A minimal, production-ready Rust reference demonstrating atomic composable flash loans on Save Finance (formerly Solend) using solana-sdk 2.x and Versioned Transactions (v0).

Overview

Unlike legacy CPI callback patterns, composable flash loans on Save Finance utilize instructions introspection via sysvar::instructions:

1. FlashBorrowReserveLiquidity (#19) — Borrows reserve liquidity.
2. Arbitrage / Swaps — Arbitrary business logic executed between borrow and repay.
3. FlashRepayReserveLiquidity (#20) — Repays the borrowed amount + protocol fees, introspecting the earlier borrow instruction.

Key Considerations Solved:

• Dynamic Introspection Indexing: The repay instruction requires the exact 0-based index of the matching borrow instruction (borrow_instruction_index). This implementation dynamically computes the index regardless of prepended Compute Budget or setup instructions.
• Fee Receiver Layout: Handles the protocol's requirement of using the Associated Token Account (ATA) of the reserve fee receiver rather than the wallet pubkey (0xd / InvalidAccountInput).

Quickstart

Prerequirements

• Rust
• A funded Solana keypair located at ~/.config/solana/id.json

1. Clone repository

git clone https://github.com/TrinityWeb3/save-flash-loan-rust.git
cd save-flash-loan-rust

Simulation transaction

cargo run

TxID

Solscan: 4ZTVMEjBnjDRHtjF14nd8jQ44aksN9Ln6nReP8TnhYfLYwrpeXeXgpB5An1zqrFBapTPL7EXSurfU1VxxuCLE1Rz