1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183

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 {
    /// 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);
        &mut *(maybe_init as *mut [MaybeUninit<u8>] as *mut UninitSlice)
    }

    /// 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 _
    }

    /// 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>
);