Contract Name:
StaticTaxHandler
Contract Source Code:
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "../utils/Context.sol";
/**
* @dev Contract module which provides a basic access control mechanism, where
* there is an account (an owner) that can be granted exclusive access to
* specific functions.
*
* By default, the owner account will be the one that deploys the contract. This
* can later be changed with {transferOwnership}.
*
* This module is used through inheritance. It will make available the modifier
* `onlyOwner`, which can be applied to your functions to restrict their use to
* the owner.
*/
abstract contract Ownable is Context {
address private _owner;
event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
/**
* @dev Initializes the contract setting the deployer as the initial owner.
*/
constructor() {
_setOwner(_msgSender());
}
/**
* @dev Returns the address of the current owner.
*/
function owner() public view virtual returns (address) {
return _owner;
}
/**
* @dev Throws if called by any account other than the owner.
*/
modifier onlyOwner() {
require(owner() == _msgSender(), "Ownable: caller is not the owner");
_;
}
/**
* @dev Leaves the contract without owner. It will not be possible to call
* `onlyOwner` functions anymore. Can only be called by the current owner.
*
* NOTE: Renouncing ownership will leave the contract without an owner,
* thereby removing any functionality that is only available to the owner.
*/
function renounceOwnership() public virtual onlyOwner {
_setOwner(address(0));
}
/**
* @dev Transfers ownership of the contract to a new account (`newOwner`).
* Can only be called by the current owner.
*/
function transferOwnership(address newOwner) public virtual onlyOwner {
require(newOwner != address(0), "Ownable: new owner is the zero address");
_setOwner(newOwner);
}
function _setOwner(address newOwner) private {
address oldOwner = _owner;
_owner = newOwner;
emit OwnershipTransferred(oldOwner, newOwner);
}
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
/**
* @dev Provides information about the current execution context, including the
* sender of the transaction and its data. While these are generally available
* via msg.sender and msg.data, they should not be accessed in such a direct
* manner, since when dealing with meta-transactions the account sending and
* paying for execution may not be the actual sender (as far as an application
* is concerned).
*
* This contract is only required for intermediate, library-like contracts.
*/
abstract contract Context {
function _msgSender() internal view virtual returns (address) {
return msg.sender;
}
function _msgData() internal view virtual returns (bytes calldata) {
return msg.data;
}
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
/**
* @dev Library for managing
* https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
* types.
*
* Sets have the following properties:
*
* - Elements are added, removed, and checked for existence in constant time
* (O(1)).
* - Elements are enumerated in O(n). No guarantees are made on the ordering.
*
* ```
* contract Example {
* // Add the library methods
* using EnumerableSet for EnumerableSet.AddressSet;
*
* // Declare a set state variable
* EnumerableSet.AddressSet private mySet;
* }
* ```
*
* As of v3.3.0, sets of type `bytes32` (`Bytes32Set`), `address` (`AddressSet`)
* and `uint256` (`UintSet`) are supported.
*/
library EnumerableSet {
// To implement this library for multiple types with as little code
// repetition as possible, we write it in terms of a generic Set type with
// bytes32 values.
// The Set implementation uses private functions, and user-facing
// implementations (such as AddressSet) are just wrappers around the
// underlying Set.
// This means that we can only create new EnumerableSets for types that fit
// in bytes32.
struct Set {
// Storage of set values
bytes32[] _values;
// Position of the value in the `values` array, plus 1 because index 0
// means a value is not in the set.
mapping(bytes32 => uint256) _indexes;
}
/**
* @dev Add a value to a set. O(1).
*
* Returns true if the value was added to the set, that is if it was not
* already present.
*/
function _add(Set storage set, bytes32 value) private returns (bool) {
if (!_contains(set, value)) {
set._values.push(value);
// The value is stored at length-1, but we add 1 to all indexes
// and use 0 as a sentinel value
set._indexes[value] = set._values.length;
return true;
} else {
return false;
}
}
/**
* @dev Removes a value from a set. O(1).
*
* Returns true if the value was removed from the set, that is if it was
* present.
*/
function _remove(Set storage set, bytes32 value) private returns (bool) {
// We read and store the value's index to prevent multiple reads from the same storage slot
uint256 valueIndex = set._indexes[value];
if (valueIndex != 0) {
// Equivalent to contains(set, value)
// To delete an element from the _values array in O(1), we swap the element to delete with the last one in
// the array, and then remove the last element (sometimes called as 'swap and pop').
// This modifies the order of the array, as noted in {at}.
uint256 toDeleteIndex = valueIndex - 1;
uint256 lastIndex = set._values.length - 1;
if (lastIndex != toDeleteIndex) {
bytes32 lastvalue = set._values[lastIndex];
// Move the last value to the index where the value to delete is
set._values[toDeleteIndex] = lastvalue;
// Update the index for the moved value
set._indexes[lastvalue] = valueIndex; // Replace lastvalue's index to valueIndex
}
// Delete the slot where the moved value was stored
set._values.pop();
// Delete the index for the deleted slot
delete set._indexes[value];
return true;
} else {
return false;
}
}
/**
* @dev Returns true if the value is in the set. O(1).
*/
function _contains(Set storage set, bytes32 value) private view returns (bool) {
return set._indexes[value] != 0;
}
/**
* @dev Returns the number of values on the set. O(1).
*/
function _length(Set storage set) private view returns (uint256) {
return set._values.length;
}
/**
* @dev Returns the value stored at position `index` in the set. O(1).
*
* Note that there are no guarantees on the ordering of values inside the
* array, and it may change when more values are added or removed.
*
* Requirements:
*
* - `index` must be strictly less than {length}.
*/
function _at(Set storage set, uint256 index) private view returns (bytes32) {
return set._values[index];
}
/**
* @dev Return the entire set in an array
*
* WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
* to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
* this function has an unbounded cost, and using it as part of a state-changing function may render the function
* uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
*/
function _values(Set storage set) private view returns (bytes32[] memory) {
return set._values;
}
// Bytes32Set
struct Bytes32Set {
Set _inner;
}
/**
* @dev Add a value to a set. O(1).
*
* Returns true if the value was added to the set, that is if it was not
* already present.
*/
function add(Bytes32Set storage set, bytes32 value) internal returns (bool) {
return _add(set._inner, value);
}
/**
* @dev Removes a value from a set. O(1).
*
* Returns true if the value was removed from the set, that is if it was
* present.
*/
function remove(Bytes32Set storage set, bytes32 value) internal returns (bool) {
return _remove(set._inner, value);
}
/**
* @dev Returns true if the value is in the set. O(1).
*/
function contains(Bytes32Set storage set, bytes32 value) internal view returns (bool) {
return _contains(set._inner, value);
}
/**
* @dev Returns the number of values in the set. O(1).
*/
function length(Bytes32Set storage set) internal view returns (uint256) {
return _length(set._inner);
}
/**
* @dev Returns the value stored at position `index` in the set. O(1).
*
* Note that there are no guarantees on the ordering of values inside the
* array, and it may change when more values are added or removed.
*
* Requirements:
*
* - `index` must be strictly less than {length}.
*/
function at(Bytes32Set storage set, uint256 index) internal view returns (bytes32) {
return _at(set._inner, index);
}
/**
* @dev Return the entire set in an array
*
* WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
* to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
* this function has an unbounded cost, and using it as part of a state-changing function may render the function
* uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
*/
function values(Bytes32Set storage set) internal view returns (bytes32[] memory) {
return _values(set._inner);
}
// AddressSet
struct AddressSet {
Set _inner;
}
/**
* @dev Add a value to a set. O(1).
*
* Returns true if the value was added to the set, that is if it was not
* already present.
*/
function add(AddressSet storage set, address value) internal returns (bool) {
return _add(set._inner, bytes32(uint256(uint160(value))));
}
/**
* @dev Removes a value from a set. O(1).
*
* Returns true if the value was removed from the set, that is if it was
* present.
*/
function remove(AddressSet storage set, address value) internal returns (bool) {
return _remove(set._inner, bytes32(uint256(uint160(value))));
}
/**
* @dev Returns true if the value is in the set. O(1).
*/
function contains(AddressSet storage set, address value) internal view returns (bool) {
return _contains(set._inner, bytes32(uint256(uint160(value))));
}
/**
* @dev Returns the number of values in the set. O(1).
*/
function length(AddressSet storage set) internal view returns (uint256) {
return _length(set._inner);
}
/**
* @dev Returns the value stored at position `index` in the set. O(1).
*
* Note that there are no guarantees on the ordering of values inside the
* array, and it may change when more values are added or removed.
*
* Requirements:
*
* - `index` must be strictly less than {length}.
*/
function at(AddressSet storage set, uint256 index) internal view returns (address) {
return address(uint160(uint256(_at(set._inner, index))));
}
/**
* @dev Return the entire set in an array
*
* WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
* to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
* this function has an unbounded cost, and using it as part of a state-changing function may render the function
* uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
*/
function values(AddressSet storage set) internal view returns (address[] memory) {
bytes32[] memory store = _values(set._inner);
address[] memory result;
assembly {
result := store
}
return result;
}
// UintSet
struct UintSet {
Set _inner;
}
/**
* @dev Add a value to a set. O(1).
*
* Returns true if the value was added to the set, that is if it was not
* already present.
*/
function add(UintSet storage set, uint256 value) internal returns (bool) {
return _add(set._inner, bytes32(value));
}
/**
* @dev Removes a value from a set. O(1).
*
* Returns true if the value was removed from the set, that is if it was
* present.
*/
function remove(UintSet storage set, uint256 value) internal returns (bool) {
return _remove(set._inner, bytes32(value));
}
/**
* @dev Returns true if the value is in the set. O(1).
*/
function contains(UintSet storage set, uint256 value) internal view returns (bool) {
return _contains(set._inner, bytes32(value));
}
/**
* @dev Returns the number of values on the set. O(1).
*/
function length(UintSet storage set) internal view returns (uint256) {
return _length(set._inner);
}
/**
* @dev Returns the value stored at position `index` in the set. O(1).
*
* Note that there are no guarantees on the ordering of values inside the
* array, and it may change when more values are added or removed.
*
* Requirements:
*
* - `index` must be strictly less than {length}.
*/
function at(UintSet storage set, uint256 index) internal view returns (uint256) {
return uint256(_at(set._inner, index));
}
/**
* @dev Return the entire set in an array
*
* WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
* to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
* this function has an unbounded cost, and using it as part of a state-changing function may render the function
* uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
*/
function values(UintSet storage set) internal view returns (uint256[] memory) {
bytes32[] memory store = _values(set._inner);
uint256[] memory result;
assembly {
result := store
}
return result;
}
}
// SPDX-License-Identifier: MIT
pragma solidity 0.8.11;
/**
* @title Tax handler interface
* @dev Any class that implements this interface can be used for protocol-specific tax calculations.
*/
interface ITaxHandler {
/**
* @notice Get number of tokens to pay as tax.
* @param benefactor Address of the benefactor.
* @param beneficiary Address of the beneficiary.
* @param amount Number of tokens in the transfer.
* @return Number of tokens to pay as tax.
*/
function getTax(
address benefactor,
address beneficiary,
uint256 amount
) external view returns (uint256);
}
// SPDX-License-Identifier: MIT
pragma solidity 0.8.11;
import "@openzeppelin/contracts/utils/structs/EnumerableSet.sol";
import "./ITaxHandler.sol";
import "../utils/ExchangePoolProcessor.sol";
/**
* @title Static tax handler contract
* @dev This contract allows protocols to collect tax on transactions that count as either sells or liquidity additions
* to exchange pools. Addresses can be exempted from tax collection, and addresses designated as exchange pools can be
* added and removed by the owner of this contract. The owner of the contract should be set to a DAO-controlled timelock
* or at the very least a multisig wallet.
*/
contract StaticTaxHandler is ITaxHandler, ExchangePoolProcessor {
using EnumerableSet for EnumerableSet.AddressSet;
/// @notice How much tax to collect in basis points. 10,000 basis points is 100%.
uint256 public taxBasisPoints;
/// @dev The set of addresses exempt from tax.
EnumerableSet.AddressSet private _exempted;
/// @notice Emitted when the tax basis points number is updated.
event TaxBasisPointsUpdated(uint256 oldBasisPoints, uint256 newBasisPoints);
/// @notice Emitted when an address is added to or removed from the exempted addresses set.
event TaxExemptionUpdated(address indexed wallet, bool exempted);
/**
* @param initialTaxBasisPoints The number of tax basis points to start out with for tax calculations.
*/
constructor(uint256 initialTaxBasisPoints) {
taxBasisPoints = initialTaxBasisPoints;
}
/**
* @notice Get number of tokens to pay as tax. This method specifically only check for sell-type transfers to
* designated exchange pool addresses.
* @dev There is no easy way to differentiate between a user selling tokens and a user adding liquidity to the pool.
* In both cases tokens are transferred to the pool. This is an unfortunate case where users have to accept being
* taxed on liquidity additions. To get around this issue, a separate liquidity addition contract can be deployed.
* This contract can be exempt from taxes if its functionality is verified to only add liquidity.
* @param benefactor Address of the benefactor.
* @param beneficiary Address of the beneficiary.
* @param amount Number of tokens in the transfer.
* @return Number of tokens to pay as tax.
*/
function getTax(
address benefactor,
address beneficiary,
uint256 amount
) external view override returns (uint256) {
if (_exempted.contains(benefactor) || _exempted.contains(beneficiary)) {
return 0;
}
require(
_exchangePools.length() > 0,
"StaticTaxHandler:getTax:INACTIVE: No exchange pools have been added yet."
);
// Transactions between regular users (this includes contracts) aren't taxed.
if (!_exchangePools.contains(benefactor) && !_exchangePools.contains(beneficiary)) {
return 0;
}
return (amount * taxBasisPoints) / 10000;
}
/**
* @notice Set new number for tax basis points.
* @param newBasisPoints New tax basis points number to set for calculations.
*/
function setTaxBasisPoints(uint256 newBasisPoints) external onlyOwner {
require(
newBasisPoints <= 4000,
"StaticTaxHandler:setTaxBasisPoints:HIGHER_VALUE: Basis points cannot exceed 4,000."
);
uint256 oldBasisPoints = taxBasisPoints;
taxBasisPoints = newBasisPoints;
emit TaxBasisPointsUpdated(oldBasisPoints, newBasisPoints);
}
/**
* @notice Add address to set of tax-exempted addresses.
* @param exemption Address to add to set of tax-exempted addresses.
*/
function addExemption(address exemption) external onlyOwner {
if (_exempted.add(exemption)) {
emit TaxExemptionUpdated(exemption, true);
}
}
/**
* @notice Remove address from set of tax-exempted addresses.
* @param exemption Address to remove from set of tax-exempted addresses.
*/
function removeExemption(address exemption) external onlyOwner {
if (_exempted.remove(exemption)) {
emit TaxExemptionUpdated(exemption, false);
}
}
}
// SPDX-License-Identifier: MIT
pragma solidity 0.8.11;
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/structs/EnumerableSet.sol";
/**
* @title Exchange pool processor abstract contract.
* @dev Keeps an enumerable set of designated exchange addresses as well as a single primary pool address.
*/
abstract contract ExchangePoolProcessor is Ownable {
using EnumerableSet for EnumerableSet.AddressSet;
/// @dev Set of exchange pool addresses.
EnumerableSet.AddressSet internal _exchangePools;
/// @notice Primary exchange pool address.
address public primaryPool;
/// @notice Emitted when an exchange pool address is added to the set of tracked pool addresses.
event ExchangePoolAdded(address exchangePool);
/// @notice Emitted when an exchange pool address is removed from the set of tracked pool addresses.
event ExchangePoolRemoved(address exchangePool);
/// @notice Emitted when the primary pool address is updated.
event PrimaryPoolUpdated(address oldPrimaryPool, address newPrimaryPool);
/**
* @notice Get list of addresses designated as exchange pools.
* @return An array of exchange pool addresses.
*/
function getExchangePoolAddresses() external view returns (address[] memory) {
return _exchangePools.values();
}
/**
* @notice Add an address to the set of exchange pool addresses.
* @dev Nothing happens if the pool already exists in the set.
* @param exchangePool Address of exchange pool to add.
*/
function addExchangePool(address exchangePool) external onlyOwner {
if (_exchangePools.add(exchangePool)) {
emit ExchangePoolAdded(exchangePool);
}
}
/**
* @notice Remove an address from the set of exchange pool addresses.
* @dev Nothing happens if the pool doesn't exist in the set..
* @param exchangePool Address of exchange pool to remove.
*/
function removeExchangePool(address exchangePool) external onlyOwner {
if (_exchangePools.remove(exchangePool)) {
emit ExchangePoolRemoved(exchangePool);
}
}
/**
* @notice Set exchange pool address as primary pool.
* @dev To prevent issues, only addresses inside the set of exchange pool addresses can be selected as primary pool.
* @param exchangePool Address of exchange pool to set as primary pool.
*/
function setPrimaryPool(address exchangePool) external onlyOwner {
require(
_exchangePools.contains(exchangePool),
"ExchangePoolProcessor:setPrimaryPool:INVALID_POOL: Given address is not registered as exchange pool."
);
require(
primaryPool != exchangePool,
"ExchangePoolProcessor:setPrimaryPool:ALREADY_SET: This address is already the primary pool address."
);
address oldPrimaryPool = primaryPool;
primaryPool = exchangePool;
emit PrimaryPoolUpdated(oldPrimaryPool, exchangePool);
}
}