Crate Organization Patterns

In this lesson, you will learn how to structure complex Rust projects into clean, maintainable hierarchies using crate organization patterns.

As a project grows—especially one interfacing with C libraries—keeping your src/ directory clean becomes critical. When you have high-level business logic mixed with low-level FFI bindings and platform-specific build logic, you risk creating a "monolithic" crate that is difficult to test and slow to compile.

The Workspace Pattern

The most robust approach is to leverage a Cargo Workspace. By splitting your project into logical crates, you enforce boundaries that prevent circular dependencies and simplify unit testing. A common pattern for an FFI-heavy project looks like this:

• -sys/: Contains the raw bindgen output and build.rs script. This crate should be minimal and expose only the unsafe FFI bindings.
• -core/: Contains the high-level, safe Rust abstractions. This crate depends on -sys and provides memory-safe wrappers, trait implementations, and error handling.
• -cli or -app/: The consumer crate that uses your core library to perform actual work.

Why this pattern works

By separating the sys crate, you ensure that any recompilation of your business logic doesn't trigger the costly bindgen process or re-linking of the C libraries unless strictly necessary. Furthermore, it forces you to explicitly define a public API in your core crate. If you find yourself trying to use an unsafe C type directly in your cli crate, it’s a clear signal that your core abstractions are leaking implementation details.

// Cargo.toml (Workspace root)
[workspace]
members = ["my-lib-sys", "my-lib-core"]

// my-lib-core/src/lib.rs
// Uses re-exports to keep the public surface clean
pub use my_lib_sys as ffi; 
pub mod safe_wrapper; 

By enforcing these boundaries, you treat your internal C-bindings as a separate dependency, mirroring how you would treat a third-party crate. This makes the project modular, easier to audit for memory safety, and significantly cleaner for future maintenance.

Key Takeaway: Use a workspace to isolate raw FFI bindings in a -sys crate, separating low-level unsafe implementations from high-level, type-safe abstractions.