zkSync features

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

• Transaction fees can be paid in ERC20 tokens.
• 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 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: {        feeToken?: Address;        ergsPerStorage?: BigNumberish;        ergsPerPubdata?: BigNumberish;        withdrawToken?: Address;        factoryDeps?: BytesLike[];    }}

Examples:

Override to pay fees in the token with the address 0xd35cceead182dcee0f148ebac9447da2c4d449c4:

{  customData: {    feeToken: "0xd35cceead182dcee0f148ebac9447da2c4d449c4";  }}

Override to withdraw ETH and pay fees in the token with the address 0xd35cceead182dcee0f148ebac9447da2c4d449c4: zzz

{    customData: {        feeToken: "0xd35cceead182dcee0f148ebac9447da2c4d449c4",        withdrawToken: "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE"    }}

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:

{    // feeToken is not supplied, using ETH by default    customData: {        ergsPerPubdata: "100",        factoryDeps: ["0xcde...12"],    }}

See in action

If you want to call the method setGreeting of an ethers Contract object called greeter, this would look the following way:

// The `setGreeting` method has a single parameter -- new greeting// We will set its value as `some new greeting`.const txHandle = greeter.setGreeting("some new greeting", {  customData: {    // Paying fee in USDC    feeToken: "0xd35cceead182dcee0f148ebac9447da2c4d449c4",  },});

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