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mgeisler merged 1 commit into from
Feb 12, 2026
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unsafe-rust: add explanatory commentary to solution #3064

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25 changes: 25 additions & 0 deletions src/unsafe-rust/solution.md
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Expand Up @@ -3,3 +3,28 @@
```rust,editable
{{#include exercise.rs:solution}}
```

- **Safety Comments:** Each `unsafe` block is preceded by a `// SAFETY:` comment
explaining why the operation is safe. This is standard practice in Rust to aid
auditing.
- **String conversions:** The code demonstrates the conversions required for
FFI:
- `&str` -> `CString`: To create a null-terminated string for C.
- `CString` -> `*const c_char`: To pass the pointer to C.
- `*const c_char` -> `&CStr`: To wrap the returned C string.
- `&CStr` -> `&[u8]` -> `&OsStr` -> `OsString`: To convert the bytes back to a
Rust OS string.
- **RAII (`Drop`):** We implement `Drop` to call `closedir` automatically when
the iterator goes out of scope. This ensures we don't leak file descriptors.
- **Iterator Interface:** We wrap the C API in a Rust `Iterator`, providing a
safe and idiomatic interface (`next` returns `Option<OsString>`) to the
underlying unsafe C functions.

<details>

- Explain that `CString` owns the data (like `String`), while `CStr` is a
borrowed reference (like `&str`).
- The `OsStrExt` trait is needed on Unix systems to convert bytes directly to
`OsStr`.

</details>