safer_ffi is a framework that helps you write foreign function interfaces (FFI) without polluting your Rust code with unsafe { ... } code blocks while making functions far easier to read and maintain.
Minimum Supported Rust Version: 1.66.1
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You may try working with the examples/point example embedded in the repo:
git clone https://github.com/getditto/safer_ffi && cd safer_ffi
(cd examples/point && make)Otherwise, to start using ::safer_ffi, follow the following steps:
Edit your Cargo.toml like so:
[package]
name = "crate_name"
version = "0.1.0"
edition = "2021"
[lib]
crate-type = [
"staticlib", # Ensure it gets compiled as a (static) C library
# "cdylib", # If you want a shared/dynamic C library (advanced)
"lib", # For `generate-headers` and other downstream rust dependents
# such as integration `tests/`, doctests, and `examples/`
]
[[bin]]
name = "generate-headers"
required-features = ["headers"] # Do not build unless generating headers.
[dependencies]
# Use `cargo add` or `cargo search` to find the latest values of x.y.z.
# For instance:
# cargo add safer-ffi
safer-ffi.version = "x.y.z"
safer-ffi.features = [] # you may add some later on.
[features]
# If you want to generate the headers, use a feature-gate
# to opt into doing so:
headers = ["safer-ffi/headers"]-
Where
"x.y.z"ought to be replaced by the last released version, which you can find by runningcargo search safer-ffi. -
See the dedicated chapter on
Cargo.tomlfor more info.
Then, to export a Rust function to FFI, add the
#[derive_ReprC] and #[ffi_export] attributes
like so:
use ::safer_ffi::prelude::*;
/// A `struct` usable from both Rust and C
#[derive_ReprC]
#[repr(C)]
#[derive(Debug, Clone, Copy)]
pub struct Point {
x: f64,
y: f64,
}
/* Export a Rust function to the C world. */
/// Returns the middle point of `[a, b]`.
#[ffi_export]
fn mid_point(a: &Point, b: &Point) -> Point {
Point {
x: (a.x + b.x) / 2.,
y: (a.y + b.y) / 2.,
}
}
/// Pretty-prints a point using Rust's formatting logic.
#[ffi_export]
fn print_point(point: &Point) {
println!("{:?}", point);
}
// The following function is only necessary for the header generation.
#[cfg(feature = "headers")] // c.f. the `Cargo.toml` section
pub fn generate_headers() -> ::std::io::Result<()> {
::safer_ffi::headers::builder()
.to_file("rust_points.h")?
.generate()
}- See the dedicated chapter on
src/lib.rsfor more info.
fn main() -> ::std::io::Result<()> {
::crate_name::generate_headers()
}# Compile the C library (in `target/{debug,release}/libcrate_name.ext`)
cargo build # --release
# Generate the C header
cargo run --features headers --bin generate-headers- See the dedicated chapter on header generation for more info.
Generated C header (rust_points.h)
/*! \file */
/*******************************************
* *
* File auto-generated by `::safer_ffi`. *
* *
* Do not manually edit this file. *
* *
*******************************************/
#ifndef __RUST_CRATE_NAME__
#define __RUST_CRATE_NAME__
#ifdef __cplusplus
extern "C" {
#endif
#include <stddef.h>
#include <stdint.h>
/** \brief
* A `struct` usable from both Rust and C
*/
typedef struct Point {
/** <No documentation available> */
double x;
/** <No documentation available> */
double y;
} Point_t;
/** \brief
* Returns the middle point of `[a, b]`.
*/
Point_t
mid_point (
Point_t const * a,
Point_t const * b);
/** \brief
* Pretty-prints a point using Rust's formatting logic.
*/
void
print_point (
Point_t const * point);
#ifdef __cplusplus
} /* extern \"C\" */
#endif
#endif /* __RUST_CRATE_NAME__ */Here is a basic example to showcase FFI calling into our exported Rust functions:
#include <stdlib.h>
#include "rust_points.h"
int
main (int argc, char const * const argv[])
{
Point_t a = { .x = 84, .y = 45 };
Point_t b = { .x = 0, .y = 39 };
Point_t m = mid_point(&a, &b);
print_point(&m);
return EXIT_SUCCESS;
}cc -o main{,.c} -L target/debug -l crate_name -l{pthread,dl,m}
# Now feel free to run the compiled binary
./main-
Note regarding the extra
-l…flags.Those vary based on the version of the Rust standard library being used, and the system being used to compile it. In order to reliably know which ones to use,
rustcitself ought to be queried for it.Simple command:
rustc --crate-type=staticlib --print=native-static-libs -</dev/nullthis yields, to the stderr, output along the lines of:
note: Link against the following native artifacts when linking against this static library. The order and any duplication can be significant on some platforms. note: native-static-libs: -lSystem -lresolv -lc -lm -liconvUsing something like
sed -nE 's/^note: native-static-libs: (.*)/\1/p'is thus a convenient way to extract these flags:rustc --crate-type=staticlib --print=native-static-libs -</dev/null \ 2>&1 | sed -nE 's/^note: native-static-libs: (.*)/\1/p'
Ideally, you would not query for this information in a vacuum (e.g.,
/dev/nullfile being used as input Rust code just above), and rather, would apply it for your actual code being compiled:cargo rustc -q -- --print=native-static-libs \ 2>&1 | sed -nE 's/^note: native-static-libs: (.*)/\1/p'And if you really wanted to polish things further, you could use the JSON-formatted compiler output (this, for instance, avoids having to redirect
stderr). But then you'd have to use a JSON parser, such asjq:RUST_STDLIB_DEPS=$(set -eo pipefail && \ cargo rustc \ --message-format=json \ -- --print=native-static-libs \ | jq -r ' select (.reason == "compiler-message") | .message.message ' | sed -nE 's/^native-static-libs: (.*)/\1/p' \ )
and then use:
cc -o main{,.c} -L target/debug -l crate_name ${RUST_STDLIB_DEPS}
which does output:
Point { x: 42.0, y: 42.0 }
🚀🚀
safer-ffi includes three different tests suites that can be run.
# In the project root:
cargo test
# FFI tests
make -C ffi_tests
# JavaScript tests
make -C js_tests
# Running the JS tests also gives you instructions for running browser tests.
# Run this command in the `js_tests` directory, open a browser and navigate to
# http://localhost:13337/
wasm-pack build --target web && python3 -m http.server 13337