const_hex/
buffer.rs

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
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
use crate::{byte2hex, imp};
use core::fmt;
use core::slice;
use core::str;

#[cfg(feature = "alloc")]
#[allow(unused_imports)]
use alloc::{string::String, vec::Vec};

/// A correctly sized stack allocation for the formatted bytes to be written
/// into.
///
/// `N` is the amount of bytes of the input, while `PREFIX` specifies whether
/// the "0x" prefix is prepended to the output.
///
/// Note that this buffer will contain only the prefix, if specified, and null
/// ('\0') bytes before any formatting is done.
///
/// # Examples
///
/// ```
/// let mut buffer = const_hex::Buffer::<4>::new();
/// let printed = buffer.format(b"1234");
/// assert_eq!(printed, "31323334");
/// ```
#[must_use]
#[repr(C)]
#[derive(Clone)]
pub struct Buffer<const N: usize, const PREFIX: bool = false> {
    // Workaround for Rust issue #76560:
    // https://github.com/rust-lang/rust/issues/76560
    // This would ideally be `[u8; (N + PREFIX as usize) * 2]`
    prefix: [u8; 2],
    bytes: [[u8; 2]; N],
}

impl<const N: usize, const PREFIX: bool> Default for Buffer<N, PREFIX> {
    #[inline]
    fn default() -> Self {
        Self::new()
    }
}

impl<const N: usize, const PREFIX: bool> fmt::Debug for Buffer<N, PREFIX> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("Buffer").field(&self.as_str()).finish()
    }
}

impl<const N: usize, const PREFIX: bool> Buffer<N, PREFIX> {
    /// The length of the buffer in bytes.
    pub const LEN: usize = (N + PREFIX as usize) * 2;

    const ASSERT_SIZE: () = assert!(core::mem::size_of::<Self>() == 2 + N * 2, "invalid size");
    const ASSERT_ALIGNMENT: () = assert!(core::mem::align_of::<Self>() == 1, "invalid alignment");

    /// This is a cheap operation; you don't need to worry about reusing buffers
    /// for efficiency.
    #[inline]
    pub const fn new() -> Self {
        let () = Self::ASSERT_SIZE;
        let () = Self::ASSERT_ALIGNMENT;
        Self {
            prefix: if PREFIX { [b'0', b'x'] } else { [0, 0] },
            bytes: [[0; 2]; N],
        }
    }

    /// Print an array of bytes into this buffer.
    #[inline]
    pub const fn const_format(self, array: &[u8; N]) -> Self {
        self.const_format_inner::<false>(array)
    }

    /// Print an array of bytes into this buffer.
    #[inline]
    pub const fn const_format_upper(self, array: &[u8; N]) -> Self {
        self.const_format_inner::<true>(array)
    }

    /// Same as `encode_to_slice_inner`, but const-stable.
    const fn const_format_inner<const UPPER: bool>(mut self, array: &[u8; N]) -> Self {
        let mut i = 0;
        while i < N {
            let (high, low) = byte2hex::<UPPER>(array[i]);
            self.bytes[i][0] = high;
            self.bytes[i][1] = low;
            i += 1;
        }
        self
    }

    /// Print an array of bytes into this buffer and return a reference to its
    /// *lower* hex string representation within the buffer.
    #[inline]
    pub fn format(&mut self, array: &[u8; N]) -> &mut str {
        // length of array is guaranteed to be N.
        self.format_inner::<false>(array)
    }

    /// Print an array of bytes into this buffer and return a reference to its
    /// *upper* hex string representation within the buffer.
    #[inline]
    pub fn format_upper(&mut self, array: &[u8; N]) -> &mut str {
        // length of array is guaranteed to be N.
        self.format_inner::<true>(array)
    }

    /// Print a slice of bytes into this buffer and return a reference to its
    /// *lower* hex string representation within the buffer.
    ///
    /// # Panics
    ///
    /// If the slice is not exactly `N` bytes long.
    #[track_caller]
    #[inline]
    pub fn format_slice<T: AsRef<[u8]>>(&mut self, slice: T) -> &mut str {
        self.format_slice_inner::<false>(slice.as_ref())
    }

    /// Print a slice of bytes into this buffer and return a reference to its
    /// *upper* hex string representation within the buffer.
    ///
    /// # Panics
    ///
    /// If the slice is not exactly `N` bytes long.
    #[track_caller]
    #[inline]
    pub fn format_slice_upper<T: AsRef<[u8]>>(&mut self, slice: T) -> &mut str {
        self.format_slice_inner::<true>(slice.as_ref())
    }

    // Checks length
    #[track_caller]
    fn format_slice_inner<const UPPER: bool>(&mut self, slice: &[u8]) -> &mut str {
        assert_eq!(slice.len(), N, "length mismatch");
        self.format_inner::<UPPER>(slice)
    }

    // Doesn't check length
    #[inline]
    fn format_inner<const UPPER: bool>(&mut self, input: &[u8]) -> &mut str {
        // SAFETY: Length was checked previously;
        // we only write only ASCII bytes.
        unsafe {
            let buf = self.as_mut_bytes();
            let output = buf.as_mut_ptr().add(PREFIX as usize * 2);
            imp::encode::<UPPER>(input, output);
            str::from_utf8_unchecked_mut(buf)
        }
    }

    /// Copies `self` into a new owned `String`.
    #[cfg(feature = "alloc")]
    #[inline]
    #[allow(clippy::inherent_to_string)] // this is intentional
    pub fn to_string(&self) -> String {
        // SAFETY: The buffer always contains valid UTF-8.
        unsafe { String::from_utf8_unchecked(self.as_bytes().to_vec()) }
    }

    /// Returns a reference to the underlying bytes casted to a string slice.
    #[inline]
    pub const fn as_str(&self) -> &str {
        // SAFETY: The buffer always contains valid UTF-8.
        unsafe { str::from_utf8_unchecked(self.as_bytes()) }
    }

    /// Returns a mutable reference to the underlying bytes casted to a string
    /// slice.
    #[inline]
    pub fn as_mut_str(&mut self) -> &mut str {
        // SAFETY: The buffer always contains valid UTF-8.
        unsafe { str::from_utf8_unchecked_mut(self.as_mut_bytes()) }
    }

    /// Copies `self` into a new `Vec`.
    #[cfg(feature = "alloc")]
    #[inline]
    pub fn to_vec(&self) -> Vec<u8> {
        self.as_bytes().to_vec()
    }

    /// Returns a reference the underlying stack-allocated byte array.
    ///
    /// # Panics
    ///
    /// If `LEN` does not equal `Self::LEN`.
    ///
    /// This is panic is evaluated at compile-time if the `nightly` feature
    /// is enabled, as inline `const` blocks are currently unstable.
    ///
    /// See Rust tracking issue [#76001](https://github.com/rust-lang/rust/issues/76001).
    #[inline]
    pub const fn as_byte_array<const LEN: usize>(&self) -> &[u8; LEN] {
        maybe_const_assert!(LEN == Self::LEN, "`LEN` must be equal to `Self::LEN`");
        // SAFETY: [u16; N] is layout-compatible with [u8; N * 2].
        unsafe { &*self.as_ptr().cast::<[u8; LEN]>() }
    }

    /// Returns a mutable reference the underlying stack-allocated byte array.
    ///
    /// # Panics
    ///
    /// If `LEN` does not equal `Self::LEN`.
    ///
    /// See [`as_byte_array`](Buffer::as_byte_array) for more information.
    #[inline]
    pub fn as_mut_byte_array<const LEN: usize>(&mut self) -> &mut [u8; LEN] {
        maybe_const_assert!(LEN == Self::LEN, "`LEN` must be equal to `Self::LEN`");
        // SAFETY: [u16; N] is layout-compatible with [u8; N * 2].
        unsafe { &mut *self.as_mut_ptr().cast::<[u8; LEN]>() }
    }

    /// Returns a reference to the underlying bytes.
    #[inline]
    pub const fn as_bytes(&self) -> &[u8] {
        // SAFETY: [u16; N] is layout-compatible with [u8; N * 2].
        unsafe { slice::from_raw_parts(self.as_ptr(), Self::LEN) }
    }

    /// Returns a mutable reference to the underlying bytes.
    ///
    /// # Safety
    ///
    /// The caller must ensure that the content of the slice is valid UTF-8
    /// before the borrow ends and the underlying `str` is used.
    ///
    /// Use of a `str` whose contents are not valid UTF-8 is undefined behavior.
    #[inline]
    pub unsafe fn as_mut_bytes(&mut self) -> &mut [u8] {
        // SAFETY: [u16; N] is layout-compatible with [u8; N * 2].
        unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), Self::LEN) }
    }

    /// Returns a mutable reference to the underlying buffer, excluding the prefix.
    ///
    /// # Safety
    ///
    /// See [`as_mut_bytes`](Buffer::as_mut_bytes).
    #[inline]
    pub unsafe fn buffer(&mut self) -> &mut [u8] {
        unsafe { slice::from_raw_parts_mut(self.bytes.as_mut_ptr().cast(), N * 2) }
    }

    /// Returns a raw pointer to the buffer.
    ///
    /// The caller must ensure that the buffer outlives the pointer this
    /// function returns, or else it will end up pointing to garbage.
    #[inline]
    pub const fn as_ptr(&self) -> *const u8 {
        unsafe { (self as *const Self).cast::<u8>().add(!PREFIX as usize * 2) }
    }

    /// Returns an unsafe mutable pointer to the slice's buffer.
    ///
    /// The caller must ensure that the slice outlives the pointer this
    /// function returns, or else it will end up pointing to garbage.
    #[inline]
    pub fn as_mut_ptr(&mut self) -> *mut u8 {
        unsafe { (self as *mut Self).cast::<u8>().add(!PREFIX as usize * 2) }
    }
}