Chainlink Median

Chainlink integrated medianizer

1. Summary

The ChainlinkPriceFeedMedianizer has a similar interface to the Governance Led Median although, instead of relying on governance whitelisted oracles, it simply keeps a reference to a Chainlink price reference contract (price aggregator).

2. Contract Variables & Functions

Variables

• authorizedAccounts [usr: address] - addAuthorization/removeAuthorization/isAuthorized - auth mechanisms

• staleThreshold - time since linkAggregatorTimestamp after which the median value is considered stale

• chainlinkAggregator - address of the Chainlink price reference contract

• rewardRelayer - address of the contract that rewards addresses that call updateResult

• medianPrice - latest fetched price

• lastUpdateTime - latest timestamp when the contract pulled a price update from Chainlink

• multiplier - scaling factor for the Chainlink result (e.g if the price has 8 decimals and we want it to be scaled to 18 decimals, multiplier = 10 and medianPrice = fetchedPrice * 10 ^ multiplier)

• symbol - the price oracle type (ex: ETHUSD)

• periodSize - the minimum delay between two consecutive updates after which the reward for updating again starts to increase

• linkAggregatorTimestamp - the timestamp of the Chainlink aggregator's latest price update

Modifiers

• isAuthorized **** - checks whether an address is part of authorizedAddresses (and thus can call authed functions).

Functions

• modifyParameters - allows governance to change contract parameters

• read() public view returns (uint256) - gets a non-zero price or fails

• getResultWithValidity() public view returns (uint256,bool) - gets the price and its validity

• updateResult(feeReceiver: address) - updates the price stored in the contract by calling the Chainlink aggregator

Events

• AddAuthorization - emitted when a new address becomes authorized. Contains:

  • account - the new authorized account

• RemoveAuthorization - emitted when an address is de-authorized. Contains:

  • account - the address that was de-authorized

• ModifyParameters **** - emitted when a parameter is updated

• UpdateResult - emitted when updateResult is called. Contains:

  • medianPrice - the latest median price

  • lastUpdateTime - timestamp of the call

3. Walkthrough

When reading the latest price feed, the contract also stores the timestamp when the price coming from Chainlink was posted on-chain. The system can incentivize anyone to call updateResult and update the median price regularly using a rewardRelayer.

4. Gotchas

This oracle is entirely dependent on Chainlink. If the Chainlink relayer contract is deprecated the Oracle needs to be updated accordingly.

5. Failure Modes (Bounds on Operating Conditions & External Risk Factors)

If the Chainlink contract is not updated the price will become stale, other contracts reading from it will revert on state changing transactions, effectively freezing the system.

If the price reported by Chainlink is wrong the system will take it as it is, possibily causing unfair liquidations, or preventing liquidations in case of higher prices reported.