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use core::marker::PhantomData;
use core::mem::{align_of, size_of, transmute};
use core::ops::Range;
use core::ptr::{self, NonNull};
use crate::error::Error;
use crate::traits::ZeroCopy;
/// Validator over a [`Buf`] constructed using [`Buf::validate_struct`].
///
/// [`Buf`]: crate::buf::Buf
/// [`Buf::validate_struct`]: crate::buf::Buf::validate_struct
#[must_use = "Must call `Validator::end` when validation is completed"]
#[repr(transparent)]
pub struct Validator<'a, T: ?Sized> {
data: NonNull<u8>,
_marker: PhantomData<&'a T>,
}
impl<'a, T: ?Sized> Validator<'a, T> {
/// Construct a validator around a slice.
///
/// This does not require that the slice is a valid instance of `T`.
pub(crate) fn from_slice(slice: &[u8]) -> Self {
// SAFETY: a slice is guaranteed to be non-null.
unsafe { Self::new(NonNull::new_unchecked(slice.as_ptr() as *mut u8)) }
}
/// Construct a validator around a pointer.
///
/// # Safety
///
/// Caller must ensure that the pointer points to an initialized slice of
/// size `T`.
#[inline]
pub(crate) unsafe fn new(data: NonNull<u8>) -> Self {
Self {
data,
_marker: PhantomData,
}
}
/// Indicate that this validate is transparent over `U`.
//
/// # Safety
///
/// This is only allowed if `T` is `#[repr(transparent)]` over `U`.
#[inline]
pub unsafe fn transparent<U>(&mut self) -> &mut Validator<'a, U> {
transmute(self)
}
/// Validate an additional field in the struct and return a reference to it.
///
/// # Safety
///
/// The current validator only guarantees that validation up to the size of
/// `T` can be performed. Advancing beyond that size causes the validator to
/// walk out of bounds.
///
/// # Examples
///
/// ```
/// use musli_zerocopy::{OwnedBuf, ZeroCopy};
///
/// #[derive(ZeroCopy)]
/// #[repr(C)]
/// struct Custom { field: u32, field2: u64 }
///
/// let mut buf = OwnedBuf::new();
///
/// let custom = buf.store(&Custom { field: 42, field2: 85 });
///
/// let mut v = buf.validate_struct::<Custom>()?;
///
/// // SAFETY: We're only validating fields we know are
/// // part of the struct, going beyond would constitute undefined behavior.
/// unsafe {
/// assert_eq!(v.field::<u32>()?, &42);
/// assert_eq!(v.field::<u64>()?, &85);
/// }
///
/// # Ok::<_, musli_zerocopy::Error>(())
/// ```
///
/// For packed structs we have to be even more careful. In fact, we're not
/// allowed to call `field` at all and must instead solely rely on
/// [`validate_with()`].
///
/// [`validate_with()`]: Validator::validate_with
#[inline]
pub unsafe fn field<F>(&mut self) -> Result<&F, Error>
where
F: ZeroCopy,
{
// SAFETY: We've ensured that the provided buffer is aligned and sized
// appropriately above.
unsafe {
self.align_with(align_of::<F>());
F::validate(&mut Validator::new(self.data))?;
let output = self.data.cast::<F>().as_ref();
self.advance::<F>();
Ok(output)
}
}
/// Load a single byte from the validator.
///
/// # Safety
///
/// The current validator only guarantees that validation up to the size of
/// `T` can be performed. Advancing beyond that size causes the validator to
/// walk out of bounds.
#[inline]
pub unsafe fn byte(&mut self) -> u8 {
let b = ptr::read(self.data.as_ptr());
self.data = NonNull::new_unchecked(self.data.as_ptr().add(1));
b
}
/// Perform an unaligned load of the given field.
///
/// # Safety
///
/// The current validator only guarantees that validation up to the size of
/// `T` can be performed. Advancing beyond that size causes the validator to
/// walk out of bounds.
#[inline]
pub unsafe fn load_unaligned<F>(&mut self) -> Result<F, Error>
where
F: Copy,
{
// SAFETY: We've ensured that the provided buffer is aligned and
// sized
// appropriately above.
unsafe {
let output = ptr::read_unaligned(self.data.cast::<F>().as_ptr());
self.advance::<F>();
Ok(output)
}
}
/// Validate an additional field in the struct.
///
/// # Safety
///
/// The current validator only guarantees that validation up to the size of
/// `T` can be performed. Advancing beyond that size causes the validator to
/// walk out of bounds.
///
/// # Examples
///
/// Validator a packed struct:
///
/// ```
/// use std::num::NonZeroU64;
///
/// use musli_zerocopy::{OwnedBuf, ZeroCopy};
///
/// #[derive(ZeroCopy)]
/// #[repr(C)]
/// struct Packed { field: u32, field2: NonZeroU64 }
///
/// let mut buf = OwnedBuf::new();
///
/// buf.store(&Packed { field: 42, field2: NonZeroU64::new(84).unwrap() });
///
/// let mut v = buf.validate_struct::<Packed>()?;
///
/// // SAFETY: We're only validating fields we know are
/// // part of the struct, and do not go beyond. We're
/// // also making sure not to construct reference to
/// // the fields which would be an error for a packed struct.
/// unsafe {
/// v.validate::<u32>()?;
/// v.validate::<NonZeroU64>()?;
/// }
///
/// # Ok::<_, musli_zerocopy::Error>(())
/// ```
#[inline]
pub unsafe fn validate<F>(&mut self) -> Result<(), Error>
where
F: ZeroCopy,
{
self.validate_with::<F>(align_of::<F>())
}
/// Validate an additional field in the struct with alignment `align`.
///
/// # Safety
///
/// The current validator only guarantees that validation up to the size of
/// `T` can be performed. Advancing beyond that size causes the validator to
/// walk out of bounds.
///
/// The `align` argument must match the alignment `N` used in the
/// `#[repr(packed(N))]` argument, note that `#[repr(packed)]` has an
/// argument of 1.
///
/// # Examples
///
/// Validator a packed struct:
///
/// ```
/// use std::num::NonZeroU64;
///
/// use musli_zerocopy::{OwnedBuf, ZeroCopy};
///
/// #[derive(ZeroCopy)]
/// #[repr(C, packed(2))]
/// struct Packed { field: u32, field2: NonZeroU64 }
///
/// let mut buf = OwnedBuf::new();
///
/// buf.store(&Packed { field: 42, field2: NonZeroU64::new(84).unwrap() });
///
/// let mut v = buf.validate_struct::<Packed>()?;
///
/// // SAFETY: We're only validating fields we know are
/// // part of the struct, and do not go beyond. We're
/// // also making sure not to construct reference to
/// // the fields which would be an error for a packed struct.
/// unsafe {
/// v.validate_with::<u32>(2)?;
/// v.validate_with::<NonZeroU64>(2)?;
/// }
///
/// # Ok::<_, musli_zerocopy::Error>(())
/// ```
#[inline]
pub unsafe fn validate_with<F>(&mut self, align: usize) -> Result<(), Error>
where
F: ZeroCopy,
{
self.align_with(align);
F::validate(&mut Validator::new(self.data))?;
self.advance::<F>();
Ok(())
}
/// Only validate the given field without aligning it.
///
/// # Safety
///
/// The caller is responsible for ensuring that the field is properly
/// aligned already by for example calling [`align_with::<F>()`].
///
/// [`align_with::<F>()`]: Self::align_with
#[inline]
pub(crate) unsafe fn validate_only<F>(&mut self) -> Result<(), Error>
where
F: ZeroCopy,
{
// SAFETY: We've ensured that the provided buffer is aligned and sized
// appropriately above.
F::validate(&mut Validator::new(self.data))?;
self.advance::<F>();
Ok(())
}
/// Align the current pointer by `F`.
#[inline]
pub(crate) unsafe fn align_with(&mut self, align: usize) {
let offset = self.data.as_ptr().align_offset(align);
self.data = NonNull::new_unchecked(self.data.as_ptr().add(offset));
}
/// Advance the current pointer by `F`.
#[inline]
pub(crate) unsafe fn advance<F>(&mut self) {
self.data = NonNull::new_unchecked(self.data.as_ptr().add(size_of::<F>()));
}
/// Return the address range associated with a just read `F` for diagnostics.
#[inline]
pub(crate) fn range<F>(&self) -> Range<usize> {
let end = self.data.as_ptr() as usize;
let start = end.wrapping_sub(size_of::<F>());
start..end
}
}