Stylus Challenges

Stylus Challenges#

These challenges are designed to test your understanding of the Stylus smart contract concepts covered in Chapter 3. Each challenge is a partially implemented Rust contract that you need to complete. The source code for each challenge (and solutions) is available in the repository under stylus-challenges/ and stylus-challenges-solved/.

Note

The contract code in these challenges was not written with ERC20 safety in mind. There are no return value checks. Not for production!

Challenge 1: Vault#

This is a simple ERC-20 token vault. Users can deposit tokens and receive shares proportional to their deposit. Later they can burn their shares to withdraw the underlying tokens. Your job is to implement the deposit and withdraw functions.

The vault uses a share-based accounting system: when you deposit tokens, you receive shares based on the ratio of your deposit to the total assets in the vault. When you withdraw, you burn shares and receive tokens proportional to your share of the vault.

Key concepts tested:

  • sol_interface! for calling external ERC-20 contracts

  • Storage maps and arithmetic with U256

  • Custom Solidity errors via sol! and SolidityError

Challenge 2: Paid Email#

This is a paid email service where recipients stipulate an amount of a token they must receive to accept email. Senders must pay that amount to add their CID email content to the queue.

The DID content should be encrypted to the recipient’s public key to avoid revealing the content.

Key concepts tested:

  • Complex storage layouts with nested maps and vectors

  • Timestamp-based logic and refund windows

  • Multi-token support via sol_interface!

  • Epoch-based time tracking

Challenge 3: Lending#

A simple single-asset lending protocol. Users can supply collateral, borrow against it, and repay with interest. The protocol tracks borrow positions using tickets and time-weighted interest accumulation.

Key concepts tested:

  • Interest rate calculations with timepoints

  • Collateral requirements and liquidation logic

  • Ticket-based position tracking

  • Macro usage for assertion patterns (assert_or!)

Tip

Start with Challenge 1 (Vault) as it is the simplest. Each challenge builds on concepts from the previous one. If you get stuck, the solved versions are in the stylus-challenges-solved/ directory.