Week 16: FFI and C Interoperability (Advanced)

Overview

Week 16 focuses on Rust’s Foreign Function Interface (FFI) capabilities, allowing seamless integration with C and other languages. You’ll learn how to create and consume C-compatible APIs, manage memory safely across language boundaries, and build reliable bindings to existing libraries. These skills are essential for systems programming and leveraging existing code ecosystems.

Day 1-3: Rust to C and C to Rust

Topics

• Understanding C ABI (Application Binary Interface)
• extern blocks and functions
• Creating C-compatible Rust APIs:
  • #[no_mangle] attribute
  • extern "C" function declaration
  • C-compatible types
  • Proper error handling
• Using C libraries from Rust:
  • Declaring external functions
  • Type mappings between Rust and C
  • Handling C error patterns
• The libc crate and platform types
• Linking with C code:
  • Static vs dynamic linking
  • Build systems integration
  • Conditional compilation
• Exposing Rust to C/C++:
  • Creating C-compatible libraries
  • Header file generation
  • Packaging for consumption by C/C++
• cbindgen and bindgen tools

Resources

• Rust FFI Omnibus
• Rustonomicon: FFI Chapter
• Bindgen User Guide
• C Types in Rust
• Using C Libraries in Rust
• CBingen Documentation

Use Cases

• Integrating with existing C/C++ codebases
• Creating Rust libraries usable from C/C++
• Interacting with system libraries
• Performance-critical code using C libraries
• Gradual migration from C/C++ to Rust
• Cross-language library development

Day 4-7: Advanced FFI Techniques

Topics

• Memory management across boundaries:
  • Ownership transfer between languages
  • Safe memory handling practices
  • Dealing with malloc/free vs Rust allocators
• Managing C strings and raw pointers:
  • CStr and CString types
  • String conversion strategies
  • Null termination and safety
• Working with callbacks:
  • Function pointers in FFI
  • Safety considerations with callbacks
  • Closures and FFI
  • Lifetime issues with callbacks
• Handling complex data structures:
  • Slices and arrays
  • Structs with special layout
  • Enums and unions
  • Generic types in FFI
• Async Rust and C interop
• Error handling across FFI boundaries
• Threading and synchronization issues
• Panics and unwinding across language boundaries
• Creating comprehensive bindings with multiple tools

Resources

• Advanced FFI Techniques
• C Strings in Rust
• FFI with Callbacks
• Memory Management in FFI
• Handling Errors in FFI
• Rust Bindgen Cookbook

Use Cases

• Audio/video processing with C libraries
• Game engine integration
• Operating system interfaces
• Hardware acceleration via C libraries
• Plugin systems across language boundaries
• Embedded systems with mixed codebases

Exercises

1. Create a simple Rust function that can be called from C
2. Write Rust bindings for a small C library
3. Implement a callback system where C code calls into Rust functions
4. Create a wrapper around a C API that provides a safe Rust interface
5. Build a Rust library that can be used from both Rust and C
6. Develop a memory management strategy for resources shared between Rust and C

Advanced Challenges

1. Create bindings for a complex C library with many types and functions
2. Implement a bidirectional callback system between Rust and C
3. Build a plugin system where C plugins can be loaded into a Rust application
4. Create a safe Rust wrapper for a complex C API with numerous safety concerns
5. Develop a zero-copy data exchange mechanism between Rust and C

Next Steps

After completing Week 16, you’ll be able to confidently integrate Rust with C and other languages through FFI. Week 17 will build on this foundation by exploring low-level programming, including memory-mapped I/O, OS interfaces, and even inline assembly for direct hardware interaction.