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//! Middle layer providing a somewhat safer (but still quite unsafe) //! API. //! //! The main idea of the middle layer is to wrap types //! [`ffi_cif`](../raw/struct.ffi_cif.html) and //! [`ffi_closure`](../raw/struct.ffi_closure.html) as //! [`Cif`](struct.Cif.html) and [`Closure`](struct.Closure.html), //! respectively, so that their resources are managed properly. However, //! calling a function via a CIF or closure is still unsafe because //! argument types aren’t checked. See the [`high`](../high/index.html) //! layer for closures with type-checked arguments. use std::any::Any; use std::marker::PhantomData; use std::os::raw::c_void; use crate::low; pub use crate::low::{ffi_abi as FfiAbi, ffi_abi_FFI_DEFAULT_ABI, Callback, CallbackMut, CodePtr}; mod util; mod types; pub use types::Type; mod builder; pub use builder::Builder; /// Contains an untyped pointer to a function argument. /// /// When calling a function via a [CIF](struct.Cif.html), each argument /// must be passed as a C `void*`. Wrapping the argument in the `Arg` /// struct accomplishes the necessary coercion. #[derive(Clone, Debug)] #[repr(C)] pub struct Arg(*mut c_void); impl Arg { /// Coerces an argument reference into the `Arg` type. /// /// This is used to wrap each argument pointer before passing them /// to [`Cif::call`](struct.Cif.html#method.call). pub fn new<T>(r: &T) -> Self { Arg(r as *const T as *mut c_void) } } /// Coerces an argument reference into the [`Arg`](struct.Arg.html) /// type. /// /// This is used to wrap each argument pointer before passing them /// to [`Cif::call`](struct.Cif.html#method.call). /// (This is the same as [`Arg::new`](struct.Arg.html#method.new)). pub fn arg<T>(r: &T) -> Arg { Arg::new(r) } /// Describes the calling convention and types for calling a function. /// /// This is the `middle` layer’s wrapping of the `low` and `raw` layers’ /// [`ffi_cif`](../raw/struct.ffi_cif.html). An initialized CIF contains /// references to an array of argument types and a result type, each of /// which may be allocated on the heap. `Cif` manages the memory of /// those referenced objects. /// /// Construct with [`Cif::new`](#method.new) or /// [`Cif::from_type_array`](#method.from_type_array). /// /// # Examples /// /// ``` /// extern "C" fn add(x: f64, y: &f64) -> f64 { /// return x + y; /// } /// /// use deno_libffi::middle::*; /// /// let args = vec![Type::f64(), Type::pointer()]; /// let cif = Cif::new(args.into_iter(), Type::f64()); /// /// let n = unsafe { cif.call(CodePtr(add as *mut _), &[arg(&5f64), arg(&&6f64)]) }; /// assert_eq!(11f64, n); /// ``` #[derive(Debug)] pub struct Cif { cif: low::ffi_cif, args: types::TypeArray, result: Type, } // To clone a Cif we need to clone the types and then make sure the new // ffi_cif refers to the clones of the types. impl Clone for Cif { fn clone(&self) -> Self { let mut copy = Cif { cif: self.cif, args: self.args.clone(), result: self.result.clone(), }; copy.cif.arg_types = copy.args.as_raw_ptr(); copy.cif.rtype = copy.result.as_raw_ptr(); copy } } impl Cif { /// Creates a new CIF for the given argument and result types. /// /// Takes ownership of the argument and result /// [`Type`](types/struct.Type.html)s, because the resulting /// `Cif` retains references to them. /// Defaults to the platform’s default calling convention; this /// can be adjusted using [`set_abi`](#method.set_abi). pub fn new<I>(args: I, result: Type) -> Self where I: IntoIterator<Item = Type>, I::IntoIter: ExactSizeIterator<Item = Type>, { let args = args.into_iter(); let nargs = args.len(); let args = types::TypeArray::new(args); let mut cif: low::ffi_cif = Default::default(); unsafe { low::prep_cif( &mut cif, low::ffi_abi_FFI_DEFAULT_ABI, nargs, result.as_raw_ptr(), args.as_raw_ptr(), ) } .expect("low::prep_cif"); // Note that cif retains references to args and result, // which is why we hold onto them here. Cif { cif, args, result } } /// Calls a function with the given arguments. /// /// In particular, this method invokes function `fun` passing it /// arguments `args`, and returns the result. /// /// # Safety /// /// There is no checking that the calling convention and types /// in the `Cif` match the actual calling convention and types of /// `fun`, nor that they match the types of `args`. pub unsafe fn call<R>(&self, fun: CodePtr, args: &[Arg]) -> R { assert_eq!( self.cif.nargs as usize, args.len(), "Cif::call: passed wrong number of arguments" ); low::call::<R>( &self.cif as *const _ as *mut _, fun, args.as_ptr() as *mut *mut c_void, ) } /// Sets the CIF to use the given calling convention. pub fn set_abi(&mut self, abi: FfiAbi) { self.cif.abi = abi; } /// Gets a raw pointer to the underlying /// [`ffi_cif`](../low/struct.ffi_cif.html). /// /// This can be used for passing a `middle::Cif` to functions from the /// [`low`](../low/index.html) and [`raw`](../raw/index.html) modules. pub fn as_raw_ptr(&self) -> *mut low::ffi_cif { &self.cif as *const _ as *mut _ } } /// Represents a closure callable from C. /// /// A libffi closure captures a `void*` (“userdata”) and passes it to a /// callback when the code pointer (obtained via /// [`code_ptr`](#method.code_ptr)) is invoked. Lifetype parameter `'a` /// ensures that the closure does not outlive the userdata. /// /// Construct with [`Closure::new`](#method.new) and /// [`Closure::new_mut`](#method.new_mut). /// /// # Examples /// /// In this example we turn a Rust lambda into a C function. We first /// define function `lambda_callback`, which will be called by libffi /// when the closure is called. The callback function takes four /// arguments: a CIF describing its arguments, a pointer for where to /// store its result, a pointer to an array of pointers to its /// arguments, and a userdata pointer. In this ase, the Rust closure /// value `lambda` is passed as userdata to `lambda_callback`, which /// then invokes it. /// /// ``` /// use std::mem; /// use std::os::raw::c_void; /// /// use deno_libffi::middle::*; /// use deno_libffi::low; /// /// unsafe extern "C" fn lambda_callback<F: Fn(u64, u64) -> u64>( /// _cif: &low::ffi_cif, /// result: &mut u64, /// args: *const *const c_void, /// userdata: &F) /// { /// let args = args as *const &u64; /// let arg1 = **args.offset(0); /// let arg2 = **args.offset(1); /// /// *result = userdata(arg1, arg2); /// } /// /// let cif = Cif::new(vec![Type::u64(), Type::u64()].into_iter(), /// Type::u64()); /// let lambda = |x: u64, y: u64| x + y; /// let closure = Closure::new(cif, lambda_callback, &lambda); /// /// let fun: &extern "C" fn(u64, u64) -> u64 = unsafe { /// closure.instantiate_code_ptr() /// }; /// /// assert_eq!(11, fun(5, 6)); /// assert_eq!(12, fun(5, 7)); /// ``` #[derive(Debug)] pub struct Closure<'a> { _cif: Box<Cif>, alloc: *mut low::ffi_closure, code: CodePtr, _marker: PhantomData<&'a ()>, } impl<'a> Drop for Closure<'a> { fn drop(&mut self) { unsafe { low::closure_free(self.alloc); } } } impl<'a> Closure<'a> { /// Creates a new closure with immutable userdata. /// /// # Arguments /// /// - `cif` — describes the calling convention and argument and /// result types /// - `callback` — the function to call when the closure is invoked /// - `userdata` — the pointer to pass to `callback` along with the /// arguments when the closure is called /// /// # Result /// /// The new closure. pub fn new<U, R>(cif: Cif, callback: Callback<U, R>, userdata: &'a U) -> Self { let cif = Box::new(cif); let (alloc, code) = low::closure_alloc(); unsafe { low::prep_closure( alloc, cif.as_raw_ptr(), callback, userdata as *const U, code, ) .unwrap(); } Closure { _cif: cif, alloc, code, _marker: PhantomData, } } /// Creates a new closure with mutable userdata. /// /// # Arguments /// /// - `cif` — describes the calling convention and argument and /// result types /// - `callback` — the function to call when the closure is invoked /// - `userdata` — the pointer to pass to `callback` along with the /// arguments when the closure is called /// /// # Result /// /// The new closure. pub fn new_mut<U, R>(cif: Cif, callback: CallbackMut<U, R>, userdata: &'a mut U) -> Self { let cif = Box::new(cif); let (alloc, code) = low::closure_alloc(); unsafe { low::prep_closure_mut(alloc, cif.as_raw_ptr(), callback, userdata as *mut U, code) .unwrap(); } Closure { _cif: cif, alloc, code, _marker: PhantomData, } } /// Obtains the callable code pointer for a closure. /// /// # Safety /// /// The result needs to be transmuted to the correct type before /// it can be called. If the type is wrong then undefined behavior /// will result. pub fn code_ptr(&self) -> &unsafe extern "C" fn() { self.code.as_fun() } /// Transmutes the callable code pointer for a closure to a reference /// to any type. This is intended to be used to transmute it to its /// correct function type in order to call it. /// /// # Safety /// /// This method allows transmuting to a reference to *any* sized type, /// and cannot check whether the code pointer actually has that type. /// If the type is wrong then undefined behavior will result. pub unsafe fn instantiate_code_ptr<T>(&self) -> &T { self.code.as_any_ref_() } } /// The type of callback invoked by a /// [`ClosureOnce`](struct.ClosureOnce.html). pub type CallbackOnce<U, R> = CallbackMut<Option<U>, R>; /// A closure that owns needs-drop data. /// /// This allows the closure’s callback to take ownership of the data, in /// which case the userdata will be gone if called again. #[derive(Debug)] pub struct ClosureOnce { alloc: *mut low::ffi_closure, code: CodePtr, _cif: Box<Cif>, _userdata: Box<dyn Any>, } impl Drop for ClosureOnce { fn drop(&mut self) { unsafe { low::closure_free(self.alloc); } } } impl ClosureOnce { /// Creates a new closure with owned userdata. /// /// # Arguments /// /// - `cif` — describes the calling convention and argument and /// result types /// - `callback` — the function to call when the closure is invoked /// - `userdata` — the value to pass to `callback` along with the /// arguments when the closure is called /// /// # Result /// /// The new closure. pub fn new<U: Any, R>(cif: Cif, callback: CallbackOnce<U, R>, userdata: U) -> Self { let _cif = Box::new(cif); let _userdata = Box::new(Some(userdata)) as Box<dyn Any>; let (alloc, code) = low::closure_alloc(); assert!(!alloc.is_null(), "closure_alloc: returned null"); { let borrow = _userdata.downcast_ref::<Option<U>>().unwrap(); unsafe { low::prep_closure_mut( alloc, _cif.as_raw_ptr(), callback, borrow as *const _ as *mut _, code, ) .unwrap(); } } ClosureOnce { alloc, code, _cif, _userdata, } } /// Obtains the callable code pointer for a closure. /// /// # Safety /// /// The result needs to be transmuted to the correct type before /// it can be called. If the type is wrong then undefined behavior /// will result. pub fn code_ptr(&self) -> &unsafe extern "C" fn() { self.code.as_fun() } /// Transmutes the callable code pointer for a closure to a reference /// to any type. This is intended to be used to transmute it to its /// correct function type in order to call it. /// /// # Safety /// /// This method allows transmuting to a reference to *any* sized type, /// and cannot check whether the code pointer actually has that type. /// If the type is wrong then undefined behavior will result. pub unsafe fn instantiate_code_ptr<T>(&self) -> &T { self.code.as_any_ref_() } } #[cfg(test)] mod test { use super::*; use crate::low; use std::os::raw::c_void; #[test] fn call() { let cif = Cif::new(vec![Type::i64(), Type::i64()].into_iter(), Type::i64()); let f = |m: i64, n: i64| -> i64 { unsafe { cif.call(CodePtr(add_it as *mut c_void), &[arg(&m), arg(&n)]) } }; assert_eq!(12, f(5, 7)); assert_eq!(13, f(6, 7)); assert_eq!(15, f(8, 7)); } extern "C" fn add_it(n: i64, m: i64) -> i64 { n + m } #[test] fn closure() { let cif = Cif::new(vec![Type::u64()].into_iter(), Type::u64()); let env: u64 = 5; let closure = Closure::new(cif, callback, &env); let fun: &extern "C" fn(u64) -> u64 = unsafe { closure.instantiate_code_ptr() }; assert_eq!(11, fun(6)); assert_eq!(12, fun(7)); } unsafe extern "C" fn callback( _cif: &low::ffi_cif, result: &mut u64, args: *const *const c_void, userdata: &u64, ) { let args = args as *const &u64; *result = **args + *userdata; } #[test] fn rust_lambda() { let cif = Cif::new(vec![Type::u64(), Type::u64()].into_iter(), Type::u64()); let env = |x: u64, y: u64| x + y; let closure = Closure::new(cif, callback2, &env); let fun: &extern "C" fn(u64, u64) -> u64 = unsafe { closure.instantiate_code_ptr() }; assert_eq!(11, fun(5, 6)); } unsafe extern "C" fn callback2<F: Fn(u64, u64) -> u64>( _cif: &low::ffi_cif, result: &mut u64, args: *const *const c_void, userdata: &F, ) { let args = args as *const &u64; let arg1 = **args.offset(0); let arg2 = **args.offset(1); *result = userdata(arg1, arg2); } }