Price Oracle

Introduction

As blockchain-powered smart contracts are unable to directly communicate with the external system, JustLend DAO protocol requires reliable price feeds. We have chosen WinkLink's price service as our price feed.

JustLend DAO protocol uses a PriceOracle contract to set and display token prices in sun(10^-6 TRX), scaled by 10^(tokenDecimal - 6). Prices of the underlying tokens are posted every 30 minutes via setPrice()by a specified poster.

Solidity API

anchors()

Calling this methods returns the current price anchor of a specified token.

function anchors(address) view returns(uint256, uint256)

Parameter description:

Parameter	Type	Description
	address	The address of the underlying token(e.g. TR7NHqjeKQxGTCi8q8ZY4pL8otSzgjLj6t for USDT)

Return Values：

Returns	Type	Description
period	uint256	The current time period. Calculated as: current block height/ 600 (the TRON network produces approx. 600 blocks per 30 mins)
priceMantissa	uint256	Token prices in sun(10^-6 TRX), scaled by 10^(tokenDecimal - 6).

const result = priceOracle.anchors(token).call();

---

poster()

Calling this methods returns the current price poster.

function poster() view returns(address)

Returns: Address of the current poster.

const result = priceOracle.poster().call();

---

assetPrices()

Calling this method returns the current price of the specified asset.

function assetPrices(address asset) public view returns (uint)

Parameter description:

Parameter	Type	Description
asset	address	The address of the token to query

Returns: The current price of the token in sun(10^-6 TRX), scaled by 10^(tokenDecimal - 6).

---

getPrice()

Calling this method returns the current price of the specified asset.

function getPrice(address asset) public view returns (uint)

Parameter description:

Parameter	Type	Description
asset	address	The address of the token to query

Returns: The current price of the token in sun(10^-6 TRX), scaled by 10^(tokenDecimal - 6).

---

setPrice()

Calling this methods sets a token price for the current time period.

function setPrice(address asset, uint requestedPriceMantissa) public returns (uint)

This method is poster-only.

Parameter description:

Parameter	Type	Description
asset	address	The address of the underlying token(e.g. TR7NHqjeKQxGTCi8q8ZY4pL8otSzgjLj6t for USDT)
requestedPriceMantissa	uint	New price, scaled by 10^18

Returns: 0 for success, otherwise an error code.

const result = priceOracle.setPrice(asset, price).send({
  feeLimit:10_000_000_000,
  callValue:0,
  shouldPollResponse:true
});