Project 8: Plugin System with Dynamic Loading (Traits as Interfaces)

A host application that loads plugins at runtime from shared libraries (.so/.dll), where plugins implement a trait interface—demonstrating Rust’s approach to polymorphism and FFI.

Quick Reference

Attribute Value
Primary Language Rust
Alternative Languages C (traditional FFI approach)
Difficulty Level 3: Advanced
Time Estimate 2-3 weeks
Knowledge Area Traits / Dynamic Dispatch / FFI / ABI
Tooling libloading, abi_stable crate
Prerequisites Projects 1 and 5 completed, understanding of trait bounds

What You Will Build

A host application that loads plugins at runtime from shared libraries (.so/.dll), where plugins implement a trait interface—demonstrating Rust’s approach to polymorphism and FFI.

Why It Matters

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

Core Challenges

  • Defining a stable plugin ABI → maps to understanding why Rust has no stable ABI
  • Loading shared libraries at runtime → maps to FFI and unsafe boundaries
  • Using trait objects for dynamic dispatch → maps to dyn Trait and vtables
  • Ensuring plugin safety → maps to sandboxing considerations

Key Concepts

  • Traits and trait objects: “The Rust Programming Language” Chapter 17 - Steve Klabnik
  • Dynamic dispatch (dyn): “Rust for Rustaceans” Chapter 2 - Jon Gjengset
  • FFI: “The Rust Programming Language” Chapter 19 - Steve Klabnik
  • ABI stability: abi_stable crate documentation

Real-World Outcome

$ ls plugins/
greeting_plugin.so
math_plugin.so
weather_plugin.so

$ cargo run
🔌 Plugin Host v1.0
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Loading plugins from ./plugins/

✅ Loaded: greeting_plugin v1.0
   Commands: greet, farewell
✅ Loaded: math_plugin v2.1
   Commands: add, multiply, factorial
✅ Loaded: weather_plugin v1.2
   Commands: forecast, temperature

> greet Alice
[greeting_plugin] Hello, Alice! Welcome!

> factorial 10
[math_plugin] 10! = 3628800

> forecast London
[weather_plugin] London: Cloudy, 12°C, 80% humidity

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_DEEP_DIVE.md
  • “Rust for Rustaceans” by Jon Gjengset