aa-batching-paymasters

# Batching & Paymasters Execute multiple contract calls atomically in a single UserOperation, and sponsor gas fees with paymasters so users don't need ETH. ## When to Use This - User wants to **batch multiple calls** (approve + swap, multi-transfer) in one atomic operation - User needs **gas sponsorship** — a paymaster pays gas instead of the user - User is building **gasless UX** for their dApp - User mentions `BatchExecuteAsync`, `ToBatchCall`, `WithPaymaster`, or `PaymasterConfig` ## Packages ```bash dotnet add package Nethereum.Web3 dotnet add package Nethereum.AccountAbstraction ``` ## Batch Multiple Calls ### Typed Batch (Same Contract) ```csharp var transfer1 = new TransferFunction { To = "0xRecipient1", Value = Web3.Convert.ToWei(50) }; var transfer2 = new TransferFunction { To = "0xRecipient2", Value = Web3.Convert.ToWei(25) }; var receipt = await handler.BatchExecuteAsync<TransferFunction>(transfer1, transfer2); ``` ### Mixed Batch (Different Contracts) Use `ToBatchCall()` to convert typed messages: ```csharp var approve = new ApproveFunction { Spender = dexAddress, Value = Web3.Convert.ToWei(1000) }; var swap = new SwapFunction { AmountIn = Web3.Convert.ToWei(1000) }; var receipt = await handler.BatchExecuteAsync( approve.ToBatchCall(), swap.ToBatchCall()); ``` ### Batch with ETH Value ```csharp var depositCall = new DepositFunction().ToBatchCall(Web3.Convert.ToWei(1)); ``` ### Raw Calldata Batch ```csharp var receipt = await handler.BatchExecuteAsync(encodedCallData1, encodedCallData2); ``` ## ERC-7579 Batch via SmartAccountService ```csharp using Nethereum.AccountAbstraction.BaseAccount.ContractDefinition; var calls = new[] { new Call { Target = tokenAddress, Value = 0, Data = approveCallData }, new Call { Target = dexAddress, Value = 0, Data = swapCallData } }; var receipt = await account.ExecuteBatchAsync(calls); ``` ## Paymasters ### Simple Paymaster ```csharp handler.WithPaymaster(paymasterAddress); // All subsequent operations use this paymaster for gas ``` ### With Static Data ```csharp handler.WithPaymaster(paymasterAddress, paymasterData); ``` ### Verifying Paymaster (Off-Chain Signature) ```csharp var paymaster = web3.GetVerifyingPaymasterAsync(paymasterAddress, paymasterSignerKey); handler.WithPaymaster(new PaymasterConfig(paymasterAddress, async userOp => { return await paymaster.GetPaymasterDataAsync(userOp); })); ``` ### Deposit Paymaster (Pre-Funded) ```csharp var depositPaymaster = web3.GetDepositPaymasterAsync(paymasterAddress); handler.WithPaymaster(paymasterAddress); ``` ### Dynamic Paymaster Data ```csharp handler.WithPaymaster(new PaymasterConfig(paymasterAddress, async userOp => { // Call external paymaster API at submission time var response = await httpClient.PostAsJsonAsync("https://paymaster.example.com/sign", new { userOp }); var result = await response.Content.ReadFromJsonAsync<PaymasterResponse>(); return result.PaymasterData.HexToByteArray(); })); ``` ## Decision Guide | Scenario | Approach | |----------|----------| | Same-contract multi-call | `BatchExecuteAsync<T>(msg1, msg2)` | | Cross-contract atomic ops | `BatchExecuteAsync(msg1.ToBatchCall(), msg2.ToBatchCall())` | | Raw calldata | `BatchExecuteAsync(bytes1, bytes2)` | | ERC-7579 modular account | `account.ExecuteBatchAsync(Call[])` | | Simple gas sponsorship | `handler.WithPaymaster(address)` | | Per-operation signature | `PaymasterConfig` with async callback | | Pre-funded sponsorship | Deposit paymaster + static address | ## Common Mistakes - **Paymaster not funded** — EntryPoint checks paymaster deposit, returns AA31/AA32 errors - **Paymaster data expired** — verifying paymasters include validity windows; use dynamic data - **Wrong batch approach** — use `ToBatchCall()` for cross-contract, generic `<T>` for same-contract For full documentation, see: https://docs.nethereum.com/docs/account-abstraction/guide-batching-and-paymasters