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| 1 | +use core::fmt; |
| 2 | +use core::mem::MaybeUninit; |
| 3 | +use core::ops::{ |
| 4 | + Index, IndexMut, Range, RangeFrom, RangeFull, RangeInclusive, RangeTo, RangeToInclusive, |
| 5 | +}; |
| 6 | + |
| 7 | +/// Uninitialized byte slice. |
| 8 | +/// |
| 9 | +/// Returned by `BufMut::bytes_mut()`, the referenced byte slice may be |
| 10 | +/// uninitialized. The wrapper provides safe access without introducing |
| 11 | +/// undefined behavior. |
| 12 | +/// |
| 13 | +/// The safety invariants of this wrapper are: |
| 14 | +/// |
| 15 | +/// 1. Reading from an `UninitSlice` is undefined behavior. |
| 16 | +/// 2. Writing uninitialized bytes to an `UninitSlice` is undefined behavior. |
| 17 | +/// |
| 18 | +/// The difference between `&mut UninitSlice` and `&mut [MaybeUninit<u8>]` is |
| 19 | +/// that it is possible in safe code to write uninitialized bytes to an |
| 20 | +/// `&mut [MaybeUninit<u8>]`, which this type prohibits. |
| 21 | +#[repr(transparent)] |
| 22 | +pub struct UninitSlice([MaybeUninit<u8>]); |
| 23 | + |
| 24 | +impl UninitSlice { |
| 25 | + /// Create a `&mut UninitSlice` from a pointer and a length. |
| 26 | + /// |
| 27 | + /// # Safety |
| 28 | + /// |
| 29 | + /// The caller must ensure that `ptr` references a valid memory region owned |
| 30 | + /// by the caller representing a byte slice for the duration of `'a`. |
| 31 | + /// |
| 32 | + /// # Examples |
| 33 | + /// |
| 34 | + /// ``` |
| 35 | + /// use bytes::buf::UninitSlice; |
| 36 | + /// |
| 37 | + /// let bytes = b"hello world".to_vec(); |
| 38 | + /// let ptr = bytes.as_ptr() as *mut _; |
| 39 | + /// let len = bytes.len(); |
| 40 | + /// |
| 41 | + /// let slice = unsafe { UninitSlice::from_raw_parts_mut(ptr, len) }; |
| 42 | + /// ``` |
| 43 | + pub unsafe fn from_raw_parts_mut<'a>(ptr: *mut u8, len: usize) -> &'a mut UninitSlice { |
| 44 | + let maybe_init: &mut [MaybeUninit<u8>] = |
| 45 | + core::slice::from_raw_parts_mut(ptr as *mut _, len); |
| 46 | + &mut *(maybe_init as *mut [MaybeUninit<u8>] as *mut UninitSlice) |
| 47 | + } |
| 48 | + |
| 49 | + /// Write a single byte at the specified offset. |
| 50 | + /// |
| 51 | + /// # Panics |
| 52 | + /// |
| 53 | + /// The function panics if `index` is out of bounds. |
| 54 | + /// |
| 55 | + /// # Examples |
| 56 | + /// |
| 57 | + /// ``` |
| 58 | + /// use bytes::buf::UninitSlice; |
| 59 | + /// |
| 60 | + /// let mut data = [b'f', b'o', b'o']; |
| 61 | + /// let slice = unsafe { UninitSlice::from_raw_parts_mut(data.as_mut_ptr(), 3) }; |
| 62 | + /// |
| 63 | + /// slice.write_byte(0, b'b'); |
| 64 | + /// |
| 65 | + /// assert_eq!(b"boo", &data[..]); |
| 66 | + /// ``` |
| 67 | + pub fn write_byte(&mut self, index: usize, byte: u8) { |
| 68 | + assert!(index < self.len()); |
| 69 | + |
| 70 | + unsafe { self[index..].as_mut_ptr().write(byte) } |
| 71 | + } |
| 72 | + |
| 73 | + /// Copies bytes from `src` into `self`. |
| 74 | + /// |
| 75 | + /// The length of `src` must be the same as `self`. |
| 76 | + /// |
| 77 | + /// # Panics |
| 78 | + /// |
| 79 | + /// The function panics if `src` has a different length than `self`. |
| 80 | + /// |
| 81 | + /// # Examples |
| 82 | + /// |
| 83 | + /// ``` |
| 84 | + /// use bytes::buf::UninitSlice; |
| 85 | + /// |
| 86 | + /// let mut data = [b'f', b'o', b'o']; |
| 87 | + /// let slice = unsafe { UninitSlice::from_raw_parts_mut(data.as_mut_ptr(), 3) }; |
| 88 | + /// |
| 89 | + /// slice.copy_from_slice(b"bar"); |
| 90 | + /// |
| 91 | + /// assert_eq!(b"bar", &data[..]); |
| 92 | + /// ``` |
| 93 | + pub fn copy_from_slice(&mut self, src: &[u8]) { |
| 94 | + use core::ptr; |
| 95 | + |
| 96 | + assert_eq!(self.len(), src.len()); |
| 97 | + |
| 98 | + unsafe { |
| 99 | + ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len()); |
| 100 | + } |
| 101 | + } |
| 102 | + |
| 103 | + /// Return a raw pointer to the slice's buffer. |
| 104 | + /// |
| 105 | + /// # Safety |
| 106 | + /// |
| 107 | + /// The caller **must not** read from the referenced memory and **must not** |
| 108 | + /// write **uninitialized** bytes to the slice either. |
| 109 | + /// |
| 110 | + /// # Examples |
| 111 | + /// |
| 112 | + /// ``` |
| 113 | + /// use bytes::BufMut; |
| 114 | + /// |
| 115 | + /// let mut data = [0, 1, 2]; |
| 116 | + /// let mut slice = &mut data[..]; |
| 117 | + /// let ptr = BufMut::bytes_mut(&mut slice).as_mut_ptr(); |
| 118 | + /// ``` |
| 119 | + pub fn as_mut_ptr(&mut self) -> *mut u8 { |
| 120 | + self.0.as_mut_ptr() as *mut _ |
| 121 | + } |
| 122 | + |
| 123 | + /// Returns the number of bytes in the slice. |
| 124 | + /// |
| 125 | + /// # Examples |
| 126 | + /// |
| 127 | + /// ``` |
| 128 | + /// use bytes::BufMut; |
| 129 | + /// |
| 130 | + /// let mut data = [0, 1, 2]; |
| 131 | + /// let mut slice = &mut data[..]; |
| 132 | + /// let len = BufMut::bytes_mut(&mut slice).len(); |
| 133 | + /// |
| 134 | + /// assert_eq!(len, 3); |
| 135 | + /// ``` |
| 136 | + pub fn len(&self) -> usize { |
| 137 | + self.0.len() |
| 138 | + } |
| 139 | +} |
| 140 | + |
| 141 | +impl fmt::Debug for UninitSlice { |
| 142 | + fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 143 | + fmt.debug_struct("UninitSlice[...]").finish() |
| 144 | + } |
| 145 | +} |
| 146 | + |
| 147 | +macro_rules! impl_index { |
| 148 | + ($($t:ty),*) => { |
| 149 | + $( |
| 150 | + impl Index<$t> for UninitSlice { |
| 151 | + type Output = UninitSlice; |
| 152 | + |
| 153 | + fn index(&self, index: $t) -> &UninitSlice { |
| 154 | + let maybe_uninit: &[MaybeUninit<u8>] = &self.0[index]; |
| 155 | + unsafe { &*(maybe_uninit as *const [MaybeUninit<u8>] as *const UninitSlice) } |
| 156 | + } |
| 157 | + } |
| 158 | + |
| 159 | + impl IndexMut<$t> for UninitSlice { |
| 160 | + fn index_mut(&mut self, index: $t) -> &mut UninitSlice { |
| 161 | + let maybe_uninit: &mut [MaybeUninit<u8>] = &mut self.0[index]; |
| 162 | + unsafe { &mut *(maybe_uninit as *mut [MaybeUninit<u8>] as *mut UninitSlice) } |
| 163 | + } |
| 164 | + } |
| 165 | + )* |
| 166 | + }; |
| 167 | +} |
| 168 | + |
| 169 | +impl_index!( |
| 170 | + Range<usize>, |
| 171 | + RangeFrom<usize>, |
| 172 | + RangeFull, |
| 173 | + RangeInclusive<usize>, |
| 174 | + RangeTo<usize>, |
| 175 | + RangeToInclusive<usize> |
| 176 | +); |
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