Add Support for Paymasters

[mationorato]

Add support for using paymasters with EIP712 trasnsactions.

Useful links:

• Building a custom paymaster
• Python SDK example

[ETeissonniere]

We'd be softly interested in adding this feature depending on how much support can be provided in terms of notes on integration points. Are you able to provide more details on this?

[aliXsed]

Checking with @IAvecilla who has recently contributed to the paymaster example in the lib. Is this feature now complete and tested?

[aliXsed]

Since no response to my previous comments, I would like to tag @ischasny in case he'd be able to update this ticket. We are currently running into an issue in interacting with a paymaster that is setup by ZyFi. We get the paymaster params from the ZyFi's api server and use the following code snippet that is based upon the latest zksync-web3-rs to make our paymaster transaction:

        info!(response = ?response, "ZyFi Response");

        let chain_id = response.tx_data.chain_id;
        let from = parse_ethereum_address(&response.tx_data.from)?;
        let to = parse_ethereum_address(&response.tx_data.to)?;
        let data = hex::decode(response.tx_data.data)?;
        let value = parse_u256(&response.tx_data.value)?;
        let paymaster =
            parse_ethereum_address(&response.tx_data.custom_data.paymaster_params.paymaster)?;
        let paymaster_input = hex::decode(
            response
                .tx_data
                .custom_data
                .paymaster_params
                .paymaster_input,
        )?;
        let gas_per_pubdata = response.tx_data.custom_data.gas_per_pubdata;
        let gas_limit = response.tx_data.gas_limit;
        let max_fee_per_gas = parse_u256(&response.tx_data.max_fee_per_gas)?;

        Ok(Eip712TransactionRequest::new()
            .from(from)
            .to(to)
            .data(data)
            .custom_data(
                Eip712Meta::new()
                    .paymaster_params(PaymasterParams {
                        paymaster,
                        paymaster_input,
                    })
                    .gas_per_pubdata(gas_per_pubdata),
            )
            .chain_id(chain_id)
            .gas_limit(gas_limit)
            .max_fee_per_gas(max_fee_per_gas)
            .value(value))
    }

When this transaction is delivered the response is:

Error: (code: 3, message: failed paymaster validation. error message: Error function_selector = 0x81b5ad68, data = 0x81b5ad68, data: Some(String("0x")))

Since we do not have such an issue when interacting with the same paymaster in our other non-rust apps, our main suspicion is the paymaster support in zksync-web3-rs may have an issue, hence our interest in the fate of this ticket.

[hoshiyari420]

Hi team, I am working with Zyfi to identify the root cause mentioned here by @aliXsed.

The error may suggest it is the paymaster validation here but it's not. The error here is that the paymaster_input should be a hex string but it's being sent as uint array because of which the validation fails on the paymaster.

zksync-web3-rs/src/eip712/paymaster_params.rs

Line 8 in 5665334

pub paymaster_input: Vec<u8>,

Please do look into this!