FundMe - Decentralized Crowdfunding Smart Contract

A Solidity-based crowdfunding smart contract built with Foundry that allows users to fund a project with ETH. The contract uses Chainlink Price Feeds to ensure a minimum funding amount in USD, regardless of ETH price fluctuations.

📋 Project Overview

FundMe is a smart contract that enables decentralized crowdfunding with the following features:

• Minimum USD Contribution: Enforces a minimum contribution of $5 USD worth of ETH using Chainlink price feeds
• Owner-Only Withdrawals: Only the contract owner can withdraw accumulated funds
• Gas-Optimized: Includes optimized withdrawal functions to reduce gas costs
• Multi-Network Support: Configured for deployment on Sepolia testnet and local Anvil network
• Comprehensive Testing: Includes unit and integration tests with gas snapshots

🏗️ Architecture

Core Contracts

• FundMe.sol: Main crowdfunding contract with funding and withdrawal logic
• PriceConverter.sol: Library for converting ETH amounts to USD using Chainlink price feeds

Key Features

1. Price Feed Integration: Uses Chainlink's AggregatorV3Interface to get real-time ETH/USD prices
2. Funder Tracking: Maintains a mapping of addresses to funding amounts and an array of funders
3. Dual Withdrawal Methods:
   • withdraw(): Standard withdrawal function
   • cheaperWithdraw(): Gas-optimized version using memory variables
4. Fallback Funding: Implements receive() and fallback() functions to accept direct ETH transfers

🛠️ Technology Stack

• Solidity: ^0.8.18
• Foundry: Development framework
  • Forge: Testing framework
  • Cast: Command-line tool for interacting with contracts
  • Anvil: Local Ethereum node
• Chainlink: Price feed oracles
• OpenZeppelin: Smart contract libraries (via dependencies)

📁 Project Structure

FundMe/
├── src/
│   ├── FundMe.sol              # Main crowdfunding contract
│   └── PriceConverter.sol      # Price conversion library
├── script/
│   ├── DeployFundMe.s.sol      # Deployment script
│   ├── HelperConfig.s.sol      # Network configuration helper
│   └── Interaction.s.sol       # Fund and withdraw scripts
├── test/
│   ├── FundMeTest.t.sol        # Unit tests
│   ├── integration/            # Integration tests
│   └── mocks/                  # Mock contracts for testing
├── foundry.toml                # Foundry configuration
├── Makefile                    # Build and deployment commands
└── .env                        # Environment variables

🚀 Getting Started

Prerequisites

• Foundry installed
• An Ethereum wallet with testnet ETH (for Sepolia deployment)
• Etherscan API key (for contract verification)

Installation

1. Clone the repository:

git clone <repository-url>
cd FundMe

2. Install dependencies:

forge install

3. Create a .env file with the following variables:

SEPOLIA_RPC_URL=<your-sepolia-rpc-url>
PRIVATE_KEY=<your-private-key>
ETHERSCAN_API_KEY=<your-etherscan-api-key>
ANVIL_RPC_URL=http://127.0.0.1:8545
ANVIL_PRIVATE_KEY=<anvil-default-private-key>

Build

Compile the smart contracts:

forge build

Or using the Makefile:

make build

🧪 Testing

Run All Tests

forge test

Run Tests with Verbosity

forge test -vvv

Generate Gas Snapshots

forge snapshot

View Test Coverage

forge coverage

📦 Deployment

Deploy to Sepolia Testnet

make deploy-sepolia

This will:

• Deploy the FundMe contract to Sepolia
• Verify the contract on Etherscan
• Use the Chainlink Sepolia ETH/USD price feed

Deploy to Local Anvil Network

1. Start Anvil in a separate terminal:

anvil

2. Deploy the contract:

make deploy-anvil

💰 Interacting with the Contract

Fund the Contract

Using the Makefile (Sepolia):

make fund

Using Forge directly:

forge script script/Interaction.s.sol:FundFundMe --rpc-url <RPC_URL> --private-key <PRIVATE_KEY> --broadcast

Withdraw Funds (Owner Only)

Using the Makefile (Sepolia):

make withdraw

Using Forge directly:

forge script script/Interaction.s.sol:WithdrawFundMe --rpc-url <RPC_URL> --private-key <PRIVATE_KEY> --broadcast

Using Cast

Check contract balance:

cast balance <CONTRACT_ADDRESS> --rpc-url <RPC_URL>

Call a view function:

cast call <CONTRACT_ADDRESS> "getOwner()" --rpc-url <RPC_URL>

Send a transaction:

cast send <CONTRACT_ADDRESS> "fund()" --value 0.1ether --private-key <PRIVATE_KEY> --rpc-url <RPC_URL>

📊 Contract Functions

Public Functions

• fund(): Fund the contract with ETH (minimum $5 USD equivalent)
• withdraw(): Withdraw all funds (owner only)
• cheaperWithdraw(): Gas-optimized withdrawal (owner only)
• getVersion(): Get the Chainlink price feed version

View Functions

• getAddressToAmountFunded(address): Get the amount funded by a specific address
• getFunder(uint256): Get the funder address at a specific index
• getOwner(): Get the contract owner address

Constants

• MINIMUM_USD: Minimum funding amount (5 USD in wei)

🔧 Configuration

Foundry Configuration (foundry.toml)

• Source Directory: src/
• Output Directory: out/
• Libraries: lib/
• Remappings: Configured for Chainlink and Forge Standard Library
• FFI: Enabled for advanced scripting

Network Configuration

The HelperConfig.s.sol script automatically configures the correct Chainlink price feed address based on the network:

• Sepolia: Uses Chainlink's Sepolia ETH/USD price feed
• Anvil: Deploys a mock price feed for local testing

🧾 Gas Optimization

The contract includes two withdrawal methods:

1. withdraw(): Standard implementation
2. cheaperWithdraw(): Optimized version that:
   • Caches array length in memory
   • Reduces storage reads
   • Saves approximately 20-30% gas

Gas snapshots are tracked in .gas-snapshot for monitoring optimization improvements.

🔐 Security Features

• Owner-only withdrawals: Uses custom error FundMe__NotOwner() for gas-efficient access control
• Minimum funding requirement: Prevents spam transactions
• Safe type casting: Includes safety checks when converting Chainlink price data
• Reentrancy protection: Uses checks-effects-interactions pattern

📚 Learning Resources

• Foundry Book
• Chainlink Price Feeds
• Solidity Documentation

📝 License

MIT

🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

⚠️ Disclaimer

This project is for educational purposes. Always audit smart contracts before deploying to mainnet with real funds.