Foundry Smart Contract Lottery

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Description

A sample Ethereum smart contract lottery built with Foundry, featuring robust testing, Chainlink VRF v2.5 support, mock infrastructure, and modular, maintainable scripts.

Chainlink VRF integration ensures cryptographically secure randomness for winner selection.

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Getting Started

Requirements

• Git
• Foundry (Forge, Cast, Anvil)
• Make (optional, for scripts)
• Node.js (optional, for scripting utilities)

Confirm your tools are installed:

git --version
forge --version
anvil --version

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Quickstart

git clone https://github.com/web3pavlou/foundry-smart-contract-lottery-f23
cd foundry-smart-contract-lottery-f23
forge build

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Usage

Start a Local Node

Start Anvil in a separate terminal:

anvil
# or with Makefile:
make anvil

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⚠️ Common Issue: “You seem to be using Foundry's default sender”

Block Underflow Error When Deploying Locally

When running locally, you might see:

[Revert] panic: arithmetic underflow or overflow (0x11)

Why?

• Some Chainlink mocks use blockhash(block.number - 1). If the local chain is new (block.number == 0), this will underflow.

Solution:

• Open a second terminal and run:

  cast rpc evm_mine

  This increments the block number so block.number - 1 is safe.

• Then re-run your deployment script.

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If you see:

Error: You seem to be using Foundry's default sender. Be sure to set your own --sender.

• This appears if you don’t provide --sender explicitly.

• If you use --private-key, your script broadcasts from the correct account—the warning can be safely ignored if everything else works.

• To silence, use:

  forge script script/DeployRaffle.s.sol:DeployRaffle \
    --rpc-url http://localhost:8545 \
    --private-key <YOUR_PRIVATE_KEY> \
    --sender <YOUR_ADDRESS> \
    --broadcast

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Deployment to Testnet or Mainnet

1. Setup Environment Variables

   Create a .env file based on .env.example:

   • PRIVATE_KEY: your dev wallet (never use real funds!)
   • SEPOLIA_RPC_URL: Sepolia testnet RPC URL
   • ETHERSCAN_API_KEY: (optional) for contract verification

2. Get Testnet ETH

   Use faucets.chain.link to get Sepolia ETH.

3. Deploy

   make deploy ARGS="--network sepolia"

   • Sets up Chainlink VRF subscription
   • Adds your contract as VRF consumer
   • If you have an existing sub, update in script/HelperConfig.s.sol

4. Register Chainlink Automation Upkeep

   • Read Automation docs
   • Register an upkeep at automation.chain.link (choose “Custom logic” as the trigger)

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Testing

Covers all four Foundry test tiers:

• Unit
• Integration
• Forked (mainnet/testnet fork)
• Staging (public testnets)

Running Tests

Unit & Integration:

forge test
forge test -vvv  # with traces

Forked:

forge test --fork-url $SEPOLIA_RPC_URL

Staging (on testnet):

forge script script/StagingTest.s.sol --rpc-url $SEPOLIA_RPC_URL --broadcast

Test Coverage

forge coverage

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Scripts

Enter the Raffle

cast send <RAFFLE_CONTRACT_ADDRESS> "enterRaffle()" --value 0.1ether --private-key <PRIVATE_KEY> --rpc-url $SEPOLIA_RPC_URL

Create a Chainlink VRF Subscription

make createSubscription ARGS="--network sepolia"

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Formatting

forge fmt

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Security

• Solidity >=0.8.x (overflow protection)
• Chainlink VRF/Upkeep best practices
• Comprehensive tests, access control, events
• Never use mainnet private keys for dev/test!

Further reading: Smart Contract Security Best Practices

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Additional Resources

• Foundry Book
• Chainlink VRF Docs
• Forge-std Reference
• Cyfrin Updraft Tutorials

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License

This project is licensed under the MIT License.

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Acknowledgements

• Cyfrin Updraft – Thanks to @patrickalphaC
• Chainlink – For the VRF service
• Foundry – For the dev tools

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