#![cfg(feature = "extern_crate_alloc")]
#![allow(clippy::duplicated_attributes)]
//! Stuff to boost things in the `alloc` crate.
//!
//! * You must enable the `extern_crate_alloc` feature of `bytemuck` or you will
//! not be able to use this module! This is generally done by adding the
//! feature to the dependency in Cargo.toml like so:
//!
//! `bytemuck = { version = "VERSION_YOU_ARE_USING", features =
//! ["extern_crate_alloc"]}`
use super::*;
#[cfg(target_has_atomic = "ptr")]
use alloc::sync::Arc;
use alloc::{
alloc::{alloc_zeroed, Layout},
boxed::Box,
rc::Rc,
vec,
vec::Vec,
};
use core::{
mem::{size_of_val, ManuallyDrop},
ops::{Deref, DerefMut},
};
/// As [`try_cast_box`], but unwraps for you.
#[inline]
pub fn cast_box<A: NoUninit, B: AnyBitPattern>(input: Box<A>) -> Box<B> {
try_cast_box(input).map_err(|(e, _v)| e).unwrap()
}
/// Attempts to cast the content type of a [`Box`].
///
/// On failure you get back an error along with the starting `Box`.
///
/// ## Failure
///
/// * The start and end content type of the `Box` must have the exact same
/// alignment.
/// * The start and end size of the `Box` must have the exact same size.
#[inline]
pub fn try_cast_box<A: NoUninit, B: AnyBitPattern>(
input: Box<A>,
) -> Result<Box<B>, (PodCastError, Box<A>)> {
if align_of::<A>() != align_of::<B>() {
Err((PodCastError::AlignmentMismatch, input))
} else if size_of::<A>() != size_of::<B>() {
Err((PodCastError::SizeMismatch, input))
} else {
// Note(Lokathor): This is much simpler than with the Vec casting!
let ptr: *mut B = Box::into_raw(input) as *mut B;
Ok(unsafe { Box::from_raw(ptr) })
}
}
/// Allocates a `Box<T>` with all of the contents being zeroed out.
///
/// This uses the global allocator to create a zeroed allocation and _then_
/// turns it into a Box. In other words, it's 100% assured that the zeroed data
/// won't be put temporarily on the stack. You can make a box of any size
/// without fear of a stack overflow.
///
/// ## Failure
///
/// This fails if the allocation fails.
#[inline]
pub fn try_zeroed_box<T: Zeroable>() -> Result<Box<T>, ()> {
if size_of::<T>() == 0 {
// This will not allocate but simply create an arbitrary non-null
// aligned pointer, valid for Box for a zero-sized pointee.
let ptr = core::ptr::NonNull::dangling().as_ptr();
return Ok(unsafe { Box::from_raw(ptr) });
}
let layout = Layout::new::<T>();
let ptr = unsafe { alloc_zeroed(layout) };
if ptr.is_null() {
// we don't know what the error is because `alloc_zeroed` is a dumb API
Err(())
} else {
Ok(unsafe { Box::<T>::from_raw(ptr as *mut T) })
}
}
/// As [`try_zeroed_box`], but unwraps for you.
#[inline]
pub fn zeroed_box<T: Zeroable>() -> Box<T> {
try_zeroed_box().unwrap()
}
/// Allocates a `Vec<T>` of length and capacity exactly equal to `length` and
/// all elements zeroed.
///
/// ## Failure
///
/// This fails if the allocation fails, or if a layout cannot be calculated for
/// the allocation.
pub fn try_zeroed_vec<T: Zeroable>(length: usize) -> Result<Vec<T>, ()> {
if length == 0 {
Ok(Vec::new())
} else {
let boxed_slice = try_zeroed_slice_box(length)?;
Ok(boxed_slice.into_vec())
}
}
/// As [`try_zeroed_vec`] but unwraps for you
pub fn zeroed_vec<T: Zeroable>(length: usize) -> Vec<T> {
try_zeroed_vec(length).unwrap()
}
/// Allocates a `Box<[T]>` with all contents being zeroed out.
///
/// This uses the global allocator to create a zeroed allocation and _then_
/// turns it into a Box. In other words, it's 100% assured that the zeroed data
/// won't be put temporarily on the stack. You can make a box of any size
/// without fear of a stack overflow.
///
/// ## Failure
///
/// This fails if the allocation fails, or if a layout cannot be calculated for
/// the allocation.
#[inline]
pub fn try_zeroed_slice_box<T: Zeroable>(
length: usize,
) -> Result<Box<[T]>, ()> {
if size_of::<T>() == 0 || length == 0 {
// This will not allocate but simply create an arbitrary non-null aligned
// slice pointer, valid for Box for a zero-sized pointee.
let ptr = core::ptr::NonNull::dangling().as_ptr();
let slice_ptr = core::ptr::slice_from_raw_parts_mut(ptr, length);
return Ok(unsafe { Box::from_raw(slice_ptr) });
}
let layout = core::alloc::Layout::array::<T>(length).map_err(|_| ())?;
let ptr = unsafe { alloc_zeroed(layout) };
if ptr.is_null() {
// we don't know what the error is because `alloc_zeroed` is a dumb API
Err(())
} else {
let slice =
unsafe { core::slice::from_raw_parts_mut(ptr as *mut T, length) };
Ok(unsafe { Box::<[T]>::from_raw(slice) })
}
}
/// As [`try_zeroed_slice_box`], but unwraps for you.
pub fn zeroed_slice_box<T: Zeroable>(length: usize) -> Box<[T]> {
try_zeroed_slice_box(length).unwrap()
}
/// As [`try_cast_slice_box`], but unwraps for you.
#[inline]
pub fn cast_slice_box<A: NoUninit, B: AnyBitPattern>(
input: Box<[A]>,
) -> Box<[B]> {
try_cast_slice_box(input).map_err(|(e, _v)| e).unwrap()
}
/// Attempts to cast the content type of a `Box<[T]>`.
///
/// On failure you get back an error along with the starting `Box<[T]>`.
///
/// ## Failure
///
/// * The start and end content type of the `Box<[T]>` must have the exact same
/// alignment.
/// * The start and end content size in bytes of the `Box<[T]>` must be the
/// exact same.
#[inline]
pub fn try_cast_slice_box<A: NoUninit, B: AnyBitPattern>(
input: Box<[A]>,
) -> Result<Box<[B]>, (PodCastError, Box<[A]>)> {
if align_of::<A>() != align_of::<B>() {
Err((PodCastError::AlignmentMismatch, input))
} else if size_of::<A>() != size_of::<B>() {
let input_bytes = size_of_val::<[A]>(&*input);
if (size_of::<B>() == 0 && input_bytes != 0)
|| (size_of::<B>() != 0 && input_bytes % size_of::<B>() != 0)
{
// If the size in bytes of the underlying buffer does not match an exact
// multiple of the size of B, we cannot cast between them.
Err((PodCastError::OutputSliceWouldHaveSlop, input))
} else {
// Because the size is an exact multiple, we can now change the length
// of the slice and recreate the Box
// NOTE: This is a valid operation because according to the docs of
// std::alloc::GlobalAlloc::dealloc(), the Layout that was used to alloc
// the block must be the same Layout that is used to dealloc the block.
// Luckily, Layout only stores two things, the alignment, and the size in
// bytes. So as long as both of those stay the same, the Layout will
// remain a valid input to dealloc.
let length =
if size_of::<B>() != 0 { input_bytes / size_of::<B>() } else { 0 };
let box_ptr: *mut A = Box::into_raw(input) as *mut A;
let ptr: *mut [B] =
unsafe { core::slice::from_raw_parts_mut(box_ptr as *mut B, length) };
Ok(unsafe { Box::<[B]>::from_raw(ptr) })
}
} else {
let box_ptr: *mut [A] = Box::into_raw(input);
let ptr: *mut [B] = box_ptr as *mut [B];
Ok(unsafe { Box::<[B]>::from_raw(ptr) })
}
}
/// As [`try_cast_vec`], but unwraps for you.
#[inline]
pub fn cast_vec<A: NoUninit, B: AnyBitPattern>(input: Vec<A>) -> Vec<B> {
try_cast_vec(input).map_err(|(e, _v)| e).unwrap()
}
/// Attempts to cast the content type of a [`Vec`].
///
/// On failure you get back an error along with the starting `Vec`.
///
/// ## Failure
///
/// * The start and end content type of the `Vec` must have the exact same
/// alignment.
/// * The start and end content size in bytes of the `Vec` must be the exact
/// same.
/// * The start and end capacity in bytes of the `Vec` must be the exact same.
#[inline]
pub fn try_cast_vec<A: NoUninit, B: AnyBitPattern>(
input: Vec<A>,
) -> Result<Vec<B>, (PodCastError, Vec<A>)> {
if align_of::<A>() != align_of::<B>() {
Err((PodCastError::AlignmentMismatch, input))
} else if size_of::<A>() != size_of::<B>() {
let input_size = size_of_val::<[A]>(&*input);
let input_capacity = input.capacity() * size_of::<A>();
if (size_of::<B>() == 0 && input_capacity != 0)
|| (size_of::<B>() != 0
&& (input_size % size_of::<B>() != 0
|| input_capacity % size_of::<B>() != 0))
{
// If the size in bytes of the underlying buffer does not match an exact
// multiple of the size of B, we cannot cast between them.
// Note that we have to pay special attention to make sure that both
// length and capacity are valid under B, as we do not want to
// change which bytes are considered part of the initialized slice
// of the Vec
Err((PodCastError::OutputSliceWouldHaveSlop, input))
} else {
// Because the size is an exact multiple, we can now change the length and
// capacity and recreate the Vec
// NOTE: This is a valid operation because according to the docs of
// std::alloc::GlobalAlloc::dealloc(), the Layout that was used to alloc
// the block must be the same Layout that is used to dealloc the block.
// Luckily, Layout only stores two things, the alignment, and the size in
// bytes. So as long as both of those stay the same, the Layout will
// remain a valid input to dealloc.
// Note(Lokathor): First we record the length and capacity, which don't
// have any secret provenance metadata.
let length: usize =
if size_of::<B>() != 0 { input_size / size_of::<B>() } else { 0 };
let capacity: usize =
if size_of::<B>() != 0 { input_capacity / size_of::<B>() } else { 0 };
// Note(Lokathor): Next we "pre-forget" the old Vec by wrapping with
// ManuallyDrop, because if we used `core::mem::forget` after taking the
// pointer then that would invalidate our pointer. In nightly there's a
// "into raw parts" method, which we can switch this too eventually.
let mut manual_drop_vec = ManuallyDrop::new(input);
let vec_ptr: *mut A = manual_drop_vec.as_mut_ptr();
let ptr: *mut B = vec_ptr as *mut B;
Ok(unsafe { Vec::from_raw_parts(ptr, length, capacity) })
}
} else {
// Note(Lokathor): First we record the length and capacity, which don't have
// any secret provenance metadata.
let length: usize = input.len();
let capacity: usize = input.capacity();
// Note(Lokathor): Next we "pre-forget" the old Vec by wrapping with
// ManuallyDrop, because if we used `core::mem::forget` after taking the
// pointer then that would invalidate our pointer. In nightly there's a
// "into raw parts" method, which we can switch this too eventually.
let mut manual_drop_vec = ManuallyDrop::new(input);
let vec_ptr: *mut A = manual_drop_vec.as_mut_ptr();
let ptr: *mut B = vec_ptr as *mut B;
Ok(unsafe { Vec::from_raw_parts(ptr, length, capacity) })
}
}
/// This "collects" a slice of pod data into a vec of a different pod type.
///
/// Unlike with [`cast_slice`] and [`cast_slice_mut`], this will always work.
///
/// The output vec will be of a minimal size/capacity to hold the slice given.
///
/// ```rust
/// # use bytemuck::*;
/// let halfwords: [u16; 4] = [5, 6, 7, 8];
/// let vec_of_words: Vec<u32> = pod_collect_to_vec(&halfwords);
/// if cfg!(target_endian = "little") {
/// assert_eq!(&vec_of_words[..], &[0x0006_0005, 0x0008_0007][..])
/// } else {
/// assert_eq!(&vec_of_words[..], &[0x0005_0006, 0x0007_0008][..])
/// }
/// ```
pub fn pod_collect_to_vec<A: NoUninit, B: NoUninit + AnyBitPattern>(
src: &[A],
) -> Vec<B> {
let src_size = core::mem::size_of_val(src);
// Note(Lokathor): dst_count is rounded up so that the dest will always be at
// least as many bytes as the src.
let dst_count = src_size / size_of::<B>()
+ if src_size % size_of::<B>() != 0 { 1 } else { 0 };
let mut dst = vec![B::zeroed(); dst_count];
let src_bytes: &[u8] = cast_slice(src);
let dst_bytes: &mut [u8] = cast_slice_mut(&mut dst[..]);
dst_bytes[..src_size].copy_from_slice(src_bytes);
dst
}
/// As [`try_cast_rc`], but unwraps for you.
#[inline]
pub fn cast_rc<A: NoUninit + AnyBitPattern, B: NoUninit + AnyBitPattern>(
input: Rc<A>,
) -> Rc<B> {
try_cast_rc(input).map_err(|(e, _v)| e).unwrap()
}
/// Attempts to cast the content type of a [`Rc`].
///
/// On failure you get back an error along with the starting `Rc`.
///
/// The bounds on this function are the same as [`cast_mut`], because a user
/// could call `Rc::get_unchecked_mut` on the output, which could be observable
/// in the input.
///
/// ## Failure
///
/// * The start and end content type of the `Rc` must have the exact same
/// alignment.
/// * The start and end size of the `Rc` must have the exact same size.
#[inline]
pub fn try_cast_rc<A: NoUninit + AnyBitPattern, B: NoUninit + AnyBitPattern>(
input: Rc<A>,
) -> Result<Rc<B>, (PodCastError, Rc<A>)> {
if align_of::<A>() != align_of::<B>() {
Err((PodCastError::AlignmentMismatch, input))
} else if size_of::<A>() != size_of::<B>() {
Err((PodCastError::SizeMismatch, input))
} else {
// Safety: Rc::from_raw requires size and alignment match, which is met.
let ptr: *const B = Rc::into_raw(input) as *const B;
Ok(unsafe { Rc::from_raw(ptr) })
}
}
/// As [`try_cast_arc`], but unwraps for you.
#[inline]
#[cfg(target_has_atomic = "ptr")]
pub fn cast_arc<A: NoUninit + AnyBitPattern, B: NoUninit + AnyBitPattern>(
input: Arc<A>,
) -> Arc<B> {
try_cast_arc(input).map_err(|(e, _v)| e).unwrap()
}
/// Attempts to cast the content type of a [`Arc`].
///
/// On failure you get back an error along with the starting `Arc`.
///
/// The bounds on this function are the same as [`cast_mut`], because a user
/// could call `Rc::get_unchecked_mut` on the output, which could be observable
/// in the input.
///
/// ## Failure
///
/// * The start and end content type of the `Arc` must have the exact same
/// alignment.
/// * The start and end size of the `Arc` must have the exact same size.
#[inline]
#[cfg(target_has_atomic = "ptr")]
pub fn try_cast_arc<
A: NoUninit + AnyBitPattern,
B: NoUninit + AnyBitPattern,
>(
input: Arc<A>,
) -> Result<Arc<B>, (PodCastError, Arc<A>)> {
if align_of::<A>() != align_of::<B>() {
Err((PodCastError::AlignmentMismatch, input))
} else if size_of::<A>() != size_of::<B>() {
Err((PodCastError::SizeMismatch, input))
} else {
// Safety: Arc::from_raw requires size and alignment match, which is met.
let ptr: *const B = Arc::into_raw(input) as *const B;
Ok(unsafe { Arc::from_raw(ptr) })
}
}
/// As [`try_cast_slice_rc`], but unwraps for you.
#[inline]
pub fn cast_slice_rc<
A: NoUninit + AnyBitPattern,
B: NoUninit + AnyBitPattern,
>(
input: Rc<[A]>,
) -> Rc<[B]> {
try_cast_slice_rc(input).map_err(|(e, _v)| e).unwrap()
}
/// Attempts to cast the content type of a `Rc<[T]>`.
///
/// On failure you get back an error along with the starting `Rc<[T]>`.
///
/// The bounds on this function are the same as [`cast_mut`], because a user
/// could call `Rc::get_unchecked_mut` on the output, which could be observable
/// in the input.
///
/// ## Failure
///
/// * The start and end content type of the `Rc<[T]>` must have the exact same
/// alignment.
/// * The start and end content size in bytes of the `Rc<[T]>` must be the exact
/// same.
#[inline]
pub fn try_cast_slice_rc<
A: NoUninit + AnyBitPattern,
B: NoUninit + AnyBitPattern,
>(
input: Rc<[A]>,
) -> Result<Rc<[B]>, (PodCastError, Rc<[A]>)> {
if align_of::<A>() != align_of::<B>() {
Err((PodCastError::AlignmentMismatch, input))
} else if size_of::<A>() != size_of::<B>() {
let input_bytes = size_of_val::<[A]>(&*input);
if (size_of::<B>() == 0 && input_bytes != 0)
|| (size_of::<B>() != 0 && input_bytes % size_of::<B>() != 0)
{
// If the size in bytes of the underlying buffer does not match an exact
// multiple of the size of B, we cannot cast between them.
Err((PodCastError::OutputSliceWouldHaveSlop, input))
} else {
// Because the size is an exact multiple, we can now change the length
// of the slice and recreate the Rc
// NOTE: This is a valid operation because according to the docs of
// std::rc::Rc::from_raw(), the type U that was in the original Rc<U>
// acquired from Rc::into_raw() must have the same size alignment and
// size of the type T in the new Rc<T>. So as long as both the size
// and alignment stay the same, the Rc will remain a valid Rc.
let length =
if size_of::<B>() != 0 { input_bytes / size_of::<B>() } else { 0 };
let rc_ptr: *const A = Rc::into_raw(input) as *const A;
// Must use ptr::slice_from_raw_parts, because we cannot make an
// intermediate const reference, because it has mutable provenance,
// nor an intermediate mutable reference, because it could be aliased.
let ptr = core::ptr::slice_from_raw_parts(rc_ptr as *const B, length);
Ok(unsafe { Rc::<[B]>::from_raw(ptr) })
}
} else {
let rc_ptr: *const [A] = Rc::into_raw(input);
let ptr: *const [B] = rc_ptr as *const [B];
Ok(unsafe { Rc::<[B]>::from_raw(ptr) })
}
}
/// As [`try_cast_slice_arc`], but unwraps for you.
#[inline]
#[cfg(target_has_atomic = "ptr")]
pub fn cast_slice_arc<
A: NoUninit + AnyBitPattern,
B: NoUninit + AnyBitPattern,
>(
input: Arc<[A]>,
) -> Arc<[B]> {
try_cast_slice_arc(input).map_err(|(e, _v)| e).unwrap()
}
/// Attempts to cast the content type of a `Arc<[T]>`.
///
/// On failure you get back an error along with the starting `Arc<[T]>`.
///
/// The bounds on this function are the same as [`cast_mut`], because a user
/// could call `Rc::get_unchecked_mut` on the output, which could be observable
/// in the input.
///
/// ## Failure
///
/// * The start and end content type of the `Arc<[T]>` must have the exact same
/// alignment.
/// * The start and end content size in bytes of the `Arc<[T]>` must be the
/// exact same.
#[inline]
#[cfg(target_has_atomic = "ptr")]
pub fn try_cast_slice_arc<
A: NoUninit + AnyBitPattern,
B: NoUninit + AnyBitPattern,
>(
input: Arc<[A]>,
) -> Result<Arc<[B]>, (PodCastError, Arc<[A]>)> {
if align_of::<A>() != align_of::<B>() {
Err((PodCastError::AlignmentMismatch, input))
} else if size_of::<A>() != size_of::<B>() {
let input_bytes = size_of_val::<[A]>(&*input);
if (size_of::<B>() == 0 && input_bytes != 0)
|| (size_of::<B>() != 0 && input_bytes % size_of::<B>() != 0)
{
// If the size in bytes of the underlying buffer does not match an exact
// multiple of the size of B, we cannot cast between them.
Err((PodCastError::OutputSliceWouldHaveSlop, input))
} else {
// Because the size is an exact multiple, we can now change the length
// of the slice and recreate the Arc
// NOTE: This is a valid operation because according to the docs of
// std::sync::Arc::from_raw(), the type U that was in the original Arc<U>
// acquired from Arc::into_raw() must have the same size alignment and
// size of the type T in the new Arc<T>. So as long as both the size
// and alignment stay the same, the Arc will remain a valid Arc.
let length =
if size_of::<B>() != 0 { input_bytes / size_of::<B>() } else { 0 };
let arc_ptr: *const A = Arc::into_raw(input) as *const A;
// Must use ptr::slice_from_raw_parts, because we cannot make an
// intermediate const reference, because it has mutable provenance,
// nor an intermediate mutable reference, because it could be aliased.
let ptr = core::ptr::slice_from_raw_parts(arc_ptr as *const B, length);
Ok(unsafe { Arc::<[B]>::from_raw(ptr) })
}
} else {
let arc_ptr: *const [A] = Arc::into_raw(input);
let ptr: *const [B] = arc_ptr as *const [B];
Ok(unsafe { Arc::<[B]>::from_raw(ptr) })
}
}
/// An extension trait for `TransparentWrapper` and alloc types.
pub trait TransparentWrapperAlloc<Inner: ?Sized>:
TransparentWrapper<Inner>
{
/// Convert a vec of the inner type into a vec of the wrapper type.
fn wrap_vec(s: Vec<Inner>) -> Vec<Self>
where
Self: Sized,
Inner: Sized,
{
let mut s = ManuallyDrop::new(s);
let length = s.len();
let capacity = s.capacity();
let ptr = s.as_mut_ptr();
unsafe {
// SAFETY:
// * ptr comes from Vec (and will not be double-dropped)
// * the two types have the identical representation
// * the len and capacity fields are valid
Vec::from_raw_parts(ptr as *mut Self, length, capacity)
}
}
/// Convert a box to the inner type into a box to the wrapper
/// type.
#[inline]
fn wrap_box(s: Box<Inner>) -> Box<Self> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
unsafe {
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the sizes are unspecified.
//
// SAFETY:
// * The unsafe contract requires that pointers to Inner and Self have
// identical representations
// * Box is guaranteed to have representation identical to a (non-null)
// pointer
// * The pointer comes from a box (and thus satisfies all safety
// requirements of Box)
let inner_ptr: *mut Inner = Box::into_raw(s);
let wrapper_ptr: *mut Self = transmute!(inner_ptr);
Box::from_raw(wrapper_ptr)
}
}
/// Convert an [`Rc`] to the inner type into an `Rc` to the wrapper type.
#[inline]
fn wrap_rc(s: Rc<Inner>) -> Rc<Self> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
unsafe {
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the layout of Rc is unspecified.
//
// SAFETY:
// * The unsafe contract requires that pointers to Inner and Self have
// identical representations, and that the size and alignment of Inner
// and Self are the same, which meets the safety requirements of
// Rc::from_raw
let inner_ptr: *const Inner = Rc::into_raw(s);
let wrapper_ptr: *const Self = transmute!(inner_ptr);
Rc::from_raw(wrapper_ptr)
}
}
/// Convert an [`Arc`] to the inner type into an `Arc` to the wrapper type.
#[inline]
#[cfg(target_has_atomic = "ptr")]
fn wrap_arc(s: Arc<Inner>) -> Arc<Self> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
unsafe {
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the layout of Arc is unspecified.
//
// SAFETY:
// * The unsafe contract requires that pointers to Inner and Self have
// identical representations, and that the size and alignment of Inner
// and Self are the same, which meets the safety requirements of
// Arc::from_raw
let inner_ptr: *const Inner = Arc::into_raw(s);
let wrapper_ptr: *const Self = transmute!(inner_ptr);
Arc::from_raw(wrapper_ptr)
}
}
/// Convert a vec of the wrapper type into a vec of the inner type.
fn peel_vec(s: Vec<Self>) -> Vec<Inner>
where
Self: Sized,
Inner: Sized,
{
let mut s = ManuallyDrop::new(s);
let length = s.len();
let capacity = s.capacity();
let ptr = s.as_mut_ptr();
unsafe {
// SAFETY:
// * ptr comes from Vec (and will not be double-dropped)
// * the two types have the identical representation
// * the len and capacity fields are valid
Vec::from_raw_parts(ptr as *mut Inner, length, capacity)
}
}
/// Convert a box to the wrapper type into a box to the inner
/// type.
#[inline]
fn peel_box(s: Box<Self>) -> Box<Inner> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
unsafe {
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the sizes are unspecified.
//
// SAFETY:
// * The unsafe contract requires that pointers to Inner and Self have
// identical representations
// * Box is guaranteed to have representation identical to a (non-null)
// pointer
// * The pointer comes from a box (and thus satisfies all safety
// requirements of Box)
let wrapper_ptr: *mut Self = Box::into_raw(s);
let inner_ptr: *mut Inner = transmute!(wrapper_ptr);
Box::from_raw(inner_ptr)
}
}
/// Convert an [`Rc`] to the wrapper type into an `Rc` to the inner type.
#[inline]
fn peel_rc(s: Rc<Self>) -> Rc<Inner> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
unsafe {
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the layout of Rc is unspecified.
//
// SAFETY:
// * The unsafe contract requires that pointers to Inner and Self have
// identical representations, and that the size and alignment of Inner
// and Self are the same, which meets the safety requirements of
// Rc::from_raw
let wrapper_ptr: *const Self = Rc::into_raw(s);
let inner_ptr: *const Inner = transmute!(wrapper_ptr);
Rc::from_raw(inner_ptr)
}
}
/// Convert an [`Arc`] to the wrapper type into an `Arc` to the inner type.
#[inline]
#[cfg(target_has_atomic = "ptr")]
fn peel_arc(s: Arc<Self>) -> Arc<Inner> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
unsafe {
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the layout of Arc is unspecified.
//
// SAFETY:
// * The unsafe contract requires that pointers to Inner and Self have
// identical representations, and that the size and alignment of Inner
// and Self are the same, which meets the safety requirements of
// Arc::from_raw
let wrapper_ptr: *const Self = Arc::into_raw(s);
let inner_ptr: *const Inner = transmute!(wrapper_ptr);
Arc::from_raw(inner_ptr)
}
}
}
impl<I: ?Sized, T: ?Sized + TransparentWrapper<I>> TransparentWrapperAlloc<I>
for T
{
}
/// As `Box<[u8]>`, but remembers the original alignment.
pub struct BoxBytes {
// SAFETY: `ptr` is aligned to `layout.align()`, points to
// `layout.size()` initialized bytes, and, if `layout.size() > 0`,
// is owned and was allocated with the global allocator with `layout`.
ptr: NonNull<u8>,
layout: Layout,
}
impl Deref for BoxBytes {
type Target = [u8];
fn deref(&self) -> &Self::Target {
// SAFETY: See type invariant.
unsafe {
core::slice::from_raw_parts(self.ptr.as_ptr(), self.layout.size())
}
}
}
impl DerefMut for BoxBytes {
fn deref_mut(&mut self) -> &mut Self::Target {
// SAFETY: See type invariant.
unsafe {
core::slice::from_raw_parts_mut(self.ptr.as_ptr(), self.layout.size())
}
}
}
impl Drop for BoxBytes {
fn drop(&mut self) {
if self.layout.size() != 0 {
// SAFETY: See type invariant: if `self.layout.size() != 0`, then
// `self.ptr` is owned and was allocated with `self.layout`.
unsafe { alloc::alloc::dealloc(self.ptr.as_ptr(), self.layout) };
}
}
}
impl<T: ?Sized + sealed::BoxBytesOf> From<Box<T>> for BoxBytes {
fn from(value: Box<T>) -> Self {
value.box_bytes_of()
}
}
mod sealed {
use crate::{BoxBytes, PodCastError};
use alloc::boxed::Box;
pub trait BoxBytesOf {
fn box_bytes_of(self: Box<Self>) -> BoxBytes;
}
pub trait FromBoxBytes {
fn try_from_box_bytes(
bytes: BoxBytes,
) -> Result<Box<Self>, (PodCastError, BoxBytes)>;
}
}
impl<T: NoUninit> sealed::BoxBytesOf for T {
fn box_bytes_of(self: Box<Self>) -> BoxBytes {
let layout = Layout::new::<T>();
let ptr = Box::into_raw(self) as *mut u8;
// SAFETY: Box::into_raw() returns a non-null pointer.
let ptr = unsafe { NonNull::new_unchecked(ptr) };
BoxBytes { ptr, layout }
}
}
impl<T: NoUninit> sealed::BoxBytesOf for [T] {
fn box_bytes_of(self: Box<Self>) -> BoxBytes {
let layout = Layout::for_value::<[T]>(&self);
let ptr = Box::into_raw(self) as *mut u8;
// SAFETY: Box::into_raw() returns a non-null pointer.
let ptr = unsafe { NonNull::new_unchecked(ptr) };
BoxBytes { ptr, layout }
}
}
impl sealed::BoxBytesOf for str {
fn box_bytes_of(self: Box<Self>) -> BoxBytes {
self.into_boxed_bytes().box_bytes_of()
}
}
impl<T: AnyBitPattern> sealed::FromBoxBytes for T {
fn try_from_box_bytes(
bytes: BoxBytes,
) -> Result<Box<Self>, (PodCastError, BoxBytes)> {
let layout = Layout::new::<T>();
if bytes.layout.align() != layout.align() {
Err((PodCastError::AlignmentMismatch, bytes))
} else if bytes.layout.size() != layout.size() {
Err((PodCastError::SizeMismatch, bytes))
} else {
let (ptr, _) = bytes.into_raw_parts();
// SAFETY: See BoxBytes type invariant.
Ok(unsafe { Box::from_raw(ptr.as_ptr() as *mut T) })
}
}
}
impl<T: AnyBitPattern> sealed::FromBoxBytes for [T] {
fn try_from_box_bytes(
bytes: BoxBytes,
) -> Result<Box<Self>, (PodCastError, BoxBytes)> {
let single_layout = Layout::new::<T>();
if bytes.layout.align() != single_layout.align() {
Err((PodCastError::AlignmentMismatch, bytes))
} else if (single_layout.size() == 0 && bytes.layout.size() != 0)
|| (single_layout.size() != 0
&& bytes.layout.size() % single_layout.size() != 0)
{
Err((PodCastError::OutputSliceWouldHaveSlop, bytes))
} else {
let (ptr, layout) = bytes.into_raw_parts();
let length = if single_layout.size() != 0 {
layout.size() / single_layout.size()
} else {
0
};
let ptr =
core::ptr::slice_from_raw_parts_mut(ptr.as_ptr() as *mut T, length);
// SAFETY: See BoxBytes type invariant.
Ok(unsafe { Box::from_raw(ptr) })
}
}
}
/// Re-interprets `Box<T>` as `BoxBytes`.
///
/// `T` must be either [`Sized`] and [`NoUninit`],
/// [`[U]`](slice) where `U: NoUninit`, or [`str`].
#[inline]
pub fn box_bytes_of<T: sealed::BoxBytesOf + ?Sized>(input: Box<T>) -> BoxBytes {
input.box_bytes_of()
}
/// Re-interprets `BoxBytes` as `Box<T>`.
///
/// `T` must be either [`Sized`] + [`AnyBitPattern`], or
/// [`[U]`](slice) where `U: AnyBitPattern`.
///
/// ## Panics
///
/// This is [`try_from_box_bytes`] but will panic on error and the input will be
/// dropped.
#[inline]
pub fn from_box_bytes<T: sealed::FromBoxBytes + ?Sized>(
input: BoxBytes,
) -> Box<T> {
try_from_box_bytes(input).map_err(|(error, _)| error).unwrap()
}
/// Re-interprets `BoxBytes` as `Box<T>`.
///
/// `T` must be either [`Sized`] + [`AnyBitPattern`], or
/// [`[U]`](slice) where `U: AnyBitPattern`.
///
/// Returns `Err`:
/// * If the input isn't aligned for `T`.
/// * If `T: Sized` and the input's length isn't exactly the size of `T`.
/// * If `T = [U]` and the input's length isn't exactly a multiple of the size
/// of `U`.
#[inline]
pub fn try_from_box_bytes<T: sealed::FromBoxBytes + ?Sized>(
input: BoxBytes,
) -> Result<Box<T>, (PodCastError, BoxBytes)> {
T::try_from_box_bytes(input)
}
impl BoxBytes {
/// Constructs a `BoxBytes` from its raw parts.
///
/// # Safety
///
/// The pointer is owned, has been allocated with the provided layout, and
/// points to `layout.size()` initialized bytes.
pub unsafe fn from_raw_parts(ptr: NonNull<u8>, layout: Layout) -> Self {
BoxBytes { ptr, layout }
}
/// Deconstructs a `BoxBytes` into its raw parts.
///
/// The pointer is owned, has been allocated with the provided layout, and
/// points to `layout.size()` initialized bytes.
pub fn into_raw_parts(self) -> (NonNull<u8>, Layout) {
let me = ManuallyDrop::new(self);
(me.ptr, me.layout)
}
/// Returns the original layout.
pub fn layout(&self) -> Layout {
self.layout
}
}
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