Project 5: A Safe Wrapper around a C Library

A safe, idiomatic Rust wrapper around a C library like libz (for compression) or sqlite3. Your Rust library will expose a clean API that uses Result for errors and handles memory management automatically, hiding the unsafe C-level details.

Quick Reference

Attribute Value
Primary Language Rust
Alternative Languages C, Python (with ctypes)
Difficulty Level 4: Expert
Time Estimate 2-3 weeks
Knowledge Area Foreign Function Interface (FFI) / API Design
Tooling bindgen, libclang
Prerequisites Project 1, basic C knowledge.

What You Will Build

A safe, idiomatic Rust wrapper around a C library like libz (for compression) or sqlite3. Your Rust library will expose a clean API that uses Result for errors and handles memory management automatically, hiding the unsafe C-level details.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Linking to a C library → maps to using a build script (build.rs)
  • Generating Rust bindings for C functions → maps to using the bindgen tool
  • Calling unsafe C functions → maps to working with raw pointers and unsafe blocks
  • Creating safe abstractions → maps to wrapping raw pointers in structs that implement Drop for automatic cleanup, and converting C integer error codes into Rust Result types

Key Concepts

  • unsafe keyword: “The Rust Programming Language” Ch. 19
  • Foreign Function Interface (FFI): “The Rustonomicon” Ch. 6
  • The Drop Trait: “The Rust Programming Language” Ch. 15 (for custom cleanup logic)
  • Build Scripts (build.rs): The Cargo Book

Real-World Outcome

// The API you will build
use my_zlib_wrapper::compress;

fn main() -> Result<(), ZlibError> {
    let data = b"hello world";
    let compressed_data = compress(data, 5)?; // 5 is compression level

    // compressed_data is a Vec<u8>, memory is managed automatically.
    // The C-level z_stream, mallocs, and frees are all hidden.

    println!("Compressed: {:?}", compressed_data);
    Ok(())
}

// Contrast with the C API:
// You'd have to manually initialize a z_stream struct, allocate buffers,
// call deflate, check integer return codes, and then call deflateEnd.

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: LEARN_RUST_FROM_FIRST_PRINCIPLES.md
  • “The Rustonomicon” Ch. 6 (FFI)