TokenLiquidityPool

Philipp Keinberger

TokenLiquidityPool

This contract is a liquidity pool, where users can swap between two ERC20 tokens. Users can also provide liquidity to the pool, while accumulating rewards over time from the swap fee. Liquidity can be withdrawn at all times. Users can swap tokens on behalf of other users by using the Allowance feature. In order to use that feature, one has to approve another user for future swaps on ones own behalf.

This contract implements the ILiquidityPool interface to allow for standardized liquidity pool functionality for exchanges. This contract also implements the IERC20 Openzeppelin inteface for the ERC20 token standard. The TokenLiquidityPool inherits from Openzeppelins Ownable contract to allow for owner features. It also inherits from Openzeppelins Initializable contract to allow for a safe initialize function, favourably used by exchanges to initialize the liquidity pool.

Methods

approve

function approve(address approvee, uint256 amount, enum ILiquidityPool.SwapDirection direction) external nonpayable

Function for approving other users to swap on ones own behalf

This function approves approvee to swap amount from caller in direction of direction. Calling this function with amount equal to zero in effect resets the allowance. This function emits the {Approval} event.

Parameters

Name	Type	Description
approvee	address	is the address that should be approved
amount	uint256	is the amount approved for `approvee` to swap
direction	enum ILiquidityPool.SwapDirection	is the direction to allow swapping in

getAllowanceOf

function getAllowanceOf(address owner, address allowee) external view returns (struct ILiquidityPool.Allowance)

Function for retrieving the allowance of allowee to swap on behalf of owner

Parameters

Name	Type	Description
owner	address	is the owner the tokens to swap
allowee	address	is the address allowed to swap according to allowance

Returns

Name	Type	Description
_0	ILiquidityPool.Allowance	Allowance of `allowee` to swap for `owner`

getEligibleXOf

function getEligibleXOf(uint256 liquidityAmount) external view returns (uint256)

Function for retrieving eligible amount of x tokens when withdrawing liquidityAmount Note that x token output fluctuates with price and therefore changes constantly

Parameters

Name	Type	Description
liquidityAmount	uint256	is the amount of liquidity to be withdrawn

Returns

Name	Type	Description
_0	uint256	X token output when withdrawing `liquidityAmount`

getEligibleYOf

function getEligibleYOf(uint256 liquidityAmount) external view returns (uint256)

Function for retrieving eligible amount of y tokens when withdrawing liquidityAmount Note that y token output fluctuates with price and therefore changes constantly

Parameters

Name	Type	Description
liquidityAmount	uint256	is the amount of liquidity to be withdrawn

Returns

Name	Type	Description
_0	uint256	Y token output when withdrawing `liquidityAmount`

getKind

function getKind() external pure returns (enum ILiquidityPool.Kind)

Function for retrieving the kind of the liquidity pool

Returns

Name	Type	Description
_0	enum ILiquidityPool.Kind	Kind of the liquidity pool

getLiquidityOf

function getLiquidityOf(address addr) external view returns (uint256)

Function for retrieving liquidity of addr

Parameters

Name	Type	Description
addr	address	is the address of the liquidity owner

Returns

Name	Type	Description
_0	uint256	Liquidity of `addr`

getPoolLiquidity

function getPoolLiquidity() external view returns (uint256)

Function for retrieving the total liquidity in the pool

Returns

Name	Type	Description
_0	uint256	Pool liquidity

getXTokenAddress

function getXTokenAddress() external view returns (address)

Function for retrieving the address of x token

Returns

Name	Type	Description
_0	address	Address of x token

getXTokenOutputForSwap

function getXTokenOutputForSwap(uint256 yAmount) external view returns (uint256)

Function for retrieving x token output for swap of y tokens yAmount Note that token output fluctuates with price and therefore changes constantly

Parameters

Name	Type	Description
yAmount	uint256	is the amount of y tokens to be swapped

Returns

Name	Type	Description
_0	uint256	Amount of x tokens expected to be received for swap

getYAmountForDepositOfX

function getYAmountForDepositOfX(uint256 xAmount) external view returns (uint256)

Function for retrieving the amount of y tokens required, when providing liquidity with xAmount to the pool Note that y amount fluctuates with price and therefore changes constantly

Parameters

Name	Type	Description
xAmount	uint256	is the amount of x tokens

Returns

Name	Type	Description
_0	uint256	Amount of y tokens required for deposit of `xAmount`

getYTokenAddress

function getYTokenAddress() external view returns (address)

Function for retrieving the address of y token

Returns

Name	Type	Description
_0	address	Address of y token

getYTokenOutputForSwap

function getYTokenOutputForSwap(uint256 xAmount) external view returns (uint256)

Function for retrieving y token output for swap of x tokens xAmount Note that token output fluctuates with price and therefore changes constantly

Parameters

Name	Type	Description
xAmount	uint256	is the amount of x tokens to be swapped

Returns

Name	Type	Description
_0	uint256	Amount of y tokens expected to be received for swap

initialize

function initialize(uint256 xDeposit, uint256 yDeposit) external nonpayable

Function for initializing (setting up) the liquidity pool

This function initializes the liquidity pool with xDeposit for x and yDeposit for y. This function reverts if the caller is not the owner of the contract. The function also reverts if xDeposit or yDeposit is not greater than zero. If the transfer of xDeposit from xToken fails or the transfer of yDeposit from yToken fails, the function will revert. Note that this function can only be called once.

Parameters

Name	Type	Description
xDeposit	uint256	is the amount deposited from xToken
yDeposit	uint256	is the mamount deposited from yToken

owner

function owner() external view returns (address)

Returns the address of the current owner.

Returns

Name	Type	Description
_0	address	undefined

provideLiquidity

function provideLiquidity(uint256 xDeposit) external nonpayable

Function for providing liquidity to the pool

The function uses xDeposit to calculate the amount of Y required for deposit. The amount of Y has to be calculated, because it and xDeposit have to be in ratio with the reserves of X and Y in the pool. Otherwise, a random amount of Y would change the price of the assets in the pool. The amount of Y required for a deposit of xDeposit can be retrieved by the getYAmountForDepositOfX function. Before calling the function, the caller has to approve the liquidity pool to transfer xDeposit at xToken and the amount of Y required at yToken. It is advised to set allowance at yToken higher than the output of getYAmountForDepositOfX because of price fluctuations. This function reverts if the transfer of xDeposit or the required (calculated) deposit of Y fails. This function emits the {LiquidityAdded} event.

Parameters

Name	Type	Description
xDeposit	uint256	is the amount deposited from xToken

renounceOwnership

function renounceOwnership() external nonpayable

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.

swap

function swap(uint256 tokenAmount, enum ILiquidityPool.SwapDirection direction) external payable

Function for swapping tokens

This function calls _swap (see _swap for more documentation)

Parameters

Name	Type	Description
tokenAmount	uint256	is the amount of tokens to be swapped to native currency. Note that `tokenAmount` can be zero if swapping native for tokens (xToY, NativeLiquidityPool)
direction	enum ILiquidityPool.SwapDirection	defines the direction of the swap (xToY or yToX)

swapFrom

function swapFrom(address from, uint256 amount) external payable

Function for swapping tokens on other users behalf

This function calls _swap (see _swap for more documentation)

Parameters

Name	Type	Description
from	address	is the address from which to swap
amount	uint256	undefined

transferOwnership

function transferOwnership(address newOwner) external nonpayable

Transfers ownership of the contract to a new account (newOwner). Can only be called by the current owner.

Parameters

Name	Type	Description
newOwner	address	undefined

withdrawLiquidity

function withdrawLiquidity(uint256 liquidityAmount) external nonpayable

Function for withdrawing liquidity from the pool

The function calculates the amount of x and y eligible for withdrawal and automatically transfers that amount to the caller. The amount of x and y eligible is dependent on the pool reserves of both assets, liquidityAmount and the total liquidity in the pool. The eligible amount of the assets for withdrawal can be lower than the liquidity provided (Impermantent Loss), but usually is greater than the amount provided, because of accumulating swap fees in the liquidity pool. The function reverts if liquidityAmount exceeds the liquidity of the caller. This function also reverts if the transfer of the amount of x or y eligible fails. The function emits the {LiquidityRemoved} event.

Parameters

Name	Type	Description
liquidityAmount	uint256	is the amount of liquidity to be withdrawn

Events

Approval

event Approval(address owner, address approvee, uint256 amount, enum ILiquidityPool.SwapDirection direction)

Event emitted when owner approves approvee to swap amount in the direction of direction

Parameters

Name	Type	Description
owner	address	undefined
approvee	address	undefined
amount	uint256	undefined
direction	enum ILiquidityPool.SwapDirection	undefined

Initialized

event Initialized(uint8 version)

Parameters

Name	Type	Description
version	uint8	undefined

LiquidityAdded

event LiquidityAdded(address liquidityProvider, uint256 liquidityAmount, uint256 xDeposit, uint256 yDeposit)

Event emitted when new liquidity is provided (added) to the pool

Parameters

Name	Type	Description
liquidityProvider	address	undefined
liquidityAmount	uint256	undefined
xDeposit	uint256	undefined
yDeposit	uint256	undefined

LiquidityRemoved

event LiquidityRemoved(address liquidityProvider, uint256 liquidityAmount, uint256 xWithdrawn, uint256 yWithdrawn)

Event emitted when liquidity is withdrawn (removed) from the pool

Parameters

Name	Type	Description
liquidityProvider	address	undefined
liquidityAmount	uint256	undefined
xWithdrawn	uint256	undefined
yWithdrawn	uint256	undefined

OwnershipTransferred

event OwnershipTransferred(address indexed previousOwner, address indexed newOwner)

Parameters

Name	Type	Description
previousOwner `indexed`	address	undefined
newOwner `indexed`	address	undefined

Swap

event Swap(address swapee, uint256 amount, uint256 output, enum ILiquidityPool.SwapDirection direction)

Event emitted when swapee swaps amount in the direction of direction. Note that amount may be zero.

Parameters

Name	Type	Description
swapee	address	undefined
amount	uint256	undefined
output	uint256	undefined
direction	enum ILiquidityPool.SwapDirection	undefined

Errors