bxc Rust FFI Bridge

bxc Rust FFI (cdylib for Bun)

The hot path of bxc lives in Rust, exposed to Bun via cdylib + N-API style FFI (or raw extern "C" with bun:ffi or manual).

Crate Layout (in rust-bridge/)

• bxc-rust-bridge (the cdylib crate exporting bxc_* symbols)
• crates/x-client (native X GraphQL/REST + rusqlite store + ranking helpers)
• crates/x-algorithm (pure Rust port of xai-org/x-algorithm For You ranking, used via FFI or re-exported)

Critical Rules

• Single rusqlite: libsqlite3-sys "links" = "sqlite3". Only one version of rusqlite (0.37) can be linked in the cdylib. All crates in the workspace must use { workspace = true } for rusqlite.
• Workspace Cargo.toml: Define [workspace.dependencies] rusqlite = { version = "0.37", features = ["bundled"] } etc. Use in member crates.
• no_mangle + extern "C": For symbols called from Bun (or via the bridge lib).
• Async in FFI: Use tokio::runtime::Builder::new_current_thread().enable_all().build().unwrap().block_on(...) inside the extern "C" fn. Never leak runtimes.
• Error handling: Return *mut c_char (JSON or null). Caller frees with CString.
• Build: cargo build -p bxc-rust-bridge --release (or via bun run build:linux). Output in rust-bridge/target/release/libbxc_rust_bridge.{so,dylib,dll}

Cross-Platform Notes

• Linux: .so (default target)
• macOS: .dylib (x86_64-apple-darwin + aarch64-apple-darwin for universal if needed)
• Windows: .dll (x86_64-pc-windows-msvc). Also produce .exe for standalone tools.
• In Bun code: use dlopen with platform-specific name or process.platform + process.arch to pick the right file. Provide BXC_RUST_BRIDGE_LIB override.

Common FFI Pattern (from bxc)

#[no_mangle]
pub extern "C" fn bxc_x_algorithm_rank(
    candidates_json: *const c_char,
    context_json: *const c_char,
    top_k: i32,
) -> *mut c_char {
    // parse with serde, call pure algo, return CString::new(json).unwrap().into_raw()
}

Bun side lazily dlopen the lib on first use; falls back to pure JS for some paths (title, stripTags, markdown) if cdylib missing.