# zkSync features

While zkSync is mostly Web3-compatible, it has some differences compared to Ethereum. The major of those are:

  • Account abstraction support (accounts may have near-arbitrary validation logic, and also paymaster support is enabled).
  • Deployment transactions require the contracts' bytecode to be passed in a separate field.
  • The fee system is somewhat different.

These require us to extend standard Ethereum transactions with new custom fields. Such extended transactions are called EIP712 transactions since EIP712 (opens new window) is used to sign them. You can look at the internal structure of the EIP712 transactions here.

This document will focus solely on how to pass these arguments to the SDK.

# Overrides

ethers has a notion of overrides. For any on-chain transaction, ethers finds the optimal gasPrice, gasLimit, nonce, and other important fields under the hood. But sometimes, you may have a need to explicitly provide these values (you want to set a smaller gasPrice for instance, or sign a transaction with future nonce).

In this case, you can provide an Overrides object as the last parameter. There you can supply fields like gasPrice, gasLimit, nonce etc.

In order to make the SDK as flexible as possible, the library uses the overrides to supply zkSync-specific fields. To supply zkSync-specific fields, you need to pass the following override:

{
    customData: {
        ergsPerPubdata?: BigNumberish;
        factoryDeps?: BytesLike[];
        customSignature?: BytesLike;
        paymasterParams?: {
            paymaster: Address;
            paymasterInput: BytesLike;
        };
    }
}

Examples:

Override to deploy a contract with bytecode 0xcde...12 and enforce that the operator will not charge more than 100 ergs per published bytes on layer 1:

{
    customData: {
        ergsPerPubdata: "100",
        factoryDeps: ["0xcde...12"],
    }
}

Use custom signature 0x123456 for account, while using paymaster with address 0x8e1DC7E4Bb15927E76a854a92Bf8053761501fdC and paymaster input 0x8c5a3445:

{
    customData: {
        customSignature: "0x123456",
        paymasterParams: {
            paymaster: "0x8e1DC7E4Bb15927E76a854a92Bf8053761501fdC",
            paymasterInput: "0x8c5a3445"
        }
    }
}

# Encoding paymaster params

While the paymaster feature by itself does not impose any limitations on values of the paymasterInput, the Matter Labs team endorses certain types of paymaster flows that are processable by EOAs.

zkSync SDK provides a utility method that can be used to get the correctly formed paymasterParams object: getPaymasterParams.

# See in action

If you want to call the method setGreeting of an ethers Contract object called greeter, this would look the following way, while paying fees with the testnet paymaster:

// The `setGreeting` method has a single parameter -- new greeting
// We will set its value as `a new greeting`.
const greeting = "a new greeting";
const tx = await greeter.populateTransaction.setGreeting(greeting);
const gasPrice = await sender.provider.getGasPrice();
const gasLimit = await greeter.estimateGas.setGreeting(greeting);
const fee = gasPrice.mul(gasLimit);

const paymasterParams = utils.getPaymasterParams(testnetPaymaster, {
    type: 'ApprovalBased',
    token,
    minimalAllowance: fee,
    innerInput: new Uint8Array()
});
const sentTx = await sender.sendTransaction({
    ...tx,
    maxFeePerGas: gasPrice,
    maxPriorityFeePerGas: BigNumber.from(0),
    gasLimit,
    customData: {
        ergsPerPubdata: utils.DEFAULT_ERGS_PER_PUBDATA_LIMIT,
        paymasterParams
    }
});

You can also check out our tutorial on the full-fledged mini-dApp, where users can choose token to pay the fee.

Last Updated: 8/30/2022, 2:33:15 PM