Chapter 7: Writing Starknet Smart Contracts in Cairo

Cairo is the native programming language for StarkNet, designed specifically for writing efficient and secure smart contracts. Here’s a breakdown of key aspects:

1. Core Concepts

• Focus on Provable Computation: Cairo is built around the concept of zero-knowledge proofs. It’s designed to make it easy to write programs that can be efficiently verified by a STARK prover.
• Constraint-Based Programming: Cairo programs are expressed as a series of constraints. These constraints define the rules and relationships between variables, ensuring that the program behaves as expected.
• Felt: Cairo’s primary data type is known as a field element (felt). It represents a large finite field, enabling efficient arithmetic operations.

2. Key Features

• Memory Management: Cairo employs a unique memory model where memory is allocated linearly and accessed through pointers. This model is crucial for efficient STARK proof generation.
• Built-in Functions: Provides a fixed of integrated features for not unusual operations like arithmetic, hashing, and cryptography.
• Starknet Integration: Seamlessly integrates with StarkNet features, such as:
  • Account Abstraction: Interacting with and leveraging the capabilities of StarkNet’s account abstraction model.
  • Event Handling: Emitting events to communicate with external systems.
  • Contract Interactions: Calling functions in other StarkNet contracts.

3. Example (Simple Counter Contract)

Code snippet

#[starknet::contract]
mod counter {
    use starknet::storage::Storage;

    struct CounterState {
        count: felt,
    }

    #[storage]
    impl CounterState {
        fn new() -> Self {
            Self { count: 0 }
        }
    }

    #[constructor]
    fn constructor(_: felt, _: felt) -> Self {
        Self::new()
    }

    #[external]
    fn increment(&mut self) {
        self.count += 1;
    }

    #[view]
    fn get_count(&self) -> felt {
        self.count
    }
}

4. Development Tools

• StarkNet Foundry: A comprehensive toolchain for developing, checking out, and deploying StarkNet contracts.
  • Includes a compiler, a testing framework, and a local development network.
• Scarb: A package manager for Cairo, simplifying dependency management for complex projects.
• StarkNet Remix Plugin: Enables Cairo development within the Remix IDE, providing a user-friendly environment for writing and deploying contracts.

5. Learning Resources

• StarkNet Documentation: The authentic documentation presents complete courses, tutorials, and API references.
• Cairo Language Documentation: Detailed data approximately the Cairo language, together with syntax, semantics, and built-in features.
• Community Resources: A vibrant community exists around StarkNet, offering resources like forums, tutorials, and examples.

Key Considerations

• Security: Thoroughly audit your Cairo contracts for vulnerabilities to prevent exploits.
• Gas Optimization: Optimize your code to reduce gas expenses and enhance transaction performance.
• Testing: Rigorously test your contracts the usage of unit exams and integration assessments to make sure their correctness and reliability.

Introduction to Starknet Smart Contracts

What is a Smart Contract?

Smart contracts are self-operating virtual agreements that validate and put in force terms automatically among the involved events. It’s like a digital merchandising device: you insert the right amount of money, push the button, and the machine dispenses the chosen item. With a clever contract, you satisfy the terms of the settlement, and the settlement routinely executes the agreed-upon moves.

Key Characteristics:

• Self-executing: Once brought on, a smart contract robotically plays the actions described in its code.
• Transparent: All moves and facts related to a smart settlement are recorded on the blockchain, making them transparent and auditable.
• Immutable: Once deployed, the code of a smart contract cannot be altered, ensuring that the terms of the agreement remain unchanged.
• Secure: Smart contracts leverage the security of the blockchain network to ensure that transactions are secure and tamper-proof.

How Smart Contracts Work:

1. Coding: The phrases of the settlement are coded into a selected programming language (like Solidity for Ethereum).
2. Deployment: The coded agreement is deployed to a blockchain network.
3. Execution: When certain situations are met (e.G., fee acquired, time elapsed), the smart contract robotically executes the predefined moves.

Use Cases of Smart Contracts:

• Decentralized Finance (DeFi):
  • Lending and borrowing platforms
  • Decentralized exchanges (DEXs)
  • Stablecoins
• Supply Chain Management:
  • Tracking the beginning and authenticity of products
  • Automating payments and logistics
• Voting Systems:
  • Secure and transparent voting systems
• Digital Asset Management:
  • Non-Fungible Tokens (NFTs)
  • Digital identity management

Benefits of Smart Contracts:

• Increased Efficiency: Automates techniques and reduces the need for intermediaries.
• Reduced Costs: Eliminates the need for third-party involvement, reducing transaction expenses.
• Enhanced Security: Ensures that agreements are achieved as supposed and reduces the threat of fraud.
• Transparency and Trust: All transactions are recorded on the blockchain, growing transparency and agree with among parties.

Challenges and Considerations:

• Security Vulnerabilities: Bugs inside the code may be exploited, main to financial losses.
• Regulatory Uncertainty: The criminal and regulatory landscape surrounding smart contracts is still evolving.
• Scalability: Some blockchains won’t be able to cope with the excessive quantity of transactions required by way of complex clever contracts.

Creating your first Cairo contract

1. Project Setup

Install StarkNet Foundry: This provides essential tools for Cairo development.

pip install starknet-foundry

Create a New Project: Use the Foundry CLI to generate a new project:

forge init MyFirstContract
cd MyFirstContract

2. Write Your First Contract

Create a Cairo File: Create a new file named contract.cairo in the src/ directory.

Basic Contract Structure:

#[starknet::contract]
mod my_contract {
    use starknet::storage::Storage;



struct MyContractState {
    value: felt,
}

#[storage]
impl MyContractState {
    fn new() -> Self {
        Self { value: 0 }
    }
}

#[constructor]
fn constructor(_: felt, _: felt) -> Self {
    Self::new()
}

#[external]
fn set_value(&mut self, new_value: felt) {
    self.value = new_value;
}

#[view]
fn get_value(&self) -> felt {
    self.value
}
}

3. Explanation

• #[starknet::contract]: Represents the contract’s data structure stored on the blockchain.
• struct MyContractState: Defines the contract’s state, which is stored on the blockchain.
• #[storage]: Indicates that this struct will be stored persistently on the blockchain.
• #[constructor]: The constructor function is called when the contract is deployed.
• #[external]: This function can be called from other contracts or externally.
• #[view]: This function is read-only and does not modify the contract’s state.

4. Compile and Deploy

Compile the Contract:

forge build

Deploy the Contract:

• You’ll need a local StarkNet development network (like StarkNet Devnet) running.
• Use the Foundry CLI to deploy:

forge create --rpc-url

5. Interact with the Contract

• Use a StarkNet client (like StarkNet.js) or a tool like Argent X to:
  • Call the set_value() function to update the contract’s state.
  • Call the get_value() function to read the current value.

Key Considerations

• Cairo Language: Familiarize yourself with the core concepts of the Cairo language, including felt, memory management, and built-in functions.
• StarkNet Documentation: Refer to the official StarkNet documentation for detailed information and best practices.
• Security: Always prioritize security by thoroughly auditing your contracts for vulnerabilities.

Deploying Contracts on StarkNet

1. Prerequisites

• StarkNet Foundry: A powerful command-line interface (CLI) for developing, testing, and deploying StarkNet contracts.
  • Installation: pip install starknet-foundry
• StarkNet Account: You’ll need an account on a StarkNet network (e.g., Goerli testnet, Mainnet).
• StarkNet Wallet: A wallet compatible with StarkNet, such as Argent X or Braavos.
• IDE: A development environment like VS Code with the Cairo extension.

2. Project Setup

Create a Foundry Project:

forge init MyContract
cd MyContract

Write Your Contract: Create a file named contract.cairo in the src/ directory. Here’s a basic example:

#[starknet::contract]
mod my_contract {
    use starknet::storage::Storage;


struct MyContractState {
    value: felt,
}

#[storage]
impl MyContractState {
    fn new() -> Self {
        Self { value: 0 }
    }
}

#[constructor]
fn constructor(_: felt, _: felt) -> Self {
    Self::new()
}

#[external]
fn set_value(&mut self, new_value: felt) {
    self.value = new_value;
}

#[view]
fn get_value(&self) -> felt {
    self.value
}
}

3. Compile the Contract

Use the Foundry CLI to compile your contract:

forge build

This generates the necessary bytecode (class hash) for deployment.

4. Deploy the Contract

Using Foundry CLI:

Configure your network:

Create a .env file in your project’s root directory to store your network configuration:

STARKNET_NETWORK=testnet  # or 'mainnet'
PRIVATE_KEY=<your_private_key> 
RPC_URL=<your_rpc_url> 

Deploy:

forge create

Foundry will interact with your wallet to sign and submit the deployment transaction.

Using a Wallet (Argent X, Braavos):

1. Obtain the contract’s class hash: Find it in the out/ directory after compilation.
   
2. Use your wallet’s interface: Most StarkNet wallets provide a way to deploy contracts using the class hash and any constructor arguments.

5. Verify Deployment

• After deployment, you can verify the contract’s address and interact with it using your wallet or a StarkNet explorer (like StarkScan).

Key Considerations

• Gas Costs: Deployment transactions consume gas. Optimize your contract code to minimize gas costs.
• Security Audits: Always audit your contracts thoroughly for vulnerabilities before deploying to a mainnet.
• Testing: Rigorously check your contracts the usage of Foundry’s trying out framework to make sure they function as anticipated.

Remember:

• Replace placeholders like <your_private_key> and <your_rpc_url> with your actual values.
• Refer to the legit StarkNet documentation and the StarkNet Foundry documentation for the most up to date information and superior deployment techniques.

Interacting with StarkNet contracts

1. Choose a Method

• Using a StarkNet Client Library:
  • StarkNet.js: A popular JavaScript library for interacting with StarkNet. It provides functions for:
    • Connecting to a StarkNet network: Specify the network (e.g., Goerli, Mainnet, Devnet).
    • Creating an Account: Use your private key or connect to a wallet.
    • Getting Contract Information: Retrieve contract ABI and address.
    • Calling Contract Functions:
      • call(): For read-only operations (e.g., getting the current value of a variable).
      • invoke(): For write operations that modify the contract’s state (e.g., transferring tokens).
  • Other Libraries: Explore libraries in Python, TypeScript, and other languages for interacting with StarkNet.
• Using a Wallet:
  • Argent X, Braavos: Many StarkNet-compatible wallets provide user interfaces for interacting with contracts. You can typically:
    • Connect your wallet to a StarkNet network.
    • View contract details.
    • Call contract functions directly within the wallet interface.

2. Connect to a StarkNet Network

• Specify the Network: Choose the StarkNet network you want to interact with (Goerli, Mainnet, Devnet).
• Obtain RPC URL: If using a library, you’ll need the RPC URL for the chosen network to communicate with the StarkNet nodes.

3. Get Contract Information

• Contract Address: Obtain the deal with of the settlement you need to engage with.
• Contract ABI: The Application Binary Interface (ABI) describes the contract’s functions, their parameters, and their go back kinds. You’ll need this to have interaction with the agreement’s methods
  

4. Call Contract Functions

• Read Operations (using call()):
  • Query data from the contract without modifying the blockchain state.
  • Example: Calling a getBalance() function to retrieve a user’s token balance.
• Write Operations (using invoke()):
  • Initiate transactions that modify the contract’s state.
  • Example: Calling a transfer() function to send tokens to another account.

5. Handle Transactions

• Wait for Transaction Confirmation: After invoking a write operation, wait for the transaction to be confirmed on the StarkNet network.
• Monitor Transaction Status: Use the transaction hash to track the transaction’s progress on a block explorer (like StarkScan).

Example (using StarkNet.js – simplified)

JavaScript

const { Invocations, Provider } = require('starknet');

const provider = new Provider({ sequencerUrl: 'https://[your-rpc-url]' }); 
const account = new Account(provider, '<your-private-key>'); 

const contractAddress = '0x...' 
const contract = new Contract(contractAddress, MyContract.abi, provider); 

// Call a read-only function
const result = await contract.call('get_value'); 

// Invoke a write function
const { transaction_hash } = await account.execute([
  Invocations.single(contractAddress, 'set_value', [new BigNumber(10)]) 
]); 

// Wait for transaction confirmation (using a loop or events) 

Important Notes

• Security: Always prioritize security when interacting with contracts. Be cautious of unknown or untrusted contracts.
• Gas Costs: Write operations (invocations) consume gas. Ensure your account has sufficient funds to cover the gas costs.
• Error Handling: Implement proper error handling to gracefully handle potential issues during contract interaction.

This provides a general overview of interacting with StarkNet contracts. Remember to consult the official documentation and tutorials for the most up-to-date information and specific examples.

StarkNet FAQ

1. What is StarkNet?

• As a Layer 2 answer, StarkNet enhances Ethereum’s scalability.
• It uses zero-knowledge proofs (ZK-STARKs) to seriously increase transaction throughput and reduce costs while maintaining Ethereum’s security.
• StarkNet permits builders to construct and install decentralized packages (dApps) with stepped forward scalability and efficiency.

2. What are the important thing blessings of the usage of StarkNet?

• Scalability: Handles a high extent of transactions with appreciably decrease latency and expenses in comparison to Ethereum.
• Security: Leverages the safety of Ethereum at the same time as supplying more suitable safety via ZK-STARK proofs.
• Developer–Friendliness: Provides a developer-friendly surroundings with gear and resources for building and deploying dApps.
• Account Abstraction: Enables superior account features like social recuperation, multi-signature wallets, and gasless transactions.

3. What is Cairo?

• StarkNet’s native programming language is Cairo.
• It’s specially designed for writing green and stable smart contracts that may be without problems demonstrated via ZK-STARK provers.

4. How does StarkNet work?

• Transactions on StarkNet are bundled collectively off-chain.
• A ZK-STARK evidence is generated to mathematically prove the validity of these transactions.
• This proof is then submitted to Ethereum, in which it’s miles fast established.
• Once demonstrated, the transactions are achieved on StarkNet, ensuing in fast and fee-effective execution.
  

How can I get started with StarkNet development?

• Install StarkNet Foundry: This affords a complete set of gear for growing, testing, and deploying StarkNet contracts.
• Learn Cairo: Familiarize yourself with the Cairo programming language.
• Explore the StarkNet Documentation: The professional documentation presents treasured resources, tutorials, and courses.
• Join the StarkNet Community: Engage with the community thru boards, Discord, and different channels for aid and learning.

6. What are a few popular dApps constructed on StarkNet?

• DYdX: A main decentralized change offering high-overall performance trading.
• ImmutableX: A platform for building and scaling NFT video games and marketplaces.
• Sorare: A delusion football sport wherein gamers can collect and alternate digital playing cards of real-lifestyles footballers.

7. What are the future prospects of StarkNet?

• StarkNet is poised to play a extensive role inside the destiny of blockchain era.
• Continued development and adoption are anticipated to similarly enhance its scalability, safety, and developer experience.
• The atmosphere is increasing unexpectedly with the regular launch of recent dApps and initiatives.