multiversx-flash-loan-patterns_skill

Overview

This skill implements the MultiversX atomic lend-execute-verify pattern for smart contracts. It provides a concise, secure template to lend assets, execute a callback on a target contract, and verify repayment (plus fee) within a single transaction. Use it to build flash loans, atomic swaps, and temporary grants that must be fully repaid before completion.

How this skill works

The pattern enforces a guarded flow: set a reentrancy guard, validate the target is on the same shard, validate the callback endpoint, record the contract balance, send assets and call the target, then re-check the balance to ensure repayment plus fee. If verification fails, the transaction reverts and no state persists. The template includes storage mappers, shard checks, endpoint validation, fee calculation, and guard lifecycle management.

When to use it

• Flash loans that must lend and be repaid atomically within one transaction
• Atomic swaps where you must verify the counterparty returned assets before finalizing
• Temporary grants where assets are lent for a callback and must be returned immediately
• Any operation that requires on-chain, same-shard atomicity for asset lending
• Avoid for simple transfers or cross-shard flows that cannot be atomic

Best practices

• Always set a reentrancy guard before sending assets and clear it only after verification
• Require the target contract to be on the same shard to guarantee atomicity
• Validate callback endpoints and disallow built-in functions that could bypass logic
• Check actual on-chain contract balance (get_sc_balance) rather than internal storage counters
• Compute and require fee repayment explicitly (e.g., fee basis points) to prevent loss

Example use cases

• A flash-loan provider lending ESDT tokens for arbitrage and verifying repayment plus fee in the same call
• An atomic swap contract sending tokens to a counterparty, invoking their execute endpoint, and ensuring tokens returned before completing
• A compute grant that lends tokens to run a gas-heavy callback and enforces immediate return
• A liquidation helper that temporarily supplies collateral to trigger a repay-and-return flow in one transaction