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use core::fmt;
use core::mem::MaybeUninit;
use core::ops::{
Index, IndexMut, Range, RangeFrom, RangeFull, RangeInclusive, RangeTo, RangeToInclusive,
};
/// Uninitialized byte slice.
///
/// Returned by `BufMut::chunk_mut()`, the referenced byte slice may be
/// uninitialized. The wrapper provides safe access without introducing
/// undefined behavior.
///
/// The safety invariants of this wrapper are:
///
/// 1. Reading from an `UninitSlice` is undefined behavior.
/// 2. Writing uninitialized bytes to an `UninitSlice` is undefined behavior.
///
/// The difference between `&mut UninitSlice` and `&mut [MaybeUninit<u8>]` is
/// that it is possible in safe code to write uninitialized bytes to an
/// `&mut [MaybeUninit<u8>]`, which this type prohibits.
#[repr(transparent)]
pub struct UninitSlice([MaybeUninit<u8>]);
impl UninitSlice {
pub(crate) fn from_slice(slice: &mut [MaybeUninit<u8>]) -> &mut UninitSlice {
unsafe { &mut *(slice as *mut [MaybeUninit<u8>] as *mut UninitSlice) }
}
/// Create a `&mut UninitSlice` from a pointer and a length.
///
/// # Safety
///
/// The caller must ensure that `ptr` references a valid memory region owned
/// by the caller representing a byte slice for the duration of `'a`.
///
/// # Examples
///
/// ```
/// use bytes::buf::UninitSlice;
///
/// let bytes = b"hello world".to_vec();
/// let ptr = bytes.as_ptr() as *mut _;
/// let len = bytes.len();
///
/// let slice = unsafe { UninitSlice::from_raw_parts_mut(ptr, len) };
/// ```
#[inline]
pub unsafe fn from_raw_parts_mut<'a>(ptr: *mut u8, len: usize) -> &'a mut UninitSlice {
let maybe_init: &mut [MaybeUninit<u8>] =
core::slice::from_raw_parts_mut(ptr as *mut _, len);
Self::from_slice(maybe_init)
}
/// Write a single byte at the specified offset.
///
/// # Panics
///
/// The function panics if `index` is out of bounds.
///
/// # Examples
///
/// ```
/// use bytes::buf::UninitSlice;
///
/// let mut data = [b'f', b'o', b'o'];
/// let slice = unsafe { UninitSlice::from_raw_parts_mut(data.as_mut_ptr(), 3) };
///
/// slice.write_byte(0, b'b');
///
/// assert_eq!(b"boo", &data[..]);
/// ```
#[inline]
pub fn write_byte(&mut self, index: usize, byte: u8) {
assert!(index < self.len());
unsafe { self[index..].as_mut_ptr().write(byte) }
}
/// Copies bytes from `src` into `self`.
///
/// The length of `src` must be the same as `self`.
///
/// # Panics
///
/// The function panics if `src` has a different length than `self`.
///
/// # Examples
///
/// ```
/// use bytes::buf::UninitSlice;
///
/// let mut data = [b'f', b'o', b'o'];
/// let slice = unsafe { UninitSlice::from_raw_parts_mut(data.as_mut_ptr(), 3) };
///
/// slice.copy_from_slice(b"bar");
///
/// assert_eq!(b"bar", &data[..]);
/// ```
#[inline]
pub fn copy_from_slice(&mut self, src: &[u8]) {
use core::ptr;
assert_eq!(self.len(), src.len());
unsafe {
ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
}
}
/// Return a raw pointer to the slice's buffer.
///
/// # Safety
///
/// The caller **must not** read from the referenced memory and **must not**
/// write **uninitialized** bytes to the slice either.
///
/// # Examples
///
/// ```
/// use bytes::BufMut;
///
/// let mut data = [0, 1, 2];
/// let mut slice = &mut data[..];
/// let ptr = BufMut::chunk_mut(&mut slice).as_mut_ptr();
/// ```
#[inline]
pub fn as_mut_ptr(&mut self) -> *mut u8 {
self.0.as_mut_ptr() as *mut _
}
/// Return a `&mut [MaybeUninit<u8>]` to this slice's buffer.
///
/// # Safety
///
/// The caller **must not** read from the referenced memory and **must not** write
/// **uninitialized** bytes to the slice either. This is because `BufMut` implementation
/// that created the `UninitSlice` knows which parts are initialized. Writing uninitalized
/// bytes to the slice may cause the `BufMut` to read those bytes and trigger undefined
/// behavior.
///
/// # Examples
///
/// ```
/// use bytes::BufMut;
///
/// let mut data = [0, 1, 2];
/// let mut slice = &mut data[..];
/// unsafe {
/// let uninit_slice = BufMut::chunk_mut(&mut slice).as_uninit_slice_mut();
/// };
/// ```
#[inline]
pub unsafe fn as_uninit_slice_mut<'a>(&'a mut self) -> &'a mut [MaybeUninit<u8>] {
&mut *(self as *mut _ as *mut [MaybeUninit<u8>])
}
/// Returns the number of bytes in the slice.
///
/// # Examples
///
/// ```
/// use bytes::BufMut;
///
/// let mut data = [0, 1, 2];
/// let mut slice = &mut data[..];
/// let len = BufMut::chunk_mut(&mut slice).len();
///
/// assert_eq!(len, 3);
/// ```
#[inline]
pub fn len(&self) -> usize {
self.0.len()
}
}
impl fmt::Debug for UninitSlice {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("UninitSlice[...]").finish()
}
}
macro_rules! impl_index {
($($t:ty),*) => {
$(
impl Index<$t> for UninitSlice {
type Output = UninitSlice;
#[inline]
fn index(&self, index: $t) -> &UninitSlice {
let maybe_uninit: &[MaybeUninit<u8>] = &self.0[index];
unsafe { &*(maybe_uninit as *const [MaybeUninit<u8>] as *const UninitSlice) }
}
}
impl IndexMut<$t> for UninitSlice {
#[inline]
fn index_mut(&mut self, index: $t) -> &mut UninitSlice {
let maybe_uninit: &mut [MaybeUninit<u8>] = &mut self.0[index];
unsafe { &mut *(maybe_uninit as *mut [MaybeUninit<u8>] as *mut UninitSlice) }
}
}
)*
};
}
impl_index!(
Range<usize>,
RangeFrom<usize>,
RangeFull,
RangeInclusive<usize>,
RangeTo<usize>,
RangeToInclusive<usize>
);