Listings & the order book

A listing is the only object Lendr has. There are no separate "market" or "vault" records — the entire protocol state is a growing array of MarketListing structs, indexed by an incrementing id starting at 1.

struct MarketListing {
  address borrower;
  address lender;          // zero address until filled
  address collateralToken;
  address loanToken;       // always USDG today
  uint256 collateralAmount;
  uint256 loanAmount;
  uint16  aprBps;          // APR in basis points, e.g. 800 = 8%
  uint32  duration;        // seconds
  uint64  createdAt;
  uint64  startTime;       // 0 until filled, then the fill block's timestamp
  uint8   status;          // see the status enum below
}

The status enum

Invariants worth knowing

• ids are never reused and never deleted — getListing(id) always returns something, even long after a listing is settled.
• lender is the zero address for the entire time a listing is open. It's set exactly once, in fillListing, and never changes after.
• collateralAmount and loanAmount are fixed at createListing and never change — there's no top-up, no partial repayment, no partial fill.
• startTime is the source of truth for maturity, and it's set from the block timestamp of the transaction that called fillListing — not from createdAt. Two listings created at the same moment can mature at completely different times depending on when each gets filled.
• aprBps and duration are set once at creation and used verbatim by interestOwed for the life of the loan, regardless of when — or whether — it's repaid.