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//! High layer providing automatic marshalling of Rust closures
//! as C function pointers.
//!
//! The main facility here is given by the structs
//! <code>Closure<em>N</em></code>,
//! <code>Closure<span></span>Mut<em>N</em></code>,
//! and <code>Closure<span></span>Once<em>N</em></code>,
//! for natural numbers *`N`*
//! from `0` to `12` (as of
//! now). These represent C closures of *`N`* arguments, which can be
//! used to turn Rust lambdas (or in generally, anything that implements
//! `Fn` or `FnMut`) into ordinary C function pointers. For example, a
//! Rust value of type `Fn(u32, u32) -> u64` can be turned into a
//! closure of type [`Closure2<u32, u32, u64>`] using
//! [`Closure2::new`]. Then a C
//! function pointer of type `extern "C" fn(u32, u32) -> u64` can be
//! borrowed from the closure and passed to C.
//!
//! The above usage case eliminates much of the boilerplate involved in
//! creating a closure as compared to the `middle` and `low` layers, but
//! at the price of flexibility. Some flexibility can be recovered by
//! manually constructing and configuring a CIF (*e.g.,* a
//! [`Cif2`]) and then creating the closure with
//! [`Closure2::new_with_cif`].
//!
//! See the [`mod@call`] submodule for a simple interface
//! to dynamic calls to C functions.
//!
//! # Examples
//!
//! Here we use [`ClosureMut1`], which is the type
//! for creating mutable closures of one argument. We use it to turn a
//! Rust lambda into a C function pointer.
//!
//! ```
//! use libffi::high::ClosureMut1;
//!
//! let mut x = 0u64;
//! let mut f = |y: u32| { x += y as u64; x };
//!
//! let closure = ClosureMut1::new(&mut f);
//! let counter = closure.code_ptr();
//!
//! assert_eq!(5, counter.call(5));
//! assert_eq!(6, counter.call(1));
//! assert_eq!(8, counter.call(2));
//! ```
//!
//! Note that in the above example, `counter` is an ordinary C function
//! pointer of type `extern "C" fn(u64) -> u64`.
//!
//! Here’s an example using `ClosureOnce3` to create a closure that owns
//! a vector:
//!
//! ```
//! use libffi::high::ClosureOnce3;
//!
//! let v = vec![1, 2, 3, 4, 5];
//! let mut f = move |x: usize, y: usize, z: usize| {
//! v[x] + v[y] + v[z]
//! };
//!
//! let closure = ClosureOnce3::new(f);
//! let call = closure.code_ptr();
//!
//! assert_eq!(12, call.call(2, 3, 4));
//! ```
//!
//! Invoking the closure a second time will panic.
pub use crate::middle::{ffi_abi_FFI_DEFAULT_ABI, FfiAbi};
pub mod types;
pub use types::{CType, Type};
pub mod call;
pub use call::*;
macro_rules! abort_on_panic {
($msg:literal, $body:expr) => {{
// Aborts when dropped (which will only happen due to an unwinding panic).
struct Bomb;
impl Drop for Bomb {
fn drop(&mut self) {
// We do our best to ignore errors that occur during printing.
// If this panics anyway, that'll still just be a double-panic which leads to abort.
let _ = writeln!(std::io::stderr(), $msg);
std::process::abort();
}
}
let b = Bomb;
// If this panics, `b` will be dropped, triggering the bomb.
$body;
// Defuse the bomb.
std::mem::forget(b);
}};
}
macro_rules! define_closure_mod {
(
$module:ident $cif:ident $fnptr:ident
$callback:ident $callback_mut:ident $callback_once:ident
$closure:ident $closure_mut:ident $closure_once:ident;
$( $T:ident )*
)
=>
{
/// CIF and closure types organized by function arity.
#[allow(clippy::too_many_arguments)]
pub mod $module {
use std::any::Any;
use std::marker::PhantomData;
use std::{mem, process, ptr};
use std::io::{self, Write};
use super::*;
use crate::{low, middle};
/// A typed CIF, which statically tracks argument and result types.
pub struct $cif<$( $T, )* R> {
untyped: middle::Cif,
_marker: PhantomData<fn($( $T, )*) -> R>,
}
impl<$( $T, )* R> $cif<$( $T, )* R> {
/// Creates a new statically-typed CIF with the given argument
/// and result types.
#[allow(non_snake_case)]
pub fn new($( $T: Type<$T>, )* result: Type<R>) -> Self {
let cif = middle::Cif::new(
vec![$( $T.into_middle() ),*].into_iter(),
result.into_middle());
$cif { untyped: cif, _marker: PhantomData }
}
/// Sets the CIF to use the given calling convention.
pub fn set_abi(&mut self, abi: FfiAbi) {
self.untyped.set_abi(abi);
}
}
impl<$( $T: CType, )* R: CType> $cif<$( $T, )* R> {
/// Creates a new statically-typed CIF by reifying the
/// argument types as `Type<T>`s.
pub fn reify() -> Self {
Self::new($( $T::reify(), )* R::reify())
}
}
/// A lifetime carrying wrapper type for [`fn`] pointers.
#[derive(Clone, Copy)]
#[repr(transparent)]
pub struct $fnptr<'a, $( $T, )* R> {
func: extern "C" fn($( $T, )*) -> R,
_lifetime: PhantomData<&'a extern "C" fn($( $T, )*) -> R>,
}
impl<'a, $( $T, )* R> $fnptr<'a, $( $T, )* R> {
/// Call the wrapped [`fn`] pointer.
// We allow non snake case variable identifiers here because
// we would otherwise need to take in a whole new list of
// argument identifiers at every invocation of this macro,
// and there would be no gain from doing so, since the parameter
// names here are entirely meaningless.
#[allow(non_snake_case)]
pub fn call(&self, $( $T : $T, )*) -> R {
(self.func)($( $T, )*)
}
}
// We use tuples of pointers to describe the arguments, and we
// extract them by pattern matching. This assumes that a tuple
// of pointers will be laid out packed and in order. This seems
// to hold true right now, and I can’t think of a reason why it
// wouldn’t be that way, but technically it may be undefined
// behavior.
/// The type of function called from an immutable, typed closure.
pub type $callback<U, $( $T, )* R>
= extern "C" fn(cif: &low::ffi_cif,
result: &mut R,
args: &($( &$T, )*),
userdata: &U);
/// An immutable, typed closure with the given argument and result
/// types.
pub struct $closure<'a, $( $T, )* R> {
untyped: middle::Closure<'a>,
_marker: PhantomData<fn($( $T, )*) -> R>,
}
impl<'a, $($T: CType,)* R: CType> $closure<'a, $($T,)* R> {
/// Constructs a typed closure callable from C from a
/// Rust closure.
pub fn new<Callback>(callback: &'a Callback) -> Self
where Callback: Fn($( $T, )*) -> R + 'a
{
Self::new_with_cif($cif::reify(), callback)
}
}
impl<'a, $( $T, )* R: CType> $closure<'a, $( $T, )* R> {
/// Gets the C code pointer that is used to invoke the
/// closure.
pub fn code_ptr(&self) -> & $fnptr <'a, $( $T, )* R> {
// Safety: Here we produce an FnPtrN wrapper for
// the correct `fn` pointer, which is repr(transparent)
// and therefore reference, layout, and otherwise ABI compatible
// with that type.
// Additionally, the FnPtrN wrapper enforces usage of the returned
// function pointer be only within the lifetime of the closure
// from which it was made.
// Other safety invariants have not been checked by
// the author of this comment, see the `instantiate_code_ptr`
// method docs for more.
unsafe {
self.untyped.instantiate_code_ptr()
}
}
/// Constructs a typed closure callable from C from a CIF
/// describing the calling convention for the resulting
/// function, a callback for the function to call, and
/// userdata to pass to the callback. Note that the return
/// type of the callback must follow the libffi implicit
/// extension rules.
pub fn from_parts<U>(cif: $cif<$( $T, )* R>,
callback: $callback<U, $( $T, )* R::RetType>,
userdata: &'a U) -> Self
{
let callback: middle::Callback<U, R::RetType>
= unsafe { mem::transmute(callback) };
let closure
= middle::Closure::new(cif.untyped,
callback,
userdata);
$closure {
untyped: closure,
_marker: PhantomData,
}
}
}
impl<'a, $( $T: Copy, )* R: CType> $closure<'a, $( $T, )* R> {
/// Constructs a typed closure callable from C from a CIF
/// describing the calling convention for the resulting
/// function and the Rust closure to call.
pub fn new_with_cif<Callback>(cif: $cif<$( $T, )* R>,
callback: &'a Callback) -> Self
where Callback: Fn($( $T, )*) -> R + 'a
{
Self::from_parts(cif,
Self::static_callback,
callback)
}
#[allow(non_snake_case)]
extern "C" fn static_callback<Callback>
(_cif: &low::ffi_cif,
result: &mut R::RetType,
&($( &$T, )*):
&($( &$T, )*),
userdata: &Callback)
where Callback: Fn($( $T, )*) -> R + 'a
{
abort_on_panic!("Cannot panic inside FFI callback", {
unsafe {
ptr::write(result, userdata($( $T, )*).into());
}
});
}
}
/// The type of function called from a mutable, typed closure.
pub type $callback_mut<U, $( $T, )* R>
= extern "C" fn(cif: &low::ffi_cif,
result: &mut R,
args: &($( &$T, )*),
userdata: &mut U);
/// A mutable, typed closure with the given argument and
/// result types.
pub struct $closure_mut<'a, $( $T, )* R> {
untyped: middle::Closure<'a>,
_marker: PhantomData<fn($( $T, )*) -> R>,
}
impl<'a, $($T: CType,)* R: CType>
$closure_mut<'a, $($T,)* R>
{
/// Constructs a typed closure callable from C from a
/// Rust closure.
pub fn new<Callback>(callback: &'a mut Callback) -> Self
where Callback: FnMut($( $T, )*) -> R + 'a
{
Self::new_with_cif($cif::reify(), callback)
}
}
impl<'a, $( $T, )* R: CType> $closure_mut<'a, $( $T, )* R> {
/// Gets the C code pointer that is used to invoke the
/// closure.
pub fn code_ptr(&self) -> & $fnptr <'a, $( $T, )* R> {
unsafe {
self.untyped.instantiate_code_ptr()
}
}
/// Constructs a typed closure callable from C from a CIF
/// describing the calling convention for the resulting
/// function, a callback for the function to call, and
/// userdata to pass to the callback. Note that the return
/// type of the callback must follow the libffi implicit
/// extension rules.
pub fn from_parts<U>(cif: $cif<$( $T, )* R>,
callback: $callback_mut<U, $( $T, )* R::RetType>,
userdata: &'a mut U) -> Self
{
let callback: middle::CallbackMut<U, R::RetType>
= unsafe { mem::transmute(callback) };
let closure
= middle::Closure::new_mut(cif.untyped,
callback,
userdata);
$closure_mut {
untyped: closure,
_marker: PhantomData,
}
}
}
impl<'a, $( $T: Copy, )* R: CType> $closure_mut<'a, $( $T, )* R> {
/// Constructs a typed closure callable from C from a CIF
/// describing the calling convention for the resulting
/// function and the Rust closure to call.
pub fn new_with_cif<Callback>(cif: $cif<$( $T, )* R>,
callback: &'a mut Callback)
-> Self
where Callback: FnMut($( $T, )*) -> R + 'a
{
Self::from_parts(cif,
Self::static_callback,
callback)
}
#[allow(non_snake_case)]
extern "C" fn static_callback<Callback>
(_cif: &low::ffi_cif,
result: &mut R::RetType,
&($( &$T, )*):
&($( &$T, )*),
userdata: &mut Callback)
where Callback: FnMut($( $T, )*) -> R + 'a
{
abort_on_panic!("Cannot panic inside FFI callback", {
unsafe {
ptr::write(result, userdata($( $T, )*).into());
}
});
}
}
/// The type of function called from a one-shot, typed closure.
pub type $callback_once<U, $( $T, )* R>
= $callback_mut<Option<U>, $( $T, )* R>;
/// A one-shot, typed closure with the given argument and
/// result types.
pub struct $closure_once<$( $T, )* R> {
untyped: middle::ClosureOnce,
_marker: PhantomData<fn($( $T, )*) -> R>,
}
impl<$($T: CType,)* R: CType> $closure_once<$($T,)* R> {
/// Constructs a typed closure callable from C from a
/// Rust closure.
pub fn new<Callback>(callback: Callback) -> Self
where Callback: FnOnce($( $T, )*) -> R + Any
{
Self::new_with_cif($cif::reify(), callback)
}
}
impl<$( $T: Copy, )* R: CType> $closure_once<$( $T, )* R> {
/// Constructs a one-shot closure callable from C from a CIF
/// describing the calling convention for the resulting
/// function and the Rust closure to call.
pub fn new_with_cif<Callback>(cif: $cif<$( $T, )* R>,
callback: Callback) -> Self
where Callback: FnOnce($( $T, )*) -> R + Any
{
Self::from_parts(cif,
Self::static_callback,
callback)
}
#[allow(non_snake_case)]
extern "C" fn static_callback<Callback>
(_cif: &low::ffi_cif,
result: &mut R::RetType,
&($( &$T, )*):
&($( &$T, )*),
userdata: &mut Option<Callback>)
where Callback: FnOnce($( $T, )*) -> R
{
if let Some(userdata) = userdata.take() {
abort_on_panic!("Cannot panic inside FFI callback", {
unsafe {
ptr::write(result, userdata($( $T, )*).into());
}
});
} else {
// There is probably a better way to abort here.
let _ =
io::stderr().write(b"FnOnce closure already used");
process::exit(2);
}
}
}
impl<$( $T, )* R: CType> $closure_once<$( $T, )* R> {
/// Gets the C code pointer that is used to invoke the
/// closure.
pub fn code_ptr(&self) -> & $fnptr <'_, $( $T, )* R> {
unsafe {
self.untyped.instantiate_code_ptr()
}
}
/// Constructs a one-shot closure callable from C from a CIF
/// describing the calling convention for the resulting
/// function, a callback for the function to call, and
/// userdata to pass to the callback. Note that the return
/// type of the callback must follow the libffi implicit
/// extension rules.
pub fn from_parts<U: Any>(
cif: $cif<$( $T, )* R>,
callback: $callback_once<U, $( $T, )* R::RetType>,
userdata: U)
-> Self
{
let callback: middle::CallbackOnce<U, R::RetType>
= unsafe { mem::transmute(callback) };
let closure
= middle::ClosureOnce::new(cif.untyped,
callback,
userdata);
$closure_once {
untyped: closure,
_marker: PhantomData,
}
}
}
}
pub use $module::*;
}
}
define_closure_mod!(arity0 Cif0 FnPtr0
Callback0 CallbackMut0 CallbackOnce0
Closure0 ClosureMut0 ClosureOnce0;
);
define_closure_mod!(arity1 Cif1 FnPtr1
Callback1 CallbackMut1 CallbackOnce1
Closure1 ClosureMut1 ClosureOnce1;
A);
define_closure_mod!(arity2 Cif2 FnPtr2
Callback2 CallbackMut2 CallbackOnce2
Closure2 ClosureMut2 ClosureOnce2;
A B);
define_closure_mod!(arity3 Cif3 FnPtr3
Callback3 CallbackMut3 CallbackOnce3
Closure3 ClosureMut3 ClosureOnce3;
A B C);
define_closure_mod!(arity4 Cif4 FnPtr4
Callback4 CallbackMut4 CallbackOnce4
Closure4 ClosureMut4 ClosureOnce4;
A B C D);
define_closure_mod!(arity5 Cif5 FnPtr5
Callback5 CallbackMut5 CallbackOnce5
Closure5 ClosureMut5 ClosureOnce5;
A B C D E);
define_closure_mod!(arity6 Cif6 FnPtr6
Callback6 CallbackMut6 CallbackOnce6
Closure6 ClosureMut6 ClosureOnce6;
A B C D E F);
define_closure_mod!(arity7 Cif7 FnPtr7
Callback7 CallbackMut7 CallbackOnce7
Closure7 ClosureMut7 ClosureOnce7;
A B C D E F G);
define_closure_mod!(arity8 Cif8 FnPtr8
Callback8 CallbackMut8 CallbackOnce8
Closure8 ClosureMut8 ClosureOnce8;
A B C D E F G H);
define_closure_mod!(arity9 Cif9 FnPtr9
Callback9 CallbackMut9 CallbackOnce9
Closure9 ClosureMut9 ClosureOnce9;
A B C D E F G H I);
define_closure_mod!(arity10 Cif10 FnPtr10
Callback10 CallbackMut10 CallbackOnce10
Closure10 ClosureMut10 ClosureOnce10;
A B C D E F G H I J);
define_closure_mod!(arity11 Cif11 FnPtr11
Callback11 CallbackMut11 CallbackOnce11
Closure11 ClosureMut11 ClosureOnce11;
A B C D E F G H I J K);
define_closure_mod!(arity12 Cif12 FnPtr12
Callback12 CallbackMut12 CallbackOnce12
Closure12 ClosureMut12 ClosureOnce12;
A B C D E F G H I J K L);
#[cfg(test)]
mod test {
use super::*;
#[test]
fn new_with_cif() {
let x: u64 = 1;
let f = |y: u64, z: u64| x + y + z;
let type_ = u64::reify();
let cif = Cif2::new(type_.clone(), type_.clone(), type_.clone());
let closure = Closure2::new_with_cif(cif, &f);
assert_eq!(12, closure.code_ptr().call(5, 6));
}
#[test]
fn new_with_cif_mut() {
let mut x: u64 = 0;
let mut f = |y: u64| {
x += y;
x
};
let type_ = u64::reify();
let cif = Cif1::new(type_.clone(), type_.clone());
let closure = ClosureMut1::new_with_cif(cif, &mut f);
let counter = closure.code_ptr();
assert_eq!(5, counter.call(5));
assert_eq!(6, counter.call(1));
assert_eq!(8, counter.call(2));
}
#[test]
fn new() {
let x: u64 = 1;
let f = |y: u64, z: u64| x + y + z;
let closure = Closure2::new(&f);
assert_eq!(12, closure.code_ptr().call(5, 6));
}
#[test]
fn new_mut() {
let mut x: u64 = 0;
let mut f = |y: u32| {
x += u64::from(y);
x
};
let closure = ClosureMut1::new(&mut f);
let counter = closure.code_ptr();
assert_eq!(5, counter.call(5));
assert_eq!(6, counter.call(1));
assert_eq!(8, counter.call(2));
}
}