## Account Abstraction Lesson 20: System Contracts We are rolling along our journey into zkSync account abstraction quite nicely. In this lesson, we are going to: - learn the phases of sending an account abstraction transaction - become more familiar with system contracts and their importance Let's get it! --- ### Sending Transactions There are essentially two phases to send an account abstraction transaction. **Phase 1: Validation** 1. The user sends the transaction to the "zkSync API client" (sort of a "light node"). 2. The zkSync API client checks to see that the nonce is unique by querying the `NonceHolder` system contract. 3. The zkSync API client calls `validateTransaction`, which MUST update the nonce. 4. The zkSync API client checks the nonce is updated. 5. The zkSync API client calls `payForTransaction`, or `prepareForPaymaster` & `validateAndPayForPaymasterTransaction`. 6. The zkSync API client verifies that the bootloader gets paid. **Phase 2: Execution** 1. The zkSync API client passes the validated transaction to the main node / sequencer (as of today, they are the same). 2. The main node calls `executeTransaction`. 3. If a paymaster was used, the `postTransaction` is called. --- ### `ContractDeployer` System Contract A system contract contains smart contracts that are deployed on zkSync by default. Let's take a look at one of the most important ones - `ContractDeployer`. - Go back to [zkSync Era Block Explorer](https://sepolia.explorer.zksync.io/) - Copy this address into the search bar. ```js 0x0000000000000000000000000000000000008006 ``` - You should see **ContractDeployer**. --- ::image{src='/foundry-account-abstraction/20-system-contracts/contract-deployer1.png' style='width: 100%; height: auto;'} --- Scroll down a bit and click on the contract tab. You should then be able to see `ContractDeployer.sol` along with many other zkSync contracts. Essentially, the ContractDeployer governs other contracts. It is a system contract that is responsible: - for deploying other smart contracts on zkSync. - for generating the address of the deployed smart contract. - incrementing the deployment nonce. - making sure that the constructor is never called twice in a contract. On Ethereum, we simply need to send a transaction containing the compiled code of a smart contract. However, things are much different on zkSync. Here, a sender will actually have to call a function on ContractDeployer. Then the function will create a smart contract. As a result, we'll have to do things a bit differently in our terminal. For example: on Ethereum we can simply run `forge create` in our terminal. In zkSync we'll need to do this: --- ```js forge create --zksync --legacy ``` If you'd like to [learn more about these system contracts, click here.](https://docs.zksync.io/build/developer-reference/era-contracts/system-contracts) As always, Let's do some review. Move on to the next lesson when you are ready. --- ### Questions for Review --- <summary>1. What are the two phases of sending an account abstraction transaction in zkSync?</summary> <details> **<summary><span style="color:red">Click for Answers</span></summary>** Validation & Execution </details> <summary>2. What is the role of the ContractDeployer system contract in zkSync?</summary> <details> **<summary><span style="color:red">Click for Answers</span></summary>** - Deploying other smart contracts on zkSync. - Generating the address of the deployed smart contract. - Incrementing the deployment nonce. - Ensuring that the constructor is never called twice in a contract. </details> <summary>3. How does deploying a smart contract on zkSync differ from deploying on Ethereum?</summary> <details> **<summary><span style="color:red">Click for Answers</span></summary>** On Ethereum, deploying a smart contract involves sending a transaction containing the compiled code of the smart contract. In zkSync a sender must call a function on a system contract, ContractDeployer, to create a smart contract. zkSync may also require different commands in the terminal, such as using forge create --zksync --legacy instead of just forge create. </details>