Paymaster with Contract method call?

[richardcatlin]

Team or Project

No response

Select the SDK

Rust

ZK chain

Era Sepolia

Environment

Testnet

Issue Description

Don't mean to be a pain, but our team is prototyping for applications that will produce tens or hundreds of millions of transactions. That is why we want to load test and zksync L3. It much easier to do with Rust than TS or JS.

Trying to translate the TS below to Rust
const contributionAmount = ethers.parseEther("0.01");

// Get paymaster params for the Gasless paymaster
const paymasterParams = utils.getPaymasterParams(PAYMASTER_ADDRESS, {
type: "General",
innerInput: new Uint8Array(),
});
// Determine the gas limit for the contribution transaction
const gasLimit = await contract.contribute.estimateGas({
value: contributionAmount,
customData: {
gasPerPubdata: utils.DEFAULT_GAS_PER_PUBDATA_LIMIT,
paymasterParams: paymasterParams,
},
});

const fees = await ethers.provider.getFeeData();
const gasPrice = fees.gasPrice;

// Contribute to the crowdfund contract
// and have the paymaster cover the funds
const transaction = await contract.contribute({
value: contributionAmount,
maxPriorityFeePerGas: 0n,
maxFeePerGas: gasPrice,
gasLimit,
// Pass the paymaster params as custom data
customData: {
gasPerPubdata: utils.DEFAULT_GAS_PER_PUBDATA_LIMIT,
paymasterParams,
},
});
await transaction.wait();

Expected Behavior

Description describes.

Code Example

Describe describes.

Repo Link (Optional)

No response

[sueun-dev]

Yes, you can do this in Rust.

The main difference is that zksync-web3-rs does not give you a getPaymasterParams(...) helper like the TS side. In Rust you build the paymaster part yourself and attach it to Eip712Meta.

For a contract call, the shape is:

• encode the contract call data for contribute()
• build PaymasterParams
• put that into Eip712Meta
• build an Eip712TransactionRequest with to, value, data, and custom_data
• use that same request for estimate_fee or zk_estimate_gas
• send it with send_transaction_eip712

One important detail: for the General flow, paymaster_input is not just an empty Vec<u8>. It should be the ABI-encoded call to the paymaster's general(bytes) function. The official Rust example does exactly that.

Roughly like this:

use ethers::{
    abi::{Address, Token},
    prelude::*,
    providers::{Http, Provider},
    types::U256,
};
use std::{str::FromStr, sync::Arc};
use zksync_web3_rs::{
    core::abi::Contract,
    eip712::{Eip712Meta, Eip712TransactionRequest, PaymasterParams},
    zks_provider::ZKSProvider,
    ZKSWallet,
};

const PAYMASTER_ABI: &str = r#"[
  {
    "inputs": [{"internalType": "bytes", "name": "input", "type": "bytes"}],
    "name": "general",
    "outputs": [],
    "stateMutability": "nonpayable",
    "type": "function"
  }
]"#;

let provider = Provider::<Http>::try_from("https://sepolia.era.zksync.dev")?;
let wallet = Wallet::from_str(PRIVATE_KEY)?.with_chain_id(300u64);
let zk_wallet = ZKSWallet::new(wallet, None, Some(provider.clone()), None)?;
let era_provider = zk_wallet.get_era_provider()?;

let contract_fn = Contract::load(MY_CONTRACT_ABI.as_bytes())?
    .function("contribute")?;
let calldata = contract_fn.encode_input(&[])?;

let paymaster_fn = Contract::load(PAYMASTER_ABI.as_bytes())?
    .function("general")?;
let paymaster_input = paymaster_fn.encode_input(&[Token::Bytes(vec![])])?;

let tx = Eip712TransactionRequest::new()
    .from(zk_wallet.l1_wallet.address())
    .to(CONTRACT_ADDRESS)
    .value(U256::exp10(16)) // 0.01 ETH
    .data(calldata)
    .custom_data(
        Eip712Meta::new().paymaster_params(PaymasterParams {
            paymaster: PAYMASTER_ADDRESS,
            paymaster_input,
        }),
    );

let fee = era_provider.estimate_fee(tx.clone()).await?;
let tx = tx
    .max_priority_fee_per_gas(0)
    .max_fee_per_gas(fee.max_fee_per_gas)
    .gas_limit(fee.gas_limit);

let pending = era_provider
    .send_transaction_eip712(&zk_wallet.l2_wallet, tx)
    .await?;

One more thing that is easy to miss: if you use the send_eip712(...) helper, that helper does not give you a way to attach paymaster data. For paymaster calls, build Eip712TransactionRequest directly.

I checked the type names and method names against zksync-web3-rs 0.2.1 locally before writing this.

[vasyl-ivanchuk]

@richardcatlin adding to the answer above, feel free to check out this example in the SDK repo here.