foundry-zksync book

Paymaster Overview

Paymasters in the ZKsync ecosystem represent a groundbreaking approach to handling transaction fees. They are special accounts designed to subsidize transaction costs for other accounts, potentially making certain transactions free for end-users. This feature is handy for dApp developers looking to improve their platform’s accessibility and user experience by covering transaction fees on behalf of their users.

How Paymasters Work

Paymasters are smart contracts that implement the IPaymaster interface. They are designed to be used with the ZKsync network’s transaction processing mechanism. The paymaster is specified in the metadata when a transaction is sent from an account. The paymaster is then responsible for paying the transaction fee and any other costs associated with the transaction.

How to interact with a Paymaster using Foundry

Currently, the ways to interact with a paymaster contract using Foundry are using cast send, forge create, or the zkUsePaymaster cheatcode.

Using cast send

cast send signs and publishes a transaction. The documentation can be found here.

The command must specify the paymaster address and the encoded paymaster input to pair this with a paymaster contract.

The flags for this are:

--zk-paymaster-address
    The address where the paymaster contract is deployed.

--zk-paymaster-input
    The encoded input for the paymaster contract. This depends on the paymaster contract implementation.

To encode the paymaster input, you can use the cast calldata command, which can be found here.

cast send 0xdb8bA5F5DfB1636361d2fE851d7D3ed93acfc487 "increment()" --rpc-url https://sepolia.era.zksync.dev --private-key <your-private-key> --zk-paymaster-address 0x3cB2b87D10Ac01736A65688F3e0Fb1b070B3eeA3 --zk-paymaster-input $(cast calldata "approvalBased(address,uint256,bytes)" 0x31c43ac5e6A0fe62954B9056441b0A214722516e 1000000000000000000 "0x")

Using forge create

forge create is a command-line tool for deploying smart contracts using the Foundry framework. The documentation can be found here.

The paymaster contract address must be specified in the command to deploy any other contract using forge create.

The flags for this are:

--zk-paymaster-address
    The address where the paymaster contract is deployed.

--zk-paymaster-input
    The encoded input for the paymaster contract. This depends on the paymaster contract implementation.

To encode the paymaster input, you can also use the cast calldata command, which can be found here.

forge create Greeter.sol:Greeter --rpc-url "https://sepolia.era.zksync.dev" --private-key <your-private-key> --zksync --zk-paymaster-address 0x3cB2b87D10Ac01736A65688F3e0Fb1b070B3eeA3 --zk-paymaster-input $(cast calldata "approvalBased(address,uint256,bytes)" 0x31c43ac5e6A0fe62954B9056441b0A214722516e 1 "0x")

Also, see the ZKsync Paymaster Documentation for more information.