DeFi Protocol Templates

Production-ready templates for common DeFi protocols including staking, AMMs, governance, lending, and flash loans.

When to Use This Skill

• Building staking platforms with reward distribution

• Implementing AMM (Automated Market Maker) protocols

• Creating governance token systems

• Developing lending/borrowing protocols

• Integrating flash loan functionality

• Launching yield farming platforms

Staking Contract

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

import "@openzeppelin/contracts/security/ReentrancyGuard.sol";

import "@openzeppelin/contracts/access/Ownable.sol";

contract StakingRewards is ReentrancyGuard, Ownable {

IERC20 public stakingToken;

IERC20 public rewardsToken;

uint256 public rewardRate = 100; // Rewards per second

uint256 public lastUpdateTime;

uint256 public rewardPerTokenStored;

mapping(address => uint256) public userRewardPerTokenPaid;

mapping(address => uint256) public rewards;

mapping(address => uint256) public balances;

uint256 private _totalSupply;

event Staked(address indexed user, uint256 amount);

event Withdrawn(address indexed user, uint256 amount);

event RewardPaid(address indexed user, uint256 reward);

constructor(address _stakingToken, address _rewardsToken) {

    stakingToken = IERC20(_stakingToken);

    rewardsToken = IERC20(_rewardsToken);

}

modifier updateReward(address account) {

    rewardPerTokenStored = rewardPerToken();

    lastUpdateTime = block.timestamp;

    if (account != address(0)) {

        rewards[account] = earned(account);

        userRewardPerTokenPaid[account] = rewardPerTokenStored;

    }

    _;

}

function rewardPerToken() public view returns (uint256) {

    if (_totalSupply == 0) {

        return rewardPerTokenStored;

    }

    return rewardPerTokenStored +

        ((block.timestamp - lastUpdateTime) * rewardRate * 1e18) / _totalSupply;

}

function earned(address account) public view returns (uint256) {

    return (balances[account] *

        (rewardPerToken() - userRewardPerTokenPaid[account])) / 1e18 +

        rewards[account];

}

function stake(uint256 amount) external nonReentrant updateReward(msg.sender) {

    require(amount > 0, "Cannot stake 0");

    _totalSupply += amount;

    balances[msg.sender] += amount;

    stakingToken.transferFrom(msg.sender, address(this), amount);

    emit Staked(msg.sender, amount);

}

function withdraw(uint256 amount) public nonReentrant updateReward(msg.sender) {

    require(amount > 0, "Cannot withdraw 0");

    _totalSupply -= amount;

    balances[msg.sender] -= amount;

    stakingToken.transfer(msg.sender, amount);

    emit Withdrawn(msg.sender, amount);

}

function getReward() public nonReentrant updateReward(msg.sender) {

    uint256 reward = rewards[msg.sender];

    if (reward > 0) {

        rewards[msg.sender] = 0;

        rewardsToken.transfer(msg.sender, reward);

        emit RewardPaid(msg.sender, reward);

    }

}

function exit() external {

    withdraw(balances[msg.sender]);

    getReward();

}

}

## AMM (Automated Market Maker)

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract SimpleAMM {

IERC20 public token0;

IERC20 public token1;

uint256 public reserve0;

uint256 public reserve1;

uint256 public totalSupply;

mapping(address => uint256) public balanceOf;

event Mint(address indexed to, uint256 amount);

event Burn(address indexed from, uint256 amount);

event Swap(address indexed trader, uint256 amount0In, uint256 amount1In, uint256 amount0Out, uint256 amount1Out);

constructor(address _token0, address _token1) {

token0 = IERC20(_token0);

token1 = IERC20(_token1);

}

function addLiquidity(uint256 amount0, uint256 amount1) external returns (uint256 shares) {

token0.transferFrom(msg.sender, address(this), amount0);

token1.transferFrom(msg.sender, address(this), amount1);

if (totalSupply == 0) {

shares = sqrt(amount0 * amount1);

} else {

shares = min(

(amount0 * totalSupply) / reserve0,

(amount1 * totalSupply) / reserve1

);

}

require(shares > 0, "Shares = 0");

_mint(msg.sender, shares);

_update(

token0.balanceOf(address(this)),

token1.balanceOf(address(this))

);

emit Mint(msg.sender, shares);

}

function removeLiquidity(uint256 shares) external returns (uint256 amount0, uint256 amount1) {

uint256 bal0 = token0.balanceOf(address(this));

uint256 bal1 = token1.balanceOf(address(this));

amount0 = (shares * bal0) / totalSupply;

amount1 = (shares * bal1) / totalSupply;

require(amount0 > 0 && amount1 > 0, "Amount0 or amount1 = 0");

_burn(msg.sender, shares);

_update(bal0 - amount0, bal1 - amount1);

token0.transfer(msg.sender, amount0);

token1.transfer(msg.sender, amount1);

emit Burn(msg.sender, shares);

}

function swap(address tokenIn, uint256 amountIn) external returns (uint256 amountOut) {

require(tokenIn == address(token0) || tokenIn == address(token1), "Invalid token");

bool isToken0 = tokenIn == address(token0);

(IERC20 tokenIn_, IERC20 tokenOut, uint256 resIn, uint256 resOut) = isToken0

? (token0, token1, reserve0, reserve1)

: (token1, token0, reserve1, reserve0);

tokenIn_.transferFrom(msg.sender, address(this), amountIn);

// 0.3% fee

uint256 amountInWithFee = (amountIn * 997) / 1000;

amountOut = (resOut * amountInWithFee) / (resIn + amountInWithFee);

tokenOut.transfer(msg.sender, amountOut);

_update(

token0.balanceOf(address(this)),

token1.balanceOf(address(this))

);

emit Swap(msg.sender, isToken0 ? amountIn : 0, isToken0 ? 0 : amountIn, isToken0 ? 0 : amountOut, isToken0 ? amountOut : 0);

}

function _mint(address to, uint256 amount) private {

balanceOf[to] += amount;

totalSupply += amount;

}

function _burn(address from, uint256 amount) private {

balanceOf[from] -= amount;

totalSupply -= amount;

}

function _update(uint256 res0, uint256 res1) private {

reserve0 = res0;

reserve1 = res1;

}

function sqrt(uint256 y) private pure returns (uint256 z) {

if (y > 3) {

z = y;

uint256 x = y / 2 + 1;

while (x < z) {

z = x;

x = (y / x + x) / 2;

}

} else if (y != 0) {

z = 1;

}

}

function min(uint256 x, uint256 y) private pure returns (uint256) {

return x <= y ? x : y;

}

}

## Governance Token

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Votes.sol";

import "@openzeppelin/contracts/access/Ownable.sol";

contract GovernanceToken is ERC20Votes, Ownable {

constructor() ERC20("Governance Token", "GOV") ERC20Permit("Governance Token") {

_mint(msg.sender, 1000000 10*decimals());

}

function _afterTokenTransfer(

address from,

address to,

uint256 amount

) internal override(ERC20Votes) {

super._afterTokenTransfer(from, to, amount);

}

function _mint(address to, uint256 amount) internal override(ERC20Votes) {

super._mint(to, amount);

}

function _burn(address account, uint256 amount) internal override(ERC20Votes) {

super._burn(account, amount);

}

}

contract Governor is Ownable {

GovernanceToken public governanceToken;

struct Proposal {

uint256 id;

address proposer;

string description;

uint256 forVotes;

uint256 againstVotes;

uint256 startBlock;

uint256 endBlock;

bool executed;

mapping(address => bool) hasVoted;

}

uint256 public proposalCount;

mapping(uint256 => Proposal) public proposals;

uint256 public votingPeriod = 17280; // ~3 days in blocks

uint256 public proposalThreshold = 100000 10*18;

event ProposalCreated(uint256 indexed proposalId, address proposer, string description);

event VoteCast(address indexed voter, uint256 indexed proposalId, bool support, uint256 weight);

event ProposalExecuted(uint256 indexed proposalId);

constructor(address _governanceToken) {

governanceToken = GovernanceToken(_governanceToken);

}

function propose(string memory description) external returns (uint256) {

require(

governanceToken.getPastVotes(msg.sender, block.number - 1) >= proposalThreshold,

"Proposer votes below threshold"

);

proposalCount++;

Proposal storage newProposal = proposals[proposalCount];

newProposal.id = proposalCount;

newProposal.proposer = msg.sender;

newProposal.description = description;

newProposal.startBlock = block.number;

newProposal.endBlock = block.number + votingPeriod;

emit ProposalCreated(proposalCount, msg.sender, description);

return proposalCount;

}

function vote(uint256 proposalId, bool support) external {

Proposal storage proposal = proposals[proposalId];

require(block.number >= proposal.startBlock, "Voting not started");

require(block.number <= proposal.endBlock, "Voting ended");

require(!proposal.hasVoted[msg.sender], "Already voted");

uint256 weight = governanceToken.getPastVotes(msg.sender, proposal.startBlock);

require(weight > 0, "No voting power");

proposal.hasVoted[msg.sender] = true;

if (support) {

proposal.forVotes += weight;

} else {

proposal.againstVotes += weight;

}

emit VoteCast(msg.sender, proposalId, support, weight);

}

function execute(uint256 proposalId) external {

Proposal storage proposal = proposals[proposalId];

require(block.number > proposal.endBlock, "Voting not ended");

require(!proposal.executed, "Already executed");

require(proposal.forVotes > proposal.againstVotes, "Proposal failed");

proposal.executed = true;

// Execute proposal logic here

emit ProposalExecuted(proposalId);

}

}

## Flash Loan

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

interface IFlashLoanReceiver {

function executeOperation(

address asset,

uint256 amount,

uint256 fee,

bytes calldata params

) external returns (bool);

}

contract FlashLoanProvider {

IERC20 public token;

uint256 public feePercentage = 9; // 0.09% fee

event FlashLoan(address indexed borrower, uint256 amount, uint256 fee);

constructor(address _token) {

token = IERC20(_token);

}

function flashLoan(

address receiver,

uint256 amount,

bytes calldata params

) external {

uint256 balanceBefore = token.balanceOf(address(this));

require(balanceBefore >= amount, "Insufficient liquidity");

uint256 fee = (amount * feePercentage) / 10000;

// Send tokens to receiver

token.transfer(receiver, amount);

// Execute callback

require(

IFlashLoanReceiver(receiver).executeOperation(

address(token),

amount,

fee,

params

),

"Flash loan failed"

);

// Verify repayment

uint256 balanceAfter = token.balanceOf(address(this));

require(balanceAfter >= balanceBefore + fee, "Flash loan not repaid");

emit FlashLoan(receiver, amount, fee);

}

}

// Example flash loan receiver

contract FlashLoanReceiver is IFlashLoanReceiver {

function executeOperation(

address asset,

uint256 amount,

uint256 fee,

bytes calldata params

) external override returns (bool) {

// Decode params and execute arbitrage, liquidation, etc.

// ...

// Approve repayment

IERC20(asset).approve(msg.sender, amount + fee);

return true;

}

}