Flash Actions

Step-by-step guide to building atomic strategies with Lotus flash loans and callbacks, including leveraged positions, refinancing, and collateral swaps.

Flash actions let you execute complex, atomic strategies in a single transaction using flash loans and optional callbacks.

Common use cases:

Lever up or down a position atomically.
Refinance between tranches or markets.
Collateral swaps and liquidation integrations.

How it works:

Flash loan transfers assets to your contract, calls your callback, then requires repayment by the end of the transaction.
Supply/repay/liquidate/collateral operations accept optional callback data. When configured, Lotus calls back into your contract so you can complete multi-step flows without intermediate state risk.

┌─────────────────────────────────────────────────────────────────────┐
│              Flash Loan and Callback Sequence                       │
└─────────────────────────────────────────────────────────────────────┘

  Caller Contract          Lotus Core           Caller Callback
  ───────────────          ──────────          ───────────────

       │                      │                       │
       │  flashLoan(...)      │                       │
       ├─────────────────────►│                       │
       │                      │                       │
       │                      │  Transfer assets      │
       │◄─────────────────────┤                       │
       │                      │                       │
       │                      │  onFlashLoan(...)     │
       │                      ├──────────────────────►│
       │                      │                       │
       │                      │              Execute custom logic:
       │                      │              - Swap assets
       │                      │              - Supply collateral
       │                      │              - Borrow from tranche
       │                      │              - Arbitrage
       │                      │                       │
       │                      │    Return control     │
       │                      │◄──────────────────────┤
       │                      │                       │
       │                      │  Verify repayment     │
       │  Repay exact amount  │  (no fee)             │
       ├─────────────────────►│                       │
       │                      │                       │
       │    Success ✓         │                       │
       │◄─────────────────────┤                       │
       │                      │                       │

Integration tips:

Ensure callback contracts are minimal and non-reentrant with clear allowlists.
Validate amounts and state before returning from callbacks.
Prefer known-good routers and auditors’ patterns for token transfers.