Uniswap V2 Local Development with Foundry

This project contains a complete local Uniswap V2 deployment using Foundry, including the core contracts, periphery contracts, and a patched frontend interface.

📋 Project Structure

Day21/
├── UniswapV2_foundry/          # Foundry project with Uniswap V2 contracts
│   ├── src/
│   │   ├── v2-core/            # UniswapV2 Core contracts (Solidity 0.5.16)
│   │   ├── v2-periphery/       # UniswapV2 Periphery contracts (Solidity 0.6.6)
│   │   ├── WETH9.sol           # Wrapped ETH contract
│   │   └── Multicall.sol       # Multicall for batch RPC calls
│   ├── script/
│   │   └── Deploy.s.sol        # Deployment script
│   └── foundry.toml            # Foundry configuration
│
└── UniswapV2-interface-2.6.4/  # Uniswap V2 Frontend
    ├── scripts/
    │   └── patch-uniswap-sdk.js  # SDK patching script
    └── src/constants/
        ├── index.ts              # Router address config
        └── multicall/index.ts    # Multicall address config

🔧 Key Technical Challenges Solved

1. Multi-Version Solidity Compilation

Uniswap V2 uses different Solidity versions:

• v2-core: =0.5.16
• v2-periphery: =0.6.6
• Deployment scripts: ^0.8.13

Solution: Enable auto_detect_solc = true in foundry.toml to let Foundry compile each contract with its required version.

2. Init Code Hash Mismatch

UniswapV2Library uses a hardcoded init_code_hash to calculate pair addresses via CREATE2. The mainnet hash doesn't match locally compiled bytecode.

Solution: Generate the correct hash and update UniswapV2Library.sol:

forge inspect UniswapV2Pair bytecode | cast keccak
# Output: 0x4a164ea51df2a6a7cb0fc4385184ca464c646f6510b5cd69201035f64e9ee391

3. SDK Hardcoded Addresses

The @uniswap/sdk package has hardcoded mainnet addresses that need patching for local development.

Solution: Create a post-install patch script that automatically updates:

• FACTORY_ADDRESS
• INIT_CODE_HASH
• WETH addresses for each network

4. Node.js OpenSSL Compatibility

Node.js 17+ uses OpenSSL 3.0 which doesn't support legacy crypto algorithms used by older webpack.

Solution: Add NODE_OPTIONS=--openssl-legacy-provider to npm scripts.

5. Chain ID Compatibility

The Uniswap SDK only supports specific chain IDs (1, 3, 4, 5, 42). Sepolia (11155111) is not supported.

Solution: Use anvil --chain-id 3 to simulate Ropsten network locally.

🚀 Quick Start

Prerequisites

• Foundry
• Node.js v16+ (v16 LTS recommended)
• Yarn
• MetaMask or compatible wallet

1. Start Local Anvil Chain

# Use chain ID 3 (Ropsten) for SDK compatibility
anvil --chain-id 3

2. Deploy Contracts

cd UniswapV2_foundry

# Build contracts
forge build

# Deploy (using Anvil default account)
forge script script/Deploy.s.sol \
  --rpc-url http://127.0.0.1:8545 \
  --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80 \
  --broadcast

Note the deployed addresses:

• Multicall: 0x5FbDB2315678afecb367f032d93F642f64180aa3
• WETH9: 0xe7f1725E7734CE288F8367e1Bb143E90bb3F0512
• Factory: 0x9fE46736679d2D9a65F0992F2272dE9f3c7fa6e0
• Router: 0xCf7Ed3AccA5a467e9e704C703E8D87F634fB0Fc9
• TestERC20: 0xDc64a140Aa3E981100a9becA4E685f962f0cF6C9

3. Configure Frontend

cd UniswapV2-interface-2.6.4

# Install dependencies (automatically patches SDK)
yarn install

# Or manually patch SDK
yarn patch-sdk

Update addresses if needed in:

• src/constants/index.ts - ROUTER_ADDRESS
• src/constants/multicall/index.ts - MULTICALL_NETWORKS[ChainId.ROPSTEN]
• scripts/patch-uniswap-sdk.js - All addresses in LOCAL_CONFIG

4. Start Frontend

yarn start

5. Configure MetaMask

Add a custom network:

Setting	Value
Network Name	Local Anvil (Ropsten)
RPC URL	http://127.0.0.1:8545
Chain ID	3
Currency Symbol	ETH

Import the Anvil test account:

Private Key: 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80
Address: 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266

🧪 Testing the Deployment

1. Deploy a Test ERC20 Token

# Example: Deploy HookERC20 from another project
cast send --rpc-url http://127.0.0.1:8545 \
  --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80 \
  --create <ERC20_BYTECODE>

2. Approve Router to Spend Tokens

# Replace TOKEN_ADDRESS with your token address
# Replace AMOUNT with the amount to approve (in wei)
cast send TOKEN_ADDRESS \
  "approve(address,uint256)" \
  0xCf7Ed3AccA5a467e9e704C703E8D87F634fB0Fc9 \
  1000000000000000000000 \
  --rpc-url http://127.0.0.1:8545 \
  --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80

3. Add Liquidity via Frontend

1. Go to http://localhost:3000/#/pool
2. Click "Add Liquidity"
3. Select ETH and paste your TestERC20 token address
4. Enter amounts and click "Supply"

4. Perform a Swap

1. Go to http://localhost:3000/#/swap
2. Select TestERC20 and ETH tokens
3. Enter amount and click "Swap"

📝 Configuration Files

foundry.toml

[profile.default]
src = "src"
out = "out"
libs = ["lib"]
auto_detect_solc = true
optimizer = true
optimizer_runs = 200

remappings = [
    "@uniswap/lib/contracts/libraries/=src/v2-periphery/libraries/",
    "@uniswap/v2-core/contracts/interfaces/=src/v2-core/interfaces/",
    "@uniswap/v2-core/contracts/libraries/=src/v2-core/libraries/",
]

Current Deployment Addresses (Chain ID: 3)

Contract	Address
Multicall	0x5FbDB2315678afecb367f032d93F642f64180aa3
WETH9	0xe7f1725E7734CE288F8367e1Bb143E90bb3F0512
UniswapV2Factory	0x9fE46736679d2D9a65F0992F2272dE9f3c7fa6e0
UniswapV2Router02	0xCf7Ed3AccA5a467e9e704C703E8D87F634fB0Fc9
TestERC20 (TERC)	0xDc64a140Aa3E981100a9becA4E685f962f0cF6C9
Init Code Hash	0x4a164ea51df2a6a7cb0fc4385184ca464c646f6510b5cd69201035f64e9ee391

🔄 Redeployment Checklist

When you restart Anvil or redeploy contracts:

1. Restart Anvil: anvil --chain-id 3

2. Deploy contracts: make deploy local or forge script ...

3. Update frontend addresses in:

   • src/constants/index.ts: ROUTER_ADDRESS
   • src/constants/multicall/index.ts: MULTICALL_NETWORKS[ChainId.ROPSTEN]

4. Update SDK patch (if addresses changed):

   // scripts/patch-uniswap-sdk.js
   const LOCAL_CONFIG = {
     FACTORY_ADDRESS: '0x...',
     INIT_CODE_HASH: '...',
     WETH_ROPSTEN: '0x...'
   };

5. Re-run patch: yarn patch-sdk

6. Restart frontend: yarn start

⚠️ Troubleshooting

"execution reverted" errors

• Ensure you've approved the Router to spend your tokens
• Check that the init code hash in UniswapV2Library.sol matches the deployed Pair bytecode

"No liquidity found"

• SDK addresses may not be patched correctly
• Run yarn patch-sdk and restart the frontend

OpenSSL errors on Node.js 17+

• The NODE_OPTIONS=--openssl-legacy-provider is already set in package.json
• If issues persist, downgrade to Node.js 16 LTS

MetaMask "Wrong network"

• Ensure you're connected to the custom network with Chain ID 3
• Clear MetaMask activity data if nonces are out of sync

📚 References

• Uniswap V2 Documentation
• Foundry Book
• Uniswap V2 Core
• Uniswap V2 Periphery

📄 License

This project is for educational purposes. Uniswap V2 contracts are licensed under GPL-3.0.