The C libffi library provides two main facilities: assembling calls to functions dynamically, and creating closures that can be called as ordinary C functions. In Rust, the latter means that we can turn a Rust lambda (or any object implementing Fn/FnMut) into an ordinary C function pointer that we can pass as a callback to C.
Building libffi will build lifbffi-sys, which will in turn build the libffi C library from github, which requires that you have a working make, C compiler, automake, and autoconf first. It’s on crates.io, so you can add
[dependencies] libffi = "3.2.0"
to your Cargo.toml.
This crate depends on the libffi-sys crate, which by default attempts to build its own version of the C libffi library. In order to use your system’s C libffi instead, enable this crate’s system feature in your Cargo.toml:
[features] libffi = { version = "3.2.0", features = ["system"] }
See the libffi-sys documentation for more information about how it finds C libffi.
This crate supports Rust version 1.48 and later.
In this example, we convert a Rust lambda containing a free variable into an ordinary C code pointer. The type of fun below is extern "C" fn(u64, u64) -> u64.
use libffi::high::Closure2; let x = 5u64; let f = |y: u64, z: u64| x + y + z; let closure = Closure2::new(&f); let fun = closure.code_ptr(); assert_eq!(18, fun(6, 7));