Calldata gas cost
fn calcdataGasCost(userOp: UserOperation) u256 {
    var cost: u256 = 0;
    const packed = packUserOp(userOp);
    for (packed) |byte| {
        cost += if (byte == 0) 4 else 16;
    }
    return cost;
}

File Structure

src/account_abstraction/
  ├── gas_estimation.zig       # Core gas estimation logic
  └── gas_middleware.zig       # Middleware for auto-estimation

Example Usage

// Automatic estimation
var userOp = try UserOperationBuilder.init(allocator)
    .setSender(account)
    .setCallData(data)
    .estimateGas(provider, entrypoint)  // <-- automatic
    .build();

// Manual estimation
const gas_estimate = try estimateUserOperationGas(
    provider,
    userOp,
    entrypoint_address,
);
userOp.callGasLimit = gas_estimate.callGasLimit;
userOp.verificationGasLimit = gas_estimate.verificationGasLimit;
userOp.preVerificationGas = gas_estimate.preVerificationGas;

References

• ERC-4337 Gas: https://eips.ethereum.org/EIPS/eip-4337#gas-estimation
• Viem estimation: https://github.com/wevm/viem/tree/main/src/account-abstraction
• Gas optimization tips: https://www.erc4337.io/docs/understanding-ERC-4337/gas