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//! Relative pointer implementations and options.
#[cfg(feature = "validation")]
mod validation;
use crate::{ArchivePointee, ArchiveUnsized, Archived};
use core::{
convert::TryFrom,
fmt,
marker::{PhantomData, PhantomPinned},
ptr,
};
/// An error where the distance between two positions cannot be represented by the offset type.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum OffsetError {
/// The offset overflowed the range of `isize`
IsizeOverflow,
/// The offset is too far for the offset type of the relative pointer
ExceedsStorageRange,
}
impl fmt::Display for OffsetError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
OffsetError::IsizeOverflow => write!(f, "the offset overflowed the range of `isize`"),
OffsetError::ExceedsStorageRange => write!(
f,
"the offset is too far for the offset type of the relative pointer"
),
}
}
}
#[cfg(feature = "std")]
impl std::error::Error for OffsetError {}
/// Calculates the offset between two positions as an `isize`.
///
/// This function exists solely to get the distance between two `usizes` as an `isize` with a full
/// range of values.
///
/// # Examples
///
/// ```
/// use rkyv::rel_ptr::{signed_offset, OffsetError};
///
/// assert_eq!(signed_offset(0, 1), Ok(1));
/// assert_eq!(signed_offset(1, 0), Ok(-1));
/// assert_eq!(signed_offset(0, isize::MAX as usize), Ok(isize::MAX));
/// assert_eq!(signed_offset(isize::MAX as usize, 0), Ok(-isize::MAX));
/// assert_eq!(signed_offset(0, isize::MAX as usize + 1), Err(OffsetError::IsizeOverflow));
/// assert_eq!(signed_offset(isize::MAX as usize + 1, 0), Ok(isize::MIN));
/// assert_eq!(signed_offset(0, isize::MAX as usize + 2), Err(OffsetError::IsizeOverflow));
/// assert_eq!(signed_offset(isize::MAX as usize + 2, 0), Err(OffsetError::IsizeOverflow));
/// ```
#[inline]
pub fn signed_offset(from: usize, to: usize) -> Result<isize, OffsetError> {
let (result, overflow) = to.overflowing_sub(from);
if (!overflow && result <= (isize::MAX as usize))
|| (overflow && result >= (isize::MIN as usize))
{
Ok(result as isize)
} else {
Err(OffsetError::IsizeOverflow)
}
}
/// A offset that can be used with [`RawRelPtr`].
pub trait Offset: Copy {
/// Creates a new offset between a `from` position and a `to` position.
fn between(from: usize, to: usize) -> Result<Self, OffsetError>;
/// Gets the offset as an `isize`.
fn to_isize(&self) -> isize;
}
macro_rules! impl_offset {
($ty:ty) => {
impl Offset for $ty {
#[inline]
fn between(from: usize, to: usize) -> Result<Self, OffsetError> {
// pointer::add and pointer::offset require that the computed offsets cannot
// overflow an isize, which is why we're using signed_offset instead of checked_sub
// for unsized types
Self::try_from(signed_offset(from, to)?)
.map_err(|_| OffsetError::ExceedsStorageRange)
}
#[inline]
fn to_isize(&self) -> isize {
// We're guaranteed that our offset will not exceed the the capacity of an `isize`
*self as isize
}
}
};
(@endian $ty:ty) => {
impl Offset for Archived<$ty> {
#[inline]
fn between(from: usize, to: usize) -> Result<Self, OffsetError> {
// pointer::add and pointer::offset require that the computed offsets cannot
// overflow an isize, which is why we're using signed_offset instead of checked_sub
// for unsized types
<$ty>::try_from(signed_offset(from, to)?)
.map(|x| to_archived!(x))
.map_err(|_| OffsetError::ExceedsStorageRange)
}
#[inline]
fn to_isize(&self) -> isize {
// We're guaranteed that our offset will not exceed the the capacity of an `isize`
from_archived!(*self) as isize
}
}
};
}
impl_offset!(i8);
impl_offset!(@endian i16);
#[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
impl_offset!(@endian i32);
#[cfg(target_pointer_width = "64")]
impl_offset!(@endian i64);
impl_offset!(u8);
impl_offset!(@endian u16);
#[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
impl_offset!(@endian u32);
#[cfg(target_pointer_width = "64")]
impl_offset!(@endian u64);
/// Errors that can occur while creating raw relative pointers.
#[derive(Debug)]
pub enum RelPtrError {
/// The given `from` and `to` positions for the relative pointer failed to form a valid offset.
///
/// This is probably because the distance between them could not be represented by the offset
/// type.
OffsetError,
}
/// An untyped pointer which resolves relative to its position in memory.
///
/// This is the most fundamental building block in rkyv. It allows the construction and use of
/// pointers that can be safely relocated as long as the source and target are moved together. This
/// is what allows memory to be moved from disk into memory and accessed without decoding.
///
/// Regular pointers are *absolute*, meaning that the pointee can be moved without invalidating the
/// pointer. However, the target cannot be moved or the pointer is invalidated.
///
/// Relative pointers are *relative*, meaning that the pointee can be moved with the target without
/// invalidating the pointer. However, if either the pointee or the target move independently, the
/// pointer will be invalidated.
#[repr(transparent)]
pub struct RawRelPtr<O> {
offset: O,
_phantom: PhantomPinned,
}
impl<O: Offset> RawRelPtr<O> {
/// Attempts to create a new `RawRelPtr` in-place between the given `from` and `to` positions.
///
/// # Safety
///
/// - `out` must be located at position `from`
/// - `to` must be a position within the archive
#[inline]
pub unsafe fn try_emplace(from: usize, to: usize, out: *mut Self) -> Result<(), OffsetError> {
let offset = O::between(from, to)?;
ptr::addr_of_mut!((*out).offset).write(offset);
Ok(())
}
/// Creates a new `RawRelPtr` in-place between the given `from` and `to` positions.
///
/// # Safety
///
/// - `out` must be located at position `from`
/// - `to` must be a position within the archive
/// - The offset between `from` and `to` must fit in an `isize` and not exceed the offset
/// storage
#[inline]
pub unsafe fn emplace(from: usize, to: usize, out: *mut Self) {
Self::try_emplace(from, to, out).unwrap();
}
/// Gets the base pointer for the relative pointer.
#[inline]
pub fn base(&self) -> *const u8 {
(self as *const Self).cast::<u8>()
}
/// Gets the mutable base pointer for the relative pointer.
#[inline]
pub fn base_mut(&mut self) -> *mut u8 {
(self as *mut Self).cast::<u8>()
}
/// Gets the offset of the relative pointer from its base.
#[inline]
pub fn offset(&self) -> isize {
self.offset.to_isize()
}
/// Gets whether the offset of the relative pointer is 0.
#[inline]
pub fn is_null(&self) -> bool {
self.offset() == 0
}
/// Calculates the memory address being pointed to by this relative pointer.
#[inline]
pub fn as_ptr(&self) -> *const () {
unsafe { self.base().offset(self.offset()).cast() }
}
/// Returns an unsafe mutable pointer to the memory address being pointed to
/// by this relative pointer.
#[inline]
pub fn as_mut_ptr(&mut self) -> *mut () {
unsafe { self.base_mut().offset(self.offset()).cast() }
}
}
impl<O: fmt::Debug> fmt::Debug for RawRelPtr<O> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("RawRelPtr")
.field("offset", &self.offset)
.finish()
}
}
impl<O: Offset> fmt::Pointer for RawRelPtr<O> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Pointer::fmt(&self.as_ptr(), f)
}
}
/// A raw relative pointer that uses an archived `i8` as the underlying offset.
pub type RawRelPtrI8 = RawRelPtr<Archived<i8>>;
/// A raw relative pointer that uses an archived `i16` as the underlying offset.
pub type RawRelPtrI16 = RawRelPtr<Archived<i16>>;
/// A raw relative pointer that uses an archived `i32` as the underlying offset.
#[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
pub type RawRelPtrI32 = RawRelPtr<Archived<i32>>;
/// A raw relative pointer that uses an archived `i64` as the underlying offset.
#[cfg(target_pointer_width = "64")]
pub type RawRelPtrI64 = RawRelPtr<Archived<i64>>;
/// A raw relative pointer that uses an archived `u8` as the underlying offset.
pub type RawRelPtrU8 = RawRelPtr<Archived<u8>>;
/// A raw relative pointer that uses an archived `u16` as the underlying offset.
pub type RawRelPtrU16 = RawRelPtr<Archived<u16>>;
/// A raw relative pointer that uses an archived `u32` as the underlying offset.
#[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
pub type RawRelPtrU32 = RawRelPtr<Archived<u32>>;
/// A raw relative pointer that uses an archived `u64` as the underlying offset.
#[cfg(target_pointer_width = "64")]
pub type RawRelPtrU64 = RawRelPtr<Archived<u64>>;
// TOOD: implement for NonZero types
/// A pointer which resolves to relative to its position in memory.
///
/// This is a strongly-typed version of [`RawRelPtr`].
///
/// See [`Archive`](crate::Archive) for an example of creating one.
pub struct RelPtr<T: ArchivePointee + ?Sized, O> {
raw_ptr: RawRelPtr<O>,
metadata: T::ArchivedMetadata,
_phantom: PhantomData<T>,
}
impl<T, O: Offset> RelPtr<T, O> {
/// Attempts to create a relative pointer from one position to another.
///
/// # Safety
///
/// - `from` must be the position of `out` within the archive
/// - `to` must be the position of some valid `T`
#[inline]
pub unsafe fn try_emplace(from: usize, to: usize, out: *mut Self) -> Result<(), OffsetError> {
let (fp, fo) = out_field!(out.raw_ptr);
// Skip metadata since sized T is guaranteed to be ()
RawRelPtr::try_emplace(from + fp, to, fo)
}
/// Creates a relative pointer from one position to another.
///
/// # Panics
///
/// - The offset between `from` and `to` does not fit in an `isize`
/// - The offset between `from` and `to` exceeds the offset storage
///
/// # Safety
///
/// - `from` must be the position of `out` within the archive
/// - `to` must be the position of some valid `T`
#[inline]
pub unsafe fn emplace(from: usize, to: usize, out: *mut Self) {
Self::try_emplace(from, to, out).unwrap();
}
}
impl<T: ArchivePointee + ?Sized, O: Offset> RelPtr<T, O>
where
T::ArchivedMetadata: Default,
{
/// Attempts to create a null relative pointer with default metadata.
///
/// # Safety
///
/// `pos` must be the position of `out` within the archive.
#[inline]
pub unsafe fn try_emplace_null(pos: usize, out: *mut Self) -> Result<(), OffsetError> {
let (fp, fo) = out_field!(out.raw_ptr);
RawRelPtr::try_emplace(pos + fp, pos, fo)?;
let (_, fo) = out_field!(out.metadata);
fo.write(Default::default());
Ok(())
}
/// Creates a null relative pointer with default metadata.
///
/// # Panics
///
/// - An offset of `0` does not fit in an `isize`
/// - An offset of `0` exceeds the offset storage
///
/// # Safety
///
/// `pos` must be the position of `out` within the archive.
#[inline]
pub unsafe fn emplace_null(pos: usize, out: *mut Self) {
Self::try_emplace_null(pos, out).unwrap()
}
}
impl<T: ArchivePointee + ?Sized, O: Offset> RelPtr<T, O> {
/// Attempts to create a relative pointer from one position to another.
///
/// # Safety
///
/// - `from` must be the position of `out` within the archive
/// - `to` must be the position of some valid `T`
/// - `value` must be the value being serialized
/// - `metadata_resolver` must be the result of serializing the metadata of `value`
#[inline]
pub unsafe fn try_resolve_emplace<U: ArchiveUnsized<Archived = T> + ?Sized>(
from: usize,
to: usize,
value: &U,
metadata_resolver: U::MetadataResolver,
out: *mut Self,
) -> Result<(), OffsetError> {
let (fp, fo) = out_field!(out.raw_ptr);
RawRelPtr::try_emplace(from + fp, to, fo)?;
let (fp, fo) = out_field!(out.metadata);
value.resolve_metadata(from + fp, metadata_resolver, fo);
Ok(())
}
/// Creates a relative pointer from one position to another.
///
/// # Panics
///
/// - The offset between `from` and `to` does not fit in an `isize`
/// - The offset between `from` and `to` exceeds the offset storage
///
/// # Safety
///
/// - `from` must be the position of `out` within the archive
/// - `to` must be the position of some valid `T`
/// - `value` must be the value being serialized
/// - `metadata_resolver` must be the result of serializing the metadata of `value`
#[inline]
pub unsafe fn resolve_emplace<U: ArchiveUnsized<Archived = T> + ?Sized>(
from: usize,
to: usize,
value: &U,
metadata_resolver: U::MetadataResolver,
out: *mut Self,
) {
Self::try_resolve_emplace(from, to, value, metadata_resolver, out).unwrap();
}
/// Gets the base pointer for the relative pointer.
#[inline]
pub fn base(&self) -> *const u8 {
self.raw_ptr.base()
}
/// Gets the mutable base pointer for the relative pointer.
#[inline]
pub fn base_mut(&mut self) -> *mut u8 {
self.raw_ptr.base_mut()
}
/// Gets the offset of the relative pointer from its base.
#[inline]
pub fn offset(&self) -> isize {
self.raw_ptr.offset()
}
/// Gets whether the offset of the relative pointer is 0.
#[inline]
pub fn is_null(&self) -> bool {
self.raw_ptr.is_null()
}
/// Gets the metadata of the relative pointer.
#[inline]
pub fn metadata(&self) -> &T::ArchivedMetadata {
&self.metadata
}
/// Calculates the memory address being pointed to by this relative pointer.
#[inline]
pub fn as_ptr(&self) -> *const T {
ptr_meta::from_raw_parts(self.raw_ptr.as_ptr(), T::pointer_metadata(&self.metadata))
}
/// Returns an unsafe mutable pointer to the memory address being pointed to by this relative
/// pointer.
#[inline]
pub fn as_mut_ptr(&mut self) -> *mut T {
ptr_meta::from_raw_parts_mut(
self.raw_ptr.as_mut_ptr(),
T::pointer_metadata(&self.metadata),
)
}
}
impl<T: ArchivePointee + ?Sized, O: fmt::Debug> fmt::Debug for RelPtr<T, O>
where
T::ArchivedMetadata: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("RelPtr")
.field("raw_ptr", &self.raw_ptr)
.field("metadata", &self.metadata)
.finish()
}
}
impl<T: ArchivePointee + ?Sized, O: Offset> fmt::Pointer for RelPtr<T, O> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Pointer::fmt(&self.as_ptr(), f)
}
}