Toucan

A C frontend and Rust binding generator, written in Rust.

Warning

This README is human-edited, but all code changes, PR summaries, and additional documentation were authored entirely by GPT-6 Astra in Codex. Use at your own risk.

Highlights

• Generate Rust bindings without libclang or a C compiler.
• Preprocess, type-check, and inspect C headers from the command line.
• Evaluate constants and compute type layouts for an explicit target, independently of the host.
• Embed the frontend in your own tools through reusable Rust libraries.

Project	Toucan	bindgen 0.72.1	Speedup
zlib 1.3.1	17.24 ms	122.04 ms	7.05×
SQLite 3.45.1	17.03 ms	161.75 ms	9.52×
zstd 1.5.7	6.84 ms	106.66 ms	15.54×
libgit2 1.9.1	152.78 ms	265.29 ms	1.76×

Toucan is fuzz-tested and checked against GCC, Clang, and bindgen, with native C/Rust tests for zlib, SQLite, zstd, and libgit2.

Installation

Install from Git with Rust 1.96 or later:

cargo install --git https://github.com/astral-sh/toucan toucan_cli --bin toucan --locked

Headers that include system or compiler headers need the corresponding sysroot and include paths.

Getting started

Given a C header, api.h:

#define API_VERSION 1

typedef struct api_point {
    double x;
    double y;
} api_point;

int api_translate(api_point *point, double dx, double dy);

Generate Rust bindings:

toucan bindgen api.h --target x86_64-unknown-linux-gnu \
  --allowlist 'api_*' --allowlist 'API_*' --output bindings.rs

This produces the following declarations in bindings.rs:

#[repr(C)]
#[derive(Clone, Copy)]
pub struct api_point {
    pub x: ::core::primitive::f64,
    pub y: ::core::primitive::f64,
}

unsafe extern "C" {
    pub fn api_translate(
        arg0: *mut api_point,
        arg1: ::core::primitive::f64,
        arg2: ::core::primitive::f64,
    ) -> ::core::ffi::c_int;
}
pub const API_VERSION: ::core::primitive::i32 = 1;

The generated file also includes compile-time target and layout checks, omitted here. See the binding guide for output options and build-script integration.

Toucan can also preprocess, check, and inspect headers:

toucan preprocess api.h --output api.i
toucan check api.h
toucan inspect api.h --output api.json

See the command-line guide for target configuration and header analysis, or the library guide to use Toucan from Rust.

License

Toucan is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Toucan by you, as defined in the Apache-2.0 license, shall be dually licensed as above, without any additional terms or conditions.