BoltFFI

A high-performance multi-language bindings generator for Rust. Up to 1,000x faster than UniFFI. Up to 450x faster than wasm-bindgen.

<p align="center"> <img src="docs/assets/demo.gif" width="700" /> </p>

Quick links: User Guide | Tutorial | Getting Started

Performance

vs UniFFI (Swift/Kotlin)

| Benchmark | BoltFFI | UniFFI | Speedup | |-----------|--------:|-------:|--------:| | noop | <1 ns | 1,416 ns | >1000x | | echo_i32 | <1 ns | 1,416 ns | >1000x | | counter_increment (1k calls) | 1,083 ns | 1,388,895 ns | 1,282x | | generate_locations (1k structs) | 4,167 ns | 1,276,333 ns | 306x | | generate_locations (10k structs) | 62,542 ns | 12,817,000 ns | 205x |

vs wasm-bindgen (WASM)

| Benchmark | BoltFFI | wasm-bindgen | Speedup | |-----------|--------:|-------------:|--------:| | 1k particles | 29,886 ns | 13,532,530 ns | 453x | | 100 particles | 3,117 ns | 748,287 ns | 240x | | 1k locations | 21,931 ns | 4,037,879 ns | 184x | | 1k trades | 42,015 ns | 5,781,767 ns | 138x | | 100 locations | 2,199 ns | 283,753 ns | 129x |

Full benchmark code: benchmarks

Why BoltFFI?

Serialization-based FFI is slow. UniFFI serializes every value to a byte buffer. wasm-bindgen materializes every struct as a JavaScript object. That overhead shows up even when you're making tens or hundreds of FFI calls per second.

BoltFFI uses zero-copy where possible. Primitives pass as raw values. Structs with primitive fields pass as pointers to memory both sides can read directly. WASM uses a wire buffer format that avoids per-field allocation. Only strings and collections go through encoding.

What it does

Mark your Rust types with #[data] and functions with #[export]:

use boltffi::*;

#[data]
pub struct Point {
    pub x: f64,
    pub y: f64,
}

#[export]
pub fn distance(a: Point, b: Point) -> f64 {
    let dx = b.x - a.x;
    let dy = b.y - a.y;
    (dx * dx + dy * dy).sqrt()
}

Run boltffi pack:

boltffi pack apple
# Produces: ./dist/apple/YourCrate.xcframework + Package.swift

boltffi pack android
# Produces: ./dist/android/jniLibs/*.so + Kotlin bindings

boltffi pack wasm
# Produces: ./dist/wasm/pkg/*.wasm + TypeScript bindings + npm package

Use it from Swift, Kotlin, or TypeScript:

let d = distance(a: Point(x: 0, y: 0), b: Point(x: 3, y: 4)) // 5.0

val d = distance(a = Point(x = 0.0, y = 0.0), b = Point(x = 3.0, y = 4.0)) // 5.0

import { distance } from 'your-crate';
const d = distance({ x: 0, y: 0 }, { x: 3, y: 4 }); // 5.0

The generated bindings use each language's idioms. Swift gets async/await. Kotlin gets coroutines. TypeScript gets Promises. Errors become native exceptions.

Supported languages

| Language | Status | |----------|--------------| | Swift | Full support | | Kotlin | Full support | | Java | Full support | | WASM/TypeScript | Full support | | C | Partial | | Python | In progress | | C++ | Planned | | C# | Planned | | Ruby | Planned | | Dart | Planned | | Scala | Planned | | Go | Planned | | Lua | Potential | | R | Potential |

Want another language? Open an issue.

Installation

cargo install boltffi_cli

Add to your Cargo.toml:

[dependencies]
boltffi = "0.1"

[lib]
crate-type = ["staticlib", "cdylib"]

Documentation

• Overview
• Getting Started
• Tutorial
• Types
• Async
• Streaming

Alternative tools

Other tools that solve similar problems:

• UniFFI - Mozilla's binding generator, uses serialization-based approach
• Diplomat - Focused on C/C++ interop
• cxx - Safe C++/Rust interop

Contributing

Contributions are warmly welcomed 🙌

• File an issue
• Submit a PR

License

BOLTFFI is released under the MIT license. See LICENSE for more information.