Borrow&Liquidate

Borrow

comptroller.borrowAllowed(cToken, borrower, borrowAmount);

CToken use these code to adjust user can borrow borrowAmount of underlying .

Then write accountBorrows[borrower] to save changes.

struct BorrowSnapshot {
    uint principal;
    uint interestIndex;
}
mapping(address => BorrowSnapshot) accountBorrows;

accountBorrows record borrow action of an account,
is used by borrowBalance.

const m = accountBorrows[user]; 
borrowBalance = user => m.principal * borrowIndex / m.interestIndex;

borroeRate

Using code below to get borrowRate from interestRateModel

interestRateModel.getBorrowRate(getCashPrior(), totalBorrows, totalReserves);

Input:

• getCashPrior: underlying balance of CToken.
• totalBorrows: total underlying borrowed.
• totalReserves: total reserves.

accrueInterest

main logic:

simpleInterestFactor = borrowRate * blockDelta
interestAccumulated = simpleInterestFactor * totalBorrows
totalBorrowsNew = interestAccumulated + totalBorrows
totalReservesNew = interestAccumulated * reserveFactor + totalReserves
borrowIndexNew = simpleInterestFactor * borrowIndex + borrowIndex

accrueInterest write:

• borrowIndex
• totalBorrows
• totalReserves

It seems that when borrow and repay called in the same block, there will be no interst.

repayBorrow

...

liquidateBorrow

Use code below to calc seize Amount

comptroller.liquidateCalculateSeizeTokens(address(this), address(cTokenCollateral), repayAmount);