[rust/en] FFI examples #5429
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[rust/en] FFI examples #5429
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Added Section 6: FFI (Foreign Function Interface) covering: **Calling C from Rust:** - extern blocks for declaring C functions - unsafe blocks for calling FFI functions - Calling standard C library functions (abs, sqrt, puts) **C-compatible types:** - #[repr(C)] for structs, enums, and unions - Type layout matching C expectations - Opaque types for hidden C struct internals - Type aliases for C types (c_int, c_char) **Exposing Rust to C:** - #[no_mangle] attribute to prevent name mangling - pub extern "C" functions callable from C - Null pointer validation - Processing C data structures from Rust **String handling:** - CString for Rust → C string conversion - CStr for C → Rust string conversion - UTF-8 validation and error handling - Safe conversion patterns **Advanced patterns:** - Function pointers and callbacks (extern "C" fn) - Opaque handles with safe wrappers - Passing arrays/slices to C functions - Output parameters (mutable pointers) - RAII pattern with Drop for cleanup **Build integration:** - Linking to C libraries with build.rs - Using cc crate to compile C code - #[link] attribute for system libraries - bindgen for auto-generating bindings from headers **Safety guidelines:** - 7 key safety rules for FFI code - Safe wrapper pattern around unsafe FFI - Pointer validation (null checks) - Lifetime and ownership considerations - SafeHandle example with Drop implementation **Resources:** - Updated Further Reading with FFI-specific links - Rustonomicon FFI chapter - Rust FFI Omnibus - bindgen, cbindgen, libc documentation Tutorial expanded from 363 to 596 lines (+233 lines, 64% increase). 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <[email protected]>
Based on deep analysis of dit-service-rust codebase, added 6 production-tested patterns from a real-world cross-platform library: **Pattern 1: Multi-Mode Callback System** - Enum supporting Rust closures, C function pointers, and JNI callbacks - Context pointer pattern for stateful C callbacks - unsafe impl Send/Sync with safety documentation - Platform-specific variants with #[cfg(target_os)] **Pattern 2: Safe Function Pointer Comparison** - Using std::ptr::fn_addr_eq instead of direct == comparison - Manual PartialEq implementation for platform-specific code - Proper handling of function pointer uniqueness guarantees **Pattern 3: Dependency Injection via Function Pointers** - HttpRequest/HttpResponse/HttpError structs - Platform HTTP client injection (NSURLSession, OkHttp) - Global function pointer registration pattern - Clear memory ownership contracts in struct docs **Pattern 4: Null-Terminated Array Handling** - Freeing C-allocated string arrays - Iterating until NULL terminator - Proper cleanup of nested malloc'd structures - Using libc::free for C-allocated memory **Pattern 5: JSON-Wrapped Error Returns** - Never failing silently in FFI - Structured error responses with codes and messages - Success and error paths return same JSON format - C callers parse consistent response structure **Pattern 6: Singleton Management with OnceLock** - Thread-safe one-time initialization - AtomicBool for destruction tracking - Preventing use-after-free with atomic flags - Proper mutex + Box::from_raw pattern - Non-recreatable after destruction **Additional enhancements:** - Real-world examples from production iOS/Android library - Memory safety patterns for cross-platform code - Platform-aware conditional compilation - Clear ownership and lifetime documentation Tutorial expanded from 596 to 793 lines (+197 lines, 33% increase). These patterns are extracted from dit-service-rust, a production library serving iOS, Android, and WebAssembly with comprehensive FFI bridges and multi-platform support. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <[email protected]>
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Found this: https://bhh32.com/posts/tutorials/rust_ffi |
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