async-ffi: FFI-compatible Futures

Convert your Rust Futures into a FFI-compatible struct without relying unstable Rust ABI and struct layout. Easily provide async functions in dynamic library maybe compiled with different Rust than the invoker.

See documentation for more details.

Provide some async functions in library: (plugin side)

// Compile with `crate-type = ["cdylib"]`.
use async_ffi::{FfiFuture, FutureExt};

#[no_mangle]
pub extern "C" fn work(arg: u32) -> FfiFuture<u32> {
    async move {
        let ret = do_some_io(arg).await;
        do_some_sleep(42).await;
        ret
    }
    .into_ffi()
}

Execute async functions from external library: (host or executor side)

use async_ffi::{FfiFuture, FutureExt};

extern "C" {
    #[no_mangle]
    fn work(arg: u32) -> FfiFuture<u32>;
}

async fn run_work(arg: u32) -> u32 {
    unsafe { work(arg).await }
}

By default FfiFuture requires the original Future to be Send. In case of single-threaded runtime or target (like wasm32-none-none), we may need to relax this requirement. So we have LocalFfiFuture, which is the almost the same as FfiFuture but without Send requirement.

// Compile with `crate-type = ["cdylib"]`, targeting `wasm32-none-none`.
use async_ffi::{LocalFfiFuture, FutureExt};

#[no_mangle]
pub extern "C" fn work(arg: u32) -> LocalFfiFuture<u32> {
    async move {
        let ret = do_some_io(arg).await;
        do_some_sleep(42).await;
        ret
    }
    .into_local_ffi()
}

abi-stable suppport

If you want to use this crate with abi-stable interfaces. You can enable the feature flag abi_stable (disabled by default), then the struct FfiFuture and friends would derive abi_stable::StableAbi.

License

MIT Licensed.