Blockchain & Web3 Development
Smart Contract Development (Solidity)
Contract Structure
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
contract MyToken is ERC20, Ownable {
constructor() ERC20("MyToken", "MTK") Ownable(msg.sender) {
_mint(msg.sender, 1000000 * 10 ** decimals());
}
}
Security Patterns
- Checks-Effects-Interactions: Validate → update state → external calls
- Reentrancy guard: Use OpenZeppelin
ReentrancyGuard or nonReentrant
- Access control:
Ownable, AccessControl, or custom modifiers
- Integer safety: Solidity 0.8+ has built-in overflow checks
- Pull over push: Let users withdraw rather than sending funds
Common Vulnerabilities
| Vulnerability | Prevention |
|---|
| Reentrancy | nonReentrant modifier, CEI pattern |
| Front-running | Commit-reveal schemes, flashbot protection |
| Oracle manipulation | Use Chainlink, TWAP over spot prices |
| Unchecked return values | Always check transfer() return or use safeTransfer |
| Delegatecall injection | Never delegatecall to user-supplied addresses |
Development Tooling
Hardhat
npx hardhat init
npx hardhat compile
npx hardhat test
npx hardhat deploy --network sepolia
Foundry
forge init
forge build
forge test -vvv
forge script script/Deploy.s.sol --rpc-url $RPC --broadcast
Frontend Integration (ethers.js v6 / viem)
// viem (recommended for new projects)
import { createPublicClient, http } from 'viem'
import { mainnet } from 'viem/chains'
const client = createPublicClient({ chain: mainnet, transport: http() })
const balance = await client.getBalance({ address: '0x...' })
// wagmi hooks (React)
import { useAccount, useBalance, useContractWrite } from 'wagmi'
const { address } = useAccount()
const { data: balance } = useBalance({ address })
DeFi Patterns
- AMM: Constant product formula (x * y = k), concentrated liquidity
- Lending: Overcollateralized loans, liquidation mechanisms, interest rate models
- Staking: Reward distribution with
rewardPerToken accumulator pattern
- Governance: Token-weighted voting, timelock controllers, proposal lifecycle
Gas Optimization
- Use
calldata over memory for read-only params
- Pack structs (smaller types together for slot efficiency)
- Use
unchecked blocks for safe arithmetic
- Minimize storage reads/writes (cache in memory)
- Use events instead of storage for data that doesn't need on-chain access
