Token Lending Program

Overview

This project implements a lending protocol for Solana blockchain, forked from solana-program-library/token-lending.

Notable Changes

This project includes several significant modifications and enhancements over the original implementation:

1. Collateral Rate Calculation Bug: as the original repo is marked as archived, I have to fix bug in this repo, and described it it.

2. Add Stateful Tests: In program/test/intergration.rs, and its dependent methods inside program/tests/stateful. I provided two stateful tests: One is Alice can borrow tokens and then successfully repay. Another test case is Alice can borrow tokens but fail to repay, so Bob come to liquidate the collateral of Alice. These stateful tests can help the developer to understand the business logic better, also it helps to find bugs as described in 1. Collateral rate calculation Bug.

3. Improved Error Handling: to handle the error, the original logic was like this:

   self.liquidity
       .compound_interest(current_borrow_rate, slots_elapsed)?;

   Which using ? to propagate the error, but errors from compound_interest are very generic, collectively named as LendingError::MathOverflow, which is not helpful what particular input makes the error. as rust solana program doesn't provide stack trace, so I use map_err to tap the error message with details:

   self.liquidity
     .compound_interest(current_borrow_rate, slots_elapsed)
     .map_err(|e| {
       debug_msg!(
           "Error in accrue_interest:, current_borrow_rate: {}, slots_elapsed: {}",
           current_borrow_rate,
           slots_elapsed
        );
       e
         })?;

   Also debug_msg! is a self-defined macro that only prints the error message in test-sbf and testnet. Note: avoid printing the log in mainnet is very important, because the log will be stored in blockchain permanently, which can increase the costs. Most importantly, too detailed log may help malicious hackers pinpoint possible loopholes of system.

4. Other Trivial Changes:

• Refactored many chunky rs files into modular architecture. As an example program/src/state/
• Cleared out sysvar accounts like Rent and Clock, which were required by old versions of solana, but since in new versions they can be populated by the program itself.
• Add assert_is_signer! to reduce boilerplate code of validating if an account is a signer, much like what Anchor does.
• In many test cases, it used &mut banks_client, but in the logic it doesn't mutate the state at all, so I changed it to &banks_client.otherwise it would cause compile error when calling a fn from another fn while both used mutable reference.
• refactored converting a decimal number to a whole number, using DECIMALS_LOOKUP array, which reduces the time complexity from O(log(n)) to O(1).

Usage

To run all tests:

cargo test-sbf --features test-sbf

To run a specific test, use a format like this :

cargo test-sbf --package spl-token-lending --test intergration --features test-sbf -- alice_can_borrow_sol_and_repay --exact --show-output

Note: Add --features test-sbf before positional arguments.

License

This project is licensed under the MIT License. See the LICENSE file for details.