Introduction

The Comptroller is the risk management layer of the ChumHum protocol; it determines how much collateral a user is required to maintain, and whether (and by how much) a user can be liquidated. Each time a user interacts with a cToken, the Comptroller is asked to approve or deny the transaction.

The Comptroller maps user balances to prices (via the Price Oracle) to risk weights (called Collateral Factors) to make its determinations. Users explicitly list which assets they would like included in their risk scoring, by calling Enter Markets and Exit Market.

Architecture

The Comptroller is implemented as an upgradeable proxy. The Unitroller proxies all logic to the Comptroller implementation, but storage values are set on the Unitroller. To call Comptroller functions, use the Comptroller ABI on the Unitroller address.

Enter Markets

Enter into a list of markets - it is not an error to enter the same market more than once. In order to supply collateral or borrow in a market, it must be entered first.

Comptroller

function enterMarkets(address[] calldata cTokens) returns (uint[] memory)
  • msg.sender: The account which shall enter the given markets.
  • cTokens: The addresses of the cToken markets to enter.
  • RETURN: For each market, returns an error code indicating whether or not it was entered. Each is 0 on success, otherwise an Error code.

Solidity

Comptroller troll = Comptroller(0xABCD...);
CToken[] memory cTokens = new CToken[](2);
cTokens[0] = CErc20(0x3FDA...);
cTokens[1] = CMATIC(0x3FDB...);
uint[] memory errors = troll.enterMarkets(cTokens);

Web3 1.0

const troll = Comptroller.at(0xABCD...);
const cTokens = [CErc20.at(0x3FDA...), CMATIC.at(0x3FDB...)];
const errors = await troll.methods.enterMarkets(cTokens).send({from: ...});

Exit Market

Exit a market - it is not an error to exit a market which is not currently entered. Exited markets will not count towards account liquidity calculations.

Comptroller

function exitMarket(address cToken) returns (uint)
  • msg.sender: The account which shall exit the given market.
  • cTokens: The addresses of the cToken market to exit.
  • RETURN: 0 on success, otherwise an Error code.

Solidity

Comptroller troll = Comptroller(0xABCD...);
uint error = troll.exitMarket(CToken(0x3FDA...));

Web3 1.0

const troll = Comptroller.at(0xABCD...);
const errors = await troll.methods.exitMarket(CMATIC.at(0x3FDB...)).send({from: ...});

Get Assets In

Get the list of markets an account is currently entered into. In order to supply collateral or borrow in a market, it must be entered first. Entered markets count towards account liquidity calculations.

Comptroller

function getAssetsIn(address account) view returns (address[] memory)
  • account: The account whose list of entered markets shall be queried.
  • RETURN: The address of each market which is currently entered into.

Solidity

Comptroller troll = Comptroller(0xABCD...);
address[] memory markets = troll.getAssetsIn(0xMyAccount);

Web3 1.0

const troll = Comptroller.at(0xABCD...);
const markets = await troll.methods.getAssetsIn(cTokens).call();

Collateral Factor

A cToken's collateral factor can range from 0-90%, and represents the proportionate increase in liquidity (borrow limit) that an account receives by minting the cToken.

Generally, large or liquid assets have high collateral factors, while small or illiquid assets have low collateral factors. If an asset has a 0% collateral factor, it can't be used as collateral (or seized in liquidation), though it can still be borrowed.

Collateral factors can be increased (or decreased) through ChumHum Governance, as market conditions change.

Comptroller

function markets(address cTokenAddress) view returns (bool, uint, bool)
  • cTokenAddress: The address of the cToken to check if listed and get the collateral factor for.
  • RETURN: Tuple of values (isListed, collateralFactorMantissa, isComped); isListed represents whether the Comptroller recognizes this cToken; collateralFactorMantissa, scaled by 1e18, is multiplied by a supply balance to determine how much value can be borrowed. The isComped boolean indicates whether or not suppliers and borrowers are distributed CHUM tokens.

Solidity

Comptroller troll = Comptroller(0xABCD...);
(bool isListed, uint collateralFactorMantissa, bool isComped) = troll.markets(0x3FDA...);

Web3 1.0

const troll = Comptroller.at(0xABCD...);
const result = await troll.methods.markets(0x3FDA...).call();
const {0: isListed, 1: collateralFactorMantissa, 2: isComped} = result;

Get Account Liquidity

Account Liquidity represents the USD value borrowable by a user, before it reaches liquidation. Users with a shortfall (negative liquidity) are subject to liquidation, and can’t withdraw or borrow assets until Account Liquidity is positive again.

For each market the user has entered into, their supplied balance is multiplied by the market’s collateral factor, and summed; borrow balances are then subtracted, to equal Account Liquidity. Borrowing an asset reduces Account Liquidity for each USD borrowed; withdrawing an asset reduces Account Liquidity by the asset’s collateral factor times each USD withdrawn.

Because the ChumHum Protocol exclusively uses unsigned integers, Account Liquidity returns either a surplus or shortfall.

Comptroller

function getAccountLiquidity(address account) view returns (uint, uint, uint)
  • account: The account whose liquidity shall be calculated.
  • RETURN: Tuple of values (error, liquidity, shortfall). The error shall be 0 on success, otherwise an error code. A non-zero liquidity value indicates the account has available account liquidity. A non-zero shortfall value indicates the account is currently below his/her collateral requirement and is subject to liquidation. At most one of liquidity or shortfall shall be non-zero.

Solidity

Comptroller troll = Comptroller(0xABCD...);
(uint error, uint liquidity, uint shortfall) = troll.getAccountLiquidity(msg.caller);
require(error == 0, "join the Discord");
require(shortfall == 0, "account underwater");
require(liquidity > 0, "account has excess collateral");

Web3 1.0

const troll = Comptroller.at(0xABCD...);
const result = await troll.methods.getAccountLiquidity(0xBorrower).call();
const {0: error, 1: liquidity, 2: shortfall} = result;

Close Factor

The percent, ranging from 0% to 100%, of a liquidatable account's borrow that can be repaid in a single liquidate transaction. If a user has multiple borrowed assets, the closeFactor applies to any single borrowed asset, not the aggregated value of a user’s outstanding borrowing.

Comptroller

function closeFactorMantissa() view returns (uint)
  • RETURN: The closeFactor, scaled by 1e18, is multiplied by an outstanding borrow balance to determine how much could be closed.

Solidity

Comptroller troll = Comptroller(0xABCD...);
uint closeFactor = troll.closeFactorMantissa();

Web3 1.0

const troll = Comptroller.at(0xABCD...);
const closeFactor = await troll.methods.closeFactoreMantissa().call();

Liquidation Incentive

The additional collateral given to liquidators as an incentive to perform liquidation of underwater accounts. For example, if the liquidation incentive is 1.1, liquidators receive an extra 10% of the borrowers collateral for every unit they close.

Comptroller

function liquidationIncentiveMantissa() view returns (uint)
  • RETURN: The liquidationIncentive, scaled by 1e18, is multiplied by the closed borrow amount from the liquidator to determine how much collateral can be seized.

Solidity

Comptroller troll = Comptroller(0xABCD...);
uint closeFactor = troll.liquidationIncentiveMantissa();

Web3 1.0

const troll = Comptroller.at(0xABCD...);
const closeFactor = await troll.methods.liquidationIncentiveMantissa().call();

Key Events

Event Description

MarketEntered(CToken cToken, address account)

Emitted upon a successful Enter Market.

MarketExited(CToken cToken, address account)

Emitted upon a successful Exit Market.

Error Codes

Code Name Description

0

NO_ERROR

Not a failure.

1

UNAUTHORIZED

The sender is not authorized to perform this action.

2

COMPTROLLER_MISMATCH

Liquidation cannot be performed in markets with different Comptrollers.

3

INSUFFICIENT_SHORTFALL

The account does not have sufficient shortfall to perform this action.

4

INSUFFICIENT_LIQUIDITY

The account does not have sufficient liquidity to perform this action.

5

INVALID_CLOSE_FACTOR

The close factor is not valid.

6

INVALID_COLLATERAL_FACTOR

The collateral factor is not valid.

7

INVALID_LIQUIDATION_INCENTIVE

The liquidation incentive is invalid.

8

MARKET_NOT_ENTERED

The market has not been entered by the account.

9

MARKET_NOT_LISTED

The market is not currently listed by the Comptroller.

10

MARKET_ALREADY_LISTED

An admin tried to list the same market more than once.

11

MATH_ERROR

A math calculation error occurred.

12

NONZERO_BORROW_BALANCE

The action cannot be performed since the account carries a borrow balance.

13

PRICE_ERROR

The Comptroller could not obtain a required price of an asset.

14

REJECTION

The Comptroller rejects the action requested by the market.

15

SNAPSHOT_ERROR

The Comptroller could not get the account borrows and exchange rate from the market.

16

TOO_MANY_ASSETS

Attempted to enter more markets than are currently supported.

17

TOO_MUCH_REPAY

Attempted to repay more than is allowed by the protocol.

18

INSUFFICIENT_BALANCE_FOR_BUM

There is no sufficient balance to mint BUM.

Failure Info

Code Name

0

ACCEPT_ADMIN_PENDING_ADMIN_CHECK

1

ACCEPT_PENDING_IMPLEMENTATION_ADDRESS_CHECK

2

EXIT_MARKET_BALANCE_OWED

3

EXIT_MARKET_REJECTION

4

SET_CLOSE_FACTOR_OWNER_CHECK

5

SET_CLOSE_FACTOR_VALIDATION

6

SET_COLLATERAL_FACTOR_OWNER_CHECK

7

SET_COLLATERAL_FACTOR_NO_EXISTS

8

SET_COLLATERAL_FACTOR_VALIDATION

9

SET_COLLATERAL_FACTOR_WITHOUT_PRICE

10

SET_IMPLEMENTATION_OWNER_CHECK

11

SET_LIQUIDATION_INCENTIVE_OWNER_CHECK

12

SET_LIQUIDATION_INCENTIVE_VALIDATION

13

SET_MAX_ASSETS_OWNER_CHECK

14

SET_PENDING_ADMIN_OWNER_CHECK

15

SET_PENDING_IMPLEMENTATION_OWNER_CHECK

16

SET_PRICE_ORACLE_OWNER_CHECK

17

SUPPORT_MARKET_EXISTS

18

SUPPORT_MARKET_OWNER_CHECK

19

SET_PAUSE_GUARDIAN_OWNER_CHECK

20

SET_BUM_MINT_RATE_CHECK

21

SET_BUMCONTROLLER_OWNER_CHECK

22

SET_MINTED_BUM_REJECTION

23

SET_TREASURY_OWNER_CHECK

24

CHUM_FOR_TEAM_CALCULATION_FAILED

CHUM Distribution Speeds

CHUM Speed

The "CHUM speed" unique to each market is an unsigned integer that specifies the amount of CHUM that is distributed, per block, to suppliers and borrowers in each market. This number can be changed for individual markets by calling the _setCompSpeed method through a successful ChumHum Governance proposal.

The following is the formula for calculating the rate that CHUM is distributed to each supported market.

utility = cTokenTotalBorrows * assetPrice
utilityFraction = utility / sumOfAllCOMPedMarketUtilities
marketCompSpeed = chumRate * utilityFraction

CHUM Distributed Per Block (All Markets)

The Comptroller contract’s chumRate is an unsigned integer that indicates the rate at which the protocol distributes CHUM to markets’ suppliers or borrowers, every Matic Chain block. The value is the amount of CHUM (in wei), per block, allocated for the markets. Note that not every market has CHUM distributed to its participants (see Market Metadata).

The chumRate indicates how much CHUM goes to the suppliers or borrowers, so doubling this number shows how much CHUM goes to all suppliers and borrowers combined. The code examples implement reading the amount of CHUM distributed, per Matic Chain block, to all markets.

Comptroller

uint public chumRate;

Solidity

Comptroller troll = Comptroller(0xABCD...);
// CHUM issued per block to suppliers OR borrowers * (1 * 10 ^ 18)
uint chumRate = troll.chumRate();
// Approximate CHUM issued per day to suppliers OR borrowers * (1 * 10 ^ 18)
uint chumRatePerDay = chumRate * 4 * 60 * 24;
// Approximate CHUM issued per day to suppliers AND borrowers * (1 * 10 ^ 18)
uint chumRatePerDayTotal = chumRatePerDay * 2;

Web3 1.2.6

const Comptroller = new web3.eth.Contract(ComptrollerAbi, ComptrollerAddress);
let chumRate = await Comptroller.methods.chumRate().call();
chumRate = chumRate / 1e18;
// CHUM issued to suppliers OR borrowers
const chumRatePerDay = chumRate * 4 * 60 * 24;
// CHUM issued to suppliers AND borrowers
const chumRatePerDayTotal = chumRatePerDay * 2;

CHUM Distributed Per Block (Single Market)

The Comptroller contract has a mapping called compSpeeds. It maps cToken addresses to an integer of each market’s CHUM distribution per Matic Chain block. The integer indicates the rate at which the protocol distributes CHUM to markets’ suppliers or borrowers. The value is the amount of CHUM (in wei), per block, allocated for the market. Note that not every market has CHUM distributed to its participants (see Market Metadata).

The speed indicates how much CHUM goes to the suppliers or the borrowers, so doubling this number shows how much CHUM goes to market suppliers and borrowers combined. The code examples implement reading the amount of CHUM distributed, per Matic Chain block, to a single market.

Comptroller

mapping(address => uint) public compSpeeds;

Solidity

Comptroller troll = Comptroller(0x123...);
address cToken = 0xabc...;
// CHUM issued per block to suppliers OR borrowers * (1 * 10 ^ 18)
uint compSpeed = troll.compSpeeds(cToken);
// Approximate CHUM issued per day to suppliers OR borrowers * (1 * 10 ^ 18)
uint compSpeedPerDay = compSpeed * 4 * 60 * 24;
// Approximate CHUM issued per day to suppliers AND borrowers * (1 * 10 ^ 18)
uint compSpeedPerDayTotal = compSpeedPerDay * 2;

Web3 1.2.6

const cTokenAddress = '0xabc...';
const Comptroller = new web3.eth.Contract(ComptrollerAbi, ComptrollerAddress);
let compSpeed = await Comptroller.methods.compSpeeds(cTokenAddress).call();
compSpeed = compSpeed / 1e18;
// CHUM issued to suppliers OR borrowers
const compSpeedPerDay = compSpeed * 4 * 60 * 24;
// CHUM issued to suppliers AND borrowers
const compSpeedPerDayTotal = compSpeedPerDay * 2;

Claim CHUM

Every ChumHum user accrues CHUM for each block they are supplying to or borrowing from the protocol. Users may call the Comptroller's claimComp method at any time to transfer CHUM accrued to their address.

Comptroller

// Claim all the CHUM accrued by holder in all markets
function claimComp(address holder) public
// Claim all the CHUM accrued by holder in specific markets
function claimComp(address holder, CToken[] memory cTokens) public
// Claim all the CHUM accrued by specific holders in specific markets for their supplies and/or borrows
function claimComp(address[] memory holders, CToken[] memory cTokens, bool borrowers, bool suppliers) public

Solidity

Comptroller troll = Comptroller(0xABCD...);
troll.claimComp(0x1234...);

Web3 1.2.6

const Comptroller = new web3.eth.Contract(ComptrollerAbi, ComptrollerAddress);
await Comptroller.methods.claimComp("0x1234...").send({ from: sender });

Market Metadata

The Comptroller contract has an array called getAllMarkets that contains the addresses of each cToken contract. Each address in the getAllMarkets array can be used to fetch a metadata struct in the Comptroller’s markets constant. See the Comptroller Storage contract for the Market struct definition.

Comptroller

CToken[] public getAllMarkets;

Solidity

Comptroller troll = Comptroller(0xABCD...);
CToken cTokens[] = troll.getAllMarkets();

Web3 1.2.6

const Comptroller = new web3.eth.Contract(ComptrollerAbi, ComptrollerAddress);
const cTokens = await Comptroller.methods.getAllMarkets().call();
const cToken = cTokens[0]; // address of a cToken